Preface

Nowadays, the rapid growth of power electronics in industry and the presence of products based on electronic components in enterprises, institutions, shops, small businesses, residences, etc. and transport systems has been welcomed by the people who already use it due to its increased productivity within all areas. The problem of this increasing use of power electronics equipment is the important distortions originated; the perfect AC power systems are a pure sinusoidal wave, both voltage and current, but the ever-increasing existence of non-linear loads modify the characteristics of voltage and current from the ideal sinusoidal wave. This deviation from the ideal wave is reflected by the harmonics and, although its effects vary depending on the type of load, it affects the efficiency of an electrical system and can cause considerable damage to the systems and infrastructures. Logic and electronic control circuits, among others, may be affected if the supply voltage has distortions, leading to, for example, damage in the consumer equipment, and noise in the different installations or unsafe working conditions. In other cases the harmonic current passes through transmission lines and causes harmonic voltage on the loads connected at the end of the line, but this will be dealt with in another book.

Ensuring optimal power quality after a good design and devices means productivity, efficiency, competitiveness and profitability. Nevertheless, nobody can assure the optimal power quality when there is a good design if the correct testing and working process from the obtained data is not properly assured at every instant; this entails processing the real data correctly. To ensure a precise measurement of the electrical power quantities, different processing techniques are necessary. The possibilities range from the design of the overall system to the testing and training of devices, checking the influence of the final design and behaviour laws in a virtual environment similar to the real one. One properly designed simulator would allow for checking the technical specifications in order to find contradictions that may be introduced during the design of the system, and their subsequent correction.

In the following chapters the reader will be introduced to the harmonics analysis from the real measurement data and to the study of different industrial environments and electronic devices. The book is divided into four sections: measurements, converters, harmonic distortion, and industrial environments; a brief discussion of each chapter is as follows.

Chapter 1 discusses the sources of harmonics and the problems caused to the power systems, and also model the voltage and current signal to account for the harmonics components when the signal is a non-sinusoidal signal. Additionally, it estimates the parameters of this signal in order to suppress the harmonics or eliminate some of them, and identifies and measures the sub-harmonics. Finally, it models the harmonic signals as fuzzy signals, identifying the parameters by using static and dynamic algorithms. Chapter 2 encompasses the poor reliability of the real measured data used for several applications dealing with power quality disturbances, and proposes a set of reliability criteria to determine the data quality, which can be directly applied to recorded data and used to determine which data are to be used for further processing, and which data should be discarded. Chapter 3 presents the problems of voltage transformers and voltage harmonic transfer accuracy, which are usually used for power quality monitoring in medium and high voltage grids. Additionally, a simplified lumped parameters circuit model of the voltage transformer is proposed and verified by simulation and experimental research.

Preface XI

presents a generic stochastic analysis to model the effect of nonlinear electronic devices in power distribution systems by using circuit models comprising several passive current sources for the electronic devices. The chapter also analyzes different combinations of loads and transmission lines and results in a method for performing the primary estimations for the planning and dimensioning of power systems with the

Chapter 9 discuses the importance of harmonic measurements and how this affects and causes problems if higher Total Harmonic Distortion (THD) levels are detected and also how to sort out the order of harmonic from such harmonics emitting devices. Different harmonics and effects will be shown in the chapter on a real practical investigation in harmonics produced in an industrial plant with an arc furnace, mainly used in steel production for the recycling of scrap, as well as in the university due to the increasing numbers of personal computers, providing different environments. Chapter 10 studies the power quality problems caused by the operation of line frequency coreless induction furnaces, which introduces imbalances that lead to increasing power and active energy losses in the network. The literature does not offer detailed information regarding the harmonic distortion in the case of these furnaces and important conclusions are obtained, such as the introduction of harmonic filters in the primary of the furnace transformer to solve the power interface problems or the addition of a load balancing system at the connection point of the furnace to the power supply network to eliminate the imbalance. Finally, in Chapter 11 a Distributed Generation (DG) installation is modelled detailing the capacitive coupling of the electric circuit with the grounding system. The capacitive grounding models for Solar Photovoltaic (PV) installations and wind farms are detailed, which allows analyzing the current distortion, ground losses and Ground Potential Rise (GPR) due to the capacitive coupling. The combined effect of the different distributed generation sources connected to the same electric network has been simulated to minimize the capacitive ground current in these installations for meeting typical power quality

flexibility of being able to choose the numbers of different devices.

regulations concerning harmonic distortion and safety conditions.

and that it will have been to your interest and liking.

different areas of Power Quality.

We hope that after reading the different sections of this book we will have succeeded in bringing across what the scientific community is doing in the field of Power Quality

Lastly, we would like to thank all the authors for their excellent contributions in the

**Dr. Gregorio Romero Rey Dra. Mª Luisa Martinez Muneta**  Universidad Politécnica de Madrid

Spain

In Chapter 4 a transistor LCC resonant DC/DC converter of electrical energy is studied, working at frequencies higher than the resonant one. It is analyzed due to the possible operating modes of the converter with accounting the influence of the damping capacitors and the parameters of the matching transformer, drawing the boundary curves between the different operating modes of the converter in the plane of the output characteristics, as well as outlining the area of natural commutation of the controllable switches. Finally, a laboratory prototype of the converter under consideration is built after suggesting a methodology for designing it. Chapter 5 investigates the thermal behaviour of the power semiconductor as a component part of the power converter (rectifier or inverter), and not as an isolated part, from different structures of power rectifiers. To do this, the parametric simulations for the transient thermal conditions of some typical power rectifiers are presented and the 3D thermal modelling and simulations of a power device as main component of power converters are described too.

Chapter 6 discusses the principle and control method of a Unified Power Quality Conditioner (UPQC), mainly used in low-voltage low-capacity applications and effective in reducing both harmonic voltage and harmonic current, but applied in this case to high power nonlinear loads. In this UPQC, a shunt Active Power Filter (APF) is connected to a series LC resonance circuit in grid fundamental frequency so as to make a shunt APF in lower voltage and lower power, and uses a hybrid APF which includes a Passive Power Filter (PPF). Chapter 7 summarizes the research of parallel and series resonances and unifies the study providing a similar expression to the series resonance case, but substantially improved for the parallel resonance case, and unique to their location. It is completed with the analysis of the impact of the Steinmetz circuit inductor resistance on the resonance and a sensitivity analysis of all variables involved in the location of the parallel and series resonance. Finally, the chapter ends with several experimental tests to validate the proposed expression and several examples of its application. Chapter 8 presents a generic stochastic analysis to model the effect of nonlinear electronic devices in power distribution systems by using circuit models comprising several passive current sources for the electronic devices. The chapter also analyzes different combinations of loads and transmission lines and results in a method for performing the primary estimations for the planning and dimensioning of power systems with the flexibility of being able to choose the numbers of different devices.

X Preface

Chapter 1 discusses the sources of harmonics and the problems caused to the power systems, and also model the voltage and current signal to account for the harmonics components when the signal is a non-sinusoidal signal. Additionally, it estimates the parameters of this signal in order to suppress the harmonics or eliminate some of them, and identifies and measures the sub-harmonics. Finally, it models the harmonic signals as fuzzy signals, identifying the parameters by using static and dynamic algorithms. Chapter 2 encompasses the poor reliability of the real measured data used for several applications dealing with power quality disturbances, and proposes a set of reliability criteria to determine the data quality, which can be directly applied to recorded data and used to determine which data are to be used for further processing, and which data should be discarded. Chapter 3 presents the problems of voltage transformers and voltage harmonic transfer accuracy, which are usually used for power quality monitoring in medium and high voltage grids. Additionally, a simplified lumped parameters circuit model of the voltage transformer is proposed

In Chapter 4 a transistor LCC resonant DC/DC converter of electrical energy is studied, working at frequencies higher than the resonant one. It is analyzed due to the possible operating modes of the converter with accounting the influence of the damping capacitors and the parameters of the matching transformer, drawing the boundary curves between the different operating modes of the converter in the plane of the output characteristics, as well as outlining the area of natural commutation of the controllable switches. Finally, a laboratory prototype of the converter under consideration is built after suggesting a methodology for designing it. Chapter 5 investigates the thermal behaviour of the power semiconductor as a component part of the power converter (rectifier or inverter), and not as an isolated part, from different structures of power rectifiers. To do this, the parametric simulations for the transient thermal conditions of some typical power rectifiers are presented and the 3D thermal modelling and simulations of a power device as main component of power converters

Chapter 6 discusses the principle and control method of a Unified Power Quality Conditioner (UPQC), mainly used in low-voltage low-capacity applications and effective in reducing both harmonic voltage and harmonic current, but applied in this case to high power nonlinear loads. In this UPQC, a shunt Active Power Filter (APF) is connected to a series LC resonance circuit in grid fundamental frequency so as to make a shunt APF in lower voltage and lower power, and uses a hybrid APF which includes a Passive Power Filter (PPF). Chapter 7 summarizes the research of parallel and series resonances and unifies the study providing a similar expression to the series resonance case, but substantially improved for the parallel resonance case, and unique to their location. It is completed with the analysis of the impact of the Steinmetz circuit inductor resistance on the resonance and a sensitivity analysis of all variables involved in the location of the parallel and series resonance. Finally, the chapter ends with several experimental tests to validate the proposed expression and several examples of its application. Chapter 8

and verified by simulation and experimental research.

are described too.

Chapter 9 discuses the importance of harmonic measurements and how this affects and causes problems if higher Total Harmonic Distortion (THD) levels are detected and also how to sort out the order of harmonic from such harmonics emitting devices. Different harmonics and effects will be shown in the chapter on a real practical investigation in harmonics produced in an industrial plant with an arc furnace, mainly used in steel production for the recycling of scrap, as well as in the university due to the increasing numbers of personal computers, providing different environments. Chapter 10 studies the power quality problems caused by the operation of line frequency coreless induction furnaces, which introduces imbalances that lead to increasing power and active energy losses in the network. The literature does not offer detailed information regarding the harmonic distortion in the case of these furnaces and important conclusions are obtained, such as the introduction of harmonic filters in the primary of the furnace transformer to solve the power interface problems or the addition of a load balancing system at the connection point of the furnace to the power supply network to eliminate the imbalance. Finally, in Chapter 11 a Distributed Generation (DG) installation is modelled detailing the capacitive coupling of the electric circuit with the grounding system. The capacitive grounding models for Solar Photovoltaic (PV) installations and wind farms are detailed, which allows analyzing the current distortion, ground losses and Ground Potential Rise (GPR) due to the capacitive coupling. The combined effect of the different distributed generation sources connected to the same electric network has been simulated to minimize the capacitive ground current in these installations for meeting typical power quality regulations concerning harmonic distortion and safety conditions.

We hope that after reading the different sections of this book we will have succeeded in bringing across what the scientific community is doing in the field of Power Quality and that it will have been to your interest and liking.

Lastly, we would like to thank all the authors for their excellent contributions in the different areas of Power Quality.

> **Dr. Gregorio Romero Rey Dra. Mª Luisa Martinez Muneta**  Universidad Politécnica de Madrid Spain

**Part 1** 

**Measurements** 

**Part 1** 

**Measurements** 

**1** 

*1Egypt 2Kuwait* 

**Electric Power Systems Harmonics -** 

The presence of non-linear loads and the increasing number of distributed generation power systems (DGPS) in electrical grids contribute to change the characteristics of voltage and current waveforms in power systems, which differ from pure sinusoidal constant amplitude signals. Under these conditions advanced signal processing techniques are required for accurate measurement of electrical power quantities. The impact of non-linear loads in electrical power systems has been increasing during the last decades. Such electrical loads, which introduce non-sinusoidal current consumption patterns (current harmonics), can be found in rectification front-ends in motor drives, electronic ballasts for discharge lamps, personal computers or electrical appliances. Harmonics in power systems mean the existence of signals, superimposed on the fundamental signal, whose frequencies are integer numbers of the fundamental frequency. The electric utility companies should supply their customers with a supply having a constant frequency equal to the fundamental frequency, 50/60 Hz, and having a constant magnitude. The presence of harmonics in the voltage or current waveform leads to a distorted signal for voltage or current, and the signal becomes non-sinusoidal signal which it should not be. Thus the study of power system harmonics is

The power system harmonics problem is not a new problem; it has been noticed since the establishment of the ac generators, where distorted voltage and current waveforms were

Concern for waveform distortion should be shared by all electrical engineers in order to establish the right balance between exercising control by distortion and keeping distortion under control. There is a need for early co-ordination of decisions between the interested parties, in order to achieve acceptable economical solutions and should be discussed

Electricity supply authorities normally abrogate responsibility on harmonic matters by introducing standards or recommendations for the limitation of voltage harmonic levels at

between manufacturers, power supply and communication authorities [1].

**1. Introduction** 

an important subject for power engineers.

observed in the thirtieth of 20th century [2].

the points of common coupling between consumers.

**Identification and Measurements** 

Soliman Abdelhady Soliman1

*2College of Technological Studies,* 

and Ahmad Mohammad Alkandari2 *1Misr University for Science and Technology,* 
