Digital Relay Research Articles

Multi-Agent Approach for Enhancing Security of Protection Schemes in Cyber-Physical Energy Systems

This paper presents a distributed multiagent scheme to detect and identify cyber threats on the protection systems of power grids. The integration of information and communication technologies into existing power grids builds critical cyber-physical energy systems, in which digital relays are networked cyber-physical components subject to various cyber threats. Cyber attacks on protection systems may mimic real faults, cause component failure, and disable the communication links. Agents utilize both cyber and physical properties to reinforce the detection technique and further distinguish cyber attacks from physical faults. This paper also introduces the problem of secure communication protocols and highlights the comparative studies for enhancing the security of the protection systems. The proposed scheme is validated using a benchmark power system under various fault and cyber attack scenarios.

A new phasor estimation method for digital protective relays

Faults and maneuvers in the system may trigger undesirable voltage and current waveforms of non-fundamental frequency that may affect the performance of protection and control systems. In this context, the proposed method aims to improve the characteristic of filtering out undesirable frequency components of signals. Comparisons are made in relation to time response and frequency response for the proposed method and four classical phasor estimation methods. A distance relay was implemented by using the MODELS language of the ATP (Alternative Transients Program) in order to evaluate the relay performance. As expected, for the proposed method, the relay exhibited good performance in terms of accuracy. In terms of relay speed, the method showed a performance comparable to that of the other methods. Theoretically, the phasor estimation proposed method here has a better frequency response than those of the four used methods. Besides, it has a response time fully compatible with these methods. Another advantage of the proposed method is that it can be easily programmed, allowing users to change design parameters according to their needs.

A new digital filter directional relay technique using active/reactive power portrait

The present paper discusses some conventional directional relay drawbacks, which are based on the relationship between voltage and current, in order to determine fault direction. In addition, it presents a new fault detection technique based on instantaneous active and reactive energy that is measured and analysed at the relaying point. This energy has a distinct characteristic which is used to distinguish the fault direction. The suggested relay has determined the fault direction in a rather short time after fault occurrence, even in 2–5ms, depending on the characteristics of the fault generated travelling waves. The algorithm used in this method has been modified in order to improve the performance of the relay. Simulation studies showed that the directional relay based on this new technique has fast speed operation with reliability and dependability.

DIGITAL FILTERS IMPLEMENTATION IN MICROPROCESSOR-BASED RELAY PROTECTION

This article presents the implementation of digital filters used in digital relay protection current measuring elements. Mathematical descriptions of the considered digital filters as well as the computer programs for their coefficients calculation are described. It has been shown that in order to reliable estimate the digital filter performance its input signals waveforms must be close to the actual secondary current waveform of the current transformer to which the digital protection with the estimated digital filter is connected. For these purposes in MatLab–Simulink dynamic simulation environment the power system and the current measuring element models were developed. Performed calculations allowed to reveal that the exponentially decaying DC component which in some cases contains in primary fault current drives the current transformer core into saturation even when its nominal parameters are not exceeded. This results in distortion of the current transformer secondary current which in this case contains higher and inter-harmonics. Moreover, such harmonic content is not completely taking into account during coefficients calculation of the considered digital filters what results in signal magnitude estimation inaccuracy. Comparison of the digital filters response to the above-mentioned input signals allowed to find out such digital filter implementations which enable signal magnitude estimation with a minimum error. Ways of filtering quality improvement concerned with the window functions are proposed. Thus, the joint usage of digital filter and Hamming window allows to achieve the zero value of the signal magnitude gain factor in high-frequency range and substantially suppress all spectral components above 100 Hz. The increasing of the signal magnitude settling time in this case can be reduced by choosing the most optimal parameters of the all components of the current measuring element.

Artificial neural-network-based fault location for power distribution lines using the frequency spectra of fault data

This study presents an artificial neural-network (ANN)-based digital fault classification and location algorithm for medium voltage (MV) overhead power distribution lines with load taps and embedded remote-end source. The algorithm utilizes frequency spectra of voltage and current samples which are recorded by the digital relay at the substation. In the algorithm, to extract useful information for ANN inputs, the frequency spectral analysis of voltage and current waveforms has been carried out using Fast Fourier Transform. To classify and locate the shunt faults on an MV distribution system, a multilayer perceptron neural network (MLPNN) with the standard back-propagation technique has been used. A 34.5 kV overhead distribution system has been simulated using MATLAB/Simulink, and the results are used to train and test the ANNs. The technique takes into account all the practical aspects of real distribution system, such as errors, originated from instrument transformers and interface. The ANN-based fault location technique has been extensively tested for a realistic model and gives satisfactory results for radial overhead distribution systems with load taps and in the presence of remote-end source connection.

Performance of transformer differential relay at different neutral grounding resistance based on wavelet transform

Power transformer protective relay should block the tripping during magnetizing inrush and rapidly should operate the tripping during internal faults. There are a variety of protective relays using different measuring techniques to provide reliable and secure transformer protection. These types of the protective relays include electro-mechanical, solid state, digital and numerical relays. Within each group of them, various algorithms are existed. A stand-alone digital relay has been designed and implemented, where its function can be modified easily to accommodate the protection of different types of transformers by only changing its attendant software. This paper suggests a possibility of improving the digital power transformer algorithm for the protection of three-phase power transformers based on the discrete wavelets transform. This algorithm is able to discriminate between the inrush and internal fault currents even in the case of an inrush with a low second harmonic component and an internal fault current with a high second harmonic component. A sample of a power transformer is simulated using the Electro Magnetic Transient Program, and the generated data are used by the MATLAB to test the performance of the technique, such as its speed of response and reliability. The obtained results showed that the proposed algorithm is reliable, accurate and fast. Also in this paper, the performance of the proposed algorithm is tested for different neutral grounding resistances of the transformer, as it greatly affects the relay sensitivity in the case of turn-to-ground fault.

Algorithms for Synchrophasor Enabled Digital Relay

Algorithms for Synchrophasor Enabled Digital Relay

Evaluation of relaying impedance algorithms for series-compensated line

A group of the algorithms of fault-loop impedance determination for digital distance relay applied for protecting a series-compensated line has been considered. The algorithms gathered in two basic families have been tested: (i) the methods based upon Fourier orthogonal components with using both full-cycle and half-cycle data windows; (ii) four variants of the method founded on differential equation techniques, i.e. with applied various digital differentiation rules, with included additional pre-filtration and combined with orthogonal components determination. Extensive simulation studies have been performed for comparing the calculation techniques. Recommendations with respect to impedance algorithms suitable for protection of a series-compensated line have been stated. The other studied algorithm is related to fault direction discrimination for the considered series-compensated line arrangement. Sample simulation results have been presented and discussed.

GUARANTEEING THE TROUBLE-FREE OPERATION OF CAPACITOR BANKS IN POWER-SUPPLY SYSTEMS OF INDUSTRIAL ENTERPRISES

Purpose. The problem of resonance phenomena in power systems of industrial enterprises using capacitor banks for reactive power compensation was detected. Circuit of the capacitor banks tier to downshift main substation tires is present. But there is no common algorithm to calculate and avoid such trouble. The main goal of this article is to introduce some basics for power supply systems with possible resonant circuits engineering. Methodology. At the first step the data on the change of the current in the chemical company network when changing capacitor banks value are received. For these purposes the oscilloscope function of digital protection relay was used. Current data samples were analyzed by spectrum detection software. Most significant levels of the 3rd and 5th harmonics were achieved. Comparison of harmonic distortion levels with and without capacitor bank is given. Results. Achieved data allow making conclusion about overloading reasons of capacitor banks while higher harmonics currents presence. A voltage and current harmonious composition measuring in the absence of power quality analyzers using digital protection relay terminals or emergencies registers are proposed. The necessity of power quality monitoring near capacitor banks connections to avoid resonance phenomena (current and voltage resonance) in industrial power supply systems is proven. The control algorithm of capacitor banks to provide electromagnetic compatibility, while various modes of nonlinear load operation is given. Originality. Using of digital protection relay oscilloscoping for current resonant detection can allow to significally reduce time and cost of solution. Replacement parallel circuit comprising a branch and one active-inductive load to another branch network in the presence of higher harmonics source are proposed. Practical value. A sequence for measuring the levels of harmonic components at the connections of capacitor banks in the absence of specialized instruments is proposed. The algorithm to avoid possible resonance currents in the presence of condensing units is proposed.

Low cost microcontroller based fault detector, classifier, zone identifier and locator for transmission lines using wavelet transform and artificial neural network: A hardware co-simulation approach

A low cost, fast and reliable microcontroller based protection scheme using wavelet transform and artificial neural network has been proposed and its effectiveness evaluated in real time. The proposed scheme, based on the hardware co-simulation approach performs all the functions of transmission line protection i.e. fault detection/classification, fault zone/section identification and location estimation. The fault detection/classification and zone identification algorithms use fundamental frequency current component to estimate a fault index. The fault location estimation module uses wavelet transform coefficients in hybridization with a parallel artificial neural network structure. For hardware implementation, a 8-bit ATmega microcontroller is used and interfaced with the simulated power system model using Integrated Development Environment (IDE). The scheme is tested on a power system model of 400kV, 50Hz three phase double circuit line with source at both the ends. Laboratory tests have been performed in real time for 20,000 fault cases including evolving faults with varying fault resistance, fault inception angle, fault distance, direction of power flow angle and its magnitude. The tests confirm the suitability and reliability of proposed scheme even with Current Transformer (CT) saturation. The implementation of the proposed approach on a low cost microcontroller with the lesser execution time, makes the prototype ideal for implementation on a digital platform (digital relay), thus leading to financial viability and sustainability of the protection scheme.

Binary particle swarm optimisation‐based optimal substation coverage algorithm for phasor measurement unit installations in practical systems

Phasor measurement units (PMUs) play an important role in the wide-area monitoring and protection of modern power systems. Historically, their deployment was limited by the prohibitive cost of the device itself. Therefore, the objective of the conventional optimal PMU placement problem was to find minimum number of devices, which when carefully placed throughout the network, maximised observability subject to different constraints. Due to improvements in relay technology, digital relays can now serve as both relays and PMUs. Under such circumstances, the substation installations consume the largest portion of the deployment cost, and not the devices themselves. Thus, for minimising cost of synchrophasor deployment, number of substation installations must be minimised. This study uses binary particle swarm optimisation to minimise number of substations in which installations must be performed for making all voltage levels observable, while being subject to various practical constraints. Standard IEEE systems have been used to explain the technique. Finally, a large-scale network of Dominion Virginia Power is used as the test bed for implementation.

Prototype of a Negative-Sequence Turn-to-Turn Fault Detection Scheme for Transformers

Digital relays are capable of computing the negative-sequence current on both primary and secondary sides of the transformer along with the phase difference between these two negative-sequence currents. By using both phase and magnitude information, negative-sequence current could be used to detect minor turn-to-turn faults involving 3% of the transformer's windings or more. Turn-to-turn faults may still occur even if no current is flowing on one side of the transformer, such as during energization. With no current flowing in the secondary windings of the transformer, negative-sequence current-based algorithms become insensitive. This paper introduces a relay prototype, using both negative-sequence current and negative-sequence voltage, which retains its sensitivity during energization. The relay's performance for several commonly encountered system scenarios, such as overexcitation, current-transformer saturation, nonzero fault resistance, transformer energization, and external faults were also examined. The experimental results presented in this paper indicate that the algorithm proposed in this paper is faster and more sensitive than restrained current differential protection and is capable of detecting turn-to-turn faults occurring during transformer energization.

Deriving operating characteristic equations for overcurrent protection devices based on eigensystem realization algorithm

Accurate representation of the operating characteristics of conventional inverse-time overcurrent (OC) protection devices plays an important role in protection coordination schemes. Based on the singular value decomposition of the Hankel matrix, this study uses the eigensystem realization algorithm to curve-fit the characteristic curves of OC protection devices under the digital state-space model and obtain the equations of their operating characteristics. This study applies the proposed method to four types of OC protection devices, including two electromechanical OC relays, one digital OC relay, and one power fuse. One characteristic curve from each protection device is selected for curve-fitting. For all four OC protection devices, the absolute error values for the hundreds of sample points between the actual characteristic curves and the corresponding curve-fitting equations are all less than 10 ms. The numbers of fitting components required are determined by the desired maximum absolute values of errors for the fitting equation. Finally, this study uses the derived equation to construct the characteristic curve of customized OC relay to solve the coordination problem of power system protection.

Enhanced Backtracking Search Algorithm for Optimal Coordination of Directional Over-current Relays Including Distributed Generation

In this article, the enhanced backtracking search algorithm is employed to achieve optimal coordination of directional over-current relays. A novel objective function is formulated to minimize the total operating times while maintaining the validity of the coordination time interval. The proposed technique is applied to optimize the influential variables of the coordination problem, which are plug tap setting, time dial setting, and type of inverse relay characteristics. Both old electromechanical and digital relays are considered in the study. The enhanced backtracking search algorithm is a recent heuristic-based optimization, and its performance in solving relay coordination problem is compared with other well-established algorithms to demonstrate its viability and effectiveness.

A novel fault protection system using communication-assisted digital relays for AC microgrids having a multiple grounding system

Abstract This paper develops a novel fault protection system for AC microgrids having a multiple grounding system. Communication-supported digital relays which have different protection modules are used for this novel microgrid protection system. The protection modules in a digital relay have various functionalities to protect AC microgrids from various fault types, such as: low/high-impedance ground faults and short-circuits. To effectively use the developed novel microgrid protection system, the first step is to reconfigure different microgrid structures into a standard microgrid configuration having a multiple-grounding system through using delta/wye-grounded or wye-grounded/wye-grounded transformers. Then, a fast–dependable–adaptable (FDA) fault protection algorithm is developed to protect AC microgrids from faults occurring at trunk lines, common buses or branch lines. At an islanded operation mode of AC microgrids, by using digital relays, a new protection module is designed to detect, locate, and classify the faults occurring at trunk lines and common AC buses, while other protection modules can use the existing protection methodologies (e.g. directional/non-directional overcurrent protection principles, etc.) to detect and clear the faults at source branches or load branches of the microgrids. At a grid-connected operation mode, standard overcurrent protection modules are applied for the FDA fault protection system. Simulation and experiment results obtained from various fault cases at a real low-voltage AC microgrid have validated the effective operation of the FDA fault protection system.

Extreme Learning Machine Based Adaptive Distance Relaying Scheme for Static Synchronous Series Compensator Based Transmission Lines

This article presents an extreme learning machine based fast and accurate adaptive distance relaying scheme for transmission lines in the presence of a static synchronous series compensator. The ideal trip characteristics of the distance relay is greatly affected by pre-fault system conditions, ground fault resistance, and zero-sequence voltage. The proposed research develops an extreme learning machine based adaptive distance relaying scheme for two-terminal transmission networks with static synchronous series compensators when a single-line-to-ground fault situation is most likely to occur. The study includes an analytical approach, including a steady-state model of static synchronous series compensator with detailed simulation on MATLAB/Simulink (The MathWorks, Natick, Massachusetts, USA) and open real-time simulation software with MATLAB (OPAL-RT) platform (OPAL-RT Technologies, Montreal, Quebec, Canada). The proposed extreme learning machine based adaptive distance relaying scheme is extensively validated on the two terminal transmission lines with static synchronous series compensators, and the performance is compared with the existing radial basis feed-forward neural network based adaptive distance relaying scheme. The results on simulation and real-time platform show significant improvements in the performance indices, such as speed, selectivity, and reliability of the digital relay.

An adaptive approach for three zone operation of digital distance relay with Static Var Compensator using PMU

Modern energy transmission systems suffer from great voltage dropping due to enormous loads. Therefore appropriate schemes should be devised to regulate the voltage. FACTS devices such as Static Var Compensator are often used for this purpose. However, SVC at mid-point of transmission line may leads to deteriorate of distance relay operation, resulting in inaccurate estimation of faults locations i.e. over-reach or under reach for different cases. This paper proposed a new algorithm that utilizes synchronized phasors measurement (SPM) to enhance the operation of distance protection zone in many aspects. The proposed method is tested for 230 kV system simulated in EMTDC/PSCAD with Bergeron model of transmission line. The results prevailed for adaptive approach scheme are more accurate, victor and robust in equivalence with usable transmission line distance protection with SVC.

PROBLEMS IN TESTING DIGITAL PROTECTIVE RELAY FOR IMMUNITY TO INTENTIONAL DESTRUCTIVE ELECTROMAGNETIC IMPACTS. CONTINUATION OF THE THEME

The article is the continuation of the theme highlighted in the previous article with same title. The new article evaluates the results of digital protective relays (DPR) testing for immunity to the E1 component of High-altitude Electromagnetic Pulse (HEMP) and to Intentional Electromagnetic Interferences (IEMI) impacts, conducted by some independent American organizations; discusses the features of relay protection devices as well as clarifies and supplements the procedure for testing these devices. Due to methodology errors during the DPR tests conducted by mentioned organizations earlier, they cannot be considered as satisfactory and their results as meaningful. At the moment there are no reliable data on the level of DPR immunity to IDEI, which suggests that the test should be conducted further.

Algorithms and field experiences for estimating transmission line parameters based on fault record data

The impedance parameters of overhead transmission lines are fundamental input data for various power system studies. The data are traditionally calculated based on the structure information of a line. This study proposes a method for estimating the parameters using fault records captured by digital relays. The fault records are the unsynchronised voltage and current waveforms recorded at both ends of a line. One of the main contributions of this work is the use of the wave propagation speed equation to simplify the problem and to improve the estimation accuracy. As a result, both the positive and zero sequence parameters can be estimated using simple algorithms in a decoupled solution process. Simulation results show that the proposed approach has good accuracy. Finally, the method was applied to estimate the impedance data of several actual transmission lines based on the fault record data provided by a utility company.

Protective Relaying: Principles and Applications [Book Reviews

This book [in its fourth edition] is applicable as a college textbook and as a reference book for protection engineers new to the industry (as an instructional text) and those with experience (as a reference text). This fourth edition has built upon the earlier editions, adding the new technology of the digital protective relays, automation, event analysis, and regulatory issues. This book is based on the principles and applications typical in the United States. It provides a solid foundation for the master-level student as well as power engineers new to protection principles, and it is most certainly a valuable reference for the experienced protection engineer. This book provides enough information of historical applications to aid the reader in understanding the protection in service today. The material is presented clearly with examples to provide practice of the fundamentals presented.