Investigations of Switching Surges Caused by 345-Kv Disconnecting-Switch Operation

De-energization of 1,300 feet of 345-kv bus with a disconnecting switch produced severe system overvoltage. Although the overvoltages were effectively limited by lightning arresters to a value below the equipment insulation strength, a severe operating duty was imposed upon the lightning arresters. Unlike the high-voltage circuits, which are adequately protected, low-voltage power and control circuits can be damaged by induced overvoltages. This is particularly true of the 115-volt station-service and carrier-communication circuits. A series resistor connected in series with each pole of the disconnecting switch effectively eliminated overvoltages on the 345-kv system, and reduced the transients on the lower voltage circuits to a safe value. A porcelain-enclosed resistor has been developed to reduce overvoltage on the high-voltage system during bus de-energization. The resistor is automatically inserted into the circuit when the switch is operated, but is bypassed when the switch is closed.