Abstract:

Modern 1140V underground coal mine electrical networks are characterized by operation of a large amount of asynchronous motors with power up to hundreds kW. When touching one-phase of the network, the power supply will disconnect after protective relay system operates. However, leakage current through human body still exists, which has done by back-electromotive force of the high power motors. The quantity of electricity through human body caused by that current is many times larger than the safe value, and it can cause death or injury from electric shock. To effectively reduce influence of the back-electromotive force of the motors on the leakage current, most effective solution is automatic connected small value resistance from the leakage phase and ground.