Number of motor poles

In the factory, often hear say: “How many poles of the motor?”
To understand, we must first know what is the concept of pole: pole refers to the generator rotor in the rotor coil into the excitation current after the formation of magnetic poles. Simply put is the rotor every turn in the stator coil of a turn can be induced to form a few cycles of current different poles to produce 50hz potential will require different speeds.
(50HZ * 60 seconds / minutes (i.e., 3000) divided by the number of poles is the number of revolutions per minute motor) motor is the same reason, just a generator of an inverse process.
The number of poles reflects the synchronous speed of the motor. 2-pole synchronous speed is 3000r/min, 4-pole synchronous speed is 1500r/min, 6-pole synchronous speed is 1000r/min, 8-pole synchronous speed is 750r/min.
Number of Motor Poles
The number of motor poles determines the synchronous speed of the motor.
Example: 4-pole motor
4-pole motor motor 1 minute synchronous speed = {frequency of the power supply (50Hz) × 60 seconds} ÷ (number of stages of the motor ÷ 2) = 3000 ÷ 2 = 1500 rpm can be interpreted in this way: 2 poles is the base (for 3000), 4 poles can only be divided by 2, 6 poles will be divided by 3, and 8 poles will be divided by 4. Rather than saying that the 2 poles have to be removed from the 2 with 3000, the higher the number of pairs of poles of the motor, the lower the motor’s speed, but the higher its torque. The more pairs of poles in a motor, the lower the speed of the motor, but the greater its torque.
When selecting a motor, you need to consider how much starting torque the load requires. For example, a motor that starts with a load requires more torque than one that starts with no load. If it is a high-power large load start, but also consider the reduced voltage start (or star-delta start); as for the decision of the number of motor poles and the load after the speed matching problem, it can be considered with a different diameter of the pulley to drive or with a variable-speed gear (gear box) to match. If due to the decision of the number of motor pole pair after the belt or gear drive cannot reach the power requirements of the load, then we must consider the use of motor power problems.

A three-phase AC motor is mainly composed of a stator and a rotor. When a three-phase AC current is passed through the stator, a rotating magnetic field is generated. The magnetic field always has two poles (which can also be said to occur in pairs), the N pole (north pole) and the S pole (south pole), also known as a counterpole. When the stator windings of an AC motor are wound differently, the number of poles of the rotating magnetic field produced is different. The number of magnetic poles directly affects the rotational speed of the motor, and they are related by the formula: synchronous rotational speed = 60 × frequency / number of pairs of stages. If the synchronous speed of the motor is 1500 rpm, the number of pole pairs can be calculated according to the above formula is 2, that is, it is a 4-pole motor. Synchronous speed and the number of poles are the basic parameters of the motor, which can be found on the nameplate of the motor. Because the number of poles can affect the speed of the motor, can be used to change the number of poles of the motor to change the speed of the motor.
For fans, pumps class fluid loads, such loads have a more prominent feature, with the proverb called resistance to sudden changes, that is, such loads on the current situation of sudden changes in the resistance generated by a large. Although to promote such loads need to change the torque is not high, but want to change the status quo more quickly will require a lot of energy, a little as boiling water, small fire can boil, to quickly boil may require the fire will be very large.
Given the size of the frequency and the size of the starting current is not necessarily related to the size of the starting current depends on the start of the V / F curve settings and the length of the acceleration time, for fluid loads, because the torque required during operation is not required to be constant, so the use of multiple power of the curve can be made more energy efficient operation of the equipment to bring economic benefits to the user.
Recognition method
1. Look at the rotational speed. Such as 1430r/min actual synchronous speed is 1500 rpm, by the speed formula: speed = time (60 seconds) × frequency (50HZ) divided by the number of magnetic pole pairs of a magnetic pole pair of 2 poles, from which you can calculate 3000 ÷ 1500 = 2 magnetic pole pairs, that is, 4-pole motor.
2. Look at the model number. More directly: for example, the motor model is Y 132 M- 4 Y → three-phase asynchronous motor, which three-phase asynchronous motor product name designation: YR for wire-wound asynchronous motor; YB for explosion-proof asynchronous motor; YQ for high starting torque asynchronous motor. 132 → the center of the seat height (mm) M → the length of the seat designation 4 → the number of magnetic poles. The asynchronous motor starts with YB, squirrel cage type is YR, increased safety type is YA, and then the center height and the number of poles, for example, YR400-4 560 6KV, which is an asynchronous squirrel cage motor with the center height of 400mm, the number of poles of 4 poles, the rated power of 560KW, and the rated voltage of 6KV.
Selection of the number of poles method 
The power of the motor is approximately equal to the pump power divided by the pump efficiency divided by the motor efficiency. Motor efficiency is generally 0.85, you correspond to the motor power told you were 5.5KW, 15KW, the speed is 2900, then the motor was 5.5KW-2P and 15KW-2P, the motor’s rotational speed = (frequency × 60S ÷ number of sections of the motor) × 2 
For example, the choice of pump motor: the choice of the number of poles should be selected according to the rated speed of the pump, 2900r/min to select 2 poles, 1450r/min to select 4 poles, 970r/min to select 6 poles and so on.