The illustration shows a typical torque/speed curve. For those unfamiliar with torque terminology, the following brief explanations may be helpful. Here, we provide an account of the various terms used to describe the torque curve of an AC motor.
Starting torque (ST) / Locked-rotor torque (LRT): The torque produced when power is applied to a motor at rest, i.e. when the motor is energised at full voltage and the shaft is locked in place. This is the torque used to start accelerating the load.
Pull-up torque (PUT): This term is used for the lowest point on the torque speed curve for a motor which is accelerating a load up to full speed. Most Grundfos motors do not have a separate pull-up torque value, as the lowest point is found at the locked-rotor point. As a result, pull-up torque is the same as starting torque/ locked-rotor torque for the majority of all Grundfos motors.
Breakdown torque (BT): The maximum torque that an AC motor develops with rated voltage applied at rated frequency without causing sudden drops in speed. This is also known as pull-out torque or maximum torque.
Full-load torque (FLT): The torque required to produce rated power at full-load speed.
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