A new adaptive loss of excitation relay augmented by rate of change of reactance

Conventional loss-of-excitation relay for a turbo alternator is an offset mho relay and has been reported to maloperate on stable power swings under certain conditions. The documented solution to this problem is to intentionally delay the operation of LOE relay, which the authors believe is not an ideal solution. This paper, basically, reports an adaptive or dynamic LOE relay, augmented by suitably selected time-derivatives of impedance seen by the relay, to ensure correct discrimination between genuine loss of excitation and power swing.