Overcurrent Relay

The user has requested enhancement of the downloaded file. All in-text references underlined in blue are added to the original document and are linked to publications on ResearchGate, letting you access and read them immediately. Abstract – Overcurrent relays (OCRs) are one of the most common protective devices implemented in power systems in order to protect the components from faults. In order to obtain a much improved protection by these protective devices, a precise coordination of these systems must be applied. One of the problems in power systems, which is very common, is that when a fault occurs in a system, two, three or even several OCRs operate instead of the designated relay to that particular fault location. This will result in power loss and disconnection of healthy lines out of the system which is extremely dire. To diminish or even abolish the extent of this catastrophe, OCRs must be well coordinated with each other. Many suggestions have been made and approaches implemented, however the most prominent method is the use of artificial intelligence (AI) to improve the function and coordination of OCRs in power systems. The most common and applicable software programs to do the simulation and for applying AI in relays are Matlab/Simulink and PSCAD/EMTDC. In this review paper, the best methods-with respect to reaching the optimal relay settings value to pave the way for coordination-are considered to be the genetic algorithm and the particle swarm optimisation technique. Keywords – overcurrent relay, overcurrent relay coordination, power systems protection, artificial intelligence, nature inspired algorithm, fault current limiter

— In recent years, voltage instability has been a major issue in power systems. There are many factors contributing to voltage collapse which might cause blackouts, such as demands of consumption growth, the influence of harmonic component and reactive power constraints. These factors are very difficult to predict in real environment. High-voltage transmission lines are an important part of the power system. As the operation of the power grid expands, the demands on long distance transmission lines will increase. These lines are often exposed to large diverse geographical areas with complex terrain and weather conditions. If a fault occurs in a transmission line, it can be very hard to find and report it. Even if the fault is fixed, the new steady state of the power systems needs to be monitored to avoid failure again. The paper aims at studying the technology which overcomes various limitations of the power system. 1. Introduction Symmetrical components consist of positive-, negative-, and zero-sequence quantities. Basically, positive-sequence quantities are present during balanced, three-phase conditions. Positive sequence quantities makeup the normal voltages and currents observed on power systems during typical, steady-state conditions. Whereas Negative-sequence quantities are a measure of the amount of unbalance existing on a power system. Zero-sequence quantities are most commonly associated with ground being involved in an unbalanced condition. Negative and zero-sequence quantities are usually only present in substantial levels during unblanced, faulted conditions on a power system. The equations to calculate positive-sequence negative-sequence and zero sequence are given as í µí±‰ 1 = 1/3 (í µí±‰ í µí±Ž + aí µí±‰ í µí± + í µí±Ž 2 í µí±‰ í µí±) í µí±‰ 2 = 1/3 (í µí±‰ í µí±Ž + í µí±Ž 2 í µí±‰ í µí± + í µí±Ží µí±‰ í µí±) í µí±‰ 0 = 1/3 (í µí±‰ í µí±Ž + í µí±‰ í µí± + í µí±‰ í µí±) Where í µí±‰ 1 , í µí±‰ 2 and í µí±‰ 0 are positive-sequence negative-sequence and zero sequence voltages respectively. a is operater whose value is 1<120° and í µí±Ž 2 is 1<240°.

As power demand is increased, power generation and especially distributed generation (DG) are being developed. Therefore, power distribution systems become increasingly complicated and short circuit level in distribution grids is being augmented. Thereby, installation of a superconducting fault current limiter (SFCL) is a logical solution to decrease the fault current level in a distribution network. Preventing distribution system degradation by high fault currents, lower equipment ratings, and economic issues are the advantages of SFCL in distribution grids. However, SFCL installation causes delayed operation of the existing overcurrent protection and requires recoordination of the relays. In addition, disconnecting the SFCL from the distribution circuit due to maintenance leads to miscoordination between the overcurrent relays. In this research work, a genetic algorithm (GA) is used to achieve optimal protection coordination in the presence of both SFCL and DG. Furthermore, the uncertainty associated with the connection status of SFCL and DGs, which are reflected in the protection coordination, is investigated in detail. Moreover, various overcurrent relay characteristics, such as long-time inverse, extremely inverse, very inverse, and normally inverse, are used in a test power system, and remarkable computation results will be shown and discussed in the next parts of the paper.