Search

Incorrect responses from protective devices weaken the reliability of microgrids. This paper investigates the effects of the protection system on the reliability performance of a microgrid integrated with weather-dependent microsources. It relies on a stochastic model to simulate the challenges existing in current protection schemes designed for microgrids. Abnormal operating conditions, including overcurrent, overvoltage, and undervoltage, which are detected by a deficient protection scheme, are analyzed by a defined fuzzy virtual setting value. Their contributions, along with the conventional random failure rate achieved by statistical results, are jointly used to evaluate the short-term outage rate of a feeder. A series of fuzzy reliability indices is further proposed for the short-term and periodical reliability of both microgrid system and customers. Subsequently, an evaluation strategy, combined with fuzzy simulation and load restoration, is presented as a solution tool. Simulations on a test system are provided to support the necessity of considering the effects of protection operation in evaluating microgrid reliability. [ABSTRACT FROM PUBLISHER]

In the condition settings of a power-frequency withstand voltage test for substation equipment, an approach based on insulation reliability evaluation using Weibull distribution is available. In this method, temporary overvoltage is evaluated using an ?independence model?. This ?independence model? assumes no remaining influence of voltage application (i.e. the model obeys the failure probability distribution starting at time 0 each time the voltage is applied). However, the authors have conducted insulation characteristics tests by applying a voltage multiple times at intervals and clarified that the influence of voltage application remains to a certain extent (i.e. the effect assumed in the ?accumulation model? appears) as well as the degree of influence depending on the conditions for oil-immersed transformer. The present paper proposes an evaluation method with the degree of influence of voltage application history taken into consideration. In the proposed method, the portions following an ?independence model? and an ?accumulation model? are respectively assumed and combined after multiplying the relevant coefficient representing the respective degrees of influence. According to the trial calculation based on the proposed method, the required withstand voltage decreased by several percentage points, while it was confirmed that the existing method is on the safer side as a means of evaluating the insulation reliability of temporary overvoltage. [ABSTRACT FROM PUBLISHER]

Due to the lack of feeder corridors, the Chinese utility companies frequently choose the technique of putting multiple overhead feeders on a same tower (MFST) to meet the load demand in a heavy load area. In many situations, the distance among the feeders of MFST in an electrical distribution network (EDN) is usually too small to meet the requirements of safety regulation for repairing and maintenance. Therefore, when a fault occurs on a feeder of MFST, the other feeders have to be in a triggered passive outage (TPO) state to assist the repairing of the failed feeder. This paper presents a reliability evaluation algorithm for EDNs containing MFST using the section technique. The definition of TPO and the equivalent TPO rate and TPO duration are also proposed. Based on the TPO parameters and the section technique, the reliability evaluation algorithm containing the MFST can be obtained. Case studies on the modified RBTS-BUS6 and the EDNs of three districts in Dongguan city, China, show that the MFST has a significant impact on the EDN reliability and should be considered in the reliability evaluation. The results also show the effectiveness and applicability of the proposed approach. [ABSTRACT FROM PUBLISHER]