Patent ID: 7345863

Claim:
An apparatus in a protective device for identifying a loss of a specific current transformer (CT) signal of a plurality of CT signals, the plurality of CT signals provided to the protective device by a corresponding plurality of CTs coupling the protective device to at least one protection zone of a power system, the apparatus comprising: a plurality of first logic circuits, each of the plurality of first logic circuits configured to provide a binary control signal pair having a first binary control signal and a second binary control signal in response to comparisons of a first RMS value of a digitized current sample stream of a corresponding CT signal sampled at first time to a second RMS value of the digitized current sample stream sampled at a second time; and at least one second logic circuit operatively coupled to the plurality of first logic circuits and configured to provide a third binary control signal in response to receipt of the plurality of binary control signal pairs, a first value for only one of the plurality of first binary control signals and a second value for all of the second binary control signals and the first value for the third binary control signal for a pre-defined time interval indicating the loss of the specific CT signal corresponding to the first logic circuit providing the first binary control signal having the first value and preventing issuance of a trip signal of the protective device.