Starting Torque of a Motor

How can we calculate the starting Torque required/experienced by an AC Induction Motor.

Starting torque required – This is the torque that the motor can develop during the starting. This can be found by the motor torque characteristic curve.

Starting torque experienced – It is the load (driven equipment) torque experienced by the motor. It depends on the size and type of the load coupled to the motor during start. Generally the driven equipment's manufacturer provides the torque versus speed curve for the load. See the link (http://www.electricity-today.com/et/issue0303/motor_torque_reqs.pdf) to find a simple way to find the load torque.

The required starting torque of a motor must be higher than the load torque. The difference (motor starting torque – load starting torque) is called the accelerating torque. The motor starting time depends on the accelerating torque. The accelerating torque should be such that the starting time of the motor should not be 10 seconds. See the link (http://www.pdhcenter.com/courses/e121/e121content.pdf) for calculating the starting time.

Also see the link http://www.eng-tips.com/faqs.cfm?fid=1131

How can we calculate the no load current that should be drawn by the motor (any thumb rule or a rough estimate).

The rule of thumb is that the 'no load current' is 1/3 of 'full load current'

See the previous threads:

http://cr4.globalspec.com/thread/41616

http://cr4.globalspec.com/thread/36784

- MS