MOTOR PROTECTOR

PURPOSE:To discriminate between locking and stagnant starting of motor easily and positively by detecting voltage amount and current amount of motor, subjecting them to time shared analysis to produce a power factor amount and a current amount and then making a decision whether the power factor amount and the current amount are increasing or decreasing with time. CONSTITUTION:A power factor operating circuit 61 calculates a power factor amount based on a voltage amount and current amount of a motor and thus calculated power factor amount is then fed to a power factor amount storing circuit 62 where it is subjected to time shared analysis and stored therein. A power factor amount increase/ decrease deciding circuit 64 then makes a decision whether the power factor amount has increased or decreased based on the power factor amount stored at each time into the storing circuit 62. On the other hand, current amount is subjected to time shared analysis and stored in the storing circuit 63 and then a current amount increase/ decrease deciding circuit 65 makes a decision whether the current amount has increased or decreased. A protective circuit 66 then makes a decision whether the motor is in locked state or stagnant starting state based on the decision results from the decision circuits 64, 65 and delivers an alarm AL and an output TR for tripping a circuit breaker.