2 Pole vs 4 Pole Motors
A motor is an electric device that converts electrical energy into mechanical energy, specifically in the form of torque delivered through a shaft. The motors operate on the principle of electromagnetic induction as described by Michael Faraday.
A motor that contain two poles (or a single pair of magnetic poles north and south) are said to be a 2-pole motor. Often stator windings are the north and south poles. Number of stator windings can give any reasonable number of poles ranging from 2 to 12. Motors with more than 12 poles are available, but they are not in common use.
The synchronous speeds of the motors are directly dependent on the number of poles as given in the following expression
Synchronous speed of the motor = (120×frequency)/(number of poles)
Therefore, the speed of a 2 pole motor connected to the main power has 3000 RPM synchronous speed. With the rated load, operating speeds may decrease to about 2900 RPM due to both slip and load.
In two pole motors, the rotor turns 1800 in half the cycle. Therefore, on one cycle of the source, rotor makes one cycle. The amount of energy used is relatively low in two pole motors, and the torque delivered is also low.
A motor that contains four poles in the stator (or two pairs of magnetic poles) in alternating order; N > S > N > S. The synchronous speed of a four pole motor connected to the mains power is 1500 RPM, which is half the speed of the 2-pole motor. With the rated load, operating speeds can decrease to a value around 1450 RPM.
In four pole motors, the rotor turns 900 for every half cycle. Therefore, the rotor completes 1 cycle for every two cycles of the source. Hence the amount of energy consumed is twice the amount of 2 pole motor and theoretically delivers twice the torque.
What is the difference between 2-Pole Motor and 4-Pole Motor?
2 pole motor has two poles (or a single pair of magnetic poles) while 4 pole motors have four magnetic poles in alternating order.
2 pole motors have twice the speed of a 4 pole motor.
Rotor of the 2 pole motor complete one cycle for every cycle of the source, while the rotor of the 4 pole motor completes only half a cycle for every single cycle of the source.
Therefore, 4 pole motors consumes twice the energy of the 2 pole motors.
Theoretically, 4 pole motors deliver twice the work output than 2 pole motors.