A single-phase preventer is used to protect the induction motor from a single phasing fault. Single phasing is a very dangerous fault to the electrical motor and Which damages the motor stator winding rapidly. Generally, single phasing is nothing but a motor runs at one of the supply is separated due to the open circuit or improper contact in a switch or other electrical equipment failure. Normally, the motor runs with the three-phase supply and which brings balance currently in each phase winding. Analyze one of the fuses has blown. But the machine still in a rotating position which tries to rotate at the same speed. At that same time, the need phase current will be shifted to the remaining live phases. Therefore, specific current in the other phases increases up to 3 times its normal value instantly. This is called a single phasing fault.