Voltage sags and swells occur on the electric network while switching inductive loads such as shunt reactors, power transformers and high-power motors and during operation of arc furnaces which work with the principle of short circuit. Voltage protection relays detect voltage sags and swells as a failure and may disable the load in an uncontrolled manner. Voltage sags and swells may also cause stress on the load insulation on the electric network, loss of operating life and even serious damages.

In order to attenuate the transient voltage that occur during the commissioning of such loads of inductive character, the snubber capacitor which do not allow sudden changes in the voltage and the series-dependent damping resistance are used. RC snubber filters are connected parallel to the network as close as possible to the load causing transient voltage. During the transient voltages occurring at high frequencies, the RC filters’ impedance decreases to low value, prevent over-voltage of the mains voltage and damp the oscillation very soon.