What Is A Permanent Magnet AC Motor?
The vast majority of AC induction motors use no magnets, so why in the title we said a permanet magnt AC Motor?
A Permanent Magnet AC Motor has permanent magnets either attached to the surface of or embedded within the rotor lamination stacks of an induction motor. This allows for synchronous operation of the motor, which eliminates the rotor “slip” inherent in conventional AC induction motors and produces better efficiency over a wider speed range, while offering more precise speed control. In addition, losses inherent in typical AC induction aluminum conductor bars are eliminated. The net result is a more power-dense, higher efficiency motor as in the illustration below.
The cutaway above shows the typical construction elements of an AC induction motor’s rotor — the kind found in 90+% of applications over one horsepower. It uses what is called a “squirrel cage” rotor because aluminum conductor bars are die cast into the slots of the stack of steel laminations that make up the rotor. The diecast conductor bars, which can also be copper, can be eiher parallel or skewed as in the above example. When you take away the laminations, it becomes obvious where the name comes from.
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