Electrical impact of a NUG under 5 MW rating when connected to a distribution feeder with various transformer connections

This paper describes electrical impact of nonutility generators (NUG) under 5 MW rating when connected to a distribution feeder. A number of problems are examined including line-to-ground fault level, overvoltage conditions, effect of harmonics, single-phase resonance and transformer backfeed with one phase open. These problems are examined with four different transformer connections. Protection requirements for various supply conditions are discussed. Two actual events involving transformer failure and starting problems are described under operating experiences