Digital Overcurrent Relays Research Articles

Development of Numerical Protection Laboratory through Industry Institute Interaction

Abstract—The development of a numerical protection laboratory is implemented through industry-institute interaction under an MOU. This paper documents the contribution of the major project of final year students on using a digital over-current and earth-fault relay. The latest numerical protection relay has been provided as a replacement for an older version by ABB India Ltd. as a part of corporate social responsibility (CSR). The laboratory experimental panel has been developed through the major project of the final year student group. There was the active participation of ABB India Ltd. by way of providing dedicated training to the student group and faculty members involved in the installation, commissioning, and design of the experimental panel. The results obtained from various case studies are reported in this paper. The facilities created are used for regular laboratory practicals for undergraduate and postgraduate students. The laboratory manuals are prepared to facilitate the implementation of the experiments. The laboratory curriculum has been updated for the UG course "Power System Protection" and the PG course "Advanced Power System Protection and Switchgear". It has resulted in improvement in the placement of UG and PG students. The training of industry and state power utility engineers can also be performed on the experimental panel developed. The outcome of this academic innovation related to industry-institute interaction is that the industry readiness of students has increased. Keywords : Industry Institute Interaction; Power system protection; laboratory development; Test setup; Over-current protection.

Modelling and performance testing of a digital over-current relay enhanced designed model

Introduction. The over-current relay is widely used to protect distribution and transmission electrical systems against excessive currents occurring due to short circuit or overload conditions. Many works have been carried out in the field of models simulation design of digital over-current relays in the literature, but unfortunately many of them are more complex design models, have very slow execution time and only work in simple faults cases. Purpose. The purpose of this work is to present the performance of a modified and improved model of a digital over-current relay designed in Simulink/MATLAB environment with more simplified design, faster execution time, and able to operate under more complex fault conditions. Methodology. Before starting tests, modelling of over-current relay is presented in details, of which the basic logics of the proposed model to implement inverse and instantaneous characteristics are well explained. Afterwards, various tests are carried out for the performance analysis of the enhanced designed relay model in terms of: operating speed for eliminating faults that has arisen, ability to distinguish between a fault current and load starting current, capacity distinguish between real and temporary fault currents, the way to manage variable faults over time, and the degree of harmony between primary protection relay and back-up protection relay. Originality. The originality of our proposed work consists in the development and improvement of a digital over-current relay model designed in Simulink/MATLAB environment in such way that it becomes able to operate under new harsh test conditions. This developed designed model is implemented and applied in a 400V radial distribution power system with a load that causes a starting current. Results. The obtained values of simulation are compared with the theoretically calculated values and known existing models. The obtained results after various tests validate the good performance of our enhanced designed model.

Multi-objective Function Optimization for Locating and Sizing of Renewable Energy Sources and Energy Storages in Radial Distribution Networks with Digital Directional Overcurrent Relays and Digital Dual-setting Directional Overcurrent Relays

Multi-objective Function Optimization for Locating and Sizing of Renewable Energy Sources and Energy Storages in Radial Distribution Networks with Digital Directional Overcurrent Relays and Digital Dual-setting Directional Overcurrent Relays

Novel Protection Coordination Scheme for Active Distribution Networks

Distribution networks are inherently radial and passive owing to the ease of operation and unidirectional power flow. Proper installation of Distributed Generators, on the one hand, makes the utility network active and mitigates certain power quality issues e.g., voltage dips, frequency deviations, losses, etc., but on the other hand, it disturbs the optimal coordination among existing protection devices e.g., over-current relays. In order to maintain the desired selectivity level, such that the primary and backup relays are synchronized against different contingencies, it necessitates design of intelligent and promising protection schemes to distinguish between the upstream and downstream power flows. This research proposes exploiting phase angle jump, an overlooked voltage sag parameter, to add directional element to digital over-current relays with inverse time characteristics. The decision on the direction of current is made on the basis of polarity of phase angle jump together with the impedance angle of the system. The proposed scheme at first is evaluated on a test system in a simulated environment under symmetrical and unsymmetrical faults and, secondly, as a proof of the concept, it is verified in real-time on a laboratory setup using a Power Hardware-in-loop (PHIL) system. Moreover, a comparative analysis is made with other state-of-the-art techniques to evaluate the performance and robustness of the proposed approach.

Inrush current detection enhancement for legacy overcurrent relays in north delta electric distribution company

The second harmonic restraint method is the most common technique used by relay manufacturers to discriminate between inrush and fault currents. Unfortunately, many relays in the Egyptian distribution networks are old versions digital overcurrent relays that don't contain the second harmonic restraint method. In developing countries like Egypt, replacing a large number of conventional relays at one time may not be possible due to difficult economic conditions. This paper proposes a novel inexpensive solution by incorporating an additional circuit with the old version over-current relays. The proposed circuit applies a second harmonic restraint function for detecting the inrush currents as in the modern digital relays. The modified overcurrent relay is applied to a test system picked from North Delta Electric Distribution Company (NDEDC) Network in Egypt. The results demonstrate the successful operation for the proposed circuit along with the overcurrent relay in normal operation, switching cases, permanent faults, and in case of faults during energization. Furthermore, the proposed circuits integrated with old version overcurrent relays are successfully tested and verified in the presence of grid-connected Distributed Generation (DG) for both switching and fault operation modes. Also, it provides a cost-effective solution for the old version digital overcurrent relay in NDEDC.

Use of Clustering to Reduce the Number of Different Setting Groups for Adaptive Coordination of Overcurrent Relays

The facility to save multiple setting groups (SGs) within digital overcurrent relays (OCRs) is to adapt the active setting of the relays to the current topology of the power network. However, the number of available SGs is much lower than the possible topologies of the network, so this facility is usually applied to a few local changes in the network. This paper aims to extend the application to a complete set of topologies. A proper index is introduced and applied with a k -means clustering technique to classify the topologies into some clusters, whose number is equal to the number of SGs. Then, for every topology cluster, the optimal settings are calculated and saved in the OCRs as a distinct SG to be activated by changing the topology to any member of the cluster. Applying this technique to OCRs of the IEEE 14-bus test network and a 63/20kV substation verifies its effectiveness on reserving coordination for all topologies and reducing the relays’ time dial setting. Using available communication links, this technique can be implemented by making a computer network between substations of the power network without needing to interact with the control center.

Optimal overcurrent relay coordination in distribution network based on Lightning Flash Algorithm

PurposeDistribution network protection is a complicated problem and mal-operation of the protective relays due to false settings make the operation of the network unreliable. Besides, obtaining proper settings could be very complicated. This paper aims to discuss an innovative evolutionary Lightning Flash Algorithm (LFA) which is developed for solving the relay coordination problems in distribution networks. The proposed method is inspired from the movements of cloud to ground lightning strikes in a thunderstorm phenomenon. LFA is applied on three case study systems including ring, interconnected and radial distribution networks. The power flow analysis is performed in Digsilent Power Factory software; then the collected data are sent to MATLAB software for optimization process. The proposed algorithm provides optimum time multiplier setting and plug setting of all digital overcurrent relays in each system. The results are compared with other methods such as particle swarm optimization and genetic algorithm. The result comparisons demonstrate that the proposed LFA can successfully obtain proper relay settings in distribution networks with faster speed of convergence and lower total operation time of relays. Also, it shows the superiority and effectiveness of this method against other algorithms.Design/methodology/approachA novel LFA is designed based on the movements of cloud to ground lightning strikes in a thunderstorm. This method is used to optimally adjust the time multiplier setting and plug setting of the relays in distribution system to provide a proper coordination scheme.FindingsThe proposed algorithm was tested on three case study systems, and the results were compared with other methods. The results confirmed that the proposed method could optimally adjust the relay settings in the electric distribution system to provide a proper protection scheme.Practical implicationsThe practical implications can be conducted on distribution networks. The studies provided in this paper approve the practical application of the proposed method in providing proper relay protection in real power system.Originality/valueThis paper proposes a new evolutionary method derived from the movements of cloud to ground lightning strikes in thunderstorm. The proposed method can be used as an optimization toolbox to solve complex optimization problems in practical engineering systems.

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.

Optimal directional digital overcurrent relays coordination and arc-flash hazard assessments in meshed networks

Summary The article addresses the arc-flash hazard assessments combining the optimal coordination of digital overcurrent relays. A novel objective function is adopted to concurrently reduce the arc-flash hazards while adapting the optimal settings of directional overcurrent relays subjects to set of coordination constraints. The flower pollination algorithm (FPA) is applied to attain the target. The proposed FPA-based technique is employed to define three main parameters for the relay settings. The performance and value of the proposed FPA-based methodology are demonstrated on the 8-bus and 15-bus meshed networks with various fault scenarios. Comparisons with the other competitive algorithms and subsequent discussions validate its good performance. Efficacious attributes of the novel objective function are compared and highlighted over the traditional objective function commonly used by the other researchers reported in the literature. Copyright © 2015 John Wiley & Sons, Ltd.

FPGA-based digital overcurrent relay with concurrent sense-process-communicate cycles

Communication between relays and the central control station is an important aspect of Special Protection Schemes (SPS) used in modern power systems. The relays are expected to perform sense-process-communicate cycles. A sequential implementation of these tasks increases the computational time and adversely affects the overall performance of the relay. This paper presents the design and hardware implementation of an overcurrent relay on Field Programmable Gate Array (FPGA) with concurrent sense-process-communicate cycles. The implementation is based on parallel pipelined architecture where sampling, measurement, processing and communication tasks are done concurrently. The relay is implemented on Xilinx Virtex-II Pro XC2VP30-FF896-7C FPGA Board. The proposed relay conforms to IEEE standard C37.112-1996 for overcurrent relays in power systems. It is equipped with serial/IP communication capability. The details of the hardware design, implementation and experimental test results on a hardware simulator of a 360km transmission line are presented in this paper. The architecture provides a platform for implementing special protection schemes in power systems.

Adaptive Protection Algorithm for Overcurrent Relay in Distribution System with DG

This paper proposes the new adaptive protection algorithm for inverse-time overcurrent relays (OCRs) to ensure their proper operating time and protective coordination. The application of the proposed algorithm requires digital protection relays with microcontroller and memory. The operating parameters of digital OCRs are adjusted based on the available data whenever system conditions (system with distributed generation (DG)) vary. Moreover, it can reduce the calculation time required to determine the operating parameters for achieving its purpose. To verify its effectiveness, several case studies are performed in time-domain simulation. The results show that the proposed adaptive protection algorithm can keep the proper operating time and provide the protective coordination time interval with fast response.

Detecting and solving the coordination curve intersection problem of overcurrent relays in subtransmission systems with a new method

This study presents a practical and effective method for inspecting and repairing curve intersection situations that occur in upstream and downstream coordinated overcurrent relay pairs in subtransmission networks. This type of miscoordination can cause backup relays to trip before their paired primary when faults occur, resulting in unexpected expansions of blackout areas. The proposed method is based on the IEEE and IEC standard characteristic curve equations of digital overcurrent relays and a customized curve equation for electromechanical overcurrent relays. Consequently, the proposed method is applicable to both digital and electromechanical relays. Two subtransmission network cases for the Taiwan Power Company were simulated to validate the proposed method.

Design and Implementation of O/C relay using Microprocessor

This work presents the design and implementation of a versatile digital overcurrent (O/C) relay using a single microprocessor. The relay is implemented by a combination of a look-up table and a counter. The software development and hardware testing are done using a microcomputer module based on a 8-bit microprocessor. The digital processing of measured currents enables a separate setting of operating values selection of all types of inverse or constant time characteristics overcurrent protection. This protection provides reasonably fast tripping, even at terminal close to the power source were the most serve faults can occur excluding the transient condition. So this method has an excellent compromise between accuracy hardware and speed.

Study of Solving the Coordination Curve Intersection of Inverse-Time Overcurrent Relays in Subtransmission Systems

This paper presents a practical and effective novel approach to solve the coordination problem caused by the curve intersection of overcurrent relays in subtransmission systems. Based on the IEEE and IEC standard characteristic curve equations of digital overcurrent relays, as well as the simulation curve equation for electromagnetic overcurrent relays, lever setting adjustment equations for a selected point on the characteristic curve is derived. Then, centered on the derived equations, a dedicated software program is developed to compute the corresponding relay lever setting with different tap value in order that, passing through the selected point, another curve with the new lever setting is chosen. Finally, assisting with the graphical capability of the commercial ASPEN OneLiner, the proposed fixed-point coordination curve adjustment procedure can completely eliminate the coordination curve intersections. In addition, an actual case of a subtransmission network in Taiwan Power Company is simulated to validate the feasibility of the technique proposed.

A Novel Approach to Fast Eliminating the Characteristic Curves Crossing Problem of Relay Coordination in Radial Subtransmission Networks

A novel approach is presented to solve the coordination problem of overcurrent relays in radial subtransmission networks resulting from the intersection of characteristic curves. Based on the ANSI/IEEE standard characteristic curve equation of digital overcurrent relays, a slope adjustment equation for a selected point on the characteristic curve is derived and then used as the core of a dedicated software program developed to compute the corresponding relay setting with different tap value in order that, passed through the selected point, another curve with steeper slope is chosen and thus able to escape from the crossed position. Finally, with the assistance of the graphical capability of commercial package OneLiner in drawing the upstream and downstream relay coordination curves after adjustment, the curves intersection problem in protection coordination can be readily eliminated. In addition, an actual case of a radial subtransmission network with six buses in Taiwan Power Company is simulated to validate the feasibility of the approach.

An enhanced method of providing sensitive bus fault protection

The application of bus fault protection in industrial facilities has been primarily limited to overcurrent relays located at the upstream breaker. This does not always provide the best protection for bus faults. The protection sensitivity is limited because of the need to coordinate with other downstream overcurrent devices. This paper describes an enhanced method of applying sensitive bus fault protection using digital overcurrent relays. In addition, this method provides both downstream feeder breaker backup protection and relay backup protection.

Applying CTs with digital ground relays

Industrial power distribution system substation transformers and generator step-up transformers in power stations often use resistance-grounded wye secondary windings for medium-voltage power distribution. The purpose of this is to limit damage due to ground-fault currents, while providing sufficient fault current for the operation of ground-fault relaying. The relaying used to protect against ground faults in the system may not provide sufficient protection of the transformer winding against internal faults because the backup ground overcurrent relay in the transformer neutral-to-ground connection must be set to coordinate with downstream relays. In order to protect the winding itself, special relays are utilized. Ground differential protection can be provided by digital overcurrent relays in conjunction with auxiliary ratio matching transformers. Ground differential protection can also be provided in multifunction digital relays. Transformer protection relays may include this feature with one of the schemes used with component relays. If a feeder-protection relay is used on the secondary, in some cases, this may have a ground-directional feature that can be utilized for ground-differential protection.

Distribution system fault identification by mapping of characteristic vectors

Abstract A new fault-locating scheme using the concept of characteristic vector is proposed. Utilizing digital overcurrent (O/C) relays, the proposed scheme can locate either a bus fault or a feeder fault by mapping corresponding fault current vector with the characteristic vectors in a pre-built database. By updating the characteristic vector database, the proposed scheme can be applied to the changed system as well, thereby achieving adaptive feature. No complex optimization technique is required. A simplified distribution system is employed to test the proposed scheme and its adaptive aspect. Test results show that the scheme has very good performance.

95/01532 Distributed approach to black point

This study presents a practical and effective method for inspecting and repairing curve intersection situations that occur in upstream and downstream coordinated overcurrent relay pairs in subtransmission networks. This type of miscoordination can cause backup relays to trip before their paired primary when faults occur, resulting in unexpected expansions of blackout areas. The proposed method is based on the IEEE and IEC standard characteristic curve equations of digital overcurrent relays and a customized curve equation for electromechanical overcurrent relays. Consequently, the proposed method is applicable to both digital and electromechanical relays. Two subtransmission network cases for the Taiwan Power Company were simulated to validate the proposed method.

A computer-aided design tool for developing digital controllers and relays

The design, development, and implementation of a computer-aided design (CAD) tool for developing digital controllers and relays are presented. The development includes modeling A/D converters, software, and the necessary logic. Procedures for modeling A/D converters and simulating the software are described. Application of the CAD tool is demonstrated by evaluating and comparing three different designs of a digital overcurrent relay. The designs are evaluated to determine both the speed and accuracy of the relays. The effects of the size of the A/D converters, the word-size used in computations, and the truncation/rounding are included in the simulation. Also described is the algorithm used in the relay design.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>