Arcing ground tests on a normally ungrounded 13-kv 3-phase bus

THE BUSSES and connected equipment in electric power stations sometimes are operated ungrounded. When a single insulation fault to ground occurs on a system of this type, the fault current is relatively small, the arc damage usually slight, and the faulted equipment in nearly all cases can be removed from service without relay action or service disturbance of any kind. However, in April 1942, faults developed simultaneously at two points 300 feet apart on the ungrounded 60-cycle 13.2-kv bus in the Holtwood station of the Pennsylvania Water and Power Company. This trouble resulted in severe arcing and damage to the bus structure before the faults were isolated.