Performance metrics for assessment of distribution system protection schemes

This paper investigates the metrics for assessing the performance of alternative protection schemes for a distribution feeder. In addition to the main criterion which is the system reliability, the paper considers the other important factors as well which include stress on the substation transformer and the impact of momentary interruptions on customer load. Traditional reliability assessment indices, most commonly used amongst utilities, consider sustained interruptions only and hence they do not capture the advantages brought forth due to faster speed of protection schemes. To include the momentary events and their impact, an index `SARFI-ITIC' based on the `ITIC curve' is considered. Test cases illustrate the use of these metrics especially in assessing the advantages of fast speed protection schemes.