Evaluation of Basic Insulation Level (BIL) Requirements for Distribution-Supplied 38kV Enclosed Switchgear

There is a long-standing practice of specification of 200kV BIL on 38kV enclosed switchgear applied at the front-end of 38kV utility substations. By extension, this practice has also proliferated for consumer-owned 38kV switchgear supplied from 38kV utility distribution feeders. This practice has its roots in the desire for utilities to avoid the installation of surge arrestors in this type of switchgear due to maintenance costs and other concerns. However, for switchgear applied as consumer-owned switchgear supplied from utility distribution feeders, it is very common to apply surge arrestors in the switchgear. The insulation coordination and surge arrester parameters of the 38kV enclosed switchgear have been studied. The PSCAD/EMTDC model has been developed for the simulation of lightning overvoltage. This paper evaluates the BIL requirements for consumer-owned switchgear fed from common configurations of 38kV utility distribution lines with and without surge arrestors applied in the switchgear. It also evaluates the need to apply surge arrestors in locations such as bus tie circuit breakers for switchgear fed from multiple distribution lines to achieve suitability of 38kV switchgear with BIL levels that are less than 200kV.