Forces due to short circuit in a 400 kV outdoor substation: A study

Abstract

Short circuit force (SCF) in an EHV substation is an important attribute for the electromechanical design of a substation. Hence, computation of SCF becomes mandatory for the substation design. The conductor phase to phase spacing within the EHV substation is an important parameter which influences the SCF. Also, in a flexible-conductor-bus, in the event of a short circuit, there will be variation in of phase to phase air clearances (dynamic) and conductor-sag (dynamic). The air clearances at any conditions should satisfy the minimum phase to phase clearance as per standard to assure safety and avoid secondary faults. The conductor-sag should also be within acceptable limits. As the conductor phase to phase spacing is varied, air clearances as well as conductor sag varies. The SCF in a 400kV substation, with flexible-bus-conductor's, is computed as a case study. With this SCF, variation in air clearances and conductor-sag are computed and analyzed. The margin given in design and construction of bus conductor spacing and their sag during static conditions are good enough even under the short circuit conditions resulting in SCF and reduced conductor spacing due to dynamic reduced phase to phase clearances and sags.