Digital Protective Relays Research Articles

A New Measure of Operating Speed and Consistency of Digital Protection Instruments Based on IEC 60255

Assessing and installing digital protection relays with higher operating performances are essential to improve the continuity of service in power networks. This article proposes a new test procedure for comparative evaluation of the dynamic performance of digital relays particularly with respect to their response speed and consistency. In the proposed test procedure, relay operating times are measured for various fault scenarios established based on the IEC 60255 standard. The measurement data are processed to calculate the averages, weighted variances, and distribution functions of the relay operating times. Given the statistics, four new indices are developed to calculate total performance scores for relative comparison of the relays. Simulation studies are conducted on the proposed and conventional test procedures when applied to several types of protection relays. Experimental studies are also carried out using real relays in a hardware-in-the-loop simulation setup. The study results verify that the proposed test procedure and numerical indices lead to comparative total scores, large decidability index values, and small equipment variation values, thus ensuring effectiveness and robustness in assessing relative performances of relays.

Sectioning of branches of distribution networks with connected wind power plants

The paper presents a developed algorithm for coordinating the response times of the devices for automatic sectioning of bilaterally power supplied lines, of the digital relay protection and the reclosers in medium-voltage distribution networks with connected wind power plants.

Identification of Digital Relay Protection Measuring Part Elements using Time of its Tripping

Identification of Digital Relay Protection Measuring Part Elements using Time of its Tripping

Two-Phase Short Circuit in the Power Grid Powered by a Transformer with a Y/Δ-11 Winding Connection

The article describes main provisions and relations for calculating short-circuit currents and phase currents in a three-phase traction transformer with a star-triangle-11 connection of windings, which feeds two single-phase loads in AC traction networks with a nominal voltage of 25 kilovolts. These transformers provide power to the enterprises of the agro-industrial complex located along the railway line. (Research purpose) The research purpose is in substantiating theoretical equations for digital intelligent relay protection in two-phase short circuits. (Materials and methods) It was found that since the sum of instantaneous currents in each phase is zero, each phase of the transformer works independently. We found that this significantly simplifies the task of analyzing processes with a two-phase short circuit. In this case, the problem of calculating short-circuit currents in the traction network can be simplified by reducing it to the calculation of an ordinary electric circuit with three unknown currents. (Results and discussion) The article describes equations for calculating short-circuit resistances for one phase of the transformer when connecting the secondary winding as a star or a triangle. The currents in the phases of the transformer winding at short circuit for the star-triangle-11 and star-star-with-ground schemes are compared. It was found that when calculating short-circuit currents, there is no need to convert the secondary winding of the traction transformer from a triangle to a star. (Conclusions) It was found that the results of the research can be used in the transition of relay protection systems from electromagnetic relays to modern high-speed digital devices, which will increase the operational reliability of power supply systems for traction and non-traction power consumers.

Optimal Selection of Time-Current Characteristic of Overcurrent Protection for Induction Motors in Drives of Mining Machines with Prolonged Starting Time

The aim of this study is to analyze the effects of mine power network impedance on the starting time of induction motors, as well as on the operation of overcurrent protection relay. Proper selection of the time-current characteristic of overcurrent protection is crucial for the operation of the drive. A specific feature of mining power grids is their high impedance, which results from long cable lines with relatively small cross-sections. This causes relatively large voltage drops and significantly reduces the starting torque of the motor. Reduced starting torque increases the starting time and intensifies the motor overheating. This study analyzes a series of standardized time-current characteristics used in Invertim company protection devices. A simulation study of startup current and starting time was conducted for an exemplary medium-power motor with a large inertia fan at different values of power supply voltage below the rated value. Parameters of the motor equivalent circuit were calculated on the basis of manufacturer data. A new shape of the time-current characteristic has been proposed that would allow for prolonged starting at significant voltage drop in the mine network, ensuring protection from failed starting. This solution can be implemented in digital protection relays in addition to the standard characteristics.

Dynamic State and Parameter Estimation of Synchronous Generator from Digital Relay Records

This paper proposes an approach for the estimation of dynamic states and parameters of a synchronous generator from digital protective relay (DPR) records. Digital fault recorder data or phasor measurement data based approaches are mostly used for aggregate generator models in the literature. The DPR records are usually available for individual generators in a plant and hence can be used for individual generator model development. Constrained Iterative Unscented Kalman Filter (CIUKF) is used in this paper which combines the benefit of iterations and constraints on variables to improve the accuracy of estimation. Adomian Decomposition Method (ADM) is used for solving the IEEE model 1.1 synchronous machine equations which has a less computational burden and higher accuracy when compared to the widely used Modified-Euler (ME) method. The effectiveness of the proposed approach is demonstrated using the WECC-3 generator 9 bus system. The simulation data is generated from a transient stability program with 1 kHz sampling rate for a duration of 3s to resemble a DPR record. The CIUKF is tailored to get good convergence and accuracy with short data records. It has been observed that the accuracy obtained with the proposed approach is good enough to preserve the rotor modes of oscillation.

On the location of a power line fault

The paper proposes an algorithm to exclude the aperiodic components from short circuit currents. The computer-implemented algorithm allows locating a fault and a phase failure in 0.5 - 0.6 milliseconds. During this time interval, the magnetic cores of current transformers (CTs) do not reach saturation and processors receive undistorted information from the current transformers. Four measurements of instantaneous values of currents that are made in equal time intervals (sampling intervals) are sufficient to implement the algorithm. The exclusion of aperiodic components increases the accuracy of the fault location. The algorithm can also be used in the location of open-phase fault and in the digital relay protection based on the measurement of current and voltage.

Elimination of aperiodic components of measuring elements of relay protection

The authors propose the algorithms to calculate the actual values of currents and their derivatives. The algorithms allow a sharp reduction in the aperiodic components of currents in the calculated actual values and their derivatives. The algorithms are developed to calculate the instantaneous values of positive- and negative-sequence currents when the information obtained during a time interval equal to two milliseconds or less is used. An algorithm is devised to calculate the sinusoidal components of the currents in the presence of aperiodic components in the samples. To eliminate the disoperation of digital relay protection and improve the accuracy of fault location, it is necessary to eliminate the influence of aperiodic components in the currents drawn to the measuring devices of relay protection. The algorithm completely eliminates the aperiodic component at any time constants and is implemented by four samples of currents. The four samples of currents separated by three sampling intervals are sufficient for calculating all the parameters of currents, including the positive and negative-sequence currents, in particular in the case when the magnetic cores of current transformers reach saturation. The proposed methods for setting the industrial frequency parameters to avoid the aperiodic components in short-circuit currents are based on the algorithms that process the data from three and four samples of currents.

DEVELOPMENT PROSPECTS OF EXTERNAL POWER SUPPLY ELECTRICAL NETWORKS OF TRACTION SUBSTATIONS

In the paper on the basis of the analysis of classical power schemes traction substations of railways and urban electric transport conceptual directions of development of electric networks of external power supply of traction substations in the conditions of market economy and normative requirements of the electric power industry of Ukraine are developed, which allow to provide energy saving modes of their operation. Based on system analysis of domestic and foreign traction power supply systems of railways and electric transport of large cities, the concept of their development is substantiated and proposed by increasing the supply voltage of traction substations and minimizing capacity upflows and energy losses, which provides resource and energy savings. It is suggested that the investment programs of the structures that are part of Corporation «Ukrzaliznytsia» and the municipal services be synchronized according to their technological indicators, as well as according to the criteria of energy efficiency and quality of energy supply with similar investment programs of external energy. For reduction of energy losses, it is proposed: realization of rational schedule of train movement and deep high voltage inputs with the prospect of transition to own 110 kV distribution networks, modernization and equipping of modern rolling stock electrical equipment and infrastructure of the main and perspective directions of the railways. The need to expand tram and trolleybus lines and modernize power supply devices in terms of resource conservation requires new technologies for the design, construction and operation of the facilities of municipal enterprise «Miskelektrotransservice». Such technologies have been implemented by the «DAK-Energetika» enterprise in the manufacture of modern electrical equipment of municipal enterprise «Miskelektrotransservice» TS. The most important tasks are the improvement of stationary and mobile substations and other linear facilities of traction power supply by completing functional modular blocks with modern switchgear with digital relay protection and diagnostics of traction networks; local and remote control of switchgear devices, as well as switch diagnostics and self-diagnosis. Keywords: external power supply, traction substations, electrical networks, power systems operation modes.

Increasing the Sensitivity of the Digital Relay Protection Against Turn-to-turn Short Circuits And Asymmetries In Wind Power Generators

The paper describes the implementation of neural networks for increasing the sensitivity of the digital relay protection against turn-to turn short circuits in the stator winding and asymmetric modes in wind power generators. Models have been developed for monitoring two standard and two emergency mode parameters, whose deviation from the set-points is an indication of occurrence of turn-to-turn short circuits and asymmetric modes, or of combinations of these types of failures. An artificial neural network, trained by error back-propagation algorithm has been used. An experiment has been conducted to define the four criteria for studying the problem at different percentage of the short-circuit turns. A comparison between the results from both the experiment and the modeling has been made using artificial neural networks. The proposed approach, realized by means of a digital relay, allows for increasing the sensitivity of the digital relay protection against turn-to-turn short circuits and asymmetric modes for wind power generators.

Throw-Over Transfer Switch for Digital Relay Protection and Automation Devices

Throw-Over Transfer Switch for Digital Relay Protection and Automation Devices

Analiza algoritama za kompenzaciju zasićenja strujnog transformatora

The main function of current transformers is to adapt the high values of the primary current to values suitable for the operation of relay protection devices, i.e. measuring devices. Under normal conditions, a current transformer transforms the current in a virtually permanent ratio, and practically without a phase shift, so the secondary current is actually a scaled value of the primary current. However, when a fault occurs in the power system, currents reach high values. As a result, the flux in the core of the current transformer can reach values above the knee of the magnetization characteristic, causing saturation of the current transformer. When saturation occurs, the secondary current is no longer a scaled value of the primary current, but is deformed. Deformation of the secondary current may cause malfunctioning of some relay protection devices. The development of digital relay protection has made it possible to perform software saturation compensation by applying certain algorithms, thus eliminating the negative consequences that saturation of the current transformer causes. In this paper, one of the possible approaches for compensation of saturation is analyzed, which is based on the application of an equivalent scheme and magnetization curve of the current transformer. Two typical approaches have been singled out, which have been analyzed and tested in more detail. Testing was performed in the MATLAB/Simulink.

교류전철의 디지털 보호계전기를 위한 고장 전류 특성 분석

교류전철의 디지털 보호계전기를 위한 고장 전류 특성 분석

The influence of IEC 61850 standard: implementation and development of a functional substation automation simulator

ABSTRACTThe IEC 61850 standard ‘Communication Networks and Systems for Power Utility Automation’ has resulted the integration and inter-operability of digital protective relays in a Substation Automation Systems (SAS). Under digital protective relays, Intelligent Electronic Devices (IEDs) are microprocessor-based devices used to perform numerous functions including protection, control and similar functions in a substation environment. The communication protocol that IEC 61850 can offer through IEDs is the Generic Object-Oriented Substation Event (GOOSE) protocol, which makes the peer to peer communication of different IEDs readily accessible. The development of portable simulators based on IEC 61850 is a benchmark for electrical engineering graduates, power engineers and protection engineers to be acquainted with a substation automation environment. This prompted Victoria University to build and develop portable IEC 61850 simulators which gained distinction among electrical utilities and developed into a real-world electrical substation called the Victoria University Zone Substation (VUZS) Simulator. This paper provides an overview of the growth and improvement of the different portable simulators that were initiated to satisfy IEC 61850 in the VUZS Simulator.

The problem of numerical simulation of digital protective relay and its analog–digital (hybrid) solution

Penetration of renewable energy sources (RES) significantly changes operating modes of electric power systems (EPS) and has an unpredictable effect on operation of relay protection devices (RP). That is a reason, why the existing methods for calculating RP’ settings need to be updated. The authors carry out research and studies focused on development of new methods and means for RP setting up. The feature of the author’s approach is application of detailed mathematical models, reproducing processes simultaneously in the whole RP’ scheme, including primary transducers, and hybrid real-time simulator (HRTSim), implementing methodically accurate analog–digital (hybrid) solution of EPS model. Within the framework of the problem solution, a mathematical model of measuring part of digital protective relay was synthesized and its research was carried out in MATLAB. It is revealed that numerical methods for solving differential equations are badly applied for solving even simple mathematical models of RP, which is manifested in the obvious distortion of the simulation results. Using hybrid approach, a software–hardware mean was created and its test was carried out that showed no distortion of the output simulated signal. In addition, the operation of numerical transformer differential protection was studied via this mean.

Directed protection of the generator

In addition to periodic components of industrial frequency, the aperiodic ones arise in windings and on the generator output leads under the conditions of shortcuts. These aperiodic components slow down the operation of the main differential protection of a generator up to ten periods of a network frequency with the application of saturated magnetic cores of current transformers as well as zero current relays and transformer differential protection [1]. This slowing down promotes accidents and can even lead to generator’s winding and steel burn-out at high-ampere currents. The present paper considers the ways to reduce the impact of aperiodic components on the operation of digital relay protection of generators and generator-transformer blocks and proposes generator’s directional digital protection.

Method of automated synthesis of the logic part of relay protection device which increases its sensitivity

Often there are such modes of operation in the electric power systems where standard methods of relay protection and automation become insufficiently effective. For example, such modes are typical for electric networks with distributed generation and renewable energy sources. Today, the task of developing new digital relay protection methods, that have high technical excellence and fully comply with the requirements of IEC 61850, is relevant. A method of organizing the logical part of multiparameter relay protection is proposed, which improves its sensitivity. The method is based on the criterion of minimizing the average risk of decision making and solving the task of abstract synthesis of automata theory. The application of the proposed method is considered on the example of multidimensional relay protection with five measuring fault detectors and the implementation of simulation models in the Matlab/Similink software package.

Real‐time digital filtering algorithm for elimination of the decaying DC component using mathematical morphology

Fundamental phasor estimation is one of the most important jobs to be done by the digital protective relay (DPR). However, fault signals given to DPR consist of decaying DC (DDC) components, harmonics, and noise which can lead to inaccuracy in phasor estimation. Hence, for accurate results, digital filtering algorithms (DFAs) are mandatory to wipe out all these unwanted components. In modern DPR, discrete Fourier transform (DFT) is extensively used DFA for fundamental phasor estimation. However, the accuracy of DFT is affected by the presence of DDC. Hence, to tackle this problem, a new real-time fast DFA based on the mathematical morphology (MM) technique is put forward. First, the DDC components are filtered out using the morphological median filter (MMF) and are subtracted from the original fault signal. Afterwards, the fundamental phasor is extracted from the residual DDC-free signal using the DFT. Several computer-simulated, EMTP-generated, and real-field fault signals are used to examine the efficacy of the proposed DFA. In addition, the proposed DFA is compared with other existing techniques. The obtained results prove that the suggested DFA has vigorous performance in the presence of multiple DDC components, noise, and severe harmonic conditions with a low computational burden and high accuracy.

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.

Investigation of Processes in the Measuring Part of Digital Devices of Relay Protection in the MATLAB Software Package

It was revealed that one of the main reasons for erroneous operation of relay protection devices (RPs) is it being set in a way that does not correspond with the real operating conditions, which in turn is determined by the design procedures of the RP settings. An analysis of modern methodologies of RP adjustment revealed that there are no significant changes as compared with the guidelines of the past decades and, accordingly, there are the same disadvantages. The development of new adjustment techniques using detailed mathematical models taking into account the features of specific RPs and the processes in the measuring converters are considered in the work. Within the framework of solving this problem, mathematical models of measuring part of digital relay protection for various types of intermediate current transformers (ICTs) (active and passive) and filters (of Butterworth and Chebyshev types) are synthesized and a comparative analysis is done of their influence on the output signal waveform in the MATLAB software package, including taking into account the magnetization of measuring current transformers. It is revealed that the simplest (explicit and implicit Euler methods) numerical methods are not suitable to solving the created mathematical models. A comparative analysis of calculation results by these methods and by the more advanced Runge–Kutta method is conducted. The presented theoretical and practical studies made it possible to reliably formulate the requirements for detailed mathematical models of RPs.