OPERATION OF GROUND SENSOR RELAYS UNDER CONDITIONS OF PARTIAL CT SATURATION

Since the publication of the paper by Barnett, et al. [1], concerning low-ratio CT saturation at high fault current and resulting misoperati on or nonoperation of overcurrent relays, there has been a great deal of well-directed concern about the problem reported in that paper. How ever, some of that concern has also been directed at the application o f ground sensor relays to low-ratio CT's in resistance grounded indust rial power systems, where no operational difficulties have been report ed. The authors conducted a series of tests to determine if there is a ny cause for concern. These tests documented both the CT secondary cur rent wave shapes and the relay contact closure times for several CT-re lay-fault current combinations. This paper reports the results of thes e tests and presents conclusions concerning the adequacy of present pr actice in this field.