Grounding Effectiveness at Grand Coulee 230-Kv Switchyards Verified by Staged Fault Tests

Very little has been published in the past regarding the hazard to the integrity of long control circuits due to possible excessive rise in ground potential at one end of the circuits during station faults; and the verification of the safety of such control circuits through actual tests. This paper describes the rather unique arrangement at Grand Coulee power plant wherein the plant is located at the bottom of the Columbia River Channel and one of the associated 230-kv switching stations is located on a rocky plateau approximately 600 feet higher in elevation, thus requiring control cables over 4,000 feet in length. By means of several fault tests staged specifically for this purpose, and as a by-product of subsequent high-interrupting capacity circuit breaker tests, the actual rise in ground potential was determined and the safety of the control circuits positively verified, under 60-cycle fault conditions.