Could anyone one please explain how the available torque for an AC motor varies with speed?
There are many many different types of AC motors so you really need to specify which type of motor you are referring to. However I'll assume the 3-phase squirrel-cage induction motor as this is one of the most commonly used. It has a moderate starting torque (at zero rpm), then the available torque increases as speed increases until just before synchronous speed (= the AC supply frequency) when it reaches the maximum drop-out torque. Torque then drops rapidly to zero at synchronous speed. Beyond synchronous speed the motor can develop negative torque - where it can function as a generator instead of a motor!
In essence: Frequency controls velocity. For a frequently used form AC motor, 50Hz will reason it to rotate on the cost on it is score plate, frequently 1440 RPM or 720 RPM. various the frequency up or down will reason the cost to alter form of in share. course is basically area sequence. change any 2 wires out of the three ranges and the area rotation is reversed. Torque is controlled (constrained) by using the attainable present day, that's circuitously controlled by using the utilized voltage and frequency. At 50Hz, and without present day limits, the motor could artwork at something as much because it is rated torque without important velocity loss. If the attainable present day became into constrained to eg. 50% of the motor score, the cost will drop off or the motor will stall at approximately 50% of it is rated torque etc. issues are somewhat greater complicated once you besides could variety the frequency, because of the fact the motor torque will drop progressively with decrease frequencies inspite of finished present day attainable. The winding impedance drops because of the fact the frequency is going down and it many times will become much less efficient, all the way down to effectively 0 torque/skill at close to DC. (AC Servo autos are a particular case, they generally have an eternal magnet rotor extremely than a squirrel cage, so torque could nicely be utilized at 0 velocity. in addition they have an inner place sensor to permit the optimal container orientation to be created interior the stator for any given rotor place).
Electrical Motor Torque Equation Torque can be calculated in Imperial units like T = Php 63025 / n where T = torque (in lbf) Php = horsepower n = revolution per minute (rpm) Alternatively Tft = Php 5252 / n (1b) where Tft = torque (ft lbf) Torque can be calculated in SI units like T = PW 9.554 / n where T = torque (Nm) PW = power (watts) n = revolution per minute (rpm)
