The slip of an AC induction motor is a measure of the difference between the synchronous speed of the rotating magnetic field produced by the stator and the actual rotor speed. It's an important parameter for understanding the motor's performance characteristics, efficiency, and torque production. Slip is typically expressed as a percentage.
The formula to calculate slip is as follows:
Slip (%) = [(Ns - Nr) / Ns] * 100
Where:
Ns is the synchronous speed of the motor's rotating magnetic field (in revolutions per minute or RPM).
Nr is the rotor speed of the motor (in RPM) during normal operation.
The synchronous speed (Ns) of an AC induction motor is determined by the frequency of the power supply (f) and the number of poles (P) in the motor. It can be calculated using the following formula:
Ns = (120 * f) / P
Where:
Ns is the synchronous speed in RPM.
f is the frequency of the power supply in Hertz (Hz).
P is the number of poles in the motor.
Keep in mind that slip is a crucial factor in determining the torque output of the motor. As slip increases, the torque produced by the motor increases as well, until it reaches its maximum value at a certain point. Beyond that point, further increase in slip can lead to reduced torque production and potentially stall the motor.
It's worth noting that slip is a relative measure and indicates the deviation from synchronous speed. Therefore, slip is only relevant when the motor is operating under load conditions and not when it's running with no load.
In practical applications, slip is used to analyze and design motor systems, determine operating conditions, and assess motor efficiency.