Modern Relays Research Articles

Polarity crossover regions of transient earth fault relays in non-radial resonant grounded networks

Transient-based earth fault protection is widely used in all types of resonant grounded networks, and though the operating principles of the commonly available relays are usually derived from radial networks, manufacturers claim applicability in meshed networks as well. This paper utilizes a laboratory setup to study the directional indication of four transient earth fault relays in non-radial resonant grounded networks. Two of the relays considered are widely used analog single-purpose transient earth fault relays, whereas the other two relays represent two transient-based earth fault functions found in modern protective devices. The paper verifies the location of crossover points according to the presented theory, i.e. fault locations for which relays transition between seeing faults as forward and reverse faults, and demonstrates the viability of the proposed theoretical analysis of crossover points. However, presented analytical formulae only describe the two analog relays accurately, whereas the two modern relays have a more complex operating principle which requires further analysis to quantify properly. Finally, it is shown that relay misoperation which is not easily fixed by communication between relays can occur, and it is suggested that network operators conduct detailed relay coordination when applying transient earth fault relays instead of relying on standardized settings.

Исследование влияния переходного сопротивления на дистанционное определение места повреждения на основе одностороннего метода

Fault location on 110–220 kV overhead power lines is one of the main functions of modern relay protection devices. Currently, the actual errors of fault location based on emergency mode (EM) parameters in most cases are about 5 %. However, there are cases when they exceed 10–20 %. One-sided fault location based on EM parameters and improvement of its accuracy are important issues to study since there isn’t a communication channel on power lines for the transmission of emergency information everywhere. The main parameter that has a significant impact on the accuracy of fault location method is the transient resistance. The aim of the research is to study the effect of transient resistance on the one-sided fault location method based on EM parameters proposed by A.E. Arzhannikov. In the course of the study, the following tasks are set: assessment of the effect of transient resistance on the accuracy of the specified fault location method; determination of the polarizing value for fault location, which ensures greater accuracy of the method, including the presence of transient resistance at the place of a short circuit; defining a criterion to recognize the type of short circuit that does not depend on the transient resistance; development of a method to determine the value of the transient resistance at the fault location. To study and evaluate the errors of distance fault location based on EM parameters, a series of calculations of short circuit currents has been made for various transient resistances at the fault location and at various distances of the fault. The calculation of currents and data processing has been carried out in the ARM SRZA software package. A single overhead line with a voltage of 110 kV with a two-sided supply and a length of 70 km is chosen as the object under study. To perform the research, the primary converters are taken as ideal. The authors have obtained the estimation of the errors of the one-sided fault location method. It is proposed to use the zero-sequence current as a polarizing quantity in the indicated fault location method, which provides greater accuracy than the use of the negative sequence current. To ensure the stable operation of one-sided fault location based on EM parameters, especially in case of short circuit with significant transient resistances, the use of methods that are insensitive to transient resistances is justified. A parameter to identify the type of short circuit is proposed, the coefficient of the image Kobr. Its values are determined for each type of short circuit, a small dependence on transient resistances is found. A calculation substantiation is given for the value of the identification coefficient of two-phase faults (Phase-to-Phase and Phases-to-Earth) according to the ratio of negative and zero sequence currents. The authors have estimated the transient resistance at the fault site by the ratio of symmetrical components for the simulated power transmission line. The results of the study can be used to improve the existing methods of fault location based on EM parameters, namely: to improve their accuracy considering the transient resistance at the fault site; to improve their accuracy using a suitable polarizing value; to determine the type of short circuit more accurately by using the proposed identification parameter.

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.

Разработка и исследование катушки Роговского для работы в условиях эксплуатации открытого распределительного устройства

The interest to use Rogowski coils (RC) as current sensors to design secondary systems increases due to application of microprocessor relay protection and automation devices, including those that support the reception and processing of information in a form of a digital code in the format of protocols defined in IEC61850, as well as the disadvantages of traditional electromagnetic current transformers. Despite the popularity of RC, there are many unstudied issues of their functioning under operating conditions of open switchgears of power facilities, especially when operating with modern relay protection and automation devices. The aim of the study is to analyze the effect of ambient temperature on the error of current conversion by Rogowski coils. Studies of Rogowski coils have been carried out using the experimental and industrial samples. During the research modern testing equipment has been used. The equipment is listed on the Unified Register of Measuring Equipment of the Russian Federation and has valid verification certificates. The analysis of the factors influencing the error of metrological channels has been carried out. The analysis is conducted based on traditional current transformers (CT). The factors influencing the measurement error of RC are systematized. Experimental data obtained as a result of the study of the RC conversion error in a wide temperature range are presented. It has been established that due to design solutions, it is possible to neutralize the influence of such factors as the position of the primary conductor, external electromagnetic fields, uneven winding, the number of layers of the secondary winding, and thermal expansion. The use of materials with a low coefficient of linear expansion to manufacture the core of the Rogowski coil makes it possible to obtain the metrological characteristics of the transducer that meet the requirements of normative technical documentation in a wide temperature range. Application of RC as a primary current sensor for relay protection and automation systems is a promising area that requires further comprehensive research, and specifically in the process of industrial operation.

A Negative Sequence Admittance Based Algorithm for Identifying Fault Direction in the Presence of Inverter Based Resources

Ever increasing integration of renewable resources into contemporary power systems has imposed a unique set of challenges for system protection. Effectiveness of techniques based on conventional system protection theory has long been questionable in protecting power systems with higher penetration of inverter-based resources (IBRs). Fault direction identification is one of the commonly affected protection functions in the presence of IBRs. This paper presents a novel algorithm to correctly identify fault direction using negative sequence admittance measurements. The proposed technique is robust and reliable and yields better results in comparison to conversional techniques in presence of IBRs. In addition, its operation is simple and can be conveniently incorporated into a modern digital relay.

Разработка математической модели функционирования электротехнических комплексов релейной защиты цифровых подстанций

The issues of introduction of electrical digital substations in the Russian Federation are considered. An existing criteria analysis for assessing the modern relay protection devices efficiency is carried out and an assessment of their sufficiency is made. A mathematical model development of the digital substations relay protection complexes operation has been developed using the queuing theory, the graphs theory and Markov chains. The failure-free operation probability calculated value of the relay protection complexes corresponds to the long-term analysis data. This indicates that the mathematical model is correct. The proposed mathematical model makes it possible to take into account the impact of the maintenance quality on the digital substation relay protection complexes efficiency.

A new fault type classification method in the presence of inverter-based resources

Fault type classification is a critical stage in modern distance relays for activating the effective phase and ground distance elements. It is also used for some supplementary functions such as single-pole tripping and reclosing, teleprotection, and fault location. Traditional fault type classifiers are based on the symmetrical or superimposed components of the current signal. However, owing to the unconventional behavior of inverter-based resources (IBRs) compared to the synchronous generators, traditional methods are not reliable in the presence of IBRs. For example, modern grid codes impose some restrictions in terms of injected current during asymmetrical fault which put the accuracy of conventional fault classification methods in danger. Fault resistance could also affect the accuracy of fault type classification method. In this paper, first, the fault current signature of IBRs is analytically derived. Then, impacts of modern grid code and fault resistance on the conventional fault classification are properly evaluated by executing some simulation studies. Finally, a new fault classifier is proposed which is based on symmetrical components of the local voltage and current during asymmetrical faults. The proposed classifier presents a satisfactory degree of security in the faulted phase identification in the presence of IBRs under different host grid codes. Performance of the proposed method is properly analysed with different simulation scenarios such as different fault locations, fault resistances, pre-fault condition, test systems, and host grid codes in PSCAD/EMTDC software.

ОГЛЯД МЕТОДІВ РОЗРАХУНКОВОЇ ПЕРЕВІРКИ ТРАНСФОРМАТОРІВ СТРУМУ, ЯКІ ПРАЦЮЮТЬ В КОЛАХ РЕЛЕЙНОГО ЗАХИСТУ

Systematized existing methods of calculation verification of current transformers that work in the circuits of modern relay protection devices. The requirements of the Ukrainian rules for the arrangement of electrical installations differ from the requirements of the standard of the International Electrotechnical Commission IES 61869-2. The difference concerns the absence of contact vibration and not exceeding the maximum allowable current error of 50% in the case of an internal short circuit is a separate case of the requirements for electromechanical protections and these requirements cannot be used for microprocessor protection devices. For any relay protection device, there is no concept of the permissible value of "voltages at the current inputs". The voltage at the terminals of the secondary winding and the voltage at the "input of the relay protection device" are two completely different voltages. There are no methods for calculating errors in the case of switching on protection based on the sum of the currents. Companies producing microprocessor relay protection devices specify in their instructions individual requirements for current transformers for each individual device. Compliance with these requirements guarantees the correct operation of the relay protection even for large values of the time constant of the primary network. Leading manufacturers of microprocessor relay protection devices develop and recommend software tools for checking the correct selection of current transformers. But they are not freely available. To increase the accuracy of the calculation of the limit multiplicity, it is advisable to use complex supports of the secondary winding and load of current transformers. Depending on the initial data and conditions, the permissible load resistance can be calculated using four methods. The question of whether the allowable load of a current transformer can exceed its nominal load requires further research. The scientific novelty is consists in the systematization of existing methods of calculation verification of current transformers that work in the circles of modern relay protection devices. The practical significance of the work is that checking current transformers that are connected to microprocessor relay protection devices do not need to check the maximum permissible current error of 50%; to check the correct operation of microprocessor relay protection devices, it is advisable to use the instructions for the requirements for current transformers of device manufacturers; for a more accurate calculation of the limit multiplicity, it is advisable to use complex supports of the secondary winding and load of current transformers.

DEVELOPMENT OF SIX-PHASE SYMMETRICAL COMPONENTS FILTERS FOR SELF-COMPENSATING POWER LINES

The paper deals with elaboration of hexaphase symmetrical components filters and their modeling to create microprocessor-assisted relay protection of self-compensating power lines. The theory is presented and the basic principial electrical schemes and mathematical models in the Matlab/Simulink of the filters of the hexaphase symmetric components are elaborated. The results of their simulation and testing at the computer are presented. The obtained results demonstrate the possibility of creating in the base on the elaborated filters of hexaphase symmetrical components the modern, efficient and high-sensitivity microprocessor-assisted relay protection of self-compensating power lines. What reacted not to phase electrical values, but symmetrical components of them.

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.

Laboratory bench for the study of the causes and means of combating unacceptable deviations of the supply voltage in domestic premises

Introduction. One of the ways to improve the level of professional training of electrical engineers studying in higher educational institutions of Ukraine is to use in the educational process modern innovative switching equipment, protection, measurement and signaling equipment, etc. This gives students the opportunity to acquire a high level of training, which will allow them to improve their professional competence, contribute to their professional development, and allow them to become qualified specialists in later life. This direction of development of training requires a significant financial investment, which cannot be realized at the expense of public funds. At the Department of Electrical Apparatus of NTU «KhPI» it was possible to find alternative sources of funding – at the expense of an international grant and sponsorship from a number of electrical companies in Ukraine. The continuation of the selected vector of development is the development of laboratory work to study the causes of the occurrence of unacceptable deviations in the supply voltage in household premises and modern means of combating this dangerous phenomenon. Relevance. The need for students to study the problem of protecting household consumers from unacceptable voltage deviations in the power supply network is due to the fact that this is required by the current situation, which has developed with the technical condition of in-house distribution networks, which in most cases is extremely unsatisfactory. Unacceptable voltage deviations in the household network, depending on their level, can lead to a reduction in the service life of expensive electrical equipment, their failure, as well as a possible fire. Therefore, acquainting students in practice with the reasons for the occurrence of unacceptable voltage deviations in the household network, teaching them how to combat this phenomenon is an urgent task. Purpose. Design and manufacture of a laboratory stand for researching the causes of occurrence and means of dealing with unacceptable deviations in the supply voltage in domestic premises. Results. The developed laboratory stand allows students to study in detail the processes occurring in general in a three-phase electrical network after the break of the neutral N conductor, and to quantitatively analyze the level of voltage dips and overvoltages under asymmetrical load. Modern relays for the protection of household consumers ZUBR D32 and ADECS ADC-0110-32, used in the developed laboratory bench, allow students to familiarize themselves with the features of their installation, configuration, operation and functioning. Discussion. A laboratory stand developed at the Department of Electrical Apparatuses of NTU «KhPI» to study the causes of occurrence and means of combating unacceptable deviations of the supply voltage in household premises will increase the professional competence of students, contribute to their professional development, and will allow them to become qualified specialists in later life.

A phasor-distance based faulty phase detection and fault classification technique for parallel transmission lines

AbstractThis paper presents a phasor-distance based faulty phase detection and fault classification technique for parallel transmission lines. Detection and classification of faulty phase(s) have been carried out by deriving indices from the change in phasor values of current with a distance of one cycle. The derived indices have zero values during normal operating conditions whereas the index corresponding to the faulty phase exceeds the pre-defined threshold in case of occurrence of a fault. A separate ground detection algorithm has been utilized for the identification of involvement of ground in a faulty situation. The performance of the proposed technique has been evaluated for intra-circuit, inter-circuit and simultaneous faults with wide variations in system and fault conditions. The suggested technique has been evaluated for over 23,000 diversified simulated fault cases as well as 14 recorded real fault events. The performance of the proposed technique remains consistent under Current Transformer (CT) saturation as well as different amount and direction of power flow. Moreover, suitability to different power system network has also been studied. Also, faults having fault current less than pre-fault conditions have been detected accurately. The results obtained suggest that it is able to detect faulty phases as well as classify faults within quarter-cycle from the inception of fault with impeccable accuracy. Besides, as modern digital relays have been already equipped with phasor computation facility, phasor-based technique can be easily incorporated with relative ease. At last, a comparative evaluation suggests its superiority in terms of fault classification accuracy, fault detection time, diversify fault scenarios and computational requirement among other existing techniques.

Adaptive directional overcurrent protection considering stability constraint

Based on the expected features of modern relays, such as adaptive and self-adjustment functions, this paper presents a model and time-domain simulation of a directional overcurrent relay (DOR) with adaptive pick-up current (Ip) provided by a fuzzy system, where the teleprotection scheme is incorporated as a performance enhancer. A comparison of the operation time of conventional relays optimally coordinated with the evolutionary particle swarm optimisation (EPSO) meta-heuristic algorithm, considering stability constraint, with the proposed adaptive method has been carried out. For the calculation of the critical stability time, the bisection and potential energy boundary surface (PEBS) methods were considered. The results of the comparison have shown the good performance of a fuzzy-based setting on the DOR with the reduction in the average operation time while ensuring the system operation in the stable region. The role of the teleprotection and the stability analysis are also shown with time-domain simulations using the Alternative Transients Program – The Electromagnetic Transients Program (ATP-EMTP).

Вдосконалення методу контролю ізоляції блока ‘’генератор-трансформатор’’

In the conditions of significant aging of the main production capacities and prolongation of the service life of electrical equipment of power plants of Ukraine, the question of development and implementation of methods of continuous control of the technical condition of the generator–transformer unit equipment is urgent. Modern information-measuring systems and relay protection terminals, operated on generator–transformer units, enable control of electrical, thermal, mechanical parameters and parameters characterizing the status or position of technological fittings and auxiliary equipment, as well as providing relay protection of electrical equipment a wide range of possible damage. However, the existing information-measurement systems do not allow the tracing of the following electrical parameters of the stator winding isolation such as resistance, capacitance and tangent of angle of the dielectric loss, and relay protection may be insensitive to the occurrence of single-phase ground fault near the neutral point of the stator winding and symmetric decrease of parameters of the stator winding insulation, and does not allow detecting the occurrence of damage at an early stage of its development and signal this to the service personnel. There is also the possibility of false actuations at unit start-ups due to the asymmetry of voltages in the machine phases, which is especially acute in synchronous hydrogenerators. The paper proposes a method of controlling the isolation of a stator winding of a synchronous generator operating in a block with a transformer, a block diagram and basic formulas for signal processing and calculation of electrical insulation parameters. The proposed method is based on the overlay on the circuit containing the stator winding, alternating voltage signals with a frequency lower than the rated network frequency, DC voltage, the use of energy of the pre-charged capacitor and the calculation of the isolation parameters of the generator–transformer unit. The proposed solutions will allow increasing the efficiency of operation of power units by providing operational and repair personnel with reliable information on the technical condition of isolation of equipment in the scheme of power unit output.

New and traditional relay protection algorithms integration in 6-35 kV distribution network

We conducted an applicability analysis of both modern and prospective relay protection types in future 6-35 kV field circuits. We demonstrated the advantages of using new differential-logic and multi-parameter relay protection algorithms, as well as the methods for relay protection tripping parameters calculation. We developed an integration scheme for existing and prospective relay protections types to increase the sensitivity and speed of the relay protection system for SmartGrid. We suggested the main stages of implementing new relay protection types.

K-Nearest Neighbors Algorithm Application in the Electrical Grid States Recognition Problems

One of the ways to improve the reliability of electrical grids is associated with the introduction of complex and resource-intensive algorithms in intelligent electronic devices (IED) that perform the functions of relay protection and automation at substations. Simulation modelling is used to study the features of the protected object functioning and its application makes it possible to take into account the variability of electrical grid states in the formation of IED algorithms, which are characteristic of the analyzed electrical grid section. In addition, this approach makes it possible to use for short circuits detection only those information features that have a high information value in a specific problem of states recognition. Machine learning methods are advisable to use for modern relay protection algorithms implementation. One of such methods is the k-nearest neighbours method. The article substantiates the effectiveness of the method application in comparison with the conventional algorithms on the example of protection of an electrical grid section with a distributed generation source. The reported study was funded by RFBR, project number 19-38-90144.

Important Considerations for Testing and Commissioning Digital Protective Relays: Avoid Misoperations

The proven advantages of digital technology for power system protective relays are now commonplace in the power producing and delivery industry. Digital relays provide unsurpassed reliability and extended capabilities at an economical cost. Keeping pace with the testing and commissioning requirements of these devices has proven to be a challenge for both protective relay engineers and technicians. Although testing procedures have been well defined for single-function electromechanical (EM) protection devices, modern relay test procedures have been left to the utility to develop, creating possible shortcuts that may compromise the protection system operation.

Improving the reliability of energy facilities

The article analyzed and identified the main sources of interference, disrupting the work and reliability indicators of the system, which can lead to malfunction of system of microprocessor relay protection and automation for electric stations and substations, as well as elements and actuators of open distribution devices. According to official data, modern microprocessor-based relay automation systems operate with a reliability coefficient that is not lower than 0.998. Further increase in reliability requires the development of technical measures, namely, requires the use of power and signal cables that must meet the requirements for specific parameters of inductance, capacitance and active resistance, and also requires the use of special placement of cross sections of conductors inside the cable. Secondly, it is shown that to increase the reliability of information transmission it is necessary to switch to serial communication channels, but the amount of information per channel should be strictly limited. The estimation of economic indicators of the system and its dependence on the reliability of the system is given. Thus, with an increase in reliability by 1.5-2 times, it is necessary to increase the cost of design and commissioning of such a system by about 2 times. It is recommended to use in addition to the regulated maintenance procedures a mandatory assessment of the level of interference in the system in order to maintain a stable and reliable operation of the relay automation system. Experimental and calculated data confirmed that the most difficult situation to ensure the reliability of the system is associated with thunderstorms and lightning. This circumstance dictates the necessity of evaluation and measuring the parameters of a common system of earthing. The methods of evaluation and diagnosis of faulty components of the system are proposed.

Impact of CT saturation on overcurrent relays

An overcurrent relay analyses and processes the secondary currents from a set of current transformers (CTs) and if the currents exceed the operating threshold initiates the tripping of a circuit breaker after an appropriate time. An important issue for a protection relay is how it responds when the steel core of the CT is saturated. The exact behaviour of a CT depends on various factors such as core size, CT ratio, primary current magnitude, DC offset, secondary burden resistance and remnant flux. The aim of this study is to investigate the impact of CT saturation on overcurrent relays using both a physical relay test bench that includes actual protection CTs, and a modern relay test set configured to simulate the test bench and its CTs. The relay operating times, obtained under similar fault conditions using both the test bench and the test set, will then be compared. The results obtained will then be used to determine how different levels of CT saturation affect different generations of an inverse time overcurrent relays. The final section of this study will explain how CT saturation affects an overcurrent grading study involving a mixture of electromechanical, static and numerical relays.

Distribution power factor monitoring in presence of high RES integration using a modified load encroachment technique

This study presents a new approach in application of distance relay in distribution system. During the heavy load conditions, the load encroachment of impedance into the distance relay protection zones is a well-known reason for distance relay mal-operation. Therefore, all the modern digital distance relays are equipped with the load encroachment scheme. This study proposes the idea of using the load encroachment scheme of distance relay for monitoring purpose in the presence of renewable energy resources (RES) integration. Furthermore, it will be presented that based on the defined monitoring zones some alarms can be defined. The OpenDSS and Matlab software are used to test the effectiveness of the method with the IEEE 8500 node test feeder. The proposed method is tested with the unbalanced distribution system feeder loading and distributed model of solar generations. The dynamic performance of the proposed method is studied for on-line power factor monitoring of the feeder with the sun irradiation dynamic. The results show the necessity of power factor monitoring in the distribution system with RES integration. In addition, the simplicity of the proposed method allows its easy application in the digital distance relay.