Starting high inertia loads on adjustable speed drives

In a cement mill there are applications that require high starting torques like draft inducer fans and ball mills. Sometimes a larger motor is required just to give enough starting torque to accelerate the load. This paper reviews how adjustable speed drives can be used to give high starting torque on a motor sized for running torque, not starting torque, with a side benefit of low starting current. This allows the user to install a smaller motor-one sized for running the load, not starting it-and gives adjustable speed capability for process flow control and speed control. While accelerating high starting torque loads is the subject of this paper, the same principles can be used to maximize the starting torque with a certain drive size (maximum torque for a given amps rating of the ASD).