What does the number of pole of the motor meaning?
In electric motor factories, it is often heard that "what pole of motor is there?"
To figure it out, we must first understand what the concept of pole is: Pole refers to the magnetic pole formed by the rotor of the generator after an excitation current is passed into the rotor coil. To put it simply, every turn of the rotor can induce several cycles of current in one turn of the stator coil, and different poles with different currents are required to generate a potential of 50Hz.
(50HZ*60 sec/min (i.e. 3000) divided by the number of poles is the number of revolutions of the motor per minute) The same is true for the motor, but it is an inverse 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.
The number of poles of the motor
The number of poles of the motor determines the synchronous speed of the motor.
Example: 4-poles motor
4-pole motor motor 1 minute synchronous speed = {frequency of power supply (50Hz) ×60 seconds} ÷ (number of stages of motor ÷2) = 3000÷2 = 1500 rpm
It can be understood in this way: 2 poles are the base number (3000), 4 poles can only be divided by 2, 6 poles are divided by 3, and 8 poles are divided by 4. Instead of saying that 2 poles should be removed with 3000.
The more pole pairs the motor has, the lower the speed of the motor, but the greater the torque it has.
When choosing a motor, you need to consider how much starting torque is required for the load.
For example, if you start with a load, you need a larger torque than if you start with no load.
If it is a high-power and high-load start, it is also necessary to consider step-down start-up (or star-delta start-up); As for the speed matching of the motor and the load after determining the number of pole pairs, it can be considered to use different diameter pulleys for transmission or variable speed gears (gearboxes) to match.
If the power requirements of the load cannot be reached after the belt or gear transmission after the number of pole pairs of the motor is determined, then the power of the motor should be considered.
Three-phase AC motors are mainly composed of stator and rotor. When a three-phase alternating current is introduced into the stator, a rotating magnetic field is generated.
A magnetic field always has two poles (which can also be said to occur in pairs), namely the N pole (north pole) and the S pole (south pole), also known as one opposite pole. When the stator windings of the AC motor are wound in different ways, the number of poles of the rotating magnetic field generated is different.
The number of 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, the number of pole pairs can be calculated as 2, that is, a 4-pole motor.
Synchronous speed and number of pole pairs are the basic parameters of the motor, which 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 the fluid load of fans and pumps, this kind of load has a more prominent feature, which is called resistance to mutation as the saying goes, that is, this kind of load has great resistance to the current abrupt change.
Although the torque required to drive this type of load change is not high, it takes a lot of energy to change the status quo relatively quickly, just like boiling water, which can be boiled over a small fire, and a large fire that can be boiled quickly.
There is no necessary relationship between the size of the given frequency and the size of the starting current, the size of the starting current depends on the V/F curve setting of the startup and the length of the acceleration time, for the fluid load,
because the torque required during operation is not required to be constant, so the use of multiple power curves can make the operation of the equipment more energy-saving, and bring economic benefits to the user.
Identification, methodology
1. Look at the rotational speed. For example, the actual synchronous speed of 1430r/min is 1500 rpm, which is determined by the speed formula: speed = time (60 seconds) × frequency (50HZ) divided by the number of pole pairs A pole pair is 2 poles, so it can be calculated that 3000÷1500 = 2 pole pairs is a 4-pole motor.
2. Look at the model. More direct: for example, the motor model is Y2 132 M- 4 Y2 → three-phase asynchronous motor, of which the product name code of the three-phase asynchronous motor is: YR is a wound asynchronous motor; YB is an explosion-proof asynchronous motor; YQ is a high starting speed asynchronous motor. 132→ frame center height (mm) m → frame length code 4 → number of 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 number of poles, such as YR400-4 560 6KV,
it is an asynchronous squirrel cage type motor with a center height of 400mm, a number of poles of 4 poles, a rated power of 560KW, and a rated voltage of 6KV.
Select the series method
The power of the motor is approximately equal to the power of the water pump, except the efficiency of the water pump, and the efficiency of the motor.
The motor efficiency is generally 0.85, and your corresponding motor power tells you that it is 5.5KW, 15KW, and the speed is 2900, so the motor is 5.5KW-2P and 15KW-2P, and the speed of the motor = (frequency×60S÷ the number of sections of the motor) ×2
For example, the selection of the pump motor: the selection of the number of poles should be selected according to the rated speed of the pump, 2 poles for 2900r/min, 4 poles for 1450r/min, 6 poles for 970r/min, etc
Get more information about electric motor from Dongchun motor directly
Dongchun Motors (Dongchun Motor Co., Ltd.) is a leading electric motor manufacturer based in China, specializing in high-efficiency motors for industrial applications.
The company offers a wide range of products, including single-phase and three-phase motors, brake motors, and frequency variable motors.
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