Impact of Surge Capacitor-SF6 Breaker Separation on Thermal Interrupting Capability

Test standards/application guidelines on breaker transient recovery voltage (TRV) assume line-side TRV is delayed by 0.5 μs by station capacitance during short-line fault (SLF) clearing on 230-kV lines. This assumption can be critical for SF6 breakers having an arc time constant comparable to the assumed delay. To delay the line-side TRV sufficiently, a 230-kV SF6 breaker may require surge capacitors at its terminals during SLF type tests. However, the surge capacitor installation in the field may only be feasible at some distances away from the breaker due to insufficient clearance at its terminals. The separation between the breaker and its required capacitor can lead to an initial TRV (ITRV) much higher than the type-tested duty. This paper investigates the consequence of this separation. Firstly, a set of TRV data collected from a 245-kV interrupter's type tests are used to calibrate Cassie-Mayr arc model parameters. Afterwards, the calibrated arc model is employed to investigate the surge capacitor-breaker separation effect on thermal interrupting capability under SLF-caused ITRVs. The studies reveal as the separation between the breaker and capacitor increases, the arc model's interrupting capability decreases significantly, suggesting there may be merit in updating the TRV test standards/application guidelines to address this phenomenon.