DOL Panel

When the contactor is first turned on, the windings get the entire line voltage. For a brief while, the motor will draw a high inrush current due to the magnetic field in the iron, but after that, the motor’s Locked Rotor Current will restrict the current. When the motor reaches Locked Rotor Torque, the acceleration begins. To see a considerable reduction in power, you’ll need to crank up the motor’s speed to roughly 85-75% of the motor’s synchronous speed. Motor design and terminal voltage determine the beginning current curve, which is completely independent of the motor load The time it takes for the motor to accelerate to full speed and hence the duration of the high beginning current will be affected by the motor load, but not the size of the starting current. At all speeds throughout the start-up cycle, if the motor’s torque exceeds the load torque, the motor will attain maximum speed. At any point in the start cycle, if the motor’s torque output is less than the load’s torque, the motor will cease accelerating. If a DOL starter’s starting torque is inadequate, a new motor with a greater starting torque must be installed. The acceleration torque is the motor torque minus the load torque, and it changes as the motor accelerates according to the motor speed torque curve and the load speed torque curve. The accelerating torque and the load inertia affect the start time.