Phase comparison techniques for transmission line protection

Using sampled values in line differential protection – Analyzing the scheme feasibility and protection performance under communication stress scenarios

Fault location and distance protection in transmission lines are essential smart grid technologies ensuring reliability of the power system and achieve the continuity of service. The objective of this chapter is to presents an accurate algorithm for estimating fault location in Extra High Voltage (EHV) transmission lines using Artificial Neural Networks (ANNs) for high speed protection. The development of this algorithm is based on disturbed transmission line models. The proposed fault protection (fault detection/classification and location) uses only the three phase currents signals at the one end of the line. The proposed technique uses five ANNs networks and consists of two steps, including fault detection/classification and fault location. For fault detection/classification, one ANN network is used in order to identify the fault type; the fault detection/classification procedure uses the fundamental components of pre-fault and post-fault sequence samples of three phase currents and zero sequence current. For fault location, four ANNs networks are used in order to estimate the exact fault location in transmission line. Magnitudes of pre-fault and post-fault of three phase currents are used. The ANNs are trained with data under a wide variety of fault conditions and used for the fault classification and fault location on the transmission line. The proposed fault detection/classification and location approaches are tested under different fault conditions such as different fault locations, different fault resistances and different fault inception angles via digital simulation using MATLAB software in order to verify the performances of the proposed methods. The ANN-based fault classifier and locator gives high accuracy for all tests under different fault conditions. The simulations results show that the proposed scheme based on ANNs can be used for on-line fault protection in transmission line.

<span lang="EN-US">Since transmission lines account for 80–86% of power system problems, protecting transmission lines is a critical concern. This research proposes a method to identify and categorize various short circuit defects on transmission lines. Various operational and fault circumstances on the transmission of high voltage lines, including L-L fault, single phase to earth fault, and double line fault, double line Three fault scenarios triple line fault, triple line to ground fault, and triple line are simulated using MATLAB software. These flaws damage the linked devices to the power grid. The main motto of this work is to analyze various kinds of faults and also to detect the type of the fault in transmission line. In order to simulate and evaluate the various faults, a 100 km transmission line model was created. A sim power system block library had a fault block, and the harmonic content of the various faults was studied using the FFT tool, the effect of faults was observed. Based on the analysis, a hardware model is designed to identify the faults in transmission line using actuating relays and Atmega 328P microcontroller and display the fault type and parameters like fault impedance, and distance at which fault occurred.</span>

An electric power system is often faced with disturbance problems. The 150 kV transmission line from GI Ngimbang to GI Babat 1 experienced several disturbances due to a single-phase short circuit to the ground. The approach to determining the value of the impedance is by considering the value of the capacitance using the Phi Nominal Method with the center of the capacitance value located at the ends of the line which is divided equally in size. The main protection system used on the transmission line is the Distance relay, but the Distance relay is still not reliable and responsive. So with these shortcomings, it can be overcome by using a Line Current Differential transmission line protection system, it is proven that the Differential Line Current performance can work well. The research was conducted to analyze the performance of the Line Current Differential protection relay on the 150 kV Ngimbang-Babat 1 transmission line by calculating the impedance and capacitance values. The calculation is simulated in modeling the system against short circuit faults in determining the protection relay settings. From the results of the study, it was found that the accuracy of the Line Current Differential setting value can work by providing a disturbance signal to the power breaker (PMT) to perform tripping when a disturbance occurs in an area that is secured by a protection relay (internal fault), while the protection relay cannot work when an external disturbance occurs. secured area protection relay(external fault).

Application of Haar functions for transmission line and transformer differential protection

Longitudinal current differential protection is often used as the main protection of ultra-high voltage (UHV)/extra-high voltage (EHV) transmission lines. It's sensitivity and selectivity will be severely influenced by the considerably increased distributed capacitive current with the increase of voltage level and transmission distance. In this study, a novel UHV/EHV transmission line protection is proposed based on longitudinal tapped impedance. For sound transmission line or transmission line with external faults, the calculated impedance is approximately equal to the capacitive reactance of the line. If internal faults occur on the line, the computed impedance of the faulty phase is approximately equal to the parallel value of the line capacitive reactance and the fault resistance. The proposed protection does not require the compensation of capacitive current and is not affected by load current and system impedance. This new protection principle has an improved selectivity and natural phase selection ability, and very high sensibility for high resistance faults. The correctness and effectiveness of the proposed protection have been verified by simulation tests.

This paper presents an improved current differential protective principle. Marti model of the transmission line is applied in this principle, which place emphasis on solving frequency-dependent line parameters. The operating current expressions for an internal fault are also deduced in frequency domain. Finally, simulating comparison have been carried out between the proposed protective principle and Bergeron model based protection for Chinese 1000kV UHVAC test demonstration project. Simulation results show that this improved principle has high reliability for both internal and external faults. The 1000kV UHVAC transmission lines which are being constructed in China, in hybrid with HVDC links, will form the backbone of the future Chinese grid to cope with the requirement of increased power transmission over longer distances. It is important for relay protection to secure normal operation of UHV grid. The split-phase current differential protection is first applied owing to its rapidity and absolute selection. But due to the negative impact of large distributed capacitive currents, the reliability and sensitivity of traditional current differential relay decay seriously (1). Therefore, some scientists proposed the novel protective principles, which can not be affected by capacitive current (2), (3), (4). Reference (2) put forward a principle of pilot differential protection based on Bergeron model. It describes that currents at both sides of a line could be calculated by means of Bergeron model formula firstly, and then compared with the measured currents at the same side. This comparative result is just operating current in this protective scheme. Here the calculated currents and the measured currents at the same side are taken for comparison, by contrast in a traditional current differential relay a current value at one side is subtracted from that at the opposite side. The advantage lies in the Bergeron model-based principle is independent on the capacitive current, and it is unnecessary to calculate the compensating current. It must be noted that a transmission line is assumed to have constant parameters in the Bergeron model. However it has long been recognized that line parameters vary with frequency in actual electromagnetic transient process. Therefore if Bergeron model formulas are used, there exits calculating errors which would cause the accuracy and sensibility of relays reduce obviously. In order to solve this problem, an improved current differential protective principle is presented in this paper. The principle applied Marti model of the transmission line, which is based on traveling wave propagation. The frequency-dependent characteristics of line parameters are taken into account. By using of this approach, we will get a more accurate result. In addition, a new criterion adapting to this principle are presented. Finally, by making use of EMTPE and MATLAB software, the improved current differential protective principle, and the protection based on Bergeron model are both simulated on the first 1000kV UHVAC transmission line in China, also called as the 1000kV UHVAC test demonstration project. Simulating comparison shows that this improved principle is correct and reliable.

The shunt large capacitor, on both sides of voltage source converter based HVDC (VSC-HVDC) transmission lines, will rapidly discharge to the fault point when a fault occurs. The system side can be equivalent to the shunt large capacitance in the fault component model. According to this characteristic of the VSC-HVDC system, a novel pilot protection scheme for VSC-HVDC transmission lines based on parameter identification is proposed in this paper. The protection principle can distinguish internal faults from external faults by identifying the capacitance on two terminals with the time-domain algorithm. The capacitance on two terminals can be accurately identified simultaneously when an internal fault occurs, while the capacitance at both ends cannot be accurately identified simultaneously when an external fault occurs. Therefore, a pilot protection criterion is constructed. The simulation results show that the protection scheme can distinguish internal faults from external faults reliably and quickly, and it is not affected by transition resistance, distributed capacitance of lines, and the control mode. In addition, the method can be implemented easily with simple computation and has certain practical value.

At present, the EHV transmission system in China has entered a new stage of large-scale construction, which is different from the general EHV transmission lines. The distributed current in the EHV transmission lines has increased substantially. To realize the overall balance of long-distance transmission in the power grid, a differential protection method for EHV transmission lines based on current traveling wave prediction is proposed. The fault current traveling wave of the EHV transmission line is predicted. The fault current traveling wave section is distinguished, and different schemes are selected to realize the traveling wave differential protection for internal and external faults. The simulation results show that the proposed method is reliable and sensitive for the protection of UHV transmission lines, and has certain practical value for ensuring the stable operation of the smart grid.

Transmission lines are an important part of a power system. Transmission lines have high power transmission capacity and they are prone to faults of larger magnitudes. Various faults occur in transmission lines. Therefore, protection relays are necessary to protect transmission lines. The purpose of protection system is to interrupt the faulty section from the healthy section because the fault currents may damage the electrical equipments. One of the protection relays is distance relay and it is mainly used in transmission line. Sometimes these relay are used for backup protection. Distance relays for determining the impedance need the voltage and current. Transmission lines are typically protected by distance protection relay. Distance relays are considered of high speed class and can provide transmission lines. Nowadays, numerical distance relays have been used instead of using electromechanical and static distance relays. The proposed model was verified under different tests such as single line to ground (L-G) fault, double line to ground (L-L-G) fault, line to line (L-L) fault and three phase (L-L-L) fault. SimPower System was used for modelling and simulation of distance relay, transmission lines and faults. The simulation results were obtained from MATLAB software shows the feasibility of analysis of transmission line protection with mho type distance relay for single line to ground fault, double line to ground fault, line to line fault and three phase fault at different location of transmission lines. The difficulties understanding on operation of distance relay can be cleared by using MATLAB/SIMULINK software.

A novel algorithm for improving the differential protection of power transmission system

According to the theory of equal transfer process of transmission lines (ETPTL), the voltages along the line and the current through the line transformed by the same linear transferring link still satisfy the original distributed parameter-based transmission-line model. It is proved that the voltage signals near power frequency along the line follow the law of linear distribution. On the basis of the aforementioned analytical results, an ETPTL-based new current differential protection scheme for long transmission lines by using restructured instantaneous value was presented. The primary voltage and current experience equal transfer processes and are transformed to be virtual instantaneous values before they are used by differential protection. According to the instantaneous voltage value of the transmission line, the instantaneous values of the capacitive current can be calculated. After removing this current, the instantaneous value-based differential criterion can be implemented. The results of Alternate Transients Program simulation test results show that the proposed technique has highly reliability, fast speed, excellent performance under high-resistance earth-fault conditions, and phase selection ability.

Preface. Chapter 1: INTRODUCTION. 1.1 A Brief History of Electric Power Systems. 1.2 The Structure of the Power System. 1.3 Outline of the Text. Chapter 2: BASICS OF ELECTRIC ENERGY SYSTEM THEORY. 2.1 Introduction. 2.2 Concepts of Power in Alternating Current Systems. 2.3 Three-Phase Systems. 2.4 The Per Unit System. 2.5 Electromagnetism and Electromechanical Energy Conversion. 2.6 Permeability and Magnetic Field Intensity. 2.7 Flux Linkages, Induced Voltages, Inductance, and Energy. 2.8 Hysteresis Loop. 2.9 Eddy Current and Core Losses. 2.10 Energy Flow Approach. 2.11 Multiply Excited Systems. 2.12 Doubly Excited Systems. 2.13 Salient-Pole Machines. 2.14 Round or Smooth Air-Gap Machines. 2.15 Machine-Type Classification. 2.16 P-Pole Machines. 2.17 Power System Representation. Problems. Chapter 3: POWER GENERATION AND THE SYNCHRONOUS MACHINE. 3.1 Introduction. 3.2 The Synchronous Machine: Preliminaries. 3.3 Synchronous Machine Fields. 3.4 A Simple Equivalent Circuit. 3.5 Principal Steady-State Characteristics. 3.6 Power-Angle Characteristics and the Infinite Bus Concept. 3.7 Accounting for Saliency. 3.8 Salient-Pole Machine Power Angle Characteristics. Problems. Chapter 4: THE TRANSFORMER. 4.1 Introduction. 4.2 General Theory of Transformer Operation. 4.3 Transformer Connections. Problems. Chapter 5: ELECTRIC POWER TRANSMISSION. 5.1 Introduction. 5.2 Electric Transmission Line Parameters. 5.3 Line Inductance. 5.4 Line Capacitance. 5.5 Two-Port Networks. 5.6 Transmission Line Models. Problems. Chapter 6: INDUCTION AND FRACTIONAL HORSEPOWER MOTORS. 6.1 Introduction. 6.2 Three-Phase Induction Motors. 6.3 Torque Relations. 6.4 Classification of Induction Motors. 6.5 Rotating Magnetic Fields in Single-Phase Induction Motors. 6.6 Equivalent Circuits for Single-Phase Induction Motors. 6.7 Power and Torque Relations. 6.8 Starting Single-Phase Induction Motors. 6.9 Single-Phase Induction Motor Types. Problems. Chapter 7: FAULTS AND PROTECTION OF ELECTRIC ENERGY SYSTEMS. 7.1 Introduction. 7.2 Transients during a Balanced Fault. 7.3 The Method of Symmetrical Components. 7.4 Sequence Networks. 7.5 Line-to-Ground Fault. 7.6 Double Line-to-Ground Fault. 7.7 Line-to-Line Fault. 7.8 The Balanced Three-Phase Fault. 7.9 System Protection, An Introduction. 7.10 Protective Relays. 7.11 Transformer Protection. 7.12 Transmission Line Protection. 7.13 Impedance-Based Protection Principles. 7.14 Computer Relaying. Problems. Chapter 8: THE ENERGY CONTROL CENTER. 8.1 Introduction 8.2 Overview of EMS Functions. 8.3 Power Flow Control 8.4 Power Flow 8.5 Stability Considerations 8.6 Power System State Estimation 8.7 Power System Security 8.8 Contingency Analysis 8.9 Optimal Preventive and Corrective Actions 8.10 Dynamic Security Analysis Chapter 9: THE PRESENT AND FUTURE OF ELECTRIC ENERGY SYSTEMS. 9.1 Introduction. 9.2 Challenges Facing the System. 9.3 Blackouts and their Impact. 9.4 Mitigating and Coping. REFERENCES. INDEX.

Transmission line protection is an important issue in power system engineering because 85-87% of power system faults are occurring in transmission lines. This paper presents a technique to detect and classify the different shunt faults on a transmission lines for quick and reliable operation of protection schemes. Discrimination among different types of faults on the transmission lines is achieved by application of evolutionary programming tools. PSCAD/EMTDC software is used to simulate different operating and fault conditions on high voltage transmission line, namely single phase to ground fault, line to line fault, double line to ground and three phase short circuit. The discrete wavelet transform (DWT) is applied for decomposition of fault transients, because of its ability to extract information from the transient signal, simultaneously both in time and frequency domain. The data sets which are obtained from the DWT are used for training and testing the SVM architecture. After extracting useful features from the measured signals, a decision of fault or no fault on any phase or multiple phases of a transmission line is carried out using three SVM classifiers. The ground detection task is carried out by a proposed ground index. Gaussian radial basis kernel function (RBF) has been used, and performances of classifiers have been evaluated based on fault classification accuracy. In order to determine the optimal parametric settings of an SVM classifier (such as the type of kernel function, its associated parameter, and the regularization parameter c), fivefold cross-validation has been applied to the training set. It is observed that an SVM with an RBF kernel provides better fault classification accuracy than that of an SVM with polynomial kernel. It has been found that the proposed scheme is very fast and accurate and it proved to be a robust classifier for digital distance protection.

Pilot protection for hybrid multi-terminal HVDC transmission lines based on Euclidean distance between differential current and distributed capacitance current