Microprocessor-based Protection Research Articles

Practical Implementation of Multithreaded Communication Protocols in Modern Protection Relays

Microprocessor-based protection relays that provide reliable and fast responses to abnormal conditions are of paramount importance to electrical grids. Modern numerical relays constitute communication protocols to facilitate data exchange among protection devices. Though it has become an integral part of electrical substation devices, there has not been any significant article that puts forth a detailed description of the preemptive multithreading implementation of multiple communication protocols for protection relays. Hence, this article is aimed at designing a preemptive multithreading system comprising IEC 61850 Manufacturing Message Specification (MMS), Generic Object-Oriented Substation Event (GOOSE), and Sampled Values (SV) along with Modbus TCP/IP and IEC 60870-5-104 communication protocols for protection relays. Latest products from prominent manufacturers of protection relays adopt preemptive multithreading on a real-time Linux operating system. In this work, the designed multi-protocol communication system is implemented on a real-time embedded Linux-based cortex-A7 core of the STM32MP157D-DK1 device. The designed system is verified by conducting an interoperability test with ABB REF615 and Thytronic NA11 protection relays.

Vulnerability of Smart Grid-enabled Protection Relays to IEMI

Abstract. The electricity sector has been undergoing transformations towards the smart grid concept, which aims to improve the robustness, efficiency, and flexibility of the power system. This transition has been achieved by the introduction of smart electronic devices (SEDs) and advanced automatic control and communication systems. Despite the benefits of such modernization, safety issues have emerged with significant concern by experts and entities worldwide. One of these issues is known as Intentional Electromagnetic Interference (IEMI), where offenders employ high-power electromagnetic sources to maliciously disrupt or damage electronic devices. One of the possible gateways for IEMI attacks targeting the smart grids is the microprocessor-based protection relays. On the one hand, the malfunctioning of these devices can lead to equipment damage, including high-voltage equipment (e.g., power transformers), which represent one of the most high-cost items of energy infrastructure. On the other hand, a possible misleading triggering of these devices could cause cascading effects along the various nodes of the power system, resulting in widespread blackouts. Thus, this study presents the possible recurring effects of IEMI exposure of a typical protection relay used in smart grid substations as part of the SCADA (Supervisory Control and Data Acquisition) system. For this purpose, a test setup containing a smart grid protective unit, a monitoring box, and the device's wiring harness is exposed to radiated IEMI threats with high-power narrowband signals using a TEM waveguide and horn antennas. The effects during the test campaigns are observed by means of an IEMI-hardened camera system and a software developed to real-time monitor the device's fibre optic communication link, which is established according to the IEC 60870-5-105 protocol. The results revealed failures ranging from display deviation to various types of protection relay shutdown. Moreover, the consequences of the identified failures in a power substation are discussed to feed into a risk analysis regarding the threat of IEMI to power infrastructures.

Protection coordination analysis applied at biogas power generation plant

Biogas from liquid waste from palm oil processing, palm oil mill effluent (POME), can be utilized in biogas power plants as a source of renewable energy (PLTBg). The PLTBg electrical system is equipped with a coordinated protection system. Then, the protection system must also maintain the continuity of electrical service in parts that are not affected by disturbances. Coordination of the protection system is essential. In this research, the electrical transient analysis program (ETAP) carries out the short circuit current analysis, and the coordination of overcurrent protection is constructed from its inverse-definite minimum time characteristics. The analyzed data contributed to selecting the right protection devices. A combination of overcurrent protection, directional protection, and frequency protection change rate supported a reliable electrical power system for a biogas power generation plant as distributed generation. The result shows that modern microprocessor-based protection relays support several protection features in one device and can be integrated into a supervisory control and data acquisition (SCADA)-controlled protection system to enhance their capabilities.

Symmetrical Components Digital Filters for Microprocessor-Based Protection Input Signals

In microprocessor protections, measuring bodies are used that react to individual symmetrical components of signals or a combination of them. This makes the corresponding protection devices more sensitive. Of all the varieties of digital filters of symmetrical components, filters of the negative and zero sequences are mainly used. As for the known algorithms of their software implementation, it is advisable to use filters that form orthogonal components of the required sequence from orthogonal components of phase or phase-to-phase values of signals. Digital Fourier filters, characterized by inertia, are used as formers of the latter. For this reason, their transient modes are accompanied by the appearance of a dynamic error, which can significantly affect the functioning of filters of symmetrical components, worsening their properties. A significant reduction in this effect can be achieved by using shapers with correction of dynamic errors to isolate the orthogonal components of the input signals. They are based on non-recursive digital Fourier filters, the orthogonal components of which are subjected to software correction processing in order to obtain equivalent components characterized by fast-fading dynamic amplitude errors. Correction of the dynamic phase error is realized in the process of obtaining the resulting orthogonal components, which are a combination of Fourier components and calculated ones that have been estimated according to them. Based on the information about the amplitudes and current phases of the signals contained in the equivalent and resultant components, respectively, the resulting orthogonal components are formed, differing in minimal amplitude and phase errors in transient modes. According to these components, the orthogonal components of the signal of the negative and zero sequences in the corresponding filter are calculated. In the dynamic modeling environment of MATLAB-Simulink-SimPowerSystems, a digital model is implemented, which includes a power system, a three-phase group of current transformers, a load, a short-circuit block, as well as models of negative and zero sequence filters. The study of the functioning of these filters was carried out using two types of test actions, viz. a three-phase system of sinusoidal signals and a three-phase system of signals close to real secondary currents in short circuits. The results of the research have demonstrated that the developed digital filters of the negative and zero sequences have 1.1–1.4 times higher performance as compared with similar Fourier filters accepted as reference and that they are distinguished by improved magnitudes of dynamic indicators.

Development of an algorithm for identifying single-phase ground fault conditions in cable and overhead lines in the networks with isolated neutral

The paper addresses the issue of identification of the type of single-phase ground fault in medium voltage networks operating mainly with an isolated neutral. By analyzing the published research, the most promising methods for detection of a single-phase ground fault were selected. Further, using the selected parameters, algorithms were designed to determine the parameters, process them, and use them to identify the type of a single-phase ground fault. The algorithm developed by the authors was formalized for the application on the basis of microprocessor-based protection systems using digital signal processors. The operation process was modeled using real oscillograms of single-phase ground fault. The use of high-frequency zero-sequence current and voltage components, as well as the root-mean-square value of the zero-sequence voltage, made it possible to design an algorithm that identifies any of the possible single-phase ground fault types (bolted, arc, or contact resistance ones). The first part of the article gives an overview of the state-of-the-art of research in the field of detection and identification of single-phase-to-earth faults. In the second part, the parameters of emergency operating conditions are analyzed and the key parameters are determined based on them. The third part contains a description of the single-phase fault identification algorithm developed by the authors and the output oscillograms. The fourth part makes conclusions on the applicability of the algorithm.

ВЫЯВЛЕНИЕ АСИНХРОННОГО РЕЖИМА И СПОСОБ УПРАВЛЕНИЯ ВОЗБУЖДЕНИЕМ СИНХРОННОГО ЭЛЕКТРОДВИГАТЕЛЯ

The paper presents the results of research aimed at identifying the asynchronous mode of excited syn-chronous electric motors and their safety and stability. It is proposed to identify the asynchronous mode using a power polynomial from the ratio of the degrees of active and reactive power, determined from measured instantaneous values of currents and stator voltages of a synchronous electric motor. It is proposed to control the excitation system of a synchro-nous motor by cyclically switching the excitation winding to an additional resistance or an exciter based on a criterion rep-resenting the derivative of the power polynomial from the ratio of the active and reactive powers of the synchronous mo-tor. The proposed methods for detecting the asynchronous mode of excited synchronous motors and controlling the excitation system to ensure successful resynchronization of a synchronous motor without unloading the driven unit can be used in microprocessor-based protection devices for synchronous electric motors. The effectiveness of the proposed methods is confirmed through mathematical modeling.

Wireless Communication-Based Design and Implementation of Digital Protection Platform on Folk Art

Numbers no longer only have a purely mathematical meaning but a code that can change the way of human existence, cognition, and thinking, and a basic element to convey information. With the advent of the “Internet+” era, the development of digital media technology, digitization, and informatization has been integrated into all walks of life and has a vital impact on the development of all walks of life, and also brought about the ideological change of fine arts. Nowadays, the digitization of fine arts is a new product of the computer age, and how to protect it is also an important topic. The continuous development of wireless mobile communications has promoted the rapid development of microprocessors. In this article, we will study the protective effect of microprocessors on the digitization of fine arts. This paper designs a microprocessor-based art digital protection website, with the purpose of preserving, inheriting, and disseminating folk art works through the website. The result of the experiment shows that the sampling rate of the microprocessor has reached the requirement of the signal. The largest number of users of the folk art digital website is young people aged 18–29, accounting for 32%; the highest average score for the website is those over 59 years old, with an average score of 90.

The.main types of wind turbines-generators in the power supply system

THE PURPOSE. This paper considers the problem of relay protection functioning when the current transformer reaches the saturation mode which is provided by transient processes.METHODS. MATLAB Simulink software environment allows reproducing the method of statespace representation by using structural blocks. The model is verified by comparison the time to saturation, obtained by calculation and according to the graphical data of the model. The separation of variables method extracts and graphically displays the investigated components.RESULTS. This paper reveals that applying the requirements of IEC 61869-2:2012 standard, which determines the worst combination of series of unfavorable factors for current transformers in transient mode, can influence a serious impact on the correct operation of relay protection based on current, reactance or differential principle of action. Saturation of the current transformer can lead to both negative results: false operation of relay protection devices and their failure.CONCLUSION. According to the results of the study, it was determined that the presence of a DC component in the primary short-circuit current has the greatest effect on the protection operation. The delays in the restoration of the RMS value of the short-circuit current reached up to 0.3 seconds, which is comparable with the response time of the second protection zones for microprocessor-based relay protection devices. The DC component of the primary current and the presence of residual magnetic induction of the current transformer provides the largest content of the magnetization current, the largest angular error and also the largest content of the second harmonic component in the secondary short-circuit current.

An Artificial Neural Network Developed in MATLAB-Simulink for Reconstruction a Distorted Secondary Current Waveform. Part 1

Recently, there has been an increased interest in the use of artificial neural networks in various branches of the electric power industry including relay protection. Аrtificial neural networks are one of the fastest growing areas in artificial intelligence technology. Recently, there has been an increased interest in the use of аrtificial neural networks in the electric power engineering, including relay protection. Existing microprocessor-based relay protection devices use a traditional digital signal processing of the monitored signals which is reduced to a multiplying the values of successive samples of the monitored current and voltage signals by predetermined coefficients in order to calculate their RMS values. In this case, the calculated RMS values often do not reflect the real processes occurring in the protected electrical equipment due to, for example, current transformer saturation because of the DC component presence in the fault current. When the current transformer is saturated, its secondary current waveform has a characteristic non-periodic distorted form, which is significantly differs from its primary (true) waveform, which causes underestimation of the calculated RMS value of the secondary current compared to its true value. In its turn, this causes to a trip time delay or even to a relay protection devices operation failure. The use of аrtificial neural networks in conjunction with a traditional digital signal processing provides a different approach to the functioning of both the measuring and logical parts of the microprocessor-based relay protection devices, which significantly increases the speed and reliability of such relay protection devices in comparison with their traditional implementation. A possible application of the аrtificial neural networks for the relay protection purposes is the fault occurrence detection and its type identification, current transformer secondary current waveform distortion restoration due to its saturation up to its true value, detection the distorted and undistorted sections of the current transformer secondary current waveform during its saturation, primary power equipment abnormal operating modes detection, for example, power transformer magnetizing current inrush. The article describes in detail the stages of the practical implementation of the аrtificial neural networks in the MATLAB-Simulink environment by the example of its use to restore the distorted current transformer secondary current waveform due to saturation.

Microprocessor-Based Current Protection Based on a Four-Dimensional Representation of Operating Parameters

Microprocessor-Based Current Protection Based on a Four-Dimensional Representation of Operating Parameters

Research on Optimal Coordination and Algorithms of Microprocessor-based Inverse Time Backup Protection

Backup protection plays an important role in the safe operation of power grid, and it has important research value in the field of power system relay protection. Firstly, the research status and development opportunities of inverse time limit protection are analyzed, and then the best cooperation between inverse time limit protection and distance protection is discussed theoretically. According to the time constraint relationship in the protection range, an objective function satisfying the selectivity and speed is proposed. Secondly, in view of the difficulty in calculating the inverse time characteristic curve, a processing algorithm combining Taylor expansion method and look-up table method is proposed. Finally, the effectiveness and practicability of the method are verified by simulation experiments.

The influence of changing resistance on the determination accuracy of short circuits in power lines

In high-voltage electrical networks, the occurrence of short circuits leads to forced interruptions in the power supply of large consumers and disruptions in intersystem communications. More than 65% of all types of occurring short circuits are single-phase short circuits [1]. In a single-phase short circuits (SPSC), a change in the zero sequence resistance (ZSR) especially significantly affects the inaccuracy in detection of damage sites (DDS). When choosing DDS methods, preference is given to remote methods according to the parameters of the emergency conditions (PEC), which are recorded by special instruments or determined from the oscillograms of emergency conditions. The use of modern microprocessor-based relay protection and automation devices (RPA) [26] or emergency event recorders allow viewing the oscillograms of emergency events. In a branched 110 kV network with a complex configuration, the DDS accuracy is influenced by a change in the ZSR. Averaging of specific parameters often leads to erroneous results. The choice of one value from the oscillograms puts the maintenance personnel in difficulty. In the scientific work, the influence of changes in the ZSR on the accuracy of the DDS is considered. The changes in the ZSR are influenced by the position of the on-load voltage regulator (OLTC) switches of transformers with a grounded neutral. In the work, for a more accurate record of the specific parameters of the network, a calculation program has been compiled, which allows making changes in the calculated specific parameters of the network. To determine the short-circuit current from the oscillograms, it is proposed to determine the stable state of accidents in which the current value will be approximately the same. The analysis of the oscillograms of SPSC in 110-220 kV networks in the southern part of the electric power system of Turkmenistan has been carried out.

Orthogonal Components Forming of the Microprocessor-Based Protection Input Signals

The use of orthogonal components (OS) is the main direction of determining information parameters in microprocessor relay protection and automation of electric power systems. Most of the measuring devices used in modern protection and automation devices can be implemented using known operating systems. Digital non-recursive frequency filters based on discrete Fourier transform are used for OS selection. The main disadvantage of these filters is their low performance that exceeds the period of industrial frequency. For the construction of high-speed measuring devices, this time of establishing the true output signal is often unacceptable. The article proposes to form the equivalent signal OS in microprocessor defenses based on the values of the cosine and sine axes of the main harmonic formed using a discrete Fourier transform, by multiplying them by a correction factor, which is a function of the values of the input signal amplitude and its main harmonic. The proposed algorithm for generating OS input signals in microprocessor defenses is characterized by high performance in transient modes and has wide functionality. A block diagram of an OS equivalent signal generator has been developed, all blocks of which can be implemented according to known schemes on a microelectronic and microprocessor element base. The OS shaper model is implemented in the MatLab-Simulink dynamic modeling environment. The model functioning was checked using two types of test actions, viz. a sinusoidal signal with a frequency of 50 Hz (idealized action) and a signal close to the real secondary current of a short-circuit current transformer. As a result of the performed calculations, a significant (up to two times) in the speed of the proposed method of OS formation in comparison with the formers based on the discrete Fourier transform, frequency properties of both formers being identical.

Technique of Performance Improvement of the Microprocessor-Based Protection Measuring Element

The technique is proposed to improve the performance of the measuring element of microprocessor-based protection and its implementation is considered at the software level. Two factors mainly influence on the performance of the measuring elements of microprocessorbased protection of electrical installations. The first one is associated with the appearance of aperiodic and harmonic components in the measured signals due to transients and nonlinearity of the electrical installation elements, and the second–with the inertia of information processing algorithms, in particular–with analog and digital filtering. This leads to the fact that the signal determining time at the output of the measuring element is delayed to unacceptable values that in some cases makes the high-speed protection of electrical equipment ineffective. To solve this problem, it is proposed to form the output signal of the measuring element in the form of special equivalent signals, which are a function of the pre-calculated correction factor and orthogonal components of the controlled signal. In the MatLab-Simulink dynamic modeling environment a mathematical model of the developed measuring element has been implemented, as well as a model of the elements of the power system. Checking the functioning of the model of the measuring element was carried out with the use of 2 types of test effects, viz. a sinusoidal signal with a frequency of 50 Hz (idealized effect), as well as a signal close to the real secondary current of the current transformer in case of short circuit. Computational experiments carried out in relation to the current measuring element using harmonic and close-to-real test effects made it possible to reveal a significant (up to 2 times) increase in the performance of the proposed measuring element as compared to existing ones based on the implementation of the discrete Fourier transform.

Determination of Electrical Parameters of a Traction Current Circuit Using Measured Data in the Traction Power Supply System of an 825-V Subway

Providing selectivity of the relay protection of a dc network has always been associated with difficulties in distinguishing between operating and emergency modes, which is especially noticeable in the traction power supply system for an 825-V subway due to the high traffic intensity and the use of electric rolling stock (ERS) with asynchronous traction motors. The practice of calculating protection settings shows that the maximum current protection settings (MCPs), both for an electromechanical relay and for microprocessor terminals, as a rule, are set off from the calculated minimum short circuit currents, which can be lower than the startup currents of the ERS. This practice of calculations and modern conditions of operation of a subway power supply system can lead to false activations, which, in turn, can lead to a rapid loss of the switching capacity of high-speed switches, as well as lead to a delay in train movement. An analysis of the current situation leads to the conclusion that simple types of protection, such as MCPs, cannot provide selectivity of outages. The situation is different with multiparameter protection of the type of protection by current increment (PCI) and current buildup rate (PCBR). The essence of the operation of the PCI and PCBR is based on the analysis of changes in the current graph, which allows determination that is faster, and sometimes more accurate, than MCP, whether or not the change in current is connected with the occurrence of a short circuit. However, taking into account the choice of protection settings for changes in current and its buildup rate requires the calculation of transients. The accuracy of such calculations directly depends on the accuracy of determining the electrical parameters of the traction circuit. In modern conditions of development of measuring and computing equipment, one of the most simple and effective methods of calculation is the method of minimizing the distance between a set function or model and the measured data. It is worth noting that the use of this method directly in the algorithmic part of microprocessor-based protection terminals together with self-learning functions will allow one to automatically select the desired values of the PCI and PCBR settings corresponding to the operating conditions of the traction power supply system.

Migration Between Two Inverse Time-Overcurrent Curves of Different Standard: Experience at Siguragura Power Station

The inevitable replacement of electro-mechanical protection relays with more recently-developed microprocessor-based protection relays poses challenges to engineer, one of which is migration from existing manufacturer’s non-standard inverse time-overcurrent curve to, usually, IEC 60255-151 or IEEE Std C37.112-1996 curve. To satisfy the required protection coordination, one may perform new study of protection coordination for the system in total, prior to replacement program. However, this exhaustive approach can be avoided by emulating existing non-standard inverse time overcurrent curve on the new microprocessor-based protection relay, provided that such curve is still adequate to be re-implemented. This paper aims to develop general procedure using nonlinear curve fitting to determine the most appropriate setting of microprocessor-based protection relay. The general procedure has been tested during renewal of feeder protection relay at Siguragura Power Station.

Testing Microprocessor-Based Numerical Transformer Differential Protection

Transformer differential protection application has always been a challenge to protection engineers and commissioning personnel, even with older electromechanical and solid-state technologies. The emergence of microprocessor-based protection, where the intelligence is implemented numerically in software algorithms, and the fact that different relay models, even from the same manufacturer, apply different algorithms and compensation techniques and use different terminology and notation, has made it increasingly more complicated to apply the protection and even more challenging to correctly test them during commissioning. This paper reviews how phase differential protection principles are implemented in numerical technology by different relay models, provide guidance in their application, and guide test personnel in performing their work. Test methods are proposed for use with modern test systems that can be applied to test all transformer phase differential protection functions easily and effectively.

Методи організації мікропроцесорних архітектур захисту фідерів контактної мережі

The analysis of the contemporary problem of traction network feeder microprocessor-based protection has been performed, and the ways to identify abnormal conditions of electric systems. Mathematical models to organize microprocessor protection have been proposed and the methods of the synthesis of microprocessor-based protection system architectures of traction networks, possessing flexible logic and broad functional capabilities of thorough recognition of abnormal conditions and malfunctions.

The method of selection of the setpoint high speed feeder switch of 3,3kV DC with microprocessor-based protection systems

In the article a new procedure of choice of minimum current jump for action of fast-acting switches of 3.3 kV DC traction substations intended for the use in the microprocessor protection system of feeders is described. This procedure is more perfect than existing one on the current increment and uses the results of mathematical simulation of the traction electric supply system.

Tests of microprocessor-based relay protection devices: Problems and solutions

Usually, the operational condition of relay protection devices is checked with specific settings used for the relay operation in a certain network point. In the author's opinion in order to verify the proper operation of complex multifunctional microprocessor-based protection devices (MPD) at their inspection, start-up after repairs or during periodic tests there is no need to use the actual settings at which the relay is to be operated in a certain network's point. It should be tested for proper operation at several of its most critical preset characteristic points as well as in several preset characteristics constituting its most complicated (combined) operation modes, including the dynamic operation modes with preset transition processes specific for standard power networks (not necessarily for a specific point). The proposed set of actions for the unification of software platforms of the modern, microprocessor-based relay protection test systems will enable examination of modern MPD in an absolutely new way. .