Analysis of the amplitude and frequencies of the voltage magnification transients in distribution networks due to capacitor switching

This paper addresses the possible voltage magnification at the terminals of low voltage shunt-compensated customer loads due to the switching of utility capacitors on the high voltage side of the supplying transformer and feeder. A closed-form expression is derived for the expected voltage magnification. The simulation results using the analytical expressions were found to be in good agreement with those published elsewhere using the sophisticated EMTP program. Expressions are also presented for the expected frequencies of the transient voltage stresses. Moreover, it could be realized that there are identifiable ranges or combinations of the network parameters that can lead to excessive amplitudes of the network overvoltage transients, and to frequencies that can coincide with one or more of the network harmonics. The main affecting parameters are found to be: 1. The preswitching level of the reactive power compensation of the considered low voltage load. 2. The rating of the additionally switched capacitor on the higher voltage level. 3. Both the kVA rating and the short-circuit impedance of the supplying transformer. 4. The short circuit level of the supply.