The suppression of switching transients by a shunt RC circuit

When apparatus incorporating shunt capacitance is suddenly switched across a low-impedance source of power through a short transmission line, an oscillatory transient over-voltage normally results. It is common practice to reduce this over-voltage by placing an RC circuit in parallel with the terminal apparatus. The behaviour of such a circuit is analysed in detail, and the conditions for the transient voltage to be non-oscillatory are deduced. It is proved that a damping circuit of this kind can never completely prevent the transient voltage from exceeding the normal working voltage, although it can reduce it greatly. The current through the switch can be made unidirectional¿an advantage where electronic switches are used. Numerical illustrations are given.