Different motors for chemical centrifugal pump

Chemical centrifugal pump is using fluorine plastic material of high temperature casting production pump, chemical centrifugal pump series has fluorine plastic centrifugal pump, fluorine plastic magnetic pump, fluorine plastic pipeline pump, fluorine plastic self-priming pump, chemical centrifugal pump operated with the form of motor driving, when the user choose according to need, there are anti-corrosion type, normal type and frequency conversion type etc., some users use frequency converter under the condition of choosing ordinary motor. Does it affect the motor? Can it be used? What is the difference between ordinary motor and variable frequency motor? Ordinary motor is designed according to constant frequency and constant voltage, it is impossible to completely meet the requirements of inverter speed regulation, so can not do more frequency conversion motor use.

One. All kinds of common motor and frequency conversion motor design

1. Electromagnetic design

For the common asynchronous motor, the specific performance parameters considered in the design are overload capacity, start-up performance, efficiency and power factor. As the critical slip is inversely proportional to the power supply frequency, the variable frequency motor can be started directly when the critical slip is nearly 1. Therefore, the overload capacity and starting performance no longer need to be considered too much, and the key problem to be dealt with is how to improve the motor's adaptability to non-sinusoidal wave power supply.

2. Structural design

In the structural design, the interference of non-sinusoidal power supply to the insulation structure, vibration and noise cooling method of the variable frequency motor should also be considered.

Two. The interference of frequency converter to the motor is specific in the efficiency and temperature rise of the motor

Inverter can produce all kinds of degree of harmonic voltage and current in operation, makes the motor operate under non-sinusoidal voltage and current. The high-order harmonics inside the motor will cause the stator copper consumption, rotor copper consumption, iron consumption and additional loss enhancement, especially the rotor copper consumption, which will make the motor extra heat, decrease the efficiency and reduce the output power. The temperature rise of ordinary motors is usually increased by 10%-20%.

Three. Cooling phenomenon at low speed of chemical centrifugal pump

When the frequency of power supply is low, the loss caused by high harmonics in power supply is large.In addition, when the motor speed drops, the cooling air volume decreases in direct proportion to the third square of the motor speed, resulting in the motor's heat emission not going out and the temperature rising sharply, making it difficult to reach the constant torque output.

Four. Phenomenon of insulation strength of motor

Frequency converter carrier frequency from thousands to tens of KHZ, can make the stator windings of the motor to bear a very high voltage rise, it is equivalent to the motor to increase a very steep impulse voltage, so that the motor turns insulation bears a more serious challenge.   Five. Harmonic electromagnetic noise and vibration

The vibration and noise caused by electromagnetic, mechanical, ventilation and other aspects will become more complicated when ordinary motors are powered by frequency converter. Various harmonics contained in the frequency conversion power supply interfere with the inherent space harmonics of the electromagnetic part of the motor, forming various electromagnetic excitation forces, thus increasing the noise. Due to the wide operating frequency range and wide rotation speed range of the motor, it is difficult to avoid the natural vibration frequency of each structure of the motor.

Six. For the above phenomena, the inverter motor adopts the following design:

1. The ordinary motor, namely the power frequency motor, only needs to consider the starting process and the work of a point of power frequency to redesign the motor; And the frequency conversion motor needs to consider the starting process and the frequency conversion range of all the working conditions of the point, the motor design.

2.In order to adapt to the PWM modulated wave output sinusoidal ac current, the frequency conversion motor specially made contains a lot of harmonics, and its effect can actually be understood as reactor plus ordinary motor.

3.The coil distribution capacitance of frequency conversion motor is smaller, the resistance of silicon steel sheet is larger, so the influence of high-frequency pulse on the motor is smaller, the inductance filtering effect of the motor is better.

4. Reduce the stator and rotor resistance as much as possible, and reduce the base wave copper consumption, thus to remedy the increase of copper consumption caused by high harmonics.

5. The unsaturated design of the main magnetic field, one is to consider that high harmonics will increase the saturation of the magnetic circuit, and the other is to consider that the output voltage of the converter can be appropriately increased in order to improve the output torque at low frequencies.

6. Structural design, mainly to improve the insulation level;Fully consider the vibration and noise of the motor;Cooling method is ventilation cooling method, that is, the main motor cooling fan uses independent motor driving method, the effect of the strong air cooler is to ensure the cooling of the motor at low speed.

Seven. How to distinguish ordinary motor and frequency conversion motor? The structural difference between ordinary motor and vfrequency conversion motor

1. Frequency conversion motor's vibration and noise standards are higher

Frequency conversion motor should be fully consider the motor components and the overall rigidity, try to improve its natural frequency, in order to avoid each force wave form resonance phenomenon.

2. Frequency conversion motor cooling methods are different

Frequency conversion motor usually uses ventilation cooling, that is the main motor cooling fan uses independent motor drive.

3. Different heat dissipation systems

Variable frequency motor cooling fan uses independent power supply to ensure continuous cooling capacity.

4. Higher insulation standards

Normally the insulation grade of frequency conversion motor is F class or a few higher, strengthen to ground insulation and wire turn insulation strength, particular consideration should be given to the ability of the insulation to withstand impulse voltages.

5. Different standards of protective measures

The bearing insulation method should be used for frequency conversion motors with a capacity greater than 160KW. The main reason is that the magnetic circuit is easy to be uneven, and the axial current will also be formed. When the current formed by other high-frequency components is combined with the effect, the axial current will be greatly increased, thus causing damage to the bearing. Therefore, insulation method is usually adopted. For constant power frequency conversion motor, when the speed is greater than 3000/min, high temperature resistant special grease should be used, to make up for the bearing temperature rise.

For more technicial questions please feel free to contact Kelly~

Kelly - International Trade Pumps Engineer

Anhui Tenglong Pump And Valve Manufacturing Co., Ltd.(TEFLOW)

Web:www.teflowpump.com

Tel:+86-15156345852

WeChat: 15156345852

Whatsapp :+86 15156345852

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