Patent ID: 6028754
Filing Date: 2000-02-22
Classification: H02H

Abstract:
A system for increasing security in a power system using a protective relay having a zone I distance element with a set reach, the relay responsive to a secondary signal from a secondary of a coupling capacitor voltage transformer, the secondary signal having a transient, wherein the system comprises:means for determining a system impedance ratio (SIR) value for the original zone 1 reach of the protective relay;means for determining a reduction in the zone 1 reach, using said SIR value;means, in response to a fault which occurs on a power line portion of the power system, for determining whether the fault is within the reduced zone 1 reach;means for providing a trip signal without a deliberate delay if the fault is determined to be within the reduced zone 1 reach; andmeans for delaying a trip signal by a selected amount of time if the fault is determined to be beyond the reduced zone 1 reach, but within the original zone 1 reach.