How to identify the number of motor stages

In factories, you often hear people ask, "What level is the motor?"

To understand, we must first know what poles are: poles refer to the magnetic poles formed by the generator rotor after the excitation current is passed through the rotor coil. Simply put, it means that each time the rotor rotates one circle, several cycles of current can be induced in one turn of the stator coil. Different pole numbers require different speeds to generate 50hz potential.

(50HZ*60 seconds/minute (i.e. 3000) divided by the number of poles is the number of revolutions the motor makes per minute.) The same principle applies to electric motors, which is just the reverse process of generators.

The number of poles reflects the synchronous speed of the motor. The synchronous speed of 2 poles is 3000r/min, the synchronous speed of 4 poles is 1500r/min, the synchronous speed of 6 poles is 1000r/min, and the synchronous speed of 8 poles is 750r/min.

Number of motor stages

The number of motor stages determines the synchronous speed of the motor.

Example: 4-pole motor 4-pole motor 1 minute synchronous speed = {power supply frequency (50Hz) × 60 seconds} ÷ (number of motor poles ÷ 2) = 3000 ÷ 2 = 1500 rpm It can be understood as follows: 2 poles are the base number (3000), 4 poles can only be divided by 2, 6 poles by 3, and 8 poles by 4. It does not mean that 2 poles also need to be divided by 3000. The more pole pairs a motor has, the lower the speed of the motor, but the greater its torque.

When choosing a motor, you need to consider how much starting torque the load requires. For example, starting with a load requires more torque than starting without a load. If it is a high-power and high-load start, you also need to consider step-down starting (or star-delta starting); as for the speed matching problem with the load after the number of motor pole pairs is determined, you can consider using pulleys of different diameters to drive or using variable speed gears (gearboxes) to match. If the power requirement of the load cannot be met after the belt or gear drive after the number of motor pole pairs is determined, then you need to consider the power of the motor.

The three-phase AC motor is mainly composed of a stator and a rotor. When three-phase AC is passed through the stator, a rotating magnetic field is generated. The magnetic field always has two poles (it can also be said to appear in pairs), namely the N pole (North Pole) and the S pole (South Pole), also known as a pair of poles. When the winding method of the AC motor stator winding is different, the number of magnetic poles of the rotating magnetic field generated is different. The number of magnetic poles directly affects the speed of the motor, and their relationship is: synchronous speed = 60×frequency/level logarithm. If the synchronous speed of the motor is 1500 rpm, then according to the above formula, the number of pole pairs can be calculated to be 2, that is, a 4-pole motor.

Synchronous speed and pole pair number are both basic parameters of the motor, which can be found on the motor nameplate. Because the pole pair number can affect the motor speed, the motor speed can be changed by changing the pole pair number of the motor. For fluid loads such as fans and water pumps, this type of load has a more prominent feature, which is commonly known as resistance to sudden changes, that is, this type of load has a great resistance to sudden changes in the current situation. Although the torque required to promote changes in this type of load is not high, it takes a lot of energy to change the status quo more quickly, just like boiling water, which can be boiled with a small fire, but may require a large fire to boil quickly. There is no necessary relationship between the given frequency and the starting current. The size of the starting current depends on the starting V/F curve setting and the length of the acceleration time. For fluid loads, since the torque required during operation is not required to be constant, the use of multiple power curves can make the equipment more energy-efficient and bring economic benefits to users.

Identification method

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) × frequency (50HZ) divided by the number of pole pairs. One pole pair is 2 poles, so we can calculate 3000÷1500=2 pole pairs, which is a 4-pole motor.

2. Look at the model.

More direct: For example, the motor model is Y 132 M- 4 Y → three-phase asynchronous motor, among which the product name codes of three-phase asynchronous motors are: YR for winding asynchronous motor; YB for explosion-proof asynchronous motor; YQ for high starting torque asynchronous motor. 132 → center height of base (mm) M → base length code 4 → number of poles. Asynchronous motors start with YB, squirrel cage type is YR, increased safety type is YA, and then the center height and number of poles, for example, YR400-4 560 6KV, which is an asynchronous squirrel cage motor with a center height of 400mm, 4 poles, rated power of 560KW, and rated voltage of 6KV.

Select the number of poles method

The power of the motor is approximately equal to the power of the pump divided by the efficiency of the pump divided by the efficiency of the motor. The motor efficiency is generally 0.85. The corresponding motor powers are 5.5KW and 15KW respectively, and the speed is 2900. Then the motors are 5.5KW-2P and 15KW-2P respectively. The speed of the motor = (frequency × 60S ÷ number of motor sections) × 2. For example, the selection of the pump motor: the number of poles should be selected according to the rated speed of the pump. For 2900r/min, choose 2 poles, for 1450r/min, choose 4 poles, for 970r/min, choose 6 poles, etc.