AC Theory

It is the speed of the magnetic field produced in the stator windings

It is the difference between synchronous speed and the actual speed of the rotor

At lower voltages, the slip speed is greater and the overall speed of the magnetic field is therefore lower. Likewise, if the voltage is higher, the slip will be lower and the speed of the magnetic field will be higher

4%

Starting torque will be high

-In the textile industry, a normal squirrel caged motor is used for starting a spinning frame. The peak torque obtained during acceleration can break the thread because of snatch. A double cage motor usually overcomes its difficulty

-It is also an advantage as a drive for conveyor belts that may be stopped, fully loaded. The motor supplies the necessary high starting torque to get the belt underway again

• -Heat losses caused by resistance of the windings
• -Magnetising the poles peices and eddy current losses in steel laminations
• -Friction due to air movement (Windage)
• -Bearing friction

At high speeds and low slip

Normal loading 

The current increases and therefore increases heat

The torque produced by a motor is determined by the motor load. A small drop in supply causes a large drop in motor torque which increases motor current. This increase in current can lead to motor burnout 

The motor will run as a single phase motor and will gradually burn out