Fast voltage-collapse line-protection algorithm based on local phasors

An algorithm for protection against voltage collapse is proposed. The algorithm makes use of the magnitudes and angles of the local phasors. The change in an apparent-power line flow during a time interval is exploited for computing the voltage-collapse criterion. The criterion is based on the fact that the line losses in the vicinity of the voltage collapse increase faster than the delivery of the apparent power, and, at the voltage-collapse point, the losses consume all the increased power. The selected criterion equals 0 when a voltage collapse occurs, which gives the protection relay with an appropriate setting an opportunity to react earlier. The proposed algorithm could be easily implemented in a numerical relay. The algorithm is simple and computationally very fast. An online protection scheme can be applied at the relay point of an endangered line. The algorithm was tested on various test systems including the Slovenian 275-busbar test system.