DELTA FILTER WITH AN ADAPTIVE TIME WINDOW FOR PROTECTIVE RELAYS

摘要

A delta filter for use in a protective relay which includes an input circuit (50) for receiving phasor signals (V) representative of electrical signal quantities on the power line. A difference value, if any, is determined between the phasor signals (V) at a present time and the phasor signals at a past point in time (reference phasor 1), the delay typically being one cycle. A first incremental output value (delta V1) is produced if there is a difference. When power line disturbance is first noted by the recognition of a first incremental output value, the phasor signal value at the beginning of the disturbance is stored (54) and then used as a reference value (reference phasor 2) for comparison with subsequent present time phasor signals to determine continuing change in power system condition.