The number of motor poles is the number of magnetic poles in each phase of the motor. The number of poles corresponds to the speed. The speed of 2 poles is about 3000 rpm, 4 poles is 1500 rpm, and 6 poles is 750 rpm.

What is the number of poles of a motor?

The "number of poles" of a three-phase asynchronous motor refers to the number of magnetic poles in the stator magnetic field. Different connection methods of the stator winding can form different numbers of poles in the stator magnetic field. The number of poles of the motor is determined by the speed required by the load, and the number of poles of the motor directly affects the speed of the motor.

Motor speed = 60f/p, which is 60 times the motor frequency divided by the number of motor pole pairs. According to the formula, it is not difficult to see that the more stages, the lower the speed, the fewer poles, and the higher the speed.

Each set of coils in a three-phase AC motor will produce N and S poles, and the number of poles contained in each phase of each motor is the number of poles. Since the poles appear in pairs, the motor has 2, 4, 6, 8... poles. In China, the power frequency is 50 Hz, the 2-pole synchronous speed is 3000r/min, the 4-pole synchronous speed is 1500r/min, the 6-pole synchronous speed is 1000r/min, and the 8-pole synchronous speed is 750r/min. The windings come and go to form a loop, that is, the number of magnetic poles, which appear in pairs. Pole means magnetic pole. When current passes through these windings, a magnetic field will be generated, and there will be corresponding magnetic poles. The current of the motor is only related to the voltage and power of the motor.

How is the number of poles of the motor divided?
Two poles are called high-speed motors, four poles are medium speed, six poles are low speed, and greater than or equal to eight poles are called ultra-low speed. Two-pole 2800-3000 rpm Four-pole 1400-1500 rpm Six-pole 900-1000 rpm Greater than or equal to eight poles are lower than 760 rpm.

Method of identifying magnetic poles
1. Look at the speed. For example, the actual synchronous speed of 1430r/min is 1500 rpm. According to the speed formula: speed = time (60 seconds) & TImes; frequency (50HZ) divided by the number of magnetic pole pairs. One magnetic pole pair is 2 poles, so we can calculate 3000÷1500=2 magnetic pole pairs, which is a 4-pole motor.
2. Look at the model, it is more direct: for example, the motor model is Y 80M- 4 Y → three-phase asynchronous motor, among which the product name codes of three-phase asynchronous motors are: YR is a winding asynchronous motor; YB is an explosion-proof asynchronous motor; YQ is a high starting torque asynchronous motor. 80 → center height of the base (mm) M → base length code 4 → number of magnetic poles
3. The asynchronous motor starts with YB, the squirrel cage type is YR, the increased safety type is YA, and then the center height and the number of poles. For example, YR400-4 560 6KV is an asynchronous squirrel cage motor with a center height of 400mm, a number of poles of 4 poles, a rated power of 560KW, and a rated voltage of 6KV.
How to determine the number of poles of the motor
When the nameplate is lost and the number of poles of the original asynchronous motor is unknown, the current μA range of the multimeter can be used for testing and judgment. The method is: open the junction box of the motor, remove the original power cord and the star or triangle wiring, and use the R×100Ω range of the multimeter to find the two leads of any phase winding from the 6 motor leads. Then turn the range switch of the multimeter to the current μA range, and replace the test lead with an alligator clip and firmly clamp it on the two leads of the winding found above. Use your hand to slowly and evenly rotate the motor pulley or shaft for one circle, and carefully observe the number of swings of the multimeter pointer.
Each swing of the multimeter pointer indicates that the current in this phase of the winding changes once, so the number of poles of the motor can be determined.
This method uses the fact that when the rotor of an asynchronous motor rotates at a constant speed for one circle, the residual magnetic flux of the rotor cuts the stator winding and induces a small induced electromotive force, thereby generating current and causing the multimeter pointer to swing.
It is worth mentioning that when the motor that has not been used for a long time is tested using the above method, the multimeter pointer may not respond at all. This is because the residual magnetism of the motor has disappeared. At this time, as long as the motor is connected to the power cord in a regular way and powered on for a few minutes, the stator winding of the motor will obtain residual magnetism after the power is turned off, and then the above method can be used to determine its number of poles.