Why should three groups of grounding be used in underground mobile substation of coal mine?

Safer. The underground mobile substation of coal mine is designed for underground power supply. It sends high-voltage electricity to the coal mine underground, and after the transformer is transformed and stepped down, it supplies all kinds of underground equipment. In order to prevent the current from flowing back normally due to electrical system failure, grounding operation must be carried out, and three groups of grounding are usually adopted, namely "star triangle grounding". This grounding method leads the current in the circuit to the earth by connecting the three phases to the grounding rod and AC neutral point respectively, thus achieving the purpose of safety.