Automatic voltage control relays and embedded generation. I

Keeping customer voltages within tolerance has always been a priority for distribution network operators. On-load tapchanging transformers and their associated automatic voltage-control relays play a pivotal role in this. Unfortunately, such relays can be affected by the connection of embedded generation. Sometimes this presents an apparent limit to the allowable penetration of embedded generation in a given area. Any such limit is in fact highly dependent on the configuration and settings of the relays and a clear understanding is necessary in order to ensure that the penetration is not unnecessarily restricted. This is the first of two articles that seek to promote such understanding by reviewing the use of voltage-control relays typically in the UK today: master-follower line-drop-compensation, true-circulating-current detection and negative-reactance compounding.