In factories, we often hear: " What level is the motor ?"

To understand, you must first know what a pole is: a pole refers to the magnetic pole formed by the generator rotor after the excitation current is passed through the rotor coil . Simply put, each revolution of the rotor can induce several cycles of current in one turn of the stator coil. Different numbers of poles require different rotational speeds to generate a 50hz potential.

(50HZ*60 seconds/minute (i.e. 3000) divided by the number of poles is the number of revolutions of the motor per minute) The same is true for electric motors, which is just a reverse process of the generator.

The number of poles reflects the synchronous speed of the motor. 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.

Motor stages

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

Example: 4-stage motor, 4-stage motor, motor synchronous speed in 1 minute = { frequency of power supply (50Hz) × 60 seconds} ÷ (number of motor stages ÷ 2) = 3000 ÷ 2 = 1500 revolutions. It can be understood like this: 2 poles are the base number ( is 3000), if it has 4 poles it can only divide by 2, if it has 6 poles it can divide by 3, and if it has 8 poles it can divide by 4. Instead of saying that 2 poles need to be divided by 3000. The greater the number of pole pairs in a motor, the lower the motor's speed, but the greater its torque.

When selecting a motor, you need to consider how much starting torque the load requires. For example: starting with load requires more torque than starting without load. If it is a high-power and large-load start, you should also consider a reduced-voltage start (or star-delta start); as for the problem of matching the speed of the motor with the load after determining the number of pole pairs, you can consider using pulleys of different diameters for transmission or variable speed. gear (gearbox) to match.

If the power requirement of the load cannot be reached after the motor pole number is determined and driven by a belt or gear, then the power of the motor must be considered.

A three-phase AC motor is mainly composed of a stator and a rotor. When three-phase alternating current is supplied to the stator, a rotating magnetic field will be generated. The magnetic field always has two poles (which can also be said to appear in pairs), namely N pole (North Pole) and S pole (South Pole), also known as an opposite pole.

When the stator windings of AC motors are wound in different ways, 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/stage logarithm. If the synchronous speed of the motor is 1500 rpm, then according to the above formula, it can be calculated that the number of pole pairs is 2, which is a 4-pole motor.

The synchronous speed and the number of pole pairs are the basic parameters of the motor and can be found on the nameplate of the motor. Because the number of pole pairs can affect the speed of the motor, the speed of the motor can be changed by changing the number of pole pairs of the motor. For fluid loads such as fans and water pumps, this type of load has a more prominent feature. As the saying goes, it is called resistance to sudden changes, which means that this type of load has great resistance to sudden changes in the current situation.

Although the torque required to promote this type of load change is not high, it requires a lot of energy to change the status quo quickly. It is a bit like boiling water. It can be boiled with a small fire. To boil it quickly, it may require The fire will be very big. There is no necessary relationship between the given frequency and the starting current. The starting current depends on the starting V/F curve setting and the length of the acceleration time. For fluid loads, the required torque is not required to be constant during operation. Therefore, using multiple power curves can make the equipment run more energy-saving and bring economic benefits to users.

recognition methods

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 magnetic pole pairs. One magnetic pole pair is 2 poles. From this, we can calculate 3000÷1500= 2 magnetic pole pairs are a 4-pole motor.

2. Look at the model number.

It’s more direct: For example, the motor model is Y 132 M- 4 Y → three-phase asynchronous motor. The product name codes of the three-phase asynchronous motor are as follows: YR is a wound asynchronous motor; YB is an explosion-proof asynchronous motor; YQ is a high-voltage asynchronous motor. Starting torque of asynchronous motor. 132 → Center height of base (mm) M → Base length code 4 → Number of magnetic poles. 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 and the number of poles is 4 poles. , rated power 560KW, rated voltage 6KV.

Select pole method

The power of the motor is approximately equal to the power of the water pump divided by the efficiency of the water pump divided by the efficiency of the motor. The motor efficiency is generally 0.85. Your corresponding motor power tells you that it is 5.5KW, 15KW, and the rotation speed is 2900. Then the motors are 5.5KW-2P and 15KW-2P respectively. The rotation speed of the motor = (frequency × 60S÷the section of the motor) Number)