Abstract
Interconections of dispersed generators like co-generation systems to distribution feeders can cause overvoltages to ground on substation bus lines during single-line-to-ground faults. These overvoltages are transient phenomena which exceed 1.73 pu and would occur at the feeder-circuitbreaker tripping. Significant point of causing the phenomena is existance of instantaneous openphases with single-line-to-ground faults. The open-phases are normal operation, because phases of three line currents on the circuit-breaker are different and don't trip exactly at the same time.
The model of a distribution system involving generators is newly made for an analysis of the above problem. This model is used for a static analysis and a transient analysis. The static analysis is to clarify the system condition under which the zero-sequence voltage on substation bus lines reaches to the maximum amount. The transient analysis is to clarify the transient maximum voltage to the ground. The results of a transient digital simulation were corroborated by means of an analog simulator. The overvoltages to ground rarely cause iron-resonances due to the saturation of a GPT (grounding potential transformer). But they can be suppressed by means of a current-limiting resistor in a GPT.
