A surge isolation transformer (SIT) is a transformer that mainly consists of isolation transformers (separates the primary and secondary windings) and SPDs (lightning arresters). SIT suppresses lightning surges that enter the power line with a SPD (lightning arrester) built into the transformer and is highly resistant to lightning due to the high insulation of the primary and secondary windings of the transformer and the effect of attenuating lightning surges. The SIT offers better more effective protection than only using an SPD.