Basic Principles of AC induction motors - FläktGroup

Considering that the short-circuited rotor windings have little resistance, even a little slip induces a large present in the rotor and produces substantial torque. At full rated load, slip varies from more than 5% for small or unique purpose motors to less than 1% for large motors. These speed variations can trigger load-sharing problems when differently sized motors are mechanically connected.

Standard torque [modify] Speed-torque curves for four induction motor types: A) Single-phase, B) Polyphase cage, C) Polyphase cage deep bar, D) Polyphase double cage Normal speed-torque curve for NEMA Style B Motor Short-term solution for an Air Conditioner induction motor from a total stop to its operating point under a differing load.

Suitable for most low performance loads such as centrifugal pumps and fans, Style B motors are constrained by the following typical torque varieties: Breakdown torque (peak torque), 175300% of rated torque Locked-rotor torque (torque at 100% slip), 75275% of ranked torque Pull-up torque, 65190% of rated torque. Over a motor's normal load range, the torque's slope is approximately linear or proportional to slip due to the fact that the worth of rotor resistance divided by slip, R r/ s \ displaystyle R _ r '/ s, dominates torque in a direct manner.

As the load torque increases beyond breakdown torque the motor stalls. Starting [edit] There are three standard types of small induction motors: split-phase single-phase, shaded-pole single-phase, and polyphase. In two-pole single-phase motors, the torque goes to zero at 100% slip (absolutely no speed), so these require alterations to the stator such as shaded-poles to supply beginning torque.

The normal running windings within such a single-phase motor can trigger the rotor to turn in either direction, so the beginning circuit figures out the operating direction. Look At This Piece in shaded pole motor. In specific smaller sized single-phase motors, starting is done by ways of a copper wire turn around part of a pole; such a pole is referred to as a shaded pole.

This imparts sufficient rotational field energy to start the motor. These motors are generally used in applications such as desk fans and record gamers, as the required beginning torque is low, and the low performance is tolerable relative to the decreased cost of the motor and starting approach compared to other A/C motor designs.