Distance relaying of 11 kV circuits to increase the installed capacity of distributed generation

The connection of generation to distribution networks may cause problems with existing protection schemes, while development of new protection schemes can facilitate an increase in generation capacity. The design and evaluation of a distribution network protection scheme based on distance relays is described. The scheme provides primary and back-up protection of 11 kV circuits. In the UK, voltage transformers and communication schemes are seldom installed on 11 kV circuits. Hence the distance relay restraint signal (voltage) is measured at the secondary winding of a distribution transformer (11/0.433 kV) to reduce costs. The development of the distance relay algorithm is discussed and a selection of simulation test results provided to illustrate the relay performance under fault conditions.