Algorithm to evaluate substations reliability with cut and path sets

ALGORITHM TO EVALUATE SUBSTATIONS RELIABILITY WITH CUT AND PATH SETS Miguel Vega Héctor G. Sarmiento
Member, IEEE Senior Member, IEEE mvega@iie.org.mx hsu@iie.org.mx Instituto de Investigaciones Eléctricas. Reforma 113, Col. Palmira Temixco, Morelos, México. 62490 Ph.: 52 777 3623811 ext 7418 and 7414.
Abstract. - An algorithm is presented to evaluate substations reliability, which takes intoaccount breaker failures, blocked breaker and breaker backup protection to isolate failures in a substation. Passive and active outages and two evaluation criteria are considered. This is, substation fails if one point of load fails or substation fails if all points of load fail. The cost of the energy not supplied is used to evaluate and economically compare the substations reliability. IndexTerms – Reliability evaluation algorithm; electrical substations; minimal cuts and path sets, passive and active outages.

λi = passive outage frequency [outages /year]. λig= active outage frequency [outages /year]. λi”= maintenance outage frequency [outages /year]. Pr(j)= breaker probability lock. ri = outage duration [hours]. Si = switching duration [hours]. ri” = maintenance outage duration[hours]. λSL= active outage frequency [outages /year]. Di = load demand of point “i”. PNS = demand or power not supplied [KW] ENS = energy not supplied [KWh]. To give a good estimate of the system reliability indexes, operation characteristics should be modeled as realistically as possible. Some of the aspects that have considerable influence on the substation reliability are: - Topology. - Outagetypes. The difference between a failure and an outage is that the failure can occur without affecting the performance of the system, but an outage affects the performance and regularly it cuts the supply to one or several load points. Outage classification: • Passive outage is when the component fails and does not affect other components. - With normally closed breaker stuck to open. - Withnormally open breaker stuck to close. • Active outage is when the component fails and affects other healthy components. - With normally closed breaker stuck to open. - With normally open breaker stuck to close. • Maintenance outage is a programmed outage. Other outages are realized when: - The circuit breaker opens without any command. - The circuit breaker closes without any command.

I. INTRODUCTIONElectrical substations are one of the strongest points in a power distribution system, but they also have their weak points and it is necessary to know them and avoid the cases where one fault can damage the substation or resulting in an outage to the costumers. During the planning process, it is necessary to establish the configuration of each one of the substations to be installed at thetransmission or distribution level and is very useful to the engineer to know the reliability of different substation configurations, based on size of load, number and load of costumers to be supplied, etc. For reliability analysis of power substations, it is more desirable to have one tool that includes the electrical and reliability parameters and also that evaluates, under the conditions of thezone, the reliability of the system. An algorithm was developed to evaluate the reliability of substations, including the performance of the protection system and the reliability of each one of its components. A way to describe in economical terms the impact of reliability is to multiply the energy cut to the consumer by the cost of the KWh not supplied. In substation planning, it is of considerableinterest to have an efficient algorithm to obtain the reliability of a system and be able to compare an alternative solution. For this evaluation the following parameters are included:

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The circuit breaker is opened to eliminate a fault and then closes again. The circuit breaker is closed to restore a fault and then opens again.

Other outages...