Starting torque requirements of machines and motor loads

Part 2 of five. What the driven machine demands from the motor during starting, and why breakaway torque is only the beginning of the requirement.

The requirement begins with breakaway torque, but it does not end there. Once the load is moving, the motor has to keep producing more torque than the machine demands. The difference between the two is all that is available to accelerate with. Different machines make almost opposite demands. A punch press driving a flywheel is high inertia with low work torque. A centrifugal fan needs torque rising with the square of speed.

Inside:

• Work torque, acceleration torque and breakaway torque
• Worked examples: punch press, fan, compressor and flywheel
• Why high inertia changes starting time without changing breakaway torque
• Equations for full-load torque, acceleration torque and reflected load inertia