# What is the Number of Poles of the Motor and How to Divide the Number of Poles?

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

### What is the number of poles in a motor

The “number of poles” of a three-phase asynchronous motor is the number of poles of the specified sub-field. The stator windings are connected in different ways, which can form different pole numbers of the stator magnetic field. The number of poles selected by 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 = 60 f/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 series, the lower the speed, and the less the number of poles, the higher the speed.

Each set of coils of a three-phase AC motor will generate N and S magnetic poles, and the number of magnetic poles contained in each phase of each motor is the number of poles. Since the magnetic 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 3000 r/min, the 4-pole synchronous speed is 1500 r/min, the 6-pole synchronous speed is 1000 r/min, and the 8-pole synchronous speed is 750 r/min. The coming and going of the windings can form a loop, that is, the number of pairs of magnetic poles, which appear in pairs, and the poles mean the magnetic poles. When the 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 motor poles divided?

Two poles are called high-speed motors, four poles are medium-speed motors, six-poles are low-speed motors, and eight poles or more are called ultra-low-speed motors.

Two-stage 2800-3000 rpm

Level 6 900-1000 rpm

Greater than or equal to eight poles is less than 760 rpm.

### Magnetic pole identification method

1. Look at the rotation speed, such as 1430 r/min. The actual synchronous rotation speed is 1500 rotations. According to the rotation speed formula: rotation speed = time (60 seconds) & Times; frequency (50 HZ) divided by the number of magnetic pole pairs. A magnetic pole pair is 2 poles, so you can Calculate 3000÷1500=2 pole pairs, which is a 4-pole motor.

2. It is more direct to look at the model: for example, the motor model is Y 80 M- 4 Y → three-phase asynchronous motor, and the product name code of the three-phase asynchronous motor is as follows: YR is a wound asynchronous motor; YB is an explosion-proof asynchronous motor ; YQ is a high starting torque asynchronous motor. 80→The height of the center of the base (mm) M→The length code of the base 4→The 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, such as YR 400-4 560 6 KV, the center height of the asynchronous squirrel cage motor is 400 mm, and the number of poles is 4 poles, rated power 560 KW, rated voltage 6 KV.

### How to judge the number of motor poles

When the nameplate is lost and the number of poles of the original asynchronous motor is not known, the current μA range of the multi-meter can be used to test and judge. In the R×100Ω gear, from the 6 motor leads, find out the two leads of any one-phase winding. Then turn the range switch of the multi-meter to the current μA level, and change the test leads to alligator clips and firmly clamp the two leads of the windings found above. Rotate the pulley or shaft of the motor slowly and uniformly for one circle by hand, and carefully observe the number of times the pointer of the multi-meter swings.

Every time the pointer of the multi-meter swings, it means that the current in the winding of this phase changes once, so that the number of pairs of poles in the motor can be determined.

This method is to use the asynchronous motor when the rotor rotates at a constant speed, the residual magnetic flux of the rotor cuts the stator winding and induces a tiny induced electromotive force, which generates a current and makes the multi-meter pointer swing.

It is worth mentioning that when the motor has not been used for a long time, the multimeter pointer may not respond when the above method is used for testing. This is because the residual magnetism of the motor has disappeared. At this time, as long as the motor is connected to the power line according to the normal method, and the motor is energized for a few minutes, the stator winding of the motor will obtain residual magnetism after the power is turned off, and then the number of poles can be determined by the above method.

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