When phase commutation especially the load is higher, transient state process shall occur on AC circuit due to instinct characteristics of rig123.net' target='_blank'>SCR rectifier. Thus, over-voltage occurs on the rig123.net' target='_blank'>SCR input end. All these over-voltage refer to peak voltage, but SCR elements are damaged, which are usually eliminated by using varistor, namely the surge suppression circuit.

Composition of system elements: varistor, fuse and indicator light.