Restoration of Directional Overcurrent Relay Coordination in Distributed Generation Systems Utilizing Fault Current Limiter
A new approach is proposed to solve the directional overcurrent relay coordination problem, which arises from installing distributed generation (DG) in looped power delivery systems (PDS). This approach involves the implementation of a fault current limiter (FCL) to locally limit the DG fault current, and thus restore the original relay coordination. The proposed restoration approach is carried out without altering the original relay settings or disconnecting DGs from PDSs during fault. Therefore, it is applicable to both the current practice of disconnecting DGs from PDSs, and the emergent trend of keeping DGs in PDSs during fault. The process of selecting FCL impedance type (inductive or resistive) and its minimum value is illustrated. Three scenarios are discussed: no DG, the implementation of DG with FCL and without FCL. Various simulations are carried out for both single- and multi-DG existence, and different DG and fault locations. The obtained results are reported and discussed.
Available from: Behrooz Vahidi
- "Another way is interrupting the DGs when a short circuit fault occurs , . One of the best proposed solutions is using of a fault current limiter to limit DG's contribution to the fault current during a short circuit fault . "
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ABSTRACT: Dispersed generation (DG) sources are rapidly opening their way to the power systems. Despite the many advantages that their introduction into the grid has, it may cause some problems. One of the problems is increasing the short-circuit current and the loss of protective devices coordination. To deal with this problem, many different approaches have been proposed. One of the best promising approaches of resolving the problem is using a fault current limiter (FCL) to limit DG's current during a short circuit fault. In this paper, a parallel-resonance-type fault current limiter is used in the interconnection point of the DG to the grid to keep its current at its pre-fault value during a short circuit fault. A comparative study is carried out through the short-circuit tests to demonstrate the superiority of using this kind of FCL over the conventional resonance-type one. The novelty of this paper is that by using the mentioned FCL, operating times of the recloser and fuse will be maintained at their values before the introduction of DG. So, the recloser-fuse coordination can be restored with higher coincidence with the pre-introduction of DG condition. Furthermore, using this kind of FCL has less effect on the normal system condition. Keywords—Dispersed generation (DG); short-circuit current; parallel-resonance-type fault current limiter; resonance-type fault current limiter; protection coordination
Available from: Akram Elmitwally
- "The time dial setting and pickup current setting are determined for each relay provided that certain coordination constraints are met . For this purpose, a two-phase optimization model is mathematically formulated in (3)–(9) . In Phase 1, the objective J given in (3) is minimized subject to the set of constraints given in (4)–(6). "
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ABSTRACT: 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.
Available from: F. Abbasi
- "In the coordination problem of DOCRs, the main aim is to determine the TSM and plug setting (PS) of each relay, so that the OF is minimized, subjected to limits on problem variables and certain coordination constraints. The main OF that is already used in most of the literature is the total weighted sum of OTs of primary relays as follows   : "
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ABSTRACT: This paper presents a new method for coordination of directional overcurrent relays to reduce the discrimination time of the primary and backup relays, by using nondominated sorting genetic algorithm-II (NSGA-II). In order to achieve a reliable protective system, it is necessary to find a solution to avoid having large discrimination times, in addition to coordination time interval (CTI). The novelty of the paper is to reduce the discrimination time of the primary and backup relays and simultaneously reduce the operating time of primary and backup relays, by introducing a new method. In contrast to the conventional intelligent methods, the proposed method does not require weighting factors for conversion of multi-objective function into an equivalent single objective function. The effects of both near and far-end faults are considered to solve the proposed problem formulation. Also, various overcurrent relays characteristics are considered within the program to select the best of them for each relay by optimization algorithm. The proposed method is implemented in three different test cases, i.e. three, eight and IEEE 30-bus network. The results are compared with previously proposed methods.
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