The Enhancement of Protective System Reliability with Immune Algorithm

This paper is to derive the optimal planning of protective relay schemes for a transmission network by Immune Algorithm. The historical data of protective relay malfunction in Taipower has been used to determine the failure rate and repair rate of each type of protective relays in Taipower system. The Markov models of protective relays are determined and integrated with the transmission network to solve the customer service interruption due to protection relay malfunction for each substation. According to the load composition and service interruption cost of customers served, the outage cost of each substation is calculated. The objective function of system reliability cost is then formulated by considering the customer interruption cost of all substations and the investment cost of protective relay systems. By minimizing the system reliability cost with the proposed IA algorithm, the optimal planning of protective relay system is therefore obtained to achieve the best cost effectiveness of protection relay investment.

I. Introduction

In Taipower, the transmission system is to deliver the power generated in power plants to distribution substations and to serve large industrial customers with 161KV/69KV voltage levels at the same time. The main transformers of distribution substations are applied to step down the voltage level to 22KV/IIKV of distribution feeder to serve the medium industrial and large commercial customers. The low voltage customers of residential and commercial customers are served by distribution transformers along the primary distribution feeders. Although different types of protection devices have been installed in the transmission network to detect and isolate the faulted area, large scale system outages still occur due to the malfunction of protection system in Taipower. To improve the customer service quality, the reliability of various types of protective relays has to be investigated. By integrating the investment cost of protective relays and the corresponding service interruption cost of customers due to malfunction of protective system, the optimal planning of protective relays for transmission lines can be achieved.