ABSTRACT
With the incoming surge and the arrester rating selected, the process of selecting the BILs of the station equipment can commence. Usually the station type and layout are known, and normally the candidate BILs for the transformer are limited to one to three values. Surge Voltages/Evaluation—Select BILs and Clearances. With the incoming surge applied to the station, the magnitude and waveshapes of voltages are measured throughout the station, usually at equipment locations and at opened points on the buses. If the required BILs and clearances are considered excessive, some alternates may be used to decrease these values. Additional arresters can be employed within the station. Alternately, the severity of the incoming surge can be decreased while maintaining the desired mean time between failure by improving the lightning performance of the towers or lines adjacent to the station.
