Operation Of Overcurrent Relays Research Articles

Detection and isolation of faulty line in an active distribution network using intelligent numerical relay

• The Intelligent Numerical Relay (INR) placed at substation majorly performs three functions, i.e., Over Current Relay (OCR), Distribution System State Estimator (DSSER) and Faulty Line Locator (FLL) to identify exact faulty line. • In OCR operation, it collects all possible supply current data from substation CT as well as PMUs at DG buses. it compares the total supply current with pickup value and identify the fault as well as faulty phase. • In DSSER operation, it collects data from optimal PMUs and estimates the states of entire system using linear Weighted Least Square (WLS) algorithm. • In FLL operation, it observes the voltage magnitudes at each bus based on estimated voltages. FLL identifies the exact faulty line which is in between maximum change in voltage bus and second maximum change in voltage bus. • After identification of faulty line, the INR remotely operates the intelligent switchgear of faulty line to isolate it. This method could detect the exact faulty line almost instantaneously, i.e., before the fuse melts. • The proposed technique is tested and validated for IEEE 33 bus active distribution network under different types of faults at various locations. In recent days Passive distribution networks are being transformed to Active Distribution Networks. The operation of Active Distribution Networks is becoming more complex with increasing energy demand and integration of distributed generations. Currently, identifying a faulty line in the distribution system is a tedious task which causes long interruptions to the consumers. Therefore, a real-time system is mandatory to monitor and control distribution network. This paper presents a novel method to detect the exact faulty line in Active Distribution Networks using an Intelligent Numerical Relay. The Intelligent Numerical Relay placed at substation collects the data from optimally placed Phasor Measurement Units and performs several functions. It operates as Over Current Relay to identify the fault, acts as Distribution System State Estimator to estimate the state of the system, and also acts as Faulty Line Locator to identify the faulty line. This Intelligent Numerical Relay placed at substation acquires all-possible supply currents data from substation current transformers as well as Phasor Measurement Units at Distributed Generator buses. In its Over Current Relay operation, it detects the fault by comparing total supply current with pick up value. The faulty line detection is performed by Faulty Line Locator using estimated voltages from Distribution System State Estimator based on optimal Phasor Measurement Units data. Faulty Line Locator observes the estimated voltages at each bus, it identifies the exact faulty line which is in between the buses with maximum change in voltage and second maximum change in voltage. After the identification of faulty line, the Intelligent Numerical Relay remotely operates the intelligent switchgear present at the faulty line to isolate it. The main advantage of this method is that, it could detect the exact faulty line almost instantaneously, i.e., before the fuse blows. IEEE 33 bus active distribution system is considered for testing and validation of the proposed method.

A Comprehensive Assessment of Fundamental Overcurrent Relay Operation Optimization Function and Its Constraints

The optimization of overcurrent relays’ operation is a topic associated with protection coordination of distribution networks. Usually, this refers to medium-voltage networks, since they are protected by numerical relay devices, as opposed to low-voltage networks, where utility operators allocate fuses. Correct setting of relays and optimal coordination is becoming a serious challenge to Distribution Network Operators around the world, since their networks’ passive operation has been greatly altered in the past two decades. Distributed generation units, a growing liberalized electricity market and more stringent legislation for distribution network planning and operation by state regulatory bodies have all indirectly affected the evolving of protection philosophy for distribution networks. In this paper the traditional optimization problem of overcurrent relay operation will be addressed and critically examined from both a theoretical and practical point of view. Optimization function, constraints and relay parameters will all be observed and compared with solutions used in distribution networks, and their modifications and improvements will be proposed and elaborated in detail.

A multi-agent solution to multi-thread protection of DG-dominated distribution networks

Integration of Distributed Generations (DGs) into Distribution Networks (DNs) has alarmingly altered the level of short circuit current, leading to some critical protection challenges. Given that proper operation of overcurrent relays depends on location, type, or generation capacity of DGs, this paper proposes an agent-based algorithm guaranteeing the protection validity, regardless of DGs’ dependencies. First, sharing their information with the main grid agent, relay agents are categorized into different zones to determine in advance the operating status of a protection system. Next, according to the network condition, the fault clearing process is divided into two parts: independent operation and operation in accordance with the relay's conditions. Last, the protection system settings are updated following the fault clearing process. Furthermore, a multi-thread processing scheme is presented to improvethe intrinsic slowness of agent-based techniques, preventing any probable malfunction during fault conditions. Accordingly, the protection structure is divided into three levels (threads) running simultaneously: relay operation status detection, fault clearing, and updating protection settings. The simulation results are in good agreement with the proposed protection scheme.

High Impedance Fault Detection and Location in Combined Overhead Line and Underground Cable Distribution Networks Equipped with Data Loggers

Power distribution networks are vulnerable to different faults, which compromise the grid performance and need to be managed effectively. Automatic and accurate fault detection and location are key components of effective fault management. This paper proposes a new framework for fault detection and location for smart distribution networks that are equipped with data loggers. The framework supports networks with mixed overhead lines and underground cables. The proposed framework consists of area detection, faulty section identification, and high impedance fault location. Firstly, the faulty zone and section are detected based on the operation of over-current relays and digital fault recorders. Then, by comparing the recorded traveling times at both ends of lines, which are related to the protection zone, the faulty line is identified. In the last step, the location of the fault is estimated based on discrete wavelet transform. The proposed method is tested on a 20 kV 13 node network, which is composed of overhead lines and underground cables. The method is tested in both balanced and unbalanced configurations. The obtained results confirm the advantages of the proposed method compared with the current state-of-the art.

Forecast-based overcurrent relay coordination in wind farms

Relay coordination ensures the appropriate isolation of healthy feeders from the faulty areas in a power system. The dynamic nature of renewable sources such as wind generators (WGs) can create variations in fault levels which affect the relay settings. This causes coordination problems, which can lead to the faulty operation of overcurrent relays (OCRs). The settings of the relay need to be modified appropriately in line with the variations of fault levels, which in turn change with the wind dynamics. As a solution, wind forecast based technique for the coordination of the OCRs in wind-integrated substations is suggested in this work. In the proposed algorithm, wind speed and its direction are predicted and the settings of the relay are predetermined using an optimization technique. This reduces the computation time required for the algorithms in the current period. The algorithm is implemented in the modified IEEE 9-bus system with wind farms and also in a typical wind-integrated substation. Further, it is validated through an experimental setup in the laboratory. The results were found to be promising and the algorithm can be applied to any substations integrated with wind farms for avoiding relay mal-operations.

Genetic Algorithm-Based Optimization of Overcurrent Relay Coordination for Improved Protection of DFIG Operated Wind Farms

Rigorous protection of wind power plants is a critical aspect of the electrical power protection engineering. A proper protection scheme must be planned thoroughly while designing the wind plants to provide safeguarding for the power components in case of fault occurrence. One of the conventional protection apparatus is overcurrent relay (OCR), which is responsible for protecting power systems from impending faults. However, the operation time of OCRs is relatively long and accurate coordination between these relays is convoluted. Moreover, when a fault occurs in wind farm-based power system, several OCRs operate instead of a designated relay to that particular fault location, which could result in unnecessary power loss and disconnection of healthy feeders out of the plant. Therefore, this article proposes a novel genetic algorithm (GA)-based optimization technique for proper coordination of the OCRs in order to provide improved protection of the wind farms. The GA optimization technique has several advantages over other intelligent algorithms, such as high accuracy, fast response, and most importantly, it is capable of achieving optimal solutions considering nonlinear characteristics of OCRs. In this article, the improvement in protection of wind farm is achieved through optimizing the relay settings, reducing their operation time, time setting multiplier of each relay, improving the coordination between relays after implementation of IEC 60255-151:2009 standard. The developed algorithm is tested in simulation for a wind farm model under various fault conditions at random buses and the results are compared with the conventional nonlinear optimization method. It is found that the new approach achieves significant improvement in the operation of OCRs for the wind farm and drastically reduces the accumulative operation time of the relays.

Impact of Short-Circuit Impedance Model for Variable-Speed Wind Turbine Generators on Operation of Overcurrent Relays

Impact of Short-Circuit Impedance Model for Variable-Speed Wind Turbine Generators on Operation of Overcurrent Relays

Study on Operational Characteristics of OCR with Voltage Component in a Power Distribution System with SFCL

Recently, the power system has been changed to introduce the loop power distribution system or the distributed generations for stability and flexibility of power supply. These changes tend to influence on the capacities of protective devices and may cause the malfunctions due to excess of the devices’ capacity. So, as one of the countermeasures of reduction of the fault current, the superconducting fault current limiter (SFCL), has been noticed. However, the reduction of the fault current due to the application of the SFCL in a power distribution system may be able to cause the unexpected malfunctions of the overcurrent relay (OCR). As the OCR, one of the representative protective equipment in a power distribution system, requires the current exceeding the pickup current to be operated, the reduction of the fault current may affect to trip operation of OCR. So, this paper will deal with a trip delay caused by application of the SFCL, which is one of the unexpected malfunctions. To improve OCR’s trip delay, the OCR with voltage component is proposed and the operational characteristics of the OCR with voltage component have been analyzed using the PSCAD/EMTDC in a power distribution system.

An Adaptive Algorithm Based on Subharmonic and Time Domain Analysis to Prevent Mal Operation of Overcurrent Relay During Subsynchronous Resonance

Subsynchronous resonance (SSR) is a phenomenon in which electrical energy is exchanged between generators and transmission systems below power frequency. It happens due to interaction of a series compensated transmission line with a generator. It results in oscillation in the shaft and power swing. In addition, SSR causes increased magnitudes of voltage and current consequently occurrence of ferroresonance. It is obviously clear that protective relays are affected in such conditions. SSR can be damped by several methods; however, protective relays must be adaptive to prevent mal operation independently. In this paper, Manitoba Hydro electrical network with series capacitor is simulated by PSCAD/EMTDC. The impact of SSR and ferroresonance on operation of overcurrent relay is analyzed. An adaptive algorithm based on subharmonic measurement and ferroresonance analysis in time domain is proposed for overcurrent relay. The algorithm detects SSR and ferroresonance, and changes setting values of the relay to prevent mal operation. Furthermore, it distinguishes protection of the hydro generator against subharmonics, which interact with natural frequencies of the rotor. Finally, the algorithm is examined in SSR condition to certify the correct operation.

Dynamic Analysis of Fault Current Limiters Performance in Distribution Systems

This article presents the impact of several designs of fault current limiters (FCL) in distribution systems. The voltage quality in not faulted feeders; the transient recovery voltage in circuit breakers and the time operation of overcurrent relay are evaluated. The aim of FCL in distribution systems is to reduce the fault current to levels below the nominal capacity of the circuit breakers, avoiding the replacement of such equipment. However the effect in the operation of FCL can be important during no maximum fault conditions like two-phase faults and minimum demand. A comparative study was assessed, by analyzing the performance for different FCL in electrical systems during maximum and minimum fault conditions. The results show that the over limitation of current fault resulting during low fault conditions can compromise the distribution networks performance.

Optimal Application of Fault Current Limiters for Assuring Overcurrent Relays Coordination with Distributed Generations

This paper addresses the problem of overcurrent relays (OCRs) coordination in presence of DGs. OCRs are optimally set to work in a coordinated manner to isolate faults with minimal impacts on customers. Penetration of DGs into the power system changes the fault current levels seen by the OCRs. This can deteriorate the coordinated operation of OCRs. Operation time difference between backup and main relays can be below the standard limit or even the backup OCR can incorrectly work before the main OCR. Though resetting of OCRs is tedious especially in large systems, it cannot alone restore the original coordinated operation in the presence of DGs. The paper investigates the optimal utilization of fault current limiters (FCLs) to maintain the directional OCR-coordinated operation without any need to OCRs resetting irrespective of DGs status. It is required to maintain the OCRs coordination at minimum cost of prospective FCLs. Hence, the FCL location and sizing problem are formulated as a constrained multi-objective optimization problem. Multi-objective particle swarm optimization is adopted for solving the optimization problem to determine the optimal locations and sizes of FCLs. The proposed algorithm is applied to meshed and radial power systems at different DGs arrangements using different types of FCLs. Moreover, the OCR coordination problem is studied when the system includes both directional and non-directional OCRs. Comparative analysis of results is provided.

Optimal allocation of fault current limiters for sustaining overcurrent relays coordination in a power system with distributed generation

This paper addresses the problem of overcurrent relays (OCRs) coordination in the presence of DGs. OCRs are optimally set to work in a coordinated manner to isolate faults with minimal impacts on customers. The penetration of DGs into the power system changes the fault current levels seen by the OCRs. This can deteriorate the coordinated operation of OCRs. Operation time difference between backup and main relays can be below the standard limit or even the backup OCR can incorrectly work before the main OCR. Though resetting of OCRs is tedious especially in large systems, it cannot alone restore the original coordinated operation in the presence of DGs. The paper investigates the optimal utilization of fault current limiters (FCLs) to maintain the directional OCRs coordinated operation without any need to OCRs resetting irrespective of DGs status. It is required to maintain the OCRs coordination at minimum cost of prospective FCLs. Hence, the FCLs location and sizing problem is formulated as a constrained multi-objective optimization problem. Multi-objective particle swarm optimization is adopted for solving the optimization problem to determine the optimal locations and sizes of FCLs. The proposed algorithm is applied to meshed and radial power systems at different DGs arrangements using different types of FCLs. Moreover, the OCRs coordination problem is studied when the system includes both directional and non-directional OCRs. Comparative analysis of results is provided.

Impact of RDG Location on IDMT Overcurrent Relay Operation and Coordination in MV Distribution System

Impact of RDG Location on IDMT Overcurrent Relay Operation and Coordination in MV Distribution System

Impact of RDG Location on IDMT Overcurrent Relay Operation and Coordination in MV Distribution System

In recent years there has been an intensive effort to increase the participation of renewable sources of electricity in the fuel and energy balance of many countries. In particular, this relates to the power of wind farms attached to the power system at both the distribution network. However, in the presence of Renewable Dispersed Generation, (RDG) some problems in coordination of protection devices will occur, due to changes in fault current levels at different points. By installing RDG in power distribution networks, the fault current levels are changed and may lead to some miscoordination in IDMT Directional Over-Current Relay (DOCR). In this paper, a novel approach is presented to study the impact of RDG location (d RDG ) on IDMT characteristic curve of relay, fault current (I F ), operation time (T) for DOCR, and coordination time interval (CTI) between backup and primary relays and short circuit level index (ISC) in the presence there phase fault on medium voltage (MV) distribution network. This new approach has been implemented on the Algerian 10 kV distribution power system in Constantine.

A proposed coordination strategy for meshed distribution systems with DG considering user-defined characteristics of directional inverse time overcurrent relays

In this paper, coordination strategy that considers using user defined characteristics for the inverse time overcurrent relays is proposed. Typically, the coordination between relays operating times within meshed systems are achieved by adjusting two relay settings; pick up current and time multiplier setting (TDS and Ip). The equation that models the digital inverse time overcurrent relay operation has two constants; one of them represents the constant for relay characteristics (A) and the other one represents the inverse time type (B). The proposed coordination strategy considers the two relay characteristics constants as continuous variable settings that can be adjusted. These (A and B) values are chosen optimally in addition to (TDS and Ip) to achieve coordination. The coordination problem is formulated as a nonlinear programming problem where the main objective is to minimize the overall time of operation of relays during primary and backup operation considering faults at different locations. The results are compared against the relay coordination using the conventional settings. The problem is applied to the meshed power distribution network of the IEEE 30 bus systems equipped with synchronous based DGs. The results show that the proposed strategy can significantly reduce the overall relay operating time and thus making it an attractive option for meshed distribution systems with DG.

Design of an interactive application for educational support and performance analysis of overcurrent relay

The analysis of overcurrent relay operation is complex when compared with other protection principles, because the time when protection should operate is unknown, as this time depends on the evolution of the fault current. The main purpose of this article is to present an analysis of the operation of overcurrent relays under different operating conditions, using computational resources. By simplifying the analysis of real or simulated events, the proposed computational tool facilitates the evaluation of the design and implementation of relays in power systems. The software also allows for the editing of the conventional and unconventional time curves. Some examples are presented to illustrate possible applications of this tool.

Using Phase Shifter and OLTC to Improve Reliability during Load Transferring and System Protection

When the system requires reconfiguring or repairing, the load on one of distribution feeder needs to be transferred to another feeder without interrupting. However, there are several conditions which affects the load transfer on distribution feeder, including substation types, feeder loads, and primary side voltage of transformer. Those conditions will result in abnormal high current on load transferring, and the high current will lead to the operation of overcurrent relay. This paper uses ASPEN and Matlab/Simulink to simulate the load transfer of distribution feeder, and investigate the factor that will affect protection relay. An OLTC and a phase shifter is used to improve the high current during load transfer. It will avoid the action of protection relay, and improve reliability in power supply.

Simulation of Power Flow and Protection of a Limited Bus Grid System with Injected Solar Power

In recent years, injection of renewable energy such as solar power into the power grid is increasing. However, inclusion of large-scale intermittent-type renewable energy requires better management in proper understanding of grid’s variable characteristics and its protection systems. In this paper, the investigation on overvoltage issue is illustrated. Overvoltage in distribution feeder occurs when large amount of solar power is injected at low power demand. Another investigation is on false operation of overcurrent relays due to reverse power to the 33 kV loads. The potential solutions to the two issues are illustrated in the small-sized power grid system using bi-directional inverters on AC buses in charging battery banks and adjusting the relay current settings. The benefits of solar power injection are illustrated whereby output power from generators is decreased and transmission losses are reduced. Electrical Transient Analysis Program (ETAP) was used for investigations.

Computer Application by Dynamic Analysis of Overcurrent Relay Coordination

In this paper we present a computational tool for analyzing the dynamic operation of overcurrent relays. The analysis of operation of the overcurrent relay is complex compared to other principles of protection because the time operation is a function of the dynamics of the fault current. The main purpose of this article is geared towards the analysis of the operation of relays with different operating conditions using computational resources. The developed tool allows the evaluation of the design and implementation stages of relay allowing the analysis of the dynamic response to real or simulated events. The application proposal also allows editing of the conventional and unconventional time curves. Finally, we present some case examples to illustrate the activities that are possible to perform with the tool presented.

Optimum Coordination of Directional Overcurrent Relays Using the Hybrid GA-NLP Approach

The time of operation of overcurrent relays (OCRs) can be reduced, and at the same time, the coordination can be maintained, by selecting the optimum values of time multiplier setting (TMS) and plug setting (PS) of OCRs. This paper presents hybrid genetic algorithm (GA) - nonlinear programming (NLP) approach for determination of optimum values of TMS and PS of OCRs. GA has a drawback of, sometimes, converging to the values which may not be optimum, and NLP methods have a drawback of converging to local optimum values, if the initial choice is nearer to local optimum. This paper proposes a hybrid method to overcome the drawback of GA and NLP method, and determine the optimum settings of OCRs. The main contributions of this paper are - 1) systematic method for formulation of problem of determining optimum values of TMS and PS of OCRs in power distribution network as a constrained nonlinear optimization problem, 2) determining initial values of TMS and PS using GA technique and finding final (global optimum) values using NLP method, thus making use of the advantages of both methods (and at the same time overcoming the drawbacks of the methods).