Testing dynamic characteristics of overcurrent relays

Test methods for determining the dynamic characteristics of an overcurrent relay are discussed. By dynamics is meant the response of the relay to a current of varying magnitude. The test method, originated by IREQ, is used by Hydro Quebec to determine the ability of new relays to coordinate with the installed base of induction relays. Concurrent with this work, working group G7 of the Power System Relay Committee for the IEEE Power Engineering Society is completing a standard for inverse time-overcurrent characteristics which define equations for microprocessor relays based on the physics of induction relays. The authors discuss the correlation between the dynamic tests of induction relays and the proposed standard equations for reset and trip characteristics of microprocessor-based relays.