Investigation of transient processes of overvoltages in transformer neutral

Neutral of major part of power transformers in electrical energy system with effectively earthed neutral is isolated. Isolated neutral is protected by valve-type arresters or lately by surge arresters. As a result travelling wave of lightning discharge to the line electromagnetic impulse is coming to transformer causing overvoltages in transformer neutral. If protective characteristics of surge arrester are improperly coordinated with insulation then insulation is broken in the area of neutral. This paper analyses character of transient processes and operating conditions of surge arresters in switchgear and it´s influence to insulation of transformer.