Protection of Wind Turbine Generators Using Microcontroller-Based Applications (Green Energy and Technology) 3030926273, 9783030926274

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Green Energy and Technology

Nagwa F. Ibrahim Sobhy S. Dessouky Hossam E. Mostafa Attia Ali H. Kasem Alaboudy

Protection of Wind Turbine Generators Using Microcontroller-Based Applications

Green Energy and Technology

Climate change, environmental impact and the limited natural resources urge scientific research and novel technical solutions. The monograph series Green Energy and Technology serves as a publishing platform for scientific and technological approaches to “green”—i.e. environmentally friendly and sustainable—technologies. While a focus lies on energy and power supply, it also covers "green" solutions in industrial engineering and engineering design. Green Energy and Technology addresses researchers, advanced students, technical consultants as well as decision makers in industries and politics. Hence, the level of presentation spans from instructional to highly technical. **Indexed in Scopus**. **Indexed in Ei Compendex**. More information about this series at https://link.springer.com/bookseries/8059

Nagwa F. Ibrahim • Sobhy S. Dessouky  Hossam E. Mostafa Attia Ali H. Kasem Alaboudy

Protection of Wind Turbine Generators Using Microcontroller-Based Applications

Nagwa F. Ibrahim Faculty of Technology and Education Suez University Suez, Egypt

Sobhy S. Dessouky Faculty of Engineering Port Said University Port Said, Egypt

Hossam E. Mostafa Attia Faculty of Technology and Education Suez University Suez, Egypt

Ali H. Kasem Alaboudy Faculty of Technology and Education Suez University Suez, Egypt

ISSN 1865-3529     ISSN 1865-3537 (electronic) Green Energy and Technology ISBN 978-3-030-92627-4    ISBN 978-3-030-92628-1 (eBook) https://doi.org/10.1007/978-3-030-92628-1 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

This book dedicated to: My mother, my sister, teachers, and friends for their love, encouragement, and endless support. I give all thanks and gratitude to my dear husband Mohammed Eid, and to my little daughter Rodyna, wishing from God their protection. Nagwa F. Ebrahim

Preface

We are presenting this book after study some applications on the Microcontroller Applications, specially protection of wind turbine generator. This work presents the design and implementation of a versatile digital Over Current (OC), Under Voltage (UV), Over Voltage (OV), Under Frequency (UF), Over Frequency (OF), and negative sequence relays using a single microcontroller. The software development and hardware testing are done using a microcontroller module based on an 8-bit microprocessor. Digital processing of measured currents is based on the CUSUM method in the programming. This protection provides reasonably fast tripping, even at terminal close to the power source were the most serve faults can occur, excluding the transient condition. So, this method provides an excellent balance between accuracy hardware and speed. Motivated by economic and environmental concerns, renewable energies become of higher potential to meet the continuous increase of loads. Wind energy is one of the promising sources of renewable energy. Although the merits given by wind energy, the stochastic nature of wind is a big hinder of integrating wind power with utility grids. The wind changes over moments, hours, days, and year seasons. This book addresses the dynamic behaviour of a wind-driven induction generator (I.G.) connected to a power system grid through a transmission line. The transient responses of protective devices associated with the I.G. are also studied. A computer simulation of the system under different disturbances is conducted through the wellknown matlab simulink. Disturbances considered are due to a variety of faults at the terminals of the generator as well as at the far end of the transmission line where it is connected to the load. Protective relaying strategy is proposed for the induction generator. The behaviour of different relays is studied under different disturbances. Suez, Egypt Port Said, Egypt Suez, Egypt Suez, Egypt

Nagwa F. Ibrahim Sobhy S. Dessouky Hossam E. Mostafa Attia Ali H. Kasem Alaboudy

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Contents

1 Introduction and Previous Work������������������������������������������������������������    1 1.1 Preface����������������������������������������������������������������������������������������������    1 1.2 Wind Energy Conversion System ����������������������������������������������������    3 1.3 Wind Energy Resources Market ������������������������������������������������������    3 1.4 Types of Wind Turbine Generators ��������������������������������������������������    4 1.5 Wind System Topologies������������������������������������������������������������������    7 1.5.1 Constant Speed Wind Turbine Systems��������������������������������    8 1.5.2 Limited Variable-Speed Wind Energy Conversion System����������������������������������������������������������������������������������    9 1.5.3 Variable Speed Wind Turbine Systems ��������������������������������    9 1.6 Induction Generator��������������������������������������������������������������������������   11 1.6.1 Induction Generator Operation ��������������������������������������������   12 1.6.2 Induction Generator Protection��������������������������������������������   12 1.6.3 Protection Requirement for Induction Generator ����������������   12 1.6.4 The Advantages Offered by Computer Relay ����������������������   17 1.7 Book Objectives��������������������������������������������������������������������������������   17 1.8 Book Contents����������������������������������������������������������������������������������   18 2 Computer Simulations for the Induction Generator Connected to Power Network ����������������������������������������������������������������   19 2.1 Introduction��������������������������������������������������������������������������������������   19 2.2 Behavior of Induction Generator������������������������������������������������������   19 2.2.1 Study system ������������������������������������������������������������������������   19 2.2.2 Types of Simulated Disturbances������������������������������������������   20 2.3 Fault, Clearing, and Successful Reclosure����������������������������������������   27 2.4 Comments and Discussion on Computer Results ����������������������������   30 3 Protective Schemes for Induction Generator����������������������������������������   45 3.1 Introduction��������������������������������������������������������������������������������������   45 3.2 Protection Requirement for Induction Generator ����������������������������   45 3.3 Sampling Methods����������������������������������������������������������������������������   45

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3.4 Conventional Fault Detection Techniques����������������������������������������   46 3.4.1 Method 1: Sample-to-Sample Comparison Method ������������   47 3.4.2 Method 2: Cycle-to-Cycle Comparison Method������������������   47 3.4.3 Method 3: Cumulative Sum (CUSUM) Method������������������   48 3.4.4 Method 4: Four Sample Method ������������������������������������������   50 3.5 Microcontroller-Based Relaying Algorithm ������������������������������������   50 3.5.1 Frequency Deviation Algorithm��������������������������������������������   51 3.5.2 Over-Current Algorithm��������������������������������������������������������   53 3.5.3 Negative Sequence Algorithm����������������������������������������������   54 4 Transient Behavior of Induction Generator Protective Relays ����������   59 4.1 Introduction��������������������������������������������������������������������������������������   59 4.2 Simulation Environment ������������������������������������������������������������������   59 4.3 Types of Simulated Disturbances������������������������������������������������������   60 4.4 Types of Simulated Results��������������������������������������������������������������   60 4.4.1 Results of Four Sample Method ������������������������������������������   60 4.4.2 Results of Sample-to-Sample Method����������������������������������   61 4.4.3 Results of Cycle-to-Cycle Method���������������������������������������   61 4.4.4 Results of Cumulative Sum Method ������������������������������������   62 4.5 Development of Relays��������������������������������������������������������������������   62 4.6 Basic Components of Microcontroller-Based Relay������������������������   65 4.7 Proposed Delay Time Setting for Different Relays��������������������������   66 4.8 Fault Response with Protection Schemes for Digital Relay ������������   66 5 Description of Microcontroller Circuit and MikroC Program������������   69 5.1 Introduction��������������������������������������������������������������������������������������   69 5.2 Microcontroller (18F452) ����������������������������������������������������������������   69 5.2.1 Features of PIC18F452 ��������������������������������������������������������   70 5.2.2 The PIC18F452 Consists of��������������������������������������������������   72 5.2.3 Oscillator Circuit������������������������������������������������������������������   72 5.3 LCD Display ������������������������������������������������������������������������������������   72 5.3.1 Features ��������������������������������������������������������������������������������   73 5.4 MAX 232������������������������������������������������������������������������������������������   74 5.4.1 Applications��������������������������������������������������������������������������   76 5.4.2 Features ��������������������������������������������������������������������������������   76 5.5 Interface of DAS ������������������������������������������������������������������������������   76 5.6 Software Design��������������������������������������������������������������������������������   77 5.7 Digital Relay MikroC Program Code ����������������������������������������������   77 5.8 Different Operating Cases of Digital Relay on Proteus ISIS������������   84 6 Experimental Setups and Results for Digital Relay Protection ����������   89 6.1 Introduction��������������������������������������������������������������������������������������   89 6.2 Experimental Setup of a SCIG-Based Wind Turbine�����������������������   89 6.2.1 Elements of the Experimental Setup������������������������������������   91 6.3 Main Components of the Interface Circuits Between Microcontroller and Power Circuit ��������������������������������������������������   93

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6.3.1 Current Transformer�������������������������������������������������������������   93 6.3.2 Sensor Current Transformer��������������������������������������������������   95 6.3.3 Contactor������������������������������������������������������������������������������   95 6.4 Hardware of Digital Relay����������������������������������������������������������������   95 6.4.1 Analog-to-Digital Interface Module ������������������������������������   96 6.4.2 Central Processing Module ��������������������������������������������������   97 6.4.3 Operator Interface and Digital/Output Module��������������������   97 6.5 Signal Condition Circuits������������������������������������������������������������������   97 6.5.1 The Voltage Circuits��������������������������������������������������������������   97 6.5.2 The Current Circuits ������������������������������������������������������������   98 6.5.3 The Frequency Circuit����������������������������������������������������������   98 6.6 Tripping Circuit��������������������������������������������������������������������������������   99 6.7 Testing the Relay Hardware��������������������������������������������������������������  100 6.7.1 Testing the Developed Software ������������������������������������������  100 6.7.2 Testing Over Current Protection Software����������������������������  100 6.7.3 Testing Over Voltage Protection Software����������������������������  100 6.7.4 Testing Under Voltage Protection Software��������������������������  100 6.7.5 Testing Over Frequency Protection Software ����������������������  101 6.7.6 Testing Under Frequency Protection Software ��������������������  101 6.8 Experimental Results and Discussion����������������������������������������������  101 6.9 The Effect of Digital Relay in Experimental Work��������������������������  106 6.10 Summary ������������������������������������������������������������������������������������������  108 7 Conclusions and Future Work����������������������������������������������������������������  111 7.1 Conclusions��������������������������������������������������������������������������������������  111 7.2 Future Work��������������������������������������������������������������������������������������  112 Appendices��������������������������������������������������������������������������������������������������������  113 References ��������������������������������������������������������������������������������������������������������  115 Index������������������������������������������������������������������������������������������������������������������  119

About the Authors

Nagwa F. Ibrahim  received her B.S. from the Faculty of Industrial Education, Suez Canal University, Suez, Egypt, in 2008; her M.Sc. from the Faculty of Industrial Education, Suez University, Suez, Egypt, in 2015; and her Ph.D. from the Faculty of Industrial Education, Suez University, Suez, Egypt, in 2019. She is currently an assistant professor in the Department of Electrical Power and Machine, Faculty of Technology and Education, Suez University. Her research interests are in the area of renewable energy sources, power system protection, power electronics, high voltage direct current (HVDC), control and power quality issues, control of power electronic converters, and electrical machine drives. Email: [email protected]   Electrical Power and Machines Department, Faculty of Technology and Education, Suez University, Suez, Egypt Sobhy  S.  Dessouky  was born in Dakahlie, Egypt, in 1946. He received his B.Sc. (1970) and M.Sc. (1977) degrees in electrical engineering from Suez Canal University and Helwan University, respectively. Dr. Dessouky received his Ph.D. degree from TU, Dresden, Germany, in 1982. From October 1970 to 1975, he worked in the Faculty of Engineering, Suez Canal University, as a demonstrator. Dr. Dessouky worked as a demonstrator from 1975 to 1977  in the Faculty of Engineering, Helwan University. In 1977, he worked as assistant lecturer in the Department of Electrical Engineering, Faculty of Engineering, Suez Canal University. From 1983 to 1987, Dr. Dessouky worked as assistant professor (lecturer) in the Department of Electrical Engineering, Faculty of Engineering, Suez Canal University, Port Said Campus. In 1987, he was promoted to associate xiii

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About the Authors

professor in the same Department. In 1991, Dr. Dessouky became a Full Professor of Electrical Power and H.V. Engineering. He is a member of IEEE since 1996. In parallel, he worked as a department chair, vice dean for community affairs and environment, and director of the Engineering Research Center for developing technological planning at Suez Canal University.  Electrical Engineering Department, Faculty of Engineering, Port Said University, Port Said, Egypt Hossam E. Mostafa Attia  (M'09) was born in Cairo, Egypt, in 1965. Received his B.Sc., M.Sc., and Ph.D. from the Faculty of Engineering, Ain Shams University, Cairo, Egypt, in 1987, 1994, and 1999, respectively. From 1991 to 1997, he worked with Egyptair as a second engineer. From 1997 to 2001, worked as a teacher assistant at the College of Technological Studies, The Public Authority of Applied Education and Training (Paaet)-, Kuwait. Since 2001, he has been a faculty member with the Electrical Department at the Faculty of Industrial Education (FIE), Suez University, Suez, Egypt. He was dean of the FIE 2011–2012. Hossam worked as an associate professor in the College of Engineering, Jazan University, Saudi Arabia, in the academic year 2008–2009. He was a faculty member in the Department of Electrical and Electronic Engineering Technology at Jubail Industrial college (JIC), Saudi Arabia, from June 2013 to August 2019 and chairman from November 2013 to August 2015. Since August 2019, Hossam has been working as a professor and dean of the Faculty of Technology and Education, Suez University, Egypt. He has published more than 41 papers in international journals and conferences. Hossam has supervised more than 25 Ph.D. and M.Sc. theses, mainly in control, protection, and power quality of power systems. HE is a peer reviewer for many international journals. Hossam was involved in preparing Egypt’s Smart Grid Roadmap “Egypt 2040” as a member of the Smart Grid working group, Egypt, 2010–2011. Email: [email protected]  Electrical Power and Machines Department, Faculty of Technology and Education, Suez University, Suez, Egypt Ali  H.  Kasem  Alaboudy  (Senior Member, IEEE) received his M.Sc. and Ph.D. degrees in electrical engineering from Minia University, Egypt, in 2002 and 2009, respectively. He joined Suez Canal University as a tenure-track demonstrator and became a teaching assistant in 2002, lecturer in 2009, assistant professor in 2011, and associate professor in May 2014. Dr. Alaboudy was an RA with ECE Department, University of Waterloo, Canada, and a PDF with Masdar Institute of Science and Technology, Abu Dhabi, UAE. Currently, Dr. Alaboudy is a program manager with a national

About the Authors

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R&D funding agency. He is expert in analyzing/addressing R&D gaps and designing thematic calls and research programs. Dr. Alaboudy was the recipient of the Suez Canal University annual awards for the excellent publication records in 2011 and 2012. His current research interests include smart grids, distributed generation, wind energy—control and power quality issues, and power system control and operation. Email: [email protected]  Electrical Power Engineering, Port Said University, Port Said, Egypt

List of Principal Symbols and Abbreviations

Symbols a, b, c, d, e, f, and g bkm c g1 and g2 i i1, i2, i3, and i4 K N n, B RL, LL Re, Le s S(n) T1 Y(n) CUSUM CTs cx CB GWEC IG IP I2 I 22 t

Description The coefficients of the quadratic

L-G L-L L-L-G L-L-L NREA PVES SCIG

Single line to ground fault Line to line fault Double line to ground fault Three phase fault New and Renewable Energy Authority Photovoltaic energy system Squirrel cage induction generator

The elements of this matrix Filter output The cusum indices Relay setting current Four equally spaced samples Constant of induction Machine Number of samples in a period The quadratic form matrix Resistance and inductance of load Resistance and inductance of transmission line Filter 2 outputs Sample value at instant n Threshold parameter Index value Cumulative sum method Current transformers Three-phase static capacitors bank Circuit breaker Global Wind Energy Council Induction generator Pickup current The negative phase sequence current The rotor heating criterion

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Symbols SEIG TF VTs WES WTGS CSWT DFIG GSC GWEC NREA PV PMSG PWM VSWT WRIG WECS

List of Principal Symbols and Abbreviations

Description Self-excited induction generator Three-phase transformer Voltage transformers Wind energy system Wind turbine generators Constant speed wind turbine Doubly-fed induction generator Grid side converter Global Wind Energy Council New and Renewable Energy Authority Photovoltaic Permanent magnet synchronous generator Pulse width modulation Variable speed wind turbine Wound rotor induction generator Wind energy conversion system

List of Figures

Fig. 1.1 Fig. 1.2 Fig. 1.3 Fig. 1.4 Fig. 1.5 Fig. 1.6 Fig. 1.7 Fig. 1.8 Fig. 1.9 Fig. 1.10

Worldwide power generation capacity (GW)�������������������������������������   2 Global PV–wind energy capacity installations�����������������������������������   3 Egypt wind atlas����������������������������������������������������������������������������������   4 Overview map for the Gulf of Suez in Egypt�������������������������������������   5 Annual and cumulative wind installations by 2030����������������������������   6 Total installed capacity of wind farms in Egypt according to the New and Renewable Energy Authority (NREA)����������������������   6 Schematic diagram of constant-speed wind turbine system���������������   8 Limited variable-speed wind turbine system��������������������������������������   9 Schematic diagram of variable-speed wind turbine with DFIG�������������������������������������������������������������������������������������������  10 Schematic diagram of variable-speed wind turbine with full-scale power converter�����������������������������������������������������������  11

Fig. 2.1 The study system���������������������������������������������������������������������������������  20 Fig. 2.2 The MATLAB/Simulink System��������������������������������������������������������  21 Fig. 2.3 Voltage and current wave form when a three-phase fault occurs at point F. (a) Voltage wave form. (b) Current wave form������  22 Fig. 2.4 Rotor speed (ωn) and electromagnetic torque (Te) form when a three-phase fault occurs at point F. (a) Rotor speed variation. (b) Electromagnetic torque variation��������������������������������������������������  23 Fig. 2.5 Active and reactive power (P, Q) form when a three-phase fault occurs at point F����������������������������������������������������������������������������������  24 Fig. 2.6 Voltage and current wave form when a double line-to-ground fault occurs at point F. (a) Voltage wave form. (b) Current wave form�����������������������������������������������������������������������������������������������������  25 Fig. 2.7 Electromagnetic torque (Te) and rotor speed (Wn) forms. (a) Electromagnetic torque variation. (b) Rotor speed variation��������  26 Fig. 2.8 Active and reactive power (P, Q) form when double line-to-ground fault occurs at point F�������������������������������������������������  27

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List of Figures

Fig. 2.9 Voltage and current wave form when a line-to-line fault occurs at point F. (a) Voltage wave form. (b) Current wave form������������������  28 Fig. 2.10 Electromagnetic torque (Te) and rotor speed (ωn) form when a line-to-line fault occurs at point F. (a) Electromagnetic torque (Te) variation. (b) Rotor speed (ωn) variation������������������������������������  29 Fig. 2.11 Active and reactive power (P, Q) form when a line-to-line fault occurs at point F����������������������������������������������������������������������������������  30 Fig. 2.12 Voltage and current wave form when a single line-to-ground fault occurs at point F. (a) Voltage wave form. (b) Current wave form�����������������������������������������������������������������������������������������������������  31 Fig. 2.13 Rotor speed (ωn) and electromagnetic torque (Te) form when a single line-to-ground fault occurs at point F. (a) Rotor speed variation. (b) Electromagnetic torque variation����������������������������������  32 Fig. 2.14 Active and reactive power (P, Q) form when a single line-to-ground fault occurs at point F��������������������������������������������������  33 Fig. 2.15 Voltage and current wave form when a three-phase fault occurs at point F, clearing through IG model. (a) Voltage wave form. (b) Current wave form������������������������������������������������������������������������  33 Fig. 2.16 Rotor speed (Wn) and electromagnetic torque (Te) form when a three-phase fault occurs at point F, clearing through IG model. (a) Rotor speed variation. (b) Electromagnetic torque variation��������  34 Fig. 2.17 Active and reactive power (P, Q) form when a three-phase fault occurs at point F, clearing through IG model�������������������������������������  35 Fig. 2.18 Voltage and current wave form when a line-to-line fault occurs at point F, clearing through IG model. (a) Voltage wave form. (b) Current wave form������������������������������������������������������������������������  36 Fig. 2.19 Rotor speed (Wn) and electromagnetic torque (Te) form when a line-to-line fault occurs at point F, clearing through IG model. (a) Rotor speed variation. (b) Electromagnetic torque variation��������  37 Fig. 2.20 Active and reactive power (P, Q) form when a line-to-line fault occurs at point F, clearing through IG model�������������������������������������  38 Fig. 2.21 Voltage and current wave form when a double line-to-ground fault occurs at point F, clearing through IG model. (a) Voltage wave form. (b) Current wave form�����������������������������������������������������  38 Fig. 2.22 Rotor speed (ωn) and electromagnetic torque (Te) form when a double line-to-ground fault occurs at point F, clearing through IG model. (a) Rotor speed variation. (b) Electromagnetic torque variation����������������������������������������������������������������������������������������������  39 Fig. 2.23 Active and reactive power (P, Q) form when a double line-to-ground fault occurs at point F, clearing through IG model�����  40 Fig. 2.24 Voltage and current wave form when a single line-to-ground fault occurs at point F, clearing through IG model. (a) Voltage wave form. (b) Current wave form���������������������������������������������������������������  41

List of Figures

xxi

Fig. 2.25 Rotor speed (Wn) and electromagnetic torque (Te) form when a single line-to-ground fault occurs at point F, clearing through IG model. (a) Rotor speed variation. (b) Electromagnetic torque variation����������������������������������������������������������������������������������������������  42 Fig. 2.26 Active and reactive power (P, Q) form when a single line-to-ground fault occurs at point F, clearing through IG model�����  43 Fig. 3.1 Fig. 3.2 Fig. 3.3 Fig. 3.4 Fig. 3.5 Fig. 3.6 Fig. 3.7 Fig. 3.8 Fig. 3.9

The induction generator protection scheme����������������������������������������  46 Sample-to-sample comparison approach��������������������������������������������  47 Cycle-to-cycle comparison approach��������������������������������������������������  48 Complementary signals and variation of indices��������������������������������  49 Four sample approach�������������������������������������������������������������������������  50 Flowchart of over/under frequency relay��������������������������������������������  53 Flowchart of digital relay��������������������������������������������������������������������  55 Flowchart of over-current relay����������������������������������������������������������  56 Flowchart of over/under voltage relay������������������������������������������������  56

Fig. 4.1 The calculated values of different algorithms under SLG fault and tripping�����������������������������������������������������������������������������������������  60 Fig. 4.2 The calculated values of different algorithms under SLG fault and tripping for (sample-­to-­sample method)��������������������������������������  61 Fig. 4.3 The calculated values of different algorithms under SLG fault and tripping for (cycle-to-­cycle method)��������������������������������������������  62 Fig. 4.4 The calculated values of different algorithms under SLG fault and tripping for cumulative sum method��������������������������������������������  63 Fig. 4.5 The calculated values of different algorithms under SLG fault and tripping for cumulative sum method��������������������������������������������  63 Fig. 4.6 The calculated values of different algorithms under SLG fault and tripping for cumulative sum method��������������������������������������������  64 Fig. 4.7 Basic components of digital relay�������������������������������������������������������  65 Fig. 4.8 Effect of circuit breaker operation on digital relay. (a) Current waveform when single line-to-ground fault occurs at point F. (b) Response of digital relay after connection circuit breaker������������  67 Fig. 4.9 Effect of circuit breaker operation on the over-current relay. (a) Current waveform when single line-to ground-fault occurs at point F when circuit breaker tripps. (b)Response of digital relay before connection circuit breaker�����������������������������������������������  68 Fig. 5.1 Fig. 5.2 Fig. 5.3 Fig. 5.4 Fig. 5.5 Fig. 5.6

Microcontroller PIC18F452 Pin Configuration����������������������������������  71 Pin Configuration of a 16 × 2 LCD Display���������������������������������������  73 Level converter circuit using MAX232����������������������������������������������  75 Pin configuration of an MAX232�������������������������������������������������������  75 Complete schematic����������������������������������������������������������������������������  84 Monitoring and transmitting the generator parameters using microcontroller with Proteus software in normal operation���������������  85

xxii

List of Figures

Fig. 5.7 Monitoring and transmitting the generator parameters using microcontroller with Proteus software in over-current case�������������   85 Fig. 5.8 Monitoring and transmitting the generator parameters using microcontroller with Proteus software in over voltage case�������������   86 Fig. 5.9 Monitoring and transmitting the generator parameters using microcontroller with Proteus software in three-phase short circuit case�����������������������������������������������������������������������������������������   86 Fig. 5.10 Monitoring and transmitting the generator parameters using microcontroller with Proteus software in three-phase short circuit and over frequency case���������������������������������������������������������   87 Fig. 5.11 Monitoring and transmitting the generator parameters using microcontroller with Proteus software in under frequency case�������   87 Fig. 6.1 Fig. 6.2 Fig. 6.3 Fig. 6.4 Fig. 6.5 Fig. 6.6 Fig. 6.7 Fig. 6.8 Fig. 6.9 Fig. 6.10 Fig. 6.11 Fig. 6.12 Fig. 6.13 Fig. 6.14 Fig. 6.15 Fig. 6.16 Fig. 6.17 Fig. 6.18 Fig. 6.19 Fig. 6.20 Fig. 6.21 Fig. 6.22 Fig. 6.23 Fig. 6.24 Fig. 6.25 Fig. 6.26 Fig. 6.27 Fig. 6.28

Schematic diagram of isolated induction generator��������������������������   90 Experimental setup of a SCIG-based wind turbine���������������������������   90 SCIG-based wind turbine setup��������������������������������������������������������   91 A wide-ranging AC/DC power supply����������������������������������������������   92 Three-phase load with resistive and inductive parts�������������������������   93 Digital storage oscilloscope device GRS -6032A-30MHz���������������   94 The circuits tie between the microcontroller and the power circuit������������������������������������������������������������������������������������������������   94 Block diagram of digital relay circuit�����������������������������������������������   96 Voltage sensor interface circuit���������������������������������������������������������   97 Current sensor interface circuit���������������������������������������������������������   98 The frequency sensor interface circuit����������������������������������������������   99 Trip circuit�����������������������������������������������������������������������������������������   99 Voltage wave form in case of over voltage���������������������������������������  101 Current wave form in case of over voltage���������������������������������������  102 Generator speed in case of over voltage�������������������������������������������  102 Voltage wave form in case of under voltage�������������������������������������  103 Current wave form when under voltage case������������������������������������  103 Generator speed in case of under voltage�����������������������������������������  104 Voltage wave form in case of short circuit fault�������������������������������  104 Current wave form in case of short circuit fault�������������������������������  105 Generator speed in case of short circuit fault������������������������������������  105 Voltage wave form in case of short circuit fault and clearing�����������  106 Current wave form in case of short circuit fault and clearing�����������  106 Generator speed in case of short circuit fault and clearing���������������  107 Normal condition for digital relay����������������������������������������������������  107 Under voltage relay���������������������������������������������������������������������������  108 Over voltage relay�����������������������������������������������������������������������������  108 (a) and (b) Effect of digital relay in experimental work�������������������  109

List of Tables

Table 1.1 Advantages and disadvantages of the major wind turbine generators�����������������������������������������������������������������������������������������   7 Table 1.2 Advantages and disadvantages of different WECS configurations.�������  11 Table 3.1 The setting of each of the induction generator relays����������������������  46 Table 5.1 The 18F452 microcontroller feature�������������������������������������������������  70 Table 5.2 The pin diagram of the 16 x 2 LCD display�������������������������������������  74 Table 6.1 SCIG and DC shunt machine data����������������������������������������������������  91 Table 6.2 Three-phase AC/DC power supply data�������������������������������������������  92 Table 6.3 Three-phase resistive and inductive load data����������������������������������  93

xxiii

Chapter 1

Introduction and Previous Work

1.1  Preface The global demand for electrical energy is increasing day by day. While demand is increasing, the fossil fuel reserves decrease and the cost of electrical energy production increases. Many old power plants will soon reach to the end of their working periods. The world may have to face a severe energy crisis in the future in the absence of suitable preventive methods, as discussed in [1]. Some projects indicate that the global energy demand will be tripled by 2050. Renewable energy production is quickly growing because of the depletion of fossil fuels and the increase of polluted emission caused by conventional sources [2]. Therefore, increasing demand of power will need clean power from renewable resources such as wind, solar, biomass, and geothermal power. Among all the renewable energy sources, wind and solar power have gained a lot more growth compared to their growth in the last few years. Recently, greater importance is placed on using the hybrid systems, especially in remote locations, for stand-alone applications [3]. The reasons behind preferring renewable energy sources over other conventional power sources can be summarized as follows [4]: • Renewable energy is environmentally friendly compared with traditional electricity generation. • Renewable energy is free and clean. • It cannot be exhausted. • Renewable energy is the lowest-priced. • High accessibility to reliable electricity at any time. • Reduce the dependency on fossil fuels and oil price fluctuations. • Increase economic productivity and create local employment opportunities. • Allow for a better use of local natural resources. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 N. F. Ibrahim et al., Protection of Wind Turbine Generators Using Microcontroller-Based Applications, Green Energy and Technology, https://doi.org/10.1007/978-3-030-92628-1_1

1

2

1  Introduction and Previous Work

The disadvantages of renewable energy sources are as follows: • • • •

They require a wide area for constructions. High fixed and construction costs. The output power fluctuates in a wide range and can be discontinued. The site locations can be far away from local loads, which require very long transmission system. • The generated power can be DC, which needs power electronic converters to be supplied to the grid or AC loads. • Sometimes, they cause environmental problems, such as killing of birds by wind turbines; to avoid that the location must be selected carefully. Based on the research of New Energy Finance, Fig. 1.1 shows the worldwide power generation capacity, which indicates the world is now adding more capacity for renewable energy every year than fossil fuels, such as coal, natural gas, and oil, since 2013. This shift will continue to accelerate, and by 2030 more than four times as much renewable capacity will be added. The key feature of the figure is the rapid expansion of renewable energy in developing countries [5]. Compared with other renewables, wind and photovoltaic (PV) system have been established as proven future sources of energy because of their environment-­ friendly, safe, wide availability around the world, and cost-effective characteristics as shown Fig. 1.2 [6].

Fig. 1.1  Worldwide power generation capacity (GW) [5]

1.3  Wind Energy Resources Market

3

Fig. 1.2  Global PV–wind energy capacity installations [6]

1.2  Wind Energy Conversion System Wind energy conversion systems (WECS) involve many fields of various disciplines, such as kinematics, mechanics, aerodynamics, meteorology, power electronics, power systems, as well as topics covered by structural and civil engineering. Wind is a sustainable energy source since it is renewable, widely distributed, and plentiful. In addition, it contributes to reducing greenhouse gas emissions since it can be used as an alternative to fossil fuel–based power generation. Wind turbines capture the kinetic energy of winds and convert it into a usable form of energy. The kinetic energy of winds rotates the blades of a wind turbine. The blades are connected to a shaft, which is coupled with an electric generator. The generator converts the mechanical power into electrical power. The electric output power is supplied to definite loads in the isolated system, and it can be also supplied to the national grid in the grid connected system [7].

1.3  Wind Energy Resources Market Egypt enjoys excellent wind along the Suez Gulf with an average wind speed of 10.5 m/s at 50 meters height, and Egypt is just one of 38 countries in the world with a published National Wind Atlas [8], as shown in Fig. 1.3. Coastal zones in Egypt enjoy a high wind energy potential. The Red Sea coast, particularly at the Gulf of Suez, is one of the windiest areas of the world [9], as shown in Fig. 1.4. Recent years have seen unprecedented growth in the global wind market. According to the Global Wind Energy Council (GWEC), the global wind energy capacity installations are being increased from 2006 to 2030 [10], as shown in Fig. 1.5. Egypt is an excellent wind regime, especially in the Gulf of Suez, where the average wind speed reaches 10 m/s according to New and Renewable Energy Authority (NREA). The total installed capacities from wind energy projects reached 550 MW

4

1  Introduction and Previous Work

Fig. 1.3  Egypt wind atlas [8]

in Zafarana and Hurghada wind farms in 2013, as shown in Fig. 1.6 [11]. The new installed capacity increased to 750 MW in the first quarter of 2015, when the construction of the new 200  MW in Gabal Elzayt wind farm was completed. These projects were implemented in cooperation with Denmark, Germany, Spain, and Japan [12]. The Supreme Council of Energy has approved an ambitious plan that aims to reach 20% of total generated electricity through renewable energy by the year 2020, including 12% from wind energy. This will be achieved by establishing grid-connected wind farms with a total capacity of 1375 MW [13-14].

1.4  Types of Wind Turbine Generators Generators can be basically classified by the type of current. There are alternating current generators and direct current generators. But in either case, the voltage generated is alternating. By adding a commutator, we convert it to direct current. So, for convenience, we go for alternating current generator.

1.4  Types of Wind Turbine Generators

Fig. 1.4  Overview map for the Gulf of Suez in Egypt [10]

5

6

1  Introduction and Previous Work 18 16

300

14 250

12

200

10

150

8 6

100

4 50

Annual Installed Capacity (GW)

Cumulative Installed Capacity (GW)

350

2 0

30

28

20

26

20

20

24 20

22 20

20

18

Cumulative GW Installed (Left Axis)

20

20

16 20

14 20

12

10

20

08

20

20

20

06

0

Annual GW Installed (Right Axis)

Fig. 1.5  Annual and cumulative wind installations by 2030 [10]

Fig. 1.6  Total installed capacity of wind farms in Egypt according to the New and Renewable Energy Authority (NREA) [14]

In the AC generators, we can further classify them based on the rotor speed. There are synchronous generators (constant speed machine) and asynchronous generators (variable-speed machine or the induction machine). In the synchronous generators, we have a salient pole rotor and a cylindrical (nonsalient pole) rotor. Based

1.5  Wind System Topologies

7

Table 1.1  Advantages and disadvantages of the major wind turbine generators Type Induction generator Synchronous generator Permanent magnet generator Doubly fed induction generator

Advantages – Full speed range, no brushes on the generator, complete control of active and reactive power – Full speed range, possible to avoid gear, complete control of active and reactive power – Full speed range, possible to avoid gear, lower losses, brushless (low maintenance), no power converter for field – Limited speed range of -30% to 30% around synchronous speed, inexpensive small capacity, PWM inverter complete control of active and reactive power

Disadvantages – Full scale power converter, need for gear – Small converter for field, full scale power converter – Full scale power converter, multi pole, expenditure of PM material is high, manufacturing, assembling, and maintenance are difficult – Need slip rings, need for gear, need to four-quadrant PWM frequency converter

on the speed requirement/availability, we can go for the cylindrical rotor for high-­ speeds and salient pole rotor for low speeds. Another classification is based on the magnetic field. The magnetism can be done by either permanent magnet or an electromagnet. In order to reduce the supply requirement, we go to the permanent magnet synchronous generator (PMSG) for power generation using wind energy. An induction motor running with negative slip can operate as an induction generator. But this generator is not self-exciting, and this has to be excited by a source of fixed frequency. It already needs an exciter for the stator. So, this machine has to be fed by two supplies, and hence, it is called doubly fed induction machine or generator (DFIG) [12-15]. So, DFIG and PMSG are suitable for wind power generation. In this thesis, DFIG is used for wind power generation. Table  1.1 briefly gives the advantages and disadvantages of the major wind turbine generators.

1.5  Wind System Topologies Based on the speed range of operation, there are two types of wind turbines: constant speed and variable speed. Generators of constant speed wind turbine systems (CSWTs) are connected to the grid directly. Therefore, the speed, which is similar to the grid frequency, is not controllable and the wind variations will affect the power quality of the grid. On the other hand, variable-speed wind turbine systems (VSWTs) are equipped with power electronics converters. The converters can control the rotor speed and stabilize the wind power fluctuations. Therefore, the VSWTs can strongly improve the power quality compared to the CSWTs. The most common types of wind turbine technologies that dominated the global market in the last decade are [14-16]:

8

1  Introduction and Previous Work

• Constant speed wind turbines (squirrel cage induction generator) • Limited-variable-speed wind turbines (wound rotor induction generator with variable rotor resistance) • Variable-speed wind turbine system that can be classified into two basic categories according to the rating of the power converters • Variable-speed wind turbine with partial-scale frequency converter (doubly fed induction generator) • Variable-speed wind turbine with full-scale frequency converter (synchronous generator and permanent magnet generator).

1.5.1  Constant Speed Wind Turbine Systems A CSWT consists of a conventional squirrel cage induction generator (SCIG) directly coupled to the grid with superior characteristics, such as brushless and rugged construction, low cost, and free maintenance. Because the SCIG operates only in a narrow range around the synchronous speed, approximately 1–2 % of the rated speed, this type of wind energy conversion system is normally referred to as a constant or fixed speed wind turbine. Regardless of its robustness and cheap and simple design of this machine, its controllability is relatively poor. Therefore, the price of constant speed turbines tends to be lower than that of variable-speed turbines [14-­ 17]. In constant speed turbines, the rotor is coupled with an induction generator via speed increasing gears, as shown in Fig. 1.7. The stator winding of the generator is directly connected to the grid. Generally, induction generators require reactive power from the grid. This may result in undesirable voltage variations, especially in weaker networks. To avoid this problem, capacitors are provided in the circuit, as shown in Fig. 1.7.

Fig. 1.7  Schematic diagram of constant-speed wind turbine system [14]

1.5  Wind System Topologies

9

Fig. 1.8  Limited variable-speed wind turbine system [14]

1.5.2  Limited Variable-Speed Wind Energy Conversion System The configuration of limited variable-speed WECS employs a wound rotor induction generator (WRIG) that is equipped with an external variable resistance connected to the rotor through a converter, as shown in Fig.  1.8. By controlling the converter, the value of the effective external resistance can be controlled. By increasing the total rotor resistance, the location of maximum torque in the torque-slip characteristic curve of the WRIG is shifted toward the higher slip region. In this configuration, the range of rotor speed control is limited to 10% over the synchronous speed (Ns) of the WRIG. During variation of the wind speed, the wind power fluctuation is converted into kinetic energy of the wind turbine shaft and then dissipated into heat in the external resistance. However, the main drawbacks of a WECS finite-velocity system are that the active and reactive power cannot be controlled independently and the energy loss in the external resistance is an important challenge to be controlled. Furthermore, the WRIG draws reactive power from the electrical grid for its excitation therefore; the capacitor banks are employed to improve the power factor [13].

1.5.3  Variable Speed Wind Turbine Systems In variable-speed systems, the generator is normally connected to the grid by a power electronics system. VSWTs can be classified according to the rating of the power converters into two configurations: • Variable-speed wind turbine with a partial-scale power converter • Variable-speed wind turbine with a full-scale power converter

10

1  Introduction and Previous Work

Fig. 1.9  Schematic diagram of variable-speed wind turbine with DFIG [14]

1.5.3.1  V  ariable Speed Wind Turbine with a Partial-Scale Power Converter This configuration is known as the DFIG-based wind turbine, which corresponds to a variable-speed wind turbine with a WRIG. A partial-scale power converter on the rotor circuit is illustrated in Fig. 1.9. The stator is directly connected to the grid, whereas the rotor is connected through a power electronic converter. The power converter controls the rotor frequency and thus the rotor speed. This concept supports a wide speed range operation, depending on the size of the frequency converter. Depending on the converter size, this concept allows a wider range of speed variations of approximately ± 30% around synchronous speed [14]. Furthermore, it is possible to control both active (Pref) and reactive power (Qref), which gives a better grid performance. Moreover, the converter system provides reactive power compensation and smooth grid connection. Since the frequency converter transmits only the rotor power, it can be designed for typically 25–30% of the total turbine power. This makes the turbine configuration very attractive from an economic point of view compared to turbines with full-scale converters. 1.5.3.2  Variable Speed Wind Turbine with a Full-Scale Power Converter In the configuration of variable-speed WECS with full-scale converter, the electrical generator is directly connected to the electrical grid through a full-scale back-to-­ back converter, as depicted in Fig. 1.10. The main objective of the generator side converter is to control the rotational speed of the generator to capture the maximum power from the wind turbine during variation of the wind speed. On the other hand, the grid side converter is employed to regulate the DC-bus voltage and control the injected reactive power into the electrical grid. This configuration has a wider range of speed control than the configuration of the variable-speed wind turbine with DFIG. Moreover, this configuration offers a great flexibility in operation and control during the grid faults. However, the main drawback of this configuration is the increased complexity and cost of the system. Furthermore, the employed power

1.6  Induction Generator

11

Fig. 1.10  Schematic diagram of variable-speed wind turbine with full-scale power converter [14] Table 1.2  Advantages and disadvantages of different WECS configurations. Configuration type Advantages Fixed-speed WECS – Simplicity, low cost, robustness

Limited-variable WECS

– Variable speed, fast control low harmonics

Variable-speed WECS with DFIG

– Independent control of active and reactive power, reduced capacity of power electronics lower losses, a wide range of speed control, smooth grid connection – A wider range of speed control, good performance during grid faults, smooth grid connection, operates at unity power factor

Variable-speed WECS with full-scale converter

Disadvantages – Need reactive power compensator low power factor, high mechanical stress, not support any speed control – Limited variable speed, low power factor, need reactive power compensator, more power losses – The existence of brush/slip ring, sensitivity to grid faults

– Higher generator and power electronics cost, full-scale converter, larger size, more complexity

converter is rated at full-scale power capacity since it handles the entire output power of the generator [13]. After giving an overview of the different configurations of the WECS, the advantages and disadvantages of these configurations can be summarized in Table 1.2.

1.6  Induction Generator The induction generator has a construction as an induction motor with some possible improvements in efficiency. There is an important operating difference; the rotor speed is advanced with respect to stator magnetic field rotation. For prime mover speed above synchronous speed, the rotor is being driven at a speed more than synchronously rotating magnetic field. The rotor conductors are now being cut by the rotating flux in a direction opposite to that during motoring mode. This shows that rotor-generated electric and magnetic fields (EMF), rotor current and hence its

12

1  Introduction and Previous Work

stator components changes their signs. As the speed during induction generator operation is not synchronous, it is also called an asynchronous generator.

1.6.1  Induction Generator Operation The induction generator like a synchronous generator requires excitation in order to produce voltage and becomes a source of electrical power. While a synchronous machine derives its excitation from a separate source, the induction unit must draw its magnetizing current from the intertied utility system or from capacitors located near the unit. Without excitation from some sources, the induction generator can’t sustain a terminal voltage with any load connected to it. The operation of connecting an induction generator with the utility grid is simpler than with synchronous generator. Until the induction generator’s circuit breaker has been closed, it will usually not be able to develop any significant terminal voltage. Because of this, accurate matching of generator voltage with utility voltage is not necessary. Short circuit performance is another difference between the induction generator and the synchronous generator. A detailed study of the IG performance under different faults is given in Chap. 2. In a three-phase fault, current can’t be transferred past the fault point to the induction generator, and therefore, the unit loses its excitation. If capacitors are provided for the unit, again resulting in removal of excitation from the generator [18].

1.6.2  Induction Generator Protection In this chapter, the problem of providing relay protection for a wind turbine–driven induction generator connected to a power system is investigated. The induction generator protection scheme and relay settings are described. It is assumed that the used relays are all digital (microcontroller-based).

1.6.3  Protection Requirement for Induction Generator The protection requirements for induction generator are divided into several fundamental categories. These protection functions are discussed in the following section: (a) Over-Current Protection Device The induction generator should be protected against excessive damage due to severe stator faults. The utility source will often be able to inflict more damage than the induction machine itself. The voltage drop should be sufficient to detect the fault

1.6  Induction Generator

13

since the fault would be very close to the relaying point. To accelerate tripping, over-current (OC) relays are used. In spite of sensitivity problems, this relay is the minimum acceptable level of protection for short circuits and often is sufficient for smaller machines [19]. This relay must be set high enough to allow the large magnetizing inrush currents on initial energization. Settings designed to ride through this high current provide only limited protection for internal machine faults. The relay is to be set at 125–135% of the rated current of the induction machine. (b) Overload Protection Device Overload protection is the truest form of protection if applied correctly to remove the generator from service before it is damaged. The damage would be a result of the generator not being able to dissipate the added heat associated with an overload current or with an ambient temperature greater than the design limit. Overload is detected by either over-current or overload relays. (c) Rotor Overheating Protection Device The rotor of an induction generator is susceptible to overheating due to unbalanced loads or voltages in the connected system. Open phases on the utility tie line represent one extreme of unbalance while a single line-to-ground fault is the other extreme. A voltage unbalance of 3.5% can produce a 25% or greater increase in induction generator temperature rise [20]. This results primarily from negative sequence current produced by the unbalanced voltage. The negative sequence current produces flux in the generator airgap rotating in the opposite direction from the rotor direction. Thus, essentially double frequency current is induced in the rotor. The rotor can quickly become overheated, and serious damage would result if the induction generator is allowed to continue operating in this condition. The temperature rise caused by this energy input to the rotor is proportional to

K = I 22 t

(1.1)

where I 22 t is the rotor heating criterion and K is a constant for the machine. The negative phase sequence current (I2) is expressed in terms of per unit stator current at rated KVA, and t is the duration of the fault in seconds [21]. Negative-sequence current relays (NS) provide a very accurate method for detecting the component of current that has the most impact on rotor heating. These relays provide very excellent protection for an induction generator [22]. However, there is a lack of design data and references for determining individual unit capabilities. Nevertheless, as indicated in reference [22], the parameter K can be chosen to be a value equal to 4 for the induction generators 125 HP. (d) Under Voltage Protection Device Because a fault at the substation (Infinite bus in Fig. 2.1) looks similar to a fault at the generator’s terminals, due to the large reactance of the small induction generators, a protective relay designed to separate the generator under terminal fault condition would probably suffice for remote faults. This effect must be taken into account,

14

1  Introduction and Previous Work

however, in specifying the trip setting [20, 24]. Three under voltage relays (UV) are used for three phase fault. Their settings are typically 80% of normal voltage; time delay is one second, assuming that the time delay of the longest substation feeder over-current relay is 0.5 seconds. One disadvantage of voltage sensing is that the faults in the voltage transformer circuit may cause malfunctions of the under voltage relays. That is why the distribution engineers are reluctant to approve a voltage relaying scheme. Since a negative sequence current relay is used for detecting asymmetrical faults, the sensitive unit of the relay and a hold circuit can be used to avoid malfunction of the under-voltage relays [25]. (e) Over Voltage Protection Device Three over voltage relays (OV) are used to protect the IG against over voltages caused by switching, resonance, and islanding. In the following two subsections, the reactance and the islanding phenomenon are explained: (f) Resonance Phenomenon As over voltages develop so fast, the induction generator could have a resonance problem. Since most small wind turbine induction generators do not have speed control mechanisms, the resonance problem could be more serious than that of the synchronous generator [20]. The possibility that resonance between the magnetizing inductance of the generator and the connected capacitance, after fault condition and the generator disconnection from a utility, may cause damaging over voltages [24]. The generator may be of sufficient size to produce an over voltage approaching 73% above normal. Under conditions of ferroressonance, voltages above 300% of normal are possible. User loads and utility lightning arresters may not be capable of withstanding such an over voltage, even for 0.2 sec. However, single line to ground (SLG) fault may cause one phase of the generator to lose its excitation. This would make resonance less severe [20]. Also the grounded wye-delta transformer with the high tension side in grounded wye will make resonance much less likely. The grounded wye-delta connections can also prevent excessive phase-to-ground over voltages, during backfeed to SLG faults [24]. Transformer grounding is a problem of the whole system. The principal purpose of grounding is to minimize potential transient over voltages; to comply with local, state, and national codes for system safety requirements; and to assist in rapid detection and isolation of the trouble or fault areas. (g) Islanding Islanding is the condition where an induction generator is separated from the utility and continues to feed load to an unfault feeder section. The voltage that the machine induces during its islanding condition can be dangerous for the maintenance personnel or damage the equipment that is sensitive to voltage or frequency deviations. A possible reclosing of the feeder line could also damage the induction generator due to out-of-phase resynchronization. The

1.6  Induction Generator

15

terminal capacitor may cause "self-excitation" and result in high voltages under disconnection from the grid and subsequent over speeding of the turbine [26]. The problem can arise also when no capacitor banks are in island if the capacitance of utility overhead lines and cables is sufficient. If the charging or capacitor bank kilovolt-ampere reactive (KVAR) exceed the reactive load in the island, at least modest over voltages are likely to occur upon trip of the breaker that causes the islanding. Self-excitation must be prevented, and voltages more than about 15% above normal should be avoided. Higher voltages cause transformer saturation that will generate harmonics. These harmonics can cause surge arresters to fail and prevent proper operation of relays [25]. Since load on the generator significantly affects the over voltages that occur upon formation of an island, predicting over voltages is difficult. Simulations are the most reliable means of assessing the potential problems and determining the solution [25]. Over voltage detection from relaying points is simulated in the next chapter with other relaying approaches. (h) Over Speed Protection Device It is usually uneconomical to build a prime mover and generator that will be able to withstand a continuous over speed. Therefore, this condition should be sensed and corresponding protection action should be taken. As a consequence of the large voltage drop, due to fault condition, the electromagnetic torque decreases significantly, resulting in an excessive acceleration. If the over speed continues beyond an acceptable time limit, then action should be taken to stop or remove the power source from the prime mover in order to avoid damage of the machine. The over speed relay (O S) setting is 110% of the normal rotor speed [20]. (i) Over and Under Frequency Protection Device When operating in an isolated mode, generator speed control (speed-controlled prime mover) may not be able to maintain frequency within acceptable limits. Under/over frequency protection provides an additional method of tripping an isolated unit to ensure that it does not supply other customers with incorrect frequency [24]. Frequency information is one of the most important parameters for system monitoring and control. Load shedding, load restoration, generator protection from over speeding and detection of the generation load out of step conditions may in general be based on the small frequency deviation measurements. For generators, the over excitation detection and voltage and current estimates during startup and shutdown procedure may be based on the off-nominal frequency deviation measurements [27]. Over and under frequency relays (OF/UF) detect islanding. The relays settings are 105% rated frequency and 95% rated frequency. In [20], Chen says that since the permissible operating range of frequency is smaller than that of the speed, one can expect that frequency relaying will be more sensitive than speed relaying upon islanding. This argument is true. Out of the simulations of the frequency deviation

16

1  Introduction and Previous Work

algorithm (next chapter), it has been found that the generator frequency relays reach their settings before the speed settings since the traces of the frequency deviation and the over speeding is almost the same. (j) Reverse Power Protection Device Reverse power relays are used to sense direction of power flow and to disconnect the induction generator when it begins to operate as a motor. A reverse power relay is recommended in all application. Many traditional protective devices are unnecessary because of the fundamental differences in performance between induction and synchronous generators. Examples of relays are not required for an induction generator; such relays included loss of excitation, synchronizing check, and voltage balance [23]. Former studies were of limited range, and, at the same time, they mostly focused on the protection of doubly fed induction generators (DFIG), e.g., crowbar protection is a well-known method in DFIG protection. Sattar et.al. [28] presented the crowbar and its usage when it comes to protecting the rotor converter against short circuit current during faults. They found that the stator and rotor transient currents decay rapidly to value with amplitude less than 1 p-u and, the rotor circuit is properly protected when the crowbar is activated. Krisztina Leban in ref. [29] has presented dump resistor protection the crowbar and dump resistor and using it to protect the rotor converter against short circuit current during faults. By comparing crowbar to dump resistor, it is concluded that the dump resistor is better than crowbar protection [30]. Microprocessor relay is a well-known method in SCIG.  Attia [26] presented the protection of the induction generator against short circuit current, under voltage, over/under frequency, and negative sequence during faults and presented the new frequency protection algorithm that based on quadratic forms of voltage signal sample, which was measured at the generator terminals. In order to overcome the difficulty described previously, this work studies the transient response of grid-connected SCIG subjected to short circuit fault at the generator terminals of wind turbine. A simulation model of wind turbine with SCIG is investigated, and the protection schemes of the system are described. In addition, four sample methods are employed to apply symmetrical and unsymmetrical faults and design the protection schemes of the SCIG with the wind turbine. Protection of an induction generator–based system differs significantly from a simpler plant with a synchronous generator. Many traditional protective devices are unnecessary because of the fundamental. Electromechanical relays are in general reliable and have low requirements on operation environment. They are still in wide application today, but they have some shortcomings, such as: maintenance problem, slow in action, high power consumption for auxiliary mechanisms, and, worst of all, incapability of implementing complex characteristics. Compared with electromechanical relays, static (solid state) relays are faster, more accurate, and can realize more complex functions. They have a wide practical application in transmission line protection. They require much less power consumption and little maintenance. But they have some points: the reliability of the overall relay is affected by individual electronic components, and these electronic components are sensitive to ambient

1.7  Book Objectives

17

temperature and may cause relay maloperation. Today computer relays are preferred for economic and technical reasons. Advances in computer hardware are accompanied by analytical developments in the field of relaying [31].

1.6.4  The Advantages Offered by Computer Relay (a) Cost It is estimated that for equal performance, the cost of the most sophisticated digital computer relays (including software costs) would be about the same as that of conventional relaying systems. (b) Self-Checking and Reliability A computer relay can be designed to fail in a safe mode (i.e., take itself out of service if a failure is detected) and send a service request alarm to the system center. This feature of computer relays is perhaps the most telling technical argument in favor of computer relaying. It is expected that with the self-checking feature of computer-based relays, the relay component failures can be detected soon after they occur and could be repaired before they have a chance to misoperate. (c) System Integration and Digital Environment In modern and future substations, computer relays will fit in very naturally. They can accept digital signals obtained from newer transducer and fiber-optic channels and become integrated with the computer-based control and monitoring systems of substations.. (d) Functional Flexibility and Adaptive Relaying A digital computer can be programmed to perform several functions as long as it has the input and output signals needed for these functions. It is a simple matter to the relay computer to do many other substation tasks. For example, measuring and monitoring flows and voltages in transformers and transmission lines, controlling the opening and closing of circuit breakers and switches, and providing backup for other devices that have failed.

1.7  Book Objectives The objectives for this book’s research can be summarized as follows: 1 Preparing comprehensive simulation of wind speed, wind turbine, and microcontroller. These models consider most of the aerodynamical and mechanical effects that can influence the instantaneous output voltage, current, and power. 2 Highlight the different types of algorithms to maintain power system reliability.

18

1  Introduction and Previous Work

3 Using new technologies that allow designing a digital relay that can be used for improving the performance of protective relay have been used.

1.8  Book Contents This book consists of seven chapters: Chapter 1: Introduction and Previous Work Presents an introduction of protection for a wind-driven induction generator connected to power system and highlights induction generator operation. Chapter 2: Computer Simulations for the Induction Generator Connected to Power Network Presents a simulation to the Chen model. Also, the MATLAB is used as a simulation environment to study the transient behavior of the induction generator connected to the power network through a local load. Chapter 3: Protective Schemes for Induction Generator Presents the problem of providing relay protection for a wind-driven induction generator connected to a power system. Different types of algorithms to maintain power system reliability and different proposed relaying algorithms to be used for induction generator protection are explained, along with comparison between other different samples method. Chapter 4: Transient Behavior of Induction Generator Protective Relays Presents a simulation method using MATLAB to study the transient behavior of induction generator connected to power network through a local load and protective devices. Chapter 5: Description of Microcontroller Circuit and MikroC Program In this chapter, we have provided a brief description of the devices and components that were used in programming the microcontroller for the book. Chapter 6: Experimental Setups and Results for Digital Relay Protection Presents experimental of the new technologies used that allow designing a digital relay that can be used for improving the performance of protective relay. Chapter 7: Conclusion and Future Work Presents the conclusions derived from this study and future works.

Chapter 2

Computer Simulations for the Induction Generator Connected to Power Network

2.1  Introduction The Chen model [20, 21] used by MATLAB simulation applied on a squirrel cage induction generator (SCIG) driven by a wind turbine through various abnormalities occurring at the machine terminals is the subject of the first part of this chapter. Afterward, the MATLAB program is used as a simulation environment to study the transient behavior of the induction generator connected to a power network through a step-up power transformer and a short feeder. A local load is connected to the high terminal (HT) side of the step-up transformer. Different types of symmetrical and unsymmetrical faults are studied in this chapter.

2.2  Behavior of Induction Generator 2.2.1  Study system The study system used is shown in Fig. 2.1. It consists of the following components: • • • • • • • •

A three-phase squirrel cage induction generator (IG) A three-phase transformer (TF) A three static phase capacitor bank (Cx) A three-phase fixed load, RL and LL Short transmission line, Re and Le Two circuit breakers, CB1 and CB2 Infinite bus represented by three ideal voltage sources Source of faults

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 N. F. Ibrahim et al., Protection of Wind Turbine Generators Using Microcontroller-Based Applications, Green Energy and Technology, https://doi.org/10.1007/978-3-030-92628-1_2

19

20

2  Computer Simulations for the Induction Generator Connected to Power Network

Fig. 2.1  The study system

TF IG

F

CB1 CX

re

Le

CB2

Infinite bus

rL IL

The parameters of the system referred to in the induction generator base power, 93.25 KVA, are as follows [33]. Rt = 0.0094 p.u Lt = 0.0140 p.u rL= 0.7964 p.u lL = 0.995 p.u re = 0.0090 p.u Le = 0.0061 p.u Cx = 1.0070 p.u

Here the parameters Rt and Lt are transformer resistance and inductance, respectively. The following conditions are considered in the simulation: • The capacitors and the load are not ground. • The input mechanical power, Pm, is assumed to remain constant during system abnormalities. • Since the squirrel cage induction generator used has a cylindrical stator and rotor, the main inductances along the two axes were assumed equal (i.e., Lmd = Lmq) [26]. • The load and the capacitance have been calculated to exactly match the generator output power, and the infinite bus voltage has been tuned to virtually supply no power to the generator local load during steady state condition.

2.2.2  Types of Simulated Disturbances Various faults with subsequent switching are applied at point F on the system shown in Fig. 2.1, and the traces of voltages, currents, active and reactive output powers, and rotor speed with electrical torque measured at the IG terminals are shown for each fault type. The voltages, currents, rotor speed, electrical torque, and the active and reactive powers are resulted as outputs from the MATLAB program. The fault inception angle is chosen to be 90o for phase "a" voltage (at peak). Three cycles later, CB2 tripped, leaving the generator isolated with the local load. (a) Three-Phase-to-Ground Fault (3LG) For three-phase or three-phase-to-ground faults at point F in Fig. 2.1,

V= V= Vc = 0 (2.1) a b

21

2.2  Behavior of Induction Generator

Fig. 2.2  The MATLAB/Simulink System

at the instant of the fault and thereafter. Fig. 2.2 shows that the generator supplies momentary currents and torque of 8.6 pu and 4 pu, respectively. Both currents and torque decay very quickly. From Fig. 2.3, it can be seen that large line currents flow initially following the fault inception as a consequence of the rapid change in currents. Figure  2.4 shows that the large transient electromagnetic torque leads to the reverse rotation of the generator and then it decelerates initially before reaching acceleration. But Fig.  2.5 shows the electromagnetic torque (Te) is momentarily greater than the input mechanical torque (Tm), the output real power suddenly drops and then oscillates. (b) Double line-to-ground fault (2LG) For a fault on phases b and c

V= V= 0 (2.2) b c

Figure 2.3 shows that during the short circuit period, vc is very small and va and vb have almost the same amplitude with 180o phase difference. There is a momentary change in the trace of voltages at the instant of opening CB2. From Fig. 2.6, the unfault phase current (Ia) is about 7 pu, which is much larger than the faulted phases’ currents (Ib and Ic). This effect is caused by loss of excitation of phases b and c. Note that the momentary current is dependent on the short circuit angle. Therefore, the maximum values of the short circuit currents observed are not definite. From Figs.  2.7 and 2.8, it can be seen that a large transient electromagnetic torque opposes the rotational direction, and hence, the machine initially slows down before accelerating. Since electromagnetic torque (Te) is momentarily greater than the input mechanical torque (Tm), the output real power suddenly drops and then oscillates.

22

2  Computer Simulations for the Induction Generator Connected to Power Network

Fig. 2.3  Voltage and current wave form when a three-phase fault occurs at point F. (a) Voltage wave form. (b) Current wave form

2.2  Behavior of Induction Generator

23

(a)

(b) 1

Te

Electromagnetic torque Te (pu)

0.5 0 -0.5 -1 -1.5 -2 -2.5 -3 -3.5 -4

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Time(sec)

Fig. 2.4  Rotor speed (ωn) and electromagnetic torque (Te) form when a three-phase fault occurs at point F. (a) Rotor speed variation. (b) Electromagnetic torque variation

24

2  Computer Simulations for the Induction Generator Connected to Power Network 5

5

x 10

P Q

4

active and reactive power

3 2 1 0 -1 -2 -3 -4 -5 0

0.1

0.2

0.3

0.4

0.5 Time(sec)

0.6

0.7

0.8

0.9

1

Fig. 2.5  Active and reactive power (P, Q) form when a three-phase fault occurs at point F

(c) Line-to-line fault (L-L) This fault applies to both phases (b) and (c) at: Vb = Vc (2.3)



Figure 2.9 shows the simulation results. An interesting phenomenon is observed here–the generator supplies momentary torque and active power greater than that in the 2LG and 3LG cases. From Fig. 2.9, the short circuit current (Ib) peaked at 5.7 p-u but did not decay and was opposite in sign to Ic for a few cycles. Figures 2.10 and 2.11 show that the electromagnetic torque, output real power, and reactive power oscillated. The average real power decreases from the steady state value since only phase a is still sending power to the infinite bus. The speed increased at a slower rate than for a three-phase fault. We observed induction generator short circuit current phase reversal in some cases, dependent on the short circuit angle and input mechanical power. (d) Single line-to-ground fault For a fault on phase a

Va = 0 (2.4)

Fig. 2.12 shows that after clearing the fault, the traces of voltages and currents build up and reach the normal values faster than the previous cases.

2.2  Behavior of Induction Generator

25

Fig. 2.6  Voltage and current wave form when a double line-to-ground fault occurs at point F. (a) Voltage wave form. (b) Current wave form

From Fig.  2.12, it can be seen that the momentary short circuit current (Ia) reached 15p-u and decayed to 9 p-u in two cycles. Phase a lost excitation, but phases b and c still have excitation, causing high current in phase a. From Figs. 2.13 and 2.14, it can be seen that the electromagnetic torque, output real power, and reactive power oscillated. The average real power decreases from

26

2  Computer Simulations for the Induction Generator Connected to Power Network

(a) Electromagnetic torque Te (pu)

1

Te

0 -1 -2 -3 -4 -5 0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Time(sec)

(b) 1.35

Wm

1.3

Rotor speed (p-u)

1.25 1.2 1.15 1.1 1.05 1 0.95

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Time

Fig. 2.7  Electromagnetic torque (Te) and rotor speed (Wn) forms. (a) Electromagnetic torque variation. (b) Rotor speed variation

2.3  Fault, Clearing, and Successful Reclosure

27

5

6

x 10

P Q

active and reactive power

4

2

0

-2

-4

-6 0

0.1

0.2

0.3

0.4

0.5 Time(sec)

0.6

0.7

0.8

0.9

1

Fig. 2.8  Active and reactive power (P, Q) form when double line-to-ground fault occurs at point F

the steady state value since only phase a is still sending power to the infinite bus. The speed increased at a slower rate than for a three-phase fault.

2.3  Fault, Clearing, and Successful Reclosure In this case, the three-phase fault (the most severe fault) and single line-to-ground fault (the most common fault) occur at point F. Three cycles later, CB2 is tripped, eliminating the fault and leaving the induction generator isolated with the local load as self-excited. Three cycles later, CB2 is reclosed. The simulation results are shown in Figs. 2.15 and 2.26. These figures show that the voltages come back immediately to normal values after reclosure to infinite bus, while the currents take a different time to come back to the normal (while 3line-to-ground (LG) takes about 9 cycles, single line-to-ground (SLG) takes shorter time, about 2.5 cycles). From Fig. 2.15, the waveform of voltage and current can be observed when a three-phase fault occurs at the output terminals of the generator. The figure also shows the success of both fault clearance through x/r ratio control and three-phase short-circuit level control of the network. Where the x/r ratio is set to be approximately in the range (10-15) (Figs. 2.16 and 2.17). Figure 2.18 shows the voltage and current signals when a line-to-line fault occurs on the generator output. It also shows successful fault clearing and reclosure by controlling the x/r ratio and three-phase short-circuit level of the network. Thus, it was possible to obtain a higher reliability and stability of the power system.

28

2  Computer Simulations for the Induction Generator Connected to Power Network

Fig. 2.9  Voltage and current wave form when a line-to-line fault occurs at point F. (a) Voltage wave form. (b) Current wave form

2.3  Fault, Clearing, and Successful Reclosure

Electromagnetic torque Te (pu)

(a)

29

3

Te

2 1 0 -1 -2 -3 -4 -5

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Time(sec)

(b)

1.18

Wm

1.16

Rotor speed (p-u)

1.14 1.12 1.1 1.08 1.06 1.04 1.02 1 0.98 0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

Fig. 2.10  Electromagnetic torque (Te) and rotor speed (ωn) form when a line-to-line fault occurs at point F. (a) Electromagnetic torque (Te) variation. (b) Rotor speed (ωn) variation

30

2  Computer Simulations for the Induction Generator Connected to Power Network 5

active and reactive power

10

x 10

P Q

5

0

-5

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Time(sec)

Fig. 2.11  Active and reactive power (P, Q) form when a line-to-line fault occurs at point F

From Fig. 2.21, the waveform of voltage and current can be seen when adouble line to ground fault occurs at the generator output. The figure shows successful fault clearing and reclosure by controlling the x/r ratio and three-phase short-circuit level of the grid. As a result, both the reliability and stability of the power system are enhanced. Figure 2.24 shows the results of the simulation on the Matlab/Simulink when a single line to ground fault is applied on the output terminals of the generator, shown in the figure of voltage and current waves. The figure shows the successful clearing of the fault effect and the successful reclosure by controlling the x/r ratio and the three-phase short-circuit level of the grid. Thus, due to the reliability and stability of the power system.

2.4  Comments and Discussion on Computer Results • When a single line-to-ground fault is applied, it is observed that a successful reclosure has occurred as shown in Figs. 2.24, 2.25, and 2.26 and that the currents, torques, and active and reactive powers momentary measured at the reclosure are greater than those at the moment of short circuit. • The shape of curves of 2LG is almost the same as L-L (Figs. 2.18, 2.19, 2.20, 2.21, 2.22 and 2.23), but there is a little difference in the magnitude. • The zero-sequence current does not appear at the machine terminals in the cases of 2LG and SLG because of transformer connection (delta star). • For the asymmetrical faults (Figs. 2.6, 2.7, 2.8, 2.9, 2.10, 2.11, 2.12, 2.13, and 2.14), the traces of torque and active and reactive powers are oscillating during the fault period and the frequency is double the normal frequency (120HZ). This results out of the negative sequence components.

2.4  Comments and Discussion on Computer Results

31

Fig. 2.12  Voltage and current wave form when a single line-to-ground fault occurs at point F. (a) Voltage wave form. (b) Current wave form

32

(a)

2  Computer Simulations for the Induction Generator Connected to Power Network

1.14

Wm

1.12

Rotor speed (p-u)

1.1 1.08 1.06 1.04 1.02 1 0.98

0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

(b)

Electromagnetic torque Te (pu)

2

Te

1 0 -1 -2 -3 -4 -5

0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

Fig. 2.13  Rotor speed (ωn) and electromagnetic torque (Te) form when a single line-to-ground fault occurs at point F. (a) Rotor speed variation. (b) Electromagnetic torque variation

2.4  Comments and Discussion on Computer Results

33

5

8

x 10

P Q

active and reactive powe

6 4 2 0 -2 -4 -6

0

0.1

0.2

0.3

0.4

0.5 Time(sec)

0.6

0.7

0.8

0.9

1

Fig. 2.14  Active and reactive power (P, Q) form when a single line-to-ground fault occurs at point F

(a) 1500

Va Vb Vc

1000

V (V)

500 0 –500 –1000 –1500 0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

Fig. 2.15  Voltage and current wave form when a three-phase fault occurs at point F, clearing through IG model. (a) Voltage wave form. (b) Current wave form

34

2  Computer Simulations for the Induction Generator Connected to Power Network

(b) 1000

Ia Ib Ic

800 600 400

I (A)

200 0 –200 –400 –600 –800 –1000

0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

Fig. 2.15 (continued)

(a)

1.09

wn

1.08

Rotor speed (p-u)

1.07 1.06 1.05 1.04 1.03 1.02 1.01 1 0.99

0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

Fig. 2.16  Rotor speed (Wn) and electromagnetic torque (Te) form when a three-phase fault occurs at point F, clearing through IG model. (a) Rotor speed variation. (b) Electromagnetic torque variation

2.4  Comments and Discussion on Computer Results

Electromagnetic torque Te (pu)

(b)

35

1

Te

0.5 0 -0.5 -1 -1.5 -2 -2.5 -3 -3.5 -4 0

0.1

0.2

0.3

0.4

0.5 0.6 Time (sec)

0.7

0.8

0.9

1

Fig. 2.16 (continued)

5

8

x 10

P Q

Active and Reactive power (P&Q)

6 4 2 0 -2 -4 -6 -8 -10 -12

0

0.1

0.2

0.3

0.4

0.5 Time (sec)

0.6

0.7

0.8

0.9

1

Fig. 2.17  Active and reactive power (P, Q) form when a three-phase fault occurs at point F, clearing through IG model

36

2  Computer Simulations for the Induction Generator Connected to Power Network

(a)

Va Vb Vc

1000

V (V)

500

0

–500

–1000 0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

(b)

800

Ia Ib Ic

600 400 200

I (A)

0 –200 –400 –600 –800 –1000 –1200

0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

Fig. 2.18  Voltage and current wave form when a line-to-line fault occurs at point F, clearing through IG model. (a) Voltage wave form. (b) Current wave form

2.4  Comments and Discussion on Computer Results

37

(a) 1.07

wn

1.06

Rotor speed (p-u)

1.05 1.04 1.03 1.02 1.01 1 0.99 0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

(b)

Electromagnetic torque Te (pu)

3

Te

2 1 0 -1 -2 -3 -4 -5

0

0.1

0.2

0.3

0.4

0.5 0.6 Time (sec)

0.7

0.8

0.9

1

Fig. 2.19  Rotor speed (Wn) and electromagnetic torque (Te) form when a line-to-line fault occurs at point F, clearing through IG model. (a) Rotor speed variation. (b) Electromagnetic torque variation

38

2  Computer Simulations for the Induction Generator Connected to Power Network 5

10

x 10

P Q

Active and Reactive power (P&Q)

8 6 4 2 0 -2 -4 -6 -8 0

0.1

0.2

0.3

0.4

0.5 0.6 Time (sec)

0.7

0.8

0.9

1

Fig. 2.20  Active and reactive power (P, Q) form when a line-to-line fault occurs at point F, clearing through IG model

(a) Va Vb Vc

1000

V (V)

500

0

–500

–1000 0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

Fig. 2.21  Voltage and current wave form when a double line-to-ground fault occurs at point F, clearing through IG model. (a) Voltage wave form. (b) Current wave form

2.4  Comments and Discussion on Computer Results

(b)

39

800

Ia Ib Ic

600 400 200 I (A)

0 –200 –400 –600 –800 –1000 –1200 0

0.1

0.2

0.3

0.4

0.5 0.6 Time(sec)

0.7

0.8

0.9

1

Fig. 2.21 (continued)

(a)

1.09

wn

1.08

Rotor speed (p-u)

1.07 1.06 1.05 1.04 1.03 1.02 1.01 1 0.99

0

0.1

0.2

0.3

0.4

0.6 0.5 Time(sec)

0.7

0.8

0.9

1

Fig. 2.22  Rotor speed (ωn) and electromagnetic torque (Te) form when a double line-to-ground fault occurs at point F, clearing through IG model. (a) Rotor speed variation. (b) Electromagnetic torque variation

40

2  Computer Simulations for the Induction Generator Connected to Power Network

(b)

Electromagnetic torque Te (pu)

1

Te

0 -1 -2 -3 -4 -5

0

0.1

0.2

0.3

0.4

0.5 0.6 Time (sec)

0.7

0.8

0.9

1

Fig. 2.22 (continued)

5

6

x 10

P Q

Active and Reactive power (P&Q)

4 2 0 -2 -4 -6 -8

0

0.1

0.2

0.3

0.4

0.5 Time (sec)

0.6

0.7

0.8

0.9

1

Fig. 2.23  Active and reactive power (P, Q) form when a double line-to-ground fault occurs at point F, clearing through IG model

2.4  Comments and Discussion on Computer Results

41

Fig. 2.24  Voltage and current wave form when a single line-to-ground fault occurs at point F, clearing through IG model. (a) Voltage wave form. (b) Current wave form

42

2  Computer Simulations for the Induction Generator Connected to Power Network

(a) 1.07

wn

Rotor speed (p-u)

1.06 1.05 1.04 1.03 1.02 1.01 1 0.99

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1

0.9

Time(sec)

(b)

Electromagnetic torque Te (pu)

2

Te

1 0 -1 -2 -3 -4 -5

0

0.1

0.2

0.3

0.4

0.5 0.6 Time (sec)

0.7

0.8

0.9

1

Fig. 2.25  Rotor speed (Wn) and electromagnetic torque (Te) form when a single line-to-ground fault occurs at point F, clearing through IG model. (a) Rotor speed variation. (b) Electromagnetic torque variation

43

2.4  Comments and Discussion on Computer Results 5

8

x 10

P Q

Active and Reactive power (P&Q)

6 4 2 0 -2 -4 -6

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Time (sec)

Fig. 2.26  Active and reactive power (P, Q) form when a single line-to-ground fault occurs at point F, clearing through IG model

Chapter 3

Protective Schemes for Induction Generator

3.1  Introduction In this chapter, the problem of providing relay protection for a wind turbine–driven induction generator connected to a power system is investigated. The induction generator protection scheme and relay settings are described (table 3.1). It is assumed that the used relays are all digital (microcontroller-based). Different proposed relaying algorithms to be used for induction generator protection are explained. A frequency protection algorithm is introduced, which is based on (CUSUM) forms of voltage signal samples measured at the generator terminals.

3.2  Protection Requirement for Induction Generator The protection requirements for induction generator as seen in Fig. 3.1 are divided into several fundamental categories. These protection functions are discussed in chapter 1:

3.3  Sampling Methods The present samples for the negative sequence, frequency, and current based on symmetrical and unsymmetrical components can be used to send a certain signal to the microcontroller to protect the induction generator in the system against over-­ current, over/under frequency, under voltage, and overheating.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 N. F. Ibrahim et al., Protection of Wind Turbine Generators Using Microcontroller-Based Applications, Green Energy and Technology, https://doi.org/10.1007/978-3-030-92628-1_3

45

46

3  Protective Schemes for Induction Generator

Table 3.1  The setting of each of the induction generator relays Relay type Over-current relays Negative sequence relay Under voltage relays Over voltage relays Over speed relay Over frequency and Under frequency relays

Setting 125 to 135% of the rated current I22t = 4 80% of rated voltage 110% of rated voltage 110% of normal rotor speed 105% of rated frequency and 95% of rated frequency

TF

IG F

CB1

re

Le

CB2 Infinite bus

CX

rL

Relaying Signal IL OC

OV UV

Protection System

OF/UF

Fig. 3.1  The induction generator protection scheme

3.4  Conventional Fault Detection Techniques With the onset of a fault in a power system, the voltage and current signals change significantly. For an effective protection requirement, these changes in the signals are to be identified online as fast as possible with the least number of false detection. This concept of fault detection is similar to the change point detection in control and diagnostics. Numerous techniques are available for this purpose as mentioned, but mainly two simple approaches are employed in relaying: 1) sample-to-sample comparison and 2) comparing a present sample value with a corresponding value one cycle earlier (cycle-to-cycle) [33–36]. In these methods, if a situation consistently provides a higher index value than a threshold (say for three consecutive samples), then it is registered as a fault. It is to be noted that the first few milliseconds after the initiation of the fault is of interest for the fault detection task as the detector has to trigger a cascade of relay algorithms. Complex filtering methods based on stage estimation or other complex filtering methods may not meet the timing requirements. On the selection of a signal, current and voltage provide similar performance in reference to decision speed.

47

3.4  Conventional Fault Detection Techniques

3.4.1  Method 1: Sample-to-Sample Comparison Method In this scheme, the present sample is compared with the previous sample to identify a change [34, 35, 37, 54]. Without any fault in the system, this difference in sample values is normally small. Under fault conditions, the difference increases to a large value, which can be used for fault detection, as depicted in Fig. 3.2. Mathematically,

X ( n ) = S ( n ) − S ( n − 1)

(3.1)

where S (n) represents sample value at the instant n. A fault is detected if

X ( n ) > T1

(3.2)

where T1 is a threshold parameter. It is observed from the figure that the difference may not always satisfy Eq. (3.2) in the faulty portion and sometimes a load change may be inferred as a fault.

3.4.2  Method 2: Cycle-to-Cycle Comparison Method In this scheme, the present sample was compared with a previous sample with only one cycle [34, 52]. It is expected that their difference is usually small under normal conditions, and after the occurrence of the fault, it increases to a large value. Based on this value, a fault can be detected. Mathematically,

Fig. 3.2  Sample-to-sample comparison approach

48



3  Protective Schemes for Induction Generator

Y ( n ) = S ( n ) − S ( n − N + 1)

(3.3)

where Y(n) is the index value of this method, s(n) represents sample value at the instant n and N is number of samples in a period. A fault is detected if,

X ( n ) > T2

(3.4)

where T2 is a threshold parameter. As shown in Fig. 3.3, it registers a fault during load change. Besides this, the above two methods are affected by the system frequency deviation and the presence of noise.

3.4.3  Method 3: Cumulative Sum (CUSUM) Method This scheme compares the sample values with a predetermined drift parameter “i,” which is equal to the relay setting current [34, 35, 51, 47]. It uses the current samples, s (n), and prepares two complementary signals, s1 (n), s2 (n), as shown in Fig. 3.4.

S1 ( n ) = S ( n )



S2 ( n ) = − S ( n )

(3.5) (3.6)

From Eqs. 3.5 and 3.6, the CUSUM indices g1 and g2 are defined as

g1 ( n ) = max ( g1 ( n − 1) + S1 ( n ) − i, 0 )

Fig. 3.3  Cycle-to-cycle comparison approach

(3.7)

3.4  Conventional Fault Detection Techniques

49

Fig. 3.4  Complementary signals and variation of indices



g2 ( n ) = max ( g2 ( n − 1) + S2 ( n ) − i, 0 )

(3.8)

A fault is detected if either of the above two indices exceeds a threshold parameter, T3.

g1 ( n ) > T3

Or

g2 ( n ) > T3

(3.9)

50

3  Protective Schemes for Induction Generator

Fig. 3.5  Four sample approach

3.4.4  Method 4: Four Sample Method The expression of the algorithm is based on four equally spaced samples 90 degrees apart, as shown in Fig. 3.5 [38, 39, 49]. A sine wave current signal is assumed. The approach chosen for identifying the root mean square (rms) value from the real-time samples of a signal offers an almost complete rejection of decaying DC components. It is based on two finite impulse-response digital filters. The two filter outputs S and C, at any instant of time, provide two Cartesian-coordinate phasor components of the input. They are defined as:

S = i1 + i2 − i3 − i4 (3.10)



C = i1 − i2 − i3 + i4 (3.11)

where i1, i2, i3, and i4 are four equally spaced samples. It can be easily shown that the rms value of a sine wave, ip, is given by Eqs. (3.12) and (3.13).



ip =

(S

2

)

+ C 2 / 16

(3.12)

C  θ = tan    S  (3.13)

3.5  Microcontroller-Based Relaying Algorithm In this section, a digital frequency deviation algorithm [33, 48] is presented. A simple digital over-current relaying approach and a negative sequence algorithm are presented. These algorithms are used in the next chapter for investigating the relaying transient behavior.

3.5  Microcontroller-Based Relaying Algorithm

51

3.5.1  Frequency Deviation Algorithm Many frequency relaying algorithms are proposed in literature (e.g. [33, 39]). The one chosen within the course of this research is a quadratic from-based algorithm introduced in reference [49]. A general algorithm expression is first introduced. This expression is recognized to be a common form for most of the previously introduced nonrecursive frequency deviation measurement algorithms. The general algorithm expression is a quotient of quadratic forms (QQF) of signal samples. Let us assume the following input voltage signal representation:

V ( t ) = vcos (ω t + ϕ )

(3.14)

Quadratic forms of a signal, v, denoted here as Kf, may be expressed using matrix notation in the following way: N −1 N −1



kf ( n ) = ∑∑bkm vn − k vn − m = vT Bv k =0 m =0

(3.15)

where

vT = vn vn −1 … vn − N +1



B = {bkm }

(3.16)

(3.17)

where. N: number of sampling rate Vn: voltage signal sample at the discrete time n, B: quadratic form matrix bkm: elements of this matrix The following quotient of quadratic forms of signal samples is recognized to be a general form for frequency deviation measurement algorithms. N −1 N −1

∆f ^ =

∑∑a

v

v

km n − k n − m

K =0 m =0 N −1 N −1

∑∑b

v

v

km n − k n − m

K =0 m =0

=

KFA KFB (3.18)

For simplicity, the electrical angle deviation estimate is used instead of frequency deviation estimate. From Equation (14), the following equation can be given:

vn = vcos (ω n∆t + ϕ ) = vcos ( nd + ϕ )

(3.19)

52

3  Protective Schemes for Induction Generator

It is noted that the electrical angel deviation Δd is proportional to the deviation of frequency since

∆d = ∆ω.∆t = 2π∆f .∆t (3.20)

and it is updated to be N −1 N −1

∆d ^ =

∑∑a

v

v

km n − k n − m

K =0 m =0 N −1 N −1

∑∑b

v

=

v

km n − k n − m

KFA KFB (3.21)

K =0m =0

where

akm = akm ∗ ( 2π∆t )

(3.22)

This expression is made constant in time and real for all frequency deviations of sinusoidal signal. This is achieved by: 1 . Imposing constrains on the coefficients of the quadratic forms 2. Applying Tailor’s Expansion on the quadratic forms to give a quotient of two frequency polynomial 3. Choosing the coefficients of the polynomials so that the quotient becomes equal to the value of signal frequency deviation The estimate of the electrical angle deviation, given by Equation (3.22), now becomes: ∆d ^ =

vn .ω0 − vn −1 .ω1 vn .δ 0 − vn −1 .δ1

(3.23)

And the general determinants can be determined from the following equations:

ω0 = a.Vn − 2 + b.Vn −3 + c.Vn − 7 + d.Vn −12 . (3.24)



ω1 = a.Vn −1 + b.Vn − 2 + c.Vn −6 + d.Vn −11 . (3.25)



δ0 = e.Vn − 2 + f .Vn −3 + g.Vn − 7 . (3.26)



δ1 = e.Vn −1 + f .Vn − 2 + g.Vn −6 . (3.27)

where a, b, c, d, e, f, and g are the coefficients of the quadratic forms. For the coefficient constraints expressed, c=0.05 and d=0.01, the following values for the coefficients of quadratic forms are deduced.

53

3.5  Microcontroller-Based Relaying Algorithm



a = −1.044303503155235



e = 0.78543321540189



b = 0.5282386282938 f = −1.05813678372674

g = −0.03443924221845

The sampling rate for the small frequency deviation algorithm is chosen to be 16 samples/cycle, then the nominal electric angle for this case is equal to d0=Л/8. The algorithm when implemented is simple, fast, and accurate [33, 38]. No lookup tables/or iterations are necessary to calculate the correction. The algorithm is well performed without noise simplification, as shown in Fig. 3.6.

3.5.2  Over-Current Algorithm The expression of the algorithm is based on four equally spaced samples (90) degrees apart. A sine wave current signal is assumed. The chosen approach for identifying the rms value from the real time samples of a signal offers an almost

Fig. 3.6  Flowchart of over/under frequency relay

54

3  Protective Schemes for Induction Generator

complete rejection of decaying DC components. It is based on two finite impulseresponse digital filters. The two filter outputs, S and C, at any instant of time provide two Cartesian-coordinate phasor components of the input. They are defined as:

s = i1 + i2 − i3 − i4 (3.28)



c = i1 − i2 − i3 + i4 (3.29)

where i1, i2, i3 and i4 are four equally spaced samples. It can be easily shown that the rms value of a sine wave ip is given by Equations (3, 4) this rms is considered as the input to the digital relay, Figs. 3.7, 3.8 and 3.9.



ip =

(s

2

)

+ c 2 / 16

(3.30)

c θ = tan    s  (3.31)

3.5.3  Negative Sequence Algorithm The algorithm expression is based on the symmetrical components theory. The relation between the phase rms quantities and the symmetrical components is given by

I o12 = 1 / 3 A I abc

(3.32)

where



I0 I o12 = I1 I2

(3.33)

≡ Zero, positive, and negative sequence components (012) vectors



1 1 A =1 a 1 a2

I abc

Ia = Ib Ic

1 a2 a

(3.34)

(3.35)

55

3.5  Microcontroller-Based Relaying Algorithm

Fig. 3.7  Flowchart of digital relay

and



 j 2π  a = exp    3 

 j 4π a 2 = exp   3

  

For real-time applications, the relationship between the symmetrical components and sampled data of the instantaneous phase quantities is considered. The relation between the instantaneous symmetrical components (time domain representation) is given by: Io (t ) Ia (t ) + Ib (t ) + I1 ( t ) = 1 / 3 I a ( t ) + I b ( t − 2T / 3 )

I2 (t )

Ia (t ) +

I b ( t − T / 3)

Ic (t ) I c ( t − T / 3)

I c ( t − 2T / 3 )

(3.36)

56

Fig. 3.8  Flowchart of over-current relay

Fig. 3.9  Flowchart of over/under voltage relay

3  Protective Schemes for Induction Generator

3.5  Microcontroller-Based Relaying Algorithm

57

where T is the time of the power frequency ω based on Eq. (3.2). The technique of overcurrent algorithm is adapted for calculating the rms values of the negative sequence components for an unbalanced three-phase system. Each of the four instantaneous samples required for signal identification consists of three instantaneous signals (one for each phase) displaced in time by 120 degrees (T/3 sec). Then, four negative sequence instantaneous samples are presented: i21, i22, i23, i24. The rms values of the negative sequence components are then determined in terms of S2 and C2 and ip as follows:

S2 = i21 + i22 + i23 − i24 (3.37)



C2 = i21 − i22 − i23 + i24 (3.38)



ip =

(S

2

)

+ C 2 / 16

(3.39)

Chapter 4

Transient Behavior of Induction Generator Protective Relays

4.1  Introduction The modeling and testing of relays for transient effects was not a critical issue until the introduction of electronic and microcontroller-based relays. Electro-mechanical relays are less sensitive to power system transient effects [40, 41]. In this chapter, the transient behavior of relaying schemes protecting an induction generator connected to a wind turbine is studied. The mutual effect between the generator performance and its protective schemes dynamics is investigated. It is that the used relays are all digital (microcontroller-based). The different induction generator relays behavior under different disturbance conditions and different types of faults and sampling methods are also investigated.

4.2  Simulation Environment The well-known MATLAB "Simulink" is the used simulation environment for the induction generator as well as the rest of the system elements, except for the protective relays. Different fault conditions are initiated to cause transient conditions. The MATLAB outputs at the relaying points are used to feed each relaying algorithm. Each relaying algorithm (i.e., frequency, overcurrent, or negative sequence) is simulated through an M-file. The output of each is then analyzed.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 N. F. Ibrahim et al., Protection of Wind Turbine Generators Using Microcontroller-Based Applications, Green Energy and Technology, https://doi.org/10.1007/978-3-030-92628-1_4

59

60

4  Transient Behavior of Induction Generator Protective Relays

4.3  Types of Simulated Disturbances Various faults with subsequent clearing are applied at point F on the system shown Fig. 3.1. The calculated values of different algorithms used by the corresponding relays of the frequency deviation, the overcurrent, the over/under voltage, the over speed, and the negative sequence relays are presented for each fault type. For each fault, the fault inception angle is chosen to be 90o for phase "a" voltage (at peak). Three cycles later, CB2 is assumed to be tripped, leaving the generator isolated with the local load.

4.4  Types of Simulated Results 4.4.1  Results of Four Sample Method In this scheme, simulations results are investigated by one case fault. Relaying algorithm is simulated through an M-File. The output of each is then analyzed before and after the fault. The simulation result of the method is shown in Fig. 4.1. From the simulation results, it is found that simulation results before the fault are not different from simulation results after the fault, but due to high ripple, as shown in Fig. 4.1, different methods are to take samples and compare.

6

1000

Ia

I Amper (rms)

I (rms)

IP

4 2 0

0

0.5

1 Cycle

1.5

I Amper (rms)

0 -500 0

0.5

1 Cycle

0

0.5

500

Ib

500

-1000

0

-500

4

x 10

1000 I Amper (rms)

2

500

1.5

2 4

x 10

1 Cycle

1.5

2

4

x 10 Ic

0 -500

-1000

0

0.5

1 Cycle

Fig. 4.1  The calculated values of different algorithms under SLG fault and tripping

1.5

2 4

x 10

10 I (rms)

Ia

0 1

500

2 Cycle

3

4

4

x 10 Ib

1

1000

2 Cycle

3

4

4

x 10 Ic

1

2 Cycle

3

4

4

x 10

2 Cycle

3

4

4

x 10 Sb

0

-5 0

1

10

0 -1000 0

1

5

0 -500 0

Sa

0

-10 0

I (rms)

-1000 0

I (rms)

I Amper (rms)

61

1000

I Amper (rms)

I Amper (rms)

4.4  Types of Simulated Results

2 Cycle

3

4

4

x 10 Sc

0

-10 0

1

2 Cycle

3

4

4

x 10

Fig. 4.2  The calculated values of different algorithms under SLG fault and tripping for (sample-­ to-­sample method)

4.4.2  Results of Sample-to-Sample Method In this scheme, simulation results are investigated by one case fault. Relaying algorithm is simulated through an M-File. The output of each is then analyzed before and after the fault. The simulation result of the method is shown in fig 4.2. From the simulation results, as shown in Fig. 4.2, it is found that simulation results before the fault are different from simulation results after the fault, but the ripple effect in this method appears, so different methods to take samples are used and compare.

4.4.3  Results of Cycle-to-Cycle Method In this scheme, the simulation results are investigated by one case fault. Relaying algorithm is simulated through an M-File. The output of each is then analyzed before and after the fault. The simulation result of the method is shown in Fig. 4.3. From the simulation results, it was found that simulation results before the fault are different from simulation results after fault, as shown in Fig. 4.3; the ripple effect in this method appears but less than the sample-to-sample method, so different methods are used to take samples and compare.

1000

0 2000

4000

1000

6000 Cycle

8000

10000 12000 Ib

0 0

2000

4000

200

6000 Cycle

8000

10000 12000 Ic

0 -200 0

2000

4000

6000 Cycle

8000

I Amper (rms)

-500 0

-1000

I Amper (rms)

Ia

500

I Amper (rms)

4  Transient Behavior of Induction Generator Protective Relays

10000

12000

I Amper (rms)

I Amper (rms)

I Amper (rms)

62

1000

Sa

0 -1000 0

2000

4000

1000

6000 Cycle

8000

10000

12000 Sb

0 -1000 0

2000

4000

500

6000 Cycle

8000

10000

12000 Sc

0 -500 0

2000

4000

6000 Cycle

8000

10000

12000

Fig. 4.3  The calculated values of different algorithms under SLG fault and tripping for (cycle-to-­ cycle method)

4.4.4  Results of Cumulative Sum Method In this scheme, simulation results have been investigated by one case fault. Relaying algorithm is simulated through an M-File. The output of each is then analyzed before and after the fault. The simulation results of method is shown in Figs. 4.4, 4.5, and 4.6. From the simulation results, it was found that simulation results before the fault are different from simulation results after fault, as shown in Figs. 4.4, 4.5, and 4.6; no found ripple in this method appears. For example, by comparing this method with the other we found that the CUSUM method is the best and most appropriate to used in the construction of digital relay.

4.5  Development of Relays Generators are usually protected by relays. The purpose of protection relays is to minimize the effects of faults on electrical power system components. The early relays designed for generator systems used electromechanical technology. The various types of electromechanical relays, such as magnetic attraction, magnetic induction, D ' Arsonval, and thermal relays, are provided for significant improvement in the protection of power systems [42]. In the late 1950s, solid-state relays were introduced. The solid-state relays use various low power components: diodes, transistors, thyristors, associated resistors, and capacitors. For several reasons, utilities did not accept those relays for almost fifteen years. However, their use has increased gradually during the last several years [43]. Electromechanically, solid-­ state relays were used for protecting generator systems for the past several years,

4.5  Development of Relays

63

Fig. 4.4  The calculated values of different algorithms under SLG fault and tripping for cumulative sum method

Fig. 4.5  The calculated values of different algorithms under SLG fault and tripping for cumulative sum method

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4  Transient Behavior of Induction Generator Protective Relays

Fig. 4.6  The calculated values of different algorithms under SLG fault and tripping for cumulative sum method

and still are, and researchers have been studying the feasibility of designing relays using microprocessors. As a consequence of substantial research in the area of digital relaying, advancements in digital technology, and decrease in digital hardware prices, microprocessor relays are now available and being used for protecting generator systems [44]. Microprocessor-based distribution relays contribute to improved reliability and reduced costs on electric generator systems. Microprocessor-based relays, also called digital relays, have a proven track record of reliability. A digital relay uses software to process quantized signals for implementing the relay logic. Digital relays provide technical improvements and cost savings in several ways, as below: • The relays use programmable logic to reduce and simplify wiring. • The relays provide protection for bus faults, breaker failure, and high-side transformer blown fuse detection at no or minimal additional cost. • The relays have metering functions to reduce or eliminate the need for panel meters and transducers. • The relays reduce maintenance costs by providing self-test functions and high reliability. • The relays provide remote targets and fault location information to assist operators in restoration of electrical service [45–47].

4.6 Basic Components of Microcontroller-Based Relay

65

Transducer Surge Protection Circuit

Signal Condition Subsystem

Analogue Multiplexer Sample and Hold Circuit A/D Converter

Conversion Subsystem

Digital Multiplexer Digital Processing Relay Subsystem D/O

D/I

D/A

Memory

CPU

Remote Location Data

Trip Signals Fig. 4.7  Basic components of digital relay

4.6  Basic Components of Microcontroller-Based Relay Any digital relay can be thought of as comprising three fundamental subsystems, as shown in Fig. 4.7: • A signal conditioning subsystem • A conversion subsystem • A digital processing relay subsystem. The first two subsystems are generally common to all digital protective schemes, while the third varies according to the application of a particular scheme. Each of the three subsystems is built up of a number of components and circuits [32].

66

4  Transient Behavior of Induction Generator Protective Relays

4.7  Proposed Delay Time Setting for Different Relays From the traces of frequency deviation, a time delay for frequency relay can be chosen to be 0.1sec (6 cycles). This delay time permits the grid installation to sense and clear any kind of short circuit on the system side without any interference between the generator and the grid protection installations. • From the traces of currents, the delaying time of the over current relay can be chosen to be 0.1sec (6 cycles). For the same purpose mentioned in the previous paragraph. • From the traces of voltages, the delaying time of under-voltage relays can be chosen to be 1 sec. • The delaying time for the over-voltage relays is to be 0.1 sec.

4.8  F  ault Response with Protection Schemes for Digital Relay The simulation results are shown in Figs. 4.8 and 4.9. In Fig. 4.8, large line currents flow initially following the fault inception can be seen, while there is no visible effect on the circuit breaker. Figure 4.8 shows that the effects of the digital relay when it is set at 125–135% of rated current of the machine. The circuit breaker is disconnected in the system, and the over-current relay is activated. Control can be gained over circuit breaker if K = 0 or K = 1. The simulation results are shown in Fig. 4.9:

4.8  Fault Response with Protection Schemes for Digital Relay

67

(a)

(b) 2

relay current

relay current

1.5 1 0.5 0 -0.5 -1

0

0.1

0.2

0.3

0.4

0.5 0.6 Time (sec)

0.7

0.8

0.9

1

Fig. 4.8  Effect of circuit breaker operation on digital relay. (a) Current waveform when single line-to-ground fault occurs at point F. (b) Response of digital relay after connection circuit breaker

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4  Transient Behavior of Induction Generator Protective Relays

(a)

(b)

2 relay current

relay current

1.5 1 0.5 0 -0.5 -1 0

0.1

0.2

0.3

0.4

0.5 0.6 Time (sec)

0.7

0.8

0.9

1

Fig. 4.9  Effect of circuit breaker operation on the over-current relay. (a) Current waveform when single line-to ground-fault occurs at point F when circuit breaker tripps. (b)Response of digital relay before connection circuit breaker

Chapter 5

Description of Microcontroller Circuit and MikroC Program

5.1  Introduction In this chapter, we have provided a brief description of the devices and components that were used in programming the microcontroller for the book. An attempt at explaining the general working mechanisms, features, applications, and advantages of the system apparatus was made since without having a common idea of all the main components, it would be quite hard for a reader to understand the application and contribution of the individual components in the procedure followed in the book [55]. The major system components include: • • • • •

Microcontroller LCD display MAX 232 Interface of distributed antenna system (DAS) Software design

All these components put together, and the features that would serve the purpose of our work built the resulting book and the proposal presented in here.

5.2  Microcontroller (18F452) The 18F452 microcontroller is suitable for beginners as well as professionals, as well as for all ages, for those who love programming and control. One of the PIC18 family produced by Microchip, the PIC18F452 microcontroller is currently the most popular due to its many features, including ease of use, as well as FLASH memory technology that enables its users to reprogram it thousands of times and reuse it in many useful applications (Table  5.1). One of the main reasons why this © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 N. F. Ibrahim et al., Protection of Wind Turbine Generators Using Microcontroller-Based Applications, Green Energy and Technology, https://doi.org/10.1007/978-3-030-92628-1_5

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5  Description of Microcontroller Circuit and MikroC Program

Table 5.1  The 18F452 microcontroller feature Feature Program memory (bytes) Data memory (bytes) EEPROM (bytes) I/O Ports Timers Interrupt sources Capture/compare/PWM Serial Communication A/D Converter (10-Bit)

PIC 18F452 32K 1536 256 A,B,C,D,E 4 18 2 MSSP-USART 8 CHANEL

microcontroller is superior compared to other microcontrollers is that it has an 8-bit program memory, which is particularly fast due to its ability to compress 12 bits of code into an 8-bit word. PIC18F452 has 40 pins by 33 paths of input/output (I/O) [56]. EEPROM (electrically erasable programmable read-only memory), a type of nonvolatile memory, makes it easier to apply microcontrollers to devices where permanent storage of various parameters is needed (codes for transmitters, motor speed, receiver frequencies, etc.). Low cost, low power consumption, easy handling, and flexibility make PIC18F452 applicable even in areas where microcontrollers had not previously been considered (e.g., timer functions, interface replacement in larger systems, and co-processor applications). The “In System Programmability” feature of this chip (along with an advantage of using only two pins in data transfer) offers flexibility of a product after the completion of assembling and testing. Creating assembly line production, storing calibration data otherwise available only after final testing, and improving programs on finished products—all of this could be done using this capability. In general, PIC18F452 perfectly fits various uses as shown in Fig. 5.1, from automotive industries and controlling home appliances to industrial instruments, remote sensors, electrical door locks, and safety devices; it is also ideal for smart cards and battery supplied devices because of its low power consumption.

5.2.1  Features of PIC18F452 [55] • • • • • • • • • •

77 instructions PIC16 source code compatible Program memory addressing up to 2Mbytes Data memory addressing up to 4Kbytes DC to 40MHz operation 8 *8 hardware multiplier Interrupt priority levels 16-bit-wide instructions, 8-bit-wide data path Up to two 8-bit timers/counters Up to three 16-bit timers/counters

5.2  Microcontroller (18F452)

71

Fig. 5.1  Microcontroller PIC18F452 Pin Configuration

• • • • • • • • • • •

Up to four external interrupts High current (25mA) sink/source capability Up to five capture/compare/PWM modules Master synchronous serial port module (SPI and I2C modes) Up to two a universal synchronous and asynchronous receiver-transmitter (USART) modules Parallel slave port (PSP) Fast 10-bit analog-to-digital converter Programmable low-voltage detection (LVD) module Power-on reset (POR), power-up timer (PWRT), and oscillator start-up timer (OST) Watchdog timer (WDT) with on-chip RC oscillator In-circuit programming

In addition, some microcontrollers in the PIC18F family offer the following special features: • • • • • •

Direct CAN 2.0 bus interface Direct USB 2.0 bus interface Direct LCD control interface Transmission Control Protocol/Internet Protocol (TCP/IP) interface ZigBee interface Direct motor control interface

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5  Description of Microcontroller Circuit and MikroC Program

5.2.2  The PIC18F452 Consists of: • • • • •

4 timers/counters 2 capture/compare/PWM modules 2 serial communication modules 8 10-bit A/D converter channels 256 bytes EEPROM

5.2.3  Oscillator Circuit The PIC18F452 can perform many reset actions including: • • • • • • • • •

Power-up timer Oscillator start-up timer Power-on reset Watchdog timer Brown-out reset Low-voltage programming In-circuit debugger Phase-locked loop (PLL) circuit Timing generation circuit

The PLL circuit is new to the PIC18F series and provides the option of multiplying the oscillator frequency to speed up the overall operation. The watchdog timer can be used to force a restart of the microcontroller in the event of a program crash. The in-circuit debugger is useful during program development and can be used to return diagnostic data, including the register values, as the microcontroller is executing a program.

5.3  LCD Display With a wide range of applications, the 16 x 2 LCD (liquid crystal display) display screen used here is a basic electronic display module and is very commonly used in various devices and circuits. This module was better suited to serve our purpose and is generally more preferred over seven segments and other multisegment LEDs because LCDs are economical, easily programmable, have no limitation of displaying special and even custom characters (unlike in seven segments), animations, and so on. Using an LCD display is essential for us for displaying the energy usage of and to the providers and users [56], as shown in Fig. 5.2. With a standard HD44780 chipset, this 16-character by 2-line display works great with any microcontroller and is very easy to interface. It is possible to use all 8 bits plus three control signals or 4 bits plus the control signals of the 8-bit parallel

5.3  LCD Display

73

Fig. 5.2  Pin Configuration of a 16 × 2 LCD Display

interface of this LCD. The pin diagram of the 16x2 LCD display is shown in Table 5.2 [55–56].

5.3.1  Features • • • • • • •

16 x 2 characters STN/transflective/positive/Y-G Yellow green/bottom-light (LED) Operating temp.: −10 °C~+60 °C 1/16 duty cycle, 1/5 bias Built-in controller (SPLC780D1 or equivalent) Viewing angle: 6 o’clock

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5  Description of Microcontroller Circuit and MikroC Program

Table 5.2  The pin diagram of the 16 x 2 LCD display Pin no. 1 2 3 4 5

Name VSS VCC VEE RS R/W

6 7 8 9 10 11 12 13 14

EN D0 D1 D2 D3 D4 D5 D6 D7

Description Power supply (ground) Power supply (+5V) Contrast adjust 0-instruction input and 1-data input 0-write to LCD module and 1-read from LCD module Enable signal Data bus line 0 (LSB) Data bus line 1 Data bus line 2 Data bus line 3 Data bus line 4 Data bus line 5 Data bus line 6 Data bus line 7 (MSB)

5.4  MAX 232 Commonly known as RS-232 transceiver, the MAX232 is a hardware layer protocol converter integrated circuit (IC) manufactured by the Maxim Corporation comprising of a pair of drivers and a pair of receivers. At a very basic level, the driver converts TTL and CMOS voltage levels to TIA/EIA232-E levels, which are compatible for serial port communications. The receiver performs the reverse conversion. According to the EIA/TIA-232-E specification in 1962, RS-232, where the letters “RS” refer to Recommended Standards, is a serial communication protocol. This protocol requires a voltage between −3 V and −15 V to represent binary 1 and a voltage between +3 V to +15 V to represent binary 0. Since TTL uses 5 V to represent binary 1 and 0 V to represent binary 0, this is 23 incompatibles for CMOS and TTL communication. This chip therefore performs the necessary protocol conversion of the electrical voltage levels in both directions. Switched-capacitor charge pump circuits are incorporated within the IC since RS-232 requires higher voltage levels. The doubler doubles the voltage level to produce +10V, while the inverter produces the negative voltage supply of −10V. For more than two decades, this IC has been one of the most popular components in the production of embedded microcontroller systems and computers, as shown in Figs. 5.3 and 5.4. It is the most preferred chip used for communication through a serial port using a microcontroller [55].

5.4  MAX 232

Fig. 5.3  Level converter circuit using MAX232 [56]

Fig. 5.4  Pin configuration of an MAX232

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5  Description of Microcontroller Circuit and MikroC Program

5.4.1  Applications [55] The applications of MAX232 IC include the following. • • • • •

Portable computers Low-power modems Interface translation Battery-powered RS-232 systems Multidrop RS-232 networks

5.4.2  Features [55] The main features of MAX232 IC include the following. • • • • • • •

Input voltage levels are compatible with standard СMOS levels. Output voltage levels are compatible with EIA/TIA-232-E levels. Single Supply voltage: 5V. Low input current: 0.1μA at ТA= 25 °С. Output current: 24Ma. Latching current is not less than 450mA at ТA= 25 °С. The transmitter outputs and receiver inputs are protected to ±15kV Air ESD.

5.5  Interface of DAS Analog-to-digital converter (ADC) takes a definite time, depending upon the clock frequency, for conversion of analog signals into digital form. The analog voltage should remain constant during the conversation period. For this purpose, a sample and hold (S/H) circuit is used. The S/H circuit samples the instantaneous value of the AC signal at the desired instant and holds it constant during the conversation period of ADC. Sampling interval can be obtained by S/H circuit from the signal. An analog multiplexer is used to select signal of any one channel from the multiinput channels and transfer this signal to its output. The circuit for interfacing of ADC to the 18f452 microcontroller is programmable I/O port. An ADC takes finite time, known as conversion time, to convert an analogue signal into digital form. If the input analog signal is not constant during the conversion period, the digital output of ADC will not correspond to the starting point analog input; a sample and hold (S/H) circuit is used to keep the instantaneous value of rapidly varying analog signal constant during the conversion period [51]. Input and output programming ports of microcontroller are as follow: PORTA, PORTB, PORTC, PORTD, and PORTE are the five parallel ports of the PIC18F452. The majority of port pins have various purposes. PORTA pins can be utilised as parallel inputs-outputs or

5.7 Digital Relay MikroC Program Code

77

analogue inputs, for example. PORTB pins can be utilised as interrupt inputs or parallel input-outputs. The digital output of the ADC is stored in memory location. The digital values corresponding to analog voltages of 0 and 5v are 80 and FF, respectively.

5.6  Software Design The relay software is developed using C language, and the flowchart arrangement for the software design is given in Chap. 4. The microcontroller sends a signal to the ADC for starting the conversation. Then the microcontroller receives the signal in digital form and then compares it with the pickup value. In case of over-current relay, the microcontroller sends the tripping signal to the circuit breaker after a predetermined time delay if the fault current exceeds the pickup value. These values are stored in the memory in tabular form. The microcontroller first determines the magnitude of the fault current and then selects the corresponding time of operation from the lookup table.

5.7  Digital Relay MikroC Program Code // Lcd pinout settings sbit LCD_RS at RB4_bit; sbit LCD_EN at RB5_bit; sbit LCD_D7 at RB3_bit; sbit LCD_D6 at RB2_bit; sbit LCD_D5 at RB1_bit; sbit LCD_D4 at RB6_bit; // Pin direction sbit LCD_RS_Direction at TRISB4_bit; sbit LCD_EN_Direction at TRISB5_bit; sbit LCD_D7_Direction at TRISB3_bit; sbit LCD_D6_Direction at TRISB2_bit; sbit LCD_D5_Direction at TRISB1_bit; sbit LCD_D4_Direction at TRISB6_bit; // floati11,i21,i31,v11,v21,v31,i12,i22,i32,v12,v22,v32,i13,i23,i33, v13,v23,v33,i14,i24,i34,v14,v24,v34; // Floatia1,ib1,ic1,va1,vb1,vc1,i12,ib2,i32,va2,vb2,vc2,i13,i23,i33, va3,vb3,vc3,i14,i24,i34,va4,vb4,vc4; float sa,sb,sc,ca,cb,cc,ia,ib,ic,sav,sbv,scv,cav,cbv,ccv,va,vb,vc;

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5  Description of Microcontroller Circuit and MikroC Program

char iaa[16],ibb[16],icc[16],vaa[16],vbb[16],vcc[16]; char i,imax=90,x=20,vmax=245,vmin=175,zz=0; char aa=0; float freq=3 ; char txt[16]; // #define portc.b0=cbb void interrupt() { intcon.b1=0; if(aa==0){ tmr0h=0; tmr0l=0; t0con.b7=1; aa=1;} else {t0con.b7=0; freq=tmr0l; freq+=tmr0himax){portc.b0=1;x=1;} else if ((ia>imax && ib>imax)||(ib>imax && ic>imax)||(ia>imax&& ic>imax)){portc.b0=1;x=2;} else if (ia>imax || ib>imax || ic>imax){portc.b0=1;x=3;} else if (va>vmax || vb>vmax || vc>vmax){portc.b0=1;x=4;} else if (va