Transient voltage phenomena occurring during the energization of shunt capacitor banks, due to prestrike and temporary interruption in the switching device of inrush currents have been considered. An analysis is made of a generalized capacitance circuit and energization transient voltage pattems are shown for a range of circuit permutations. An application guide is discussed for reduction of overvoltages during capacitor bank energization by proper choice of circuit elements. The influence of circuit resistance on the bus voltage patterns is reviewed.

Control of Overvoltages on Energizing Capacitor Banks

Back to back switching of grounded Wye shunt capacitors cause high frequency, high magnitude current flow in overhead bus and ground mat conductors. Measurements of induced voltages on control cables and receptacles, transverse voltages on fuse blown PT secondaries and personnel intercept voltages are reported. BPA methods of confining transients to capacitor areas and shielding techniques are reviewed.

Shunt Capacitor Switching EMI Voltages, Their Reduction in Bonneville Power Administration Substations

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Reduction of capacitor switching transients by controlled closing

Station capacitor bank energization transients predicted by a circuit model are compared to field test results. Selection of a suitable model is discussed. A computer solution of the model is presented.

Station Capacitor Switching Transients - Analytical and Experimental Results

High-energy transients or faults cause failures in low voltage substation equipment such as solid-state relays, remote terminal units, or communication equipment. Sometimes, due to these influences, relays operate erroneously causing interruptions that were not called for. Operational problems resulting from the failed equipment also include loss of audio/video signals and data transmission. The overvoltages may even destroy the protective devices such as gas discharge tubes or metal oxide varistors. The objective of this paper is to present protection guidelines that address the above concerns and prevent the electronic equipment failures in substations. Test methodologies and data supporting these guidelines are also presented. The specific areas of focus include grounding and shielding practices for substation control and communication cables.

Protection of electronic equipment in a substation environment

Induced control circuit transients from energizing the first 230-kV shunt capacitor banks at Pinnacle Peak Substation damaged solid-state devices, caused flashovers at terminal blocks and initiated false supervisory control indications. Simulated, reduced voltage and full voltage switching of 230-kV capacitors were performed to explore the transient problem. The nature of the transient, its transfer mechanism to control circuits, how to reduce it at the source, and how to improve immunity of control circuits to the transient were studied. Simulation tests used actual power circuits in an inservice substation, which were impulsed at 20 kV. Reduced voltage tests were made on an isolated system at 30-50% voltage. Full voltage tests were made on a 230-kV interconnected system. Plastic-jacketed and lead- sheathed control cables and copper-braid- shielded coaxial cable specimens in a variety of grounding and shielding techniques were tested. Radio frequency, electromagnetic and electrostatic components of control circuit transients were measured separately. Transients up to 7,500 volts on unshielded cables were indicated, and frequencies-from 6-80 kHz and 0.4-7 MHz were recorded. Power circuit lumped parameter oscillations and distributed parameter propagation and reflection-type transient components were observed. Unshielded control cables were protected by grounding spare conductors and aluminum trench covers, paralleling two No. 4/ 0 bare ground cables, and installing 0.1 ?F bypass capacitors. Switches with 1 602 resistors per phase were used to suppress transients at the source. With these measures, control circuit transients were reduced to 65 volts for energizing 230-kV capacitors on an interconnected system.

R. E. Harris

Papers

Exploration of Transients by Switching Capacitors