Overvoltage Considerations for Interconnecting Dispersed Generators with Wye-Grounded Distribution Feeders

A dispersed generator on a distribution system can continue to energize the feeder during fault disturbances. In particular, when a permanent single-line-to-ground (SLG) fault exists, generators connected through delta-delta transformers tend to force the unfaulted phase voltage to 1.73 pu. Because of this, some utilities require that the customer generator be connected through an effectively grounded source. Other utilities are not concerned with the overvoltages and do not use effectively grounded sources on a distribution feeder because they may defeat the coordination schemes that use fast tripping to protect fuses on temporary SLG faults. In some cases, providing a solidly grounded source can be prohibitively expensive for some dispersed-generation systems.