In the context of AC (alternating current) motor operation, "slip frequency" refers to the difference in frequency between the synchronous speed of the motor and the actual operating speed. To understand this concept, let's break down a few key terms:
Synchronous Speed: Synchronous speed is the theoretical speed at which the rotating magnetic field produced by the motor's stator windings would rotate if there were no load or slip. It is determined by the frequency of the AC power supply and the number of poles in the motor. For a motor with 'P' poles, the synchronous speed (Ns) is given by the formula:
Ns = 120 * Frequency (Hz) / P
Where 120 is a constant that converts frequency to speed in RPM.
Operating Speed: The actual speed at which the motor operates under load conditions.
Slip: Slip is the relative difference between the synchronous speed and the actual operating speed of the motor. It is expressed as a percentage or a fraction of the synchronous speed. Slip is necessary for the motor to develop torque, as torque is generated due to the interaction between the rotating magnetic field (produced by the stator) and the rotor.
Slip (%) = ((Ns - N) / Ns) * 100
Where N is the actual operating speed of the motor.
Slip Frequency: Slip frequency is the frequency of the electrical currents induced in the rotor bars of an induction motor due to the slip. It is proportional to the difference between the frequency of the stator's rotating magnetic field (determined by the AC power supply frequency) and the actual frequency of the rotor's movement (which is slightly slower due to the slip).
Slip Frequency (fslip) = Frequency (f) * Slip
In summary, slip frequency represents the frequency of the electrical currents generated within the rotor of an AC induction motor due to the difference between the synchronous speed and the operating speed. This slip frequency is a key factor in understanding the behavior and performance characteristics of AC motors, especially in terms of torque production and efficiency.