Slip, in the context of an AC induction motor, refers to the difference between the synchronous speed of the rotating magnetic field produced by the stator and the actual speed of the rotor. AC induction motors operate based on the principle of electromagnetic induction. The stator generates a rotating magnetic field due to the alternating current, and this magnetic field induces currents in the rotor, causing it to turn.
The synchronous speed
synchronous
N
synchronous
of the rotating magnetic field is determined by the frequency
f of the AC power supply and the number of poles
P in the motor:
synchronous
=
120
×
N
synchronous
=
P
120×f
Where:
synchronous
N
synchronous
= Synchronous speed in revolutions per minute (RPM)
f = Frequency of the AC power supply in hertz (Hz)
P = Number of poles in the motor
However, due to various factors such as load, friction, and losses, the rotor cannot keep up with this synchronous speed. As a result, the actual speed of the rotor
actual
N
actual
is always slightly less than the synchronous speed. The slip (
S) is defined as the difference between the synchronous speed and the actual speed of the rotor, expressed as a fraction or a percentage:
=
synchronous
−
actual
synchronous
S=
N
synchronous
N
synchronous
−N
actual
Slip percentage
=
×
100
%
Slip percentage=S×100%
The slip is a critical parameter in AC induction motors because it directly affects the motor's performance, efficiency, and ability to deliver torque. At no load (when there is no external resistance), the slip is minimal, and the motor approaches its synchronous speed. As the load on the motor increases, the slip also increases, resulting in a decrease in speed and efficiency.
Slip is an essential consideration in various applications that use induction motors, such as industrial machinery, pumps, fans, and conveyor systems. By understanding and controlling slip, engineers can design and operate these motors efficiently for specific tasks and operating conditions.