A novel scheme of local protection against voltage collapse based on the apparent-power losses

A new algorithm for protection against voltage collapse is proposed using local phasors' magnitudes and angles. A change in apparent power line flow in a time interval is exploited for computation of the voltage collapse criterion. The criterion is based on the fact that the line losses in the vicinity of voltage collapse increase faster than delivery of the apparent power and at the voltage collapse point the losses take all the increase. The selected criterion equals zero when a voltage collapse occurs, which gives the relay an opportunity to react earlier with an appropriate setting. The proposed algorithm could be easily implemented in a numerical relay. The algorithm is simple and computationally very fast. An on-line protection scheme could be applied at the end of an endangered line. The algorithm was tested on various test systems including New England 39-bus test system. (C) 2003 Elsevier Ltd. All rights reserved.