Impact of Special Protection Scheme on Cascading Failure in Iran Power System

Today’s complex power systems operate close to their operating limits. The (N-1) criterion is considered for the design of these systems. Partial or total blackouts are unavoidable in them. There is a mechanism denoted as cascading failures which is considered as the main cause for blackouts in power systems. The propagation of cascading failures in power systems results from local activation of protective relays due to overload or voltage drop. Special protection schemes (SPS) are designed to alleviate voltage drop and line overloading by fast load shedding. Because the SPS work fast following the initial disturbance, they can quickly control the line loading and voltage drop and consequently can reduce the potential for propagation of cascading failure. In this paper, the impact of SPS on the propagation of cascading failure and their associated load loss in Iran power grid is investigated. In order to simulate the mechanism of cascading failure and the impact of SPS on that, by using Power Factory
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software and modelling all control and protection devices within that, cascading failure simulating module (CFSM) is developed which is able to simulate of cascading failure mechanism. In Iran power system, 5 types of SPS have been used. By simulating 30 multiple contingencies, it is shown that in the case of severe contingencies SPS can alleviate the consequence of cascading failure.