Reducing transformer inrush current during energization

The Point-on-Wave switching function is used to reduce increased electrodynamic and dielectric loads which are caused by non-optimal switching of circuit breakers in the network. These loads reduce the reliability and life of the equipment installed in the network or in extreme cases, lead to unnecessary opening operations by the protection device. To avoid effects such as over voltages and inrush currents, this function can control the closing and opening instants of circuit breakers. The PoW switching function is always started via a control command, either from the device’s internal control or from an external control function.

Protection functions generally directly trip the circuit breaker and have no interaction with the PoW switching function. On large transformers the inrush current during energization is detrimental to the power system and the service life of the transformer. By timing the close command in each phase of the circuit breaker it is possible to minimize the inrush current and the transient over-voltage.