Calculate size of each part of DOL motor starter for the system voltage 415V, 5HP three phase house hold application induction motor, code A, motor efficiency 80%, motor RPM 750, power factor 0.8 and overload relay of starter is put before motor.
Basic Calculation of Motor Torque and Current
- Motor Rated Torque (Full Load Torque) = 5252xHPxRPM
- Motor Rated Torque (Full Load Torque) = 5252x5x750 = 35 lb-ft.
- Motor Rated Torque (Full Load Torque) = 9500xKWxRPM
- Motor Rated Torque (Full Load Torque) = 9500x(5×0.746)x750 = 47 Nm
- If Motor Capacity is less than 30 KW than Motor Starting Torque is 3xMotor Full Load Current or 2X Motor Full Load Current.
- Motor Starting Torque = 3xMotor Full Load Current.
- Motor Starting Torque = 3×47 = 142Nm.
- Motor Lock Rotor Current = 1000xHPx figure from below Chart/1.732×415