The number of poles in a motor refers to the number of magnetic poles in each phase of the motor . The number of poles corresponds to the rotational speed. A 2-pole motor has a rotational speed of approximately 3000 rpm, a 4-pole motor has a rotational speed of approximately 1500 rpm, and a 6-pole motor has a rotational speed of approximately 750 rpm.
What is the number of poles in an electric motor?
The "number of poles" in a three-phase asynchronous motor refers to the number of magnetic poles in the stator magnetic field. Different connection methods of the stator windings can result in different numbers of poles in the stator magnetic field. The selection of 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 motor speed.
The motor speed = 60f/p, which is 60 multiplied by the motor frequency and divided by the number of pole pairs. From this formula, it's easy to see that the more poles, the lower the speed; the fewer poles, the higher the speed.
A three-phase AC motor generates N and S magnetic poles in each coil group. The number of magnetic poles in each phase of the motor is called the pole number. Since magnetic poles appear in pairs, motors are classified as 2-, 4-, 6-, 8-, etc. In China, the power frequency is 50 Hz. The synchronous speed for a 2-pole motor is 3000 r/min, for a 4-pole motor it is 1500 r/min, for a 6-pole motor it is 1000 r/min, and for an 8-pole motor it is 750 r/min. The windings must move back and forth to form a circuit, which is the number of pole pairs. These windings generate a magnetic field when current flows through them, resulting in magnetic poles. The current in a motor is only related to its voltage and power.
How are the pole numbers of an electric motor classified?
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 levels of 2800-3000 RPM
Four-pole 1400-1500 RPM
Level 6 900-1000 RPM
If it is greater than or equal to eight poles, it will be less than 760 revolutions per minute.
Methods for identifying magnetic poles
1. Observe the speed. For example, 1430 r/min is actually 1500 rpm. According to the speed formula: speed = time (60 seconds) ÷ frequency (50 Hz) divided by the number of magnetic pole pairs. One magnetic pole pair is 2 poles. Therefore, we can calculate that 3000 ÷ 1500 = 2 magnetic pole pairs, which is a 4-pole motor.
2. Checking the model number is even more direct: For example, the motor model is Y80M-4Y → a three-phase asynchronous motor. The product name codes for three-phase asynchronous motors also include: YR for wound-rotor asynchronous motors; YB for explosion-proof asynchronous motors; and YQ for high starting torque asynchronous motors. 80 → center height of the frame (mm); M → frame length code; 4 → number of poles.
3. Asynchronous motors are indicated by prefixes starting with YB, YR for squirrel-cage type and YA for increased safety type, followed by the center height and number of poles. For example, YR400-45606KV indicates an asynchronous squirrel-cage motor with a center height of 400mm, 4 poles, a rated power of 560KW, and a rated voltage of 6KV.
