Power Quality

Electrical power is becoming one of the most dominant factors in our society. Power generation, transmission, distribution and usage are undergoing signifi cant changes that will aff ect the electrical quality and performance needs of our 21st century industry. One major aspect of electrical power is its quality and stability – or so called Power Quality. The view on Power Quality did change over the past few years. It seems that Power Quality is becoming a more important term in the academic world dealing with electrical power, and it is becoming more visible in all areas of commerce and industry, because of the ever increasing industry automation using sensitive electrical equipment on one hand and due to the dramatic change of our global electrical infrastructure on the other. For the past century, grid stability was maintained with a limited amount of major generators that have a large amount of rotational inertia. And the rate of change of phase angle is slow. Unfortunately, this does not work anymore with renewable energy sources adding their share to the grid like wind turbines or PV modules. Although the basic idea to use renewable energies is great and will be our path into the next century, it comes with a curse for the power grid as power fl ow stability will suff er. It is not only the source side that is about to change. We have also seen signifi cant changes on the load side as well. Industry is using machines and electrical products such as AC drives or PLCs that are sensitive to the slightest change of power quality, and we at home use more and more electrical products with switching power supplies or starting to plug in our electric cars to charge batt eries. In addition, many of us have begun installing our own distributed generation systems on our rooft ops using the latest solar panels. So we did look for a way to address this severe impact on our distribution network. To match supply and demand, we are about to create a new, intelligent and self-healing electric power infrastructure. The Smart Grid. The basic idea is to maintain the necessary balance between generators and loads on a grid. In other words, to make sure we have a good grid balance at all times. But the key question that you should ask yourself is: Does it also improve Power Quality? Probably not! Further on, the way how Power Quality is measured is going to be changed. Traditionally, each country had its own Power Quality standards and defi ned its own power quality instrument requirements. But more and more international harmonization efforts can be seen. Such as IEC 61000-4-30, which is an excellent standard that ensures that all compliant power quality instruments, regardless of manufacturer, will produce of measurement instruments so that they can also be used in volume applications and even directly embedded into sensitive loads. But work still has to be done. We still use Power Quality standards that have been writt en decades ago and don’t match today’s technology any more, such as fl icker standards that use parameters that have been defi ned by the behavior of 60-watt incandescent light bulbs, which are becoming extinct. Almost all experts are in agreement - although we will see an improvement in metering and control of the power fl ow, Power Quality will suff er. This book will give an overview of how power quality might impact our lives today and tomorrow, introduce new ways to monitor power quality and inform us about interesting possibilities to mitigate power quality problems. Regardless of any enhancements of the power grid, “Power Quality is just compatibility” like my good old friend and teacher Alex McEachern used to say. Power Quality will always remain an economic compromise between supply and load. The power available on the grid must be suffi ciently clean for the loads to operate correctly, and the loads must be suffi ciently strong to tolerate normal disturbances on the grid

Protection Scheme based on Artificial Neural Network for Fault Detection and Classification in Low Voltage PV-Based DC Microgrid

With the expansion of the DC distribution market, protection, and operational concerns for Direct Current (DC) Microgrids have increased. Different systems have been investigated for detecting, finding, and isolating defects utilising a variety of protective mechanisms. It might be difficult to locate high-resistance faults and shorted DC faults on low-voltage DC (LVDC) microgrids. Therefore, in this study, a Field Transform Technique like Short-Time Fourier Transform (STFT) is proposed for detecting the Fault Current (FC). This method detects the faults Pole-ground (PG), pole-pole (PP), and Arc fault are the major fault types in the DC network with PG fault as the most common and less severe. One of the difficulties the DC system faces in the incidence of a malfunction is the protection of essential converters. During this fault, the diodes, being the most vulnerable component of the system, may encounter a substantial surge in current, which can potentially cause damage if the current surpasses double their specified capacity for withstanding. After the Fault detection (FD), a Taguchi-based ANN is presented to classify the detected faults. This method effectively classifies PV-based faults. Then, to safeguard the FC, the Improved Self-Adaptive Solid State Circuit Breaker (I-SSCB) is introduced. It safeguards the FC in the low-voltage PV-based DC microgrid (DCMG) and restricts FC in the DCMG. The suggested approach is evaluated using the Matlab software and the proposed method produces 400A current and 100 KW power during the PV temperature of 25°C. The output current of the ANN is then 1A for a duration of 0.3 to 0.4 seconds. The fault voltage and FC produced in this proposed work are 1900V and 1950A. Therefore, the proposed work's current and voltage values are 21 KV and 0.35 I. Therefore, the proposed method produces more power and limits the FC in the LV-DCMG. In future studies, the improved or modified neural network or machine learning (ML)-based techniques can be utilized which may improve the protection scheme of the work

Design and implementation of ANN based phase comparators applied to transmission line protection

There has been significant development in the area of neural network based power system protection in the previous decade. Neural network technology has been applied for various protective relaying functions including distance protection. The reliability and efficiency of ANN based distance relays is improving with the developing digital technologies. There are, however, some inherent deficiencies that still exist in the way these relays are designed. This research addresses some of these issues and proposes an improved protective relaying scheme. The traditional ANN distance relay designs use parameter estimation algorithms to determine the phasors of currents and voltages. These phasors are used as inputs to determine the distance of a fault from relay location. The relays are trained and tested on this criterion; however, no specific relay characteristic has been defined. There is a need for development of a new methodology that will enable designing of an ANN that works as a generic distance relay with clearly defined operating boundary. This research work presents a modified distance relaying algorithm that has been combined with a neural network approach to eliminate the use of phasors. The neural network is trained to recognize faults on basis of a specific relay characteristic. The algorithm is flexible and has been extended for the design of other relays. The neural network has been trained using pure sinusoidal values and has been tested on a 17-bus power system simulated in PSCAD. The training and testing of the neural network on different systems ensures that the relay is generic in nature. The proposed relay can be used on any transmission line without re-training the neural network. The design has been tested for different fault conditions including different fault resistances and fault inception angles. The test results show that the relay is able to detect faults in lesser time as compared to conventional relay algorithms while maintaining the integrity of relay boundaries

Coordination of Generator Protection and Control in the Over and Under Excited Regions

This thesis deals with the coordination of protection and control functions associated with the synchronous generators. The excitation control functions are a key component in maintaining the stability of machines and the network. The overall objective of coordination is simple; to allow excitation control functions, the automatic recovery from excursions beyond normal limits, and only take protective action as a last resort. This thesis focuses on four areas of generator control and protection : a) Loss of excitation protection, b) Dynamic underexcitation coordination, c) Dynamic Overexcitation coordination, and d) a generic protective relay development platform for hardware and software development. Loss of excitation (LOE) is a condition in the underexcited region that presents a risk of severe damage to a generator. The state of the art in the detection of a loss of excitation condition is based on the principle that, for a zero Thevenin voltage, the generator becomes a reactance as seen from the power system. The difficulty in detecting a loss of excitation is that several other disturbances may temporarily present a similar behavior, for instance a fault followed by a power swing. In this part of the work, a new algorithm for the detection of a loss of excitation condition is proposed by using the Support Vector Machine (SVM) classification method and a careful design of the necessary feature vectors. The proposed method is robust to changes in conditions including initial load, fault types, line impedance, as well as generator parameter inaccuracies. Coordination in the underexcited region presents difficulties due to the commonly used static characteristics instead of dynamic simulation. The underexcited limit presents an overload characteristic that is not normally known or used. Once the limit is exceeded, the limiting control action is a control loop that presents a dynamic behavior not typically represented in studies in the current industry practice. It is also important to properly model and include dynamic performance of protection functions. An important consideration not typically taken into account is the actual stability limit, which depends on the characteristics and the mode of excitation control used. This thesis includes all the above considerations necessary to achieve the required coordination using the more accurate dynamic simulations. Specific scenarios that present risk to the machine or the system are included to assess the coordination achieved. A real generator from the Alberta power system is used as a case study to demonstrate the proposed coordination methodology. Coordination in the overexcited region again presents practical difficulties due to static characteristics instead of dynamic simulation of conditions that exercise the overexcitation limits. The problems observed relate to coordination methodology and modeling methods for both protection and control limits. Once the limit boundary characteristic is exceeded, the limiting action is a control loop that presents dynamic behavior that needs to be represented. Similar considerations need to be made with the protection function protecting against rotor overload. Current modeling methods mostly use low bandwidth simulations, i.e., transient stability studies. A modeling methodology as well as specific model improvements to the IEEE ST1A excitation control model are proposed to achieve the required coordination. The ST1A type is one model that can represent a wide variety of system models from different manufacturers. The proposed modeling methodology applies to high bandwidth simulations such as electromagnetic simulations. Specific important scenarios, such as severe temporary reactive overload or severe power swing conditions, where the protection and control are required to coordinate but that present risk to the machine or the system are proposed as part of the coordination considerations. The detection of LOE conditions by the proposed SVM method and by traditional methods was implemented in hardware by using a digital signal processor (DSP) platform and tested using real time power system simulations. A new platform for real time protective relay development was designed and used for the purpose of implementation. In the proposed platform, a processor independent code is used so that development can be performed using native host computer development tools. By using the proposed platform-independent code, off line testing can be performed either interactively or in batch mode for evaluating multiple cases

The Impact of Transmission Protection System Reliability on Power System Resilience

Power transmission operation regimes are being changed for various technical and economic reasons seeking an improved power system resilience as a goal. However, some of these changes introduce new challenges in maintaining conventional transmission protection system dependability and security when meeting the operating complexities affecting power system resilience. Frequently evolving network topology, as a result of multiple switching actions for corrective, predictive and post event purposes, as well as high penetration of distributed generation into the system are considered as major contradictory changes from the legacy transmission protection standpoint. This research investigates the above-mentioned challenges and proposes effective solutions to improve the transmission protection reliability facing the above-mentioned risks and power system resilience consequently. A fundamental protection scheme based on the Hierarchically Coordinated Protection (HCP) concept is proposed to illustrate various approaches to predictive, adaptive and corrective protection actions aimed at improving power system resilience. Novel computation techniques as well as intelligent machine-learning algorithms are employed in proposing predictive, adaptive, and corrective solutions which fit various layers of the HCP concept and incorporate a fundamental HCP-based approach to supervise the legacy transmission protection function for a dynamic balance between dependability and security. The proposed predictive, adaptive, and corrective protection approaches are tested and verified on various systems, including real-life and IEEE test systems, and their performance effectiveness is compared with the state of the art

Application of Kalman filtering in computer relaying of power systems

Kalman-filter models for the optimal estimation of the post-fault currents and voltages for computer relaying purposes of power systems are presented. As a prerequisite for the Kalman-filtering implementation, the random description of the fault-induced noise signals was quantitatively studied. Empirical formulas that describe the random nature of the noise based on the probability of fault location and the frequency of occurrence of the different types of faults are given. These empirical formulas offer the possibility of developing other new techniques in computer relaying of power systems;Sensitivity of the Kalman filters to incorrect model parameters was studied through extensive simulation. A Kalman-filtering-based digital distance relay was designed to detect, classify, and locate faults in a high voltage transmission line in the shortest period of time;Comparison of the developed technique with four other algorithms demonstrated that the Kalman-filtering-based algorithm is superior to other techniques in the rate of convergence to the exact values, accuracy, and computer burden. Thus the Kalman-filtering approach appears to be especially well-suited to the power system protection problem

An artificial neutral network fault-diagnostic adviser for a nuclear power plant with error prediction

Since the accidents at the Three-Mile Island (TMI) and m Chernobyl nuclear power plants (NPPs), the safety of NPPs has become an even more important concern to both the nuclear power industry and the general public. The demand for safer plants has ever since. Responding to the demand, many scientists increased have investigated augmenting NPP safety in various ways. For m example, innovative reactor designs, better safety system R designs, human factor studies, stricter safety regulations, and so on, have been developed and implemented in the years since the above-mentioned accidents

Transformada wavelet para análisis del motor de inducción: revisión

This study makes a revision of the most recent investigations that have implemented the wavelet transform by analyzing the electrical and mechanical variables of the induction motors. The investigations can be grouped into three main topics: diagnosis and detection of faults, control and detection systems and the classification of electromagnetic disturbances.Este trabajo realiza una revisión de las investigaciones más recientes que han implementado la transformada wavelet analizando las variables eléctricas y mecánicas de los motores de inducción. Las investigaciones se pueden agrupar en tres temas principales: diagnóstico y detección de fallas; sistemas de control y detección y la clasificación de perturbaciones electromagnéticas