Can inverter motors be replaced by ordinary motors?

Issuing time:2019-12-19 16:19

Above: Variable frequency motor and conventional motor

In the range of 30-60HZ, short-term variable frequency use, ordinary motors can be replaced, but beyond this range or long-term frequency conversion use, special inverter motors must be used to strengthen the chiller.

1. Ordinary motors are designed according to constant frequency and constant voltage. It is impossible to fully adapt to the requirements of inverter speed regulation, so it cannot be used as a variable frequency motor.

2. Inverter motors use special anti-corona enameled wire, and reinforced insulation after multiple washing and dipping. Large-scale inverter motors also need to use special ceramic surface insulated bearings.

变频器对电机的影响主要在电动机的效率和温升The effect of the inverter on the motor is mainly the efficiency and temperature rise of the motor

The inverter can generate different levels of harmonic voltages and currents during operation,allowing the motor to operate at non-sinusoidal voltages and currents. The higher harmonics inside it will cause increased copper loss in the stator, rotor, iron, and additional losses of the motor. The most significant is the copper loss of the rotor. These losses will cause the motor to generate additional heat, reduce efficiency, and reduce output power. Generally, the temperature rise of ordinary motors will increase by 10% -20%.

电动机的绝缘强度Motor insulation strength

The carrier frequency of the inverter is from several thousand to more than ten kilohertz, which makes the motor stator winding to withstand a high voltage rise rate, which is equivalent to applying a steep shock voltage to the motor, which makes the interturn insulation of the motor withstand severe tests.

谐波电磁噪声与震动Harmonic electromagnetic noise and vibration

When ordinary motors are powered by inverters, vibration and noise caused by electromagnetic, mechanical, and ventilation factors will become more complicated. The various harmonics contained in the variable frequency power supply interfere with the inherent space harmonics of the electromagnetic part of the motor to form various electromagnetic excitation forces, thereby increasing noise. Because the motor has a wide operating frequency range and a large speed variation range, it is difficult for the frequency of various electromagnetic force waves to avoid the natural vibration frequencies of various structural parts of the motor.

低转速时的冷却问题Cooling problems at low speeds

When the power frequency is low, the losses caused by high-order harmonics in the power supply are large; secondly, when the speed of the motor is reduced, the cooling air volume decreases in proportion to the third power of the speed, causing the heat of the motor to not be emitted and the temperature rise sharply. Increase, it is difficult to achieve constant torque output.

The frequency conversion motor adopts the following design:

1. Reduce the stator and rotor resistance as much as possible, and reduce the fundamental copper loss to compensate for the increase in copper loss caused by higher harmonics.

2, the main magnetic field unsaturated design:

(1) Higher harmonics will deepen magnetic circuit saturation.

2. In order to increase the output torque at low frequencies, the output voltage of the inverter can be appropriately increased.

3. Structural design:

1. Insulation grade of frequency conversion motor is F grade and above, improve the ability of withstand impulse withstand voltage, and strengthen the insulation strength of ground insulation and turns

2. Improve the mechanical parts and overall rigidity, avoid resonance with magnetic force waves

3. Strong cooling fan is driven independently.

4. Bearing insulation measures should be adopted for variable frequency motors with a capacity exceeding 160KW. The asymmetry of the magnetic circuit will generate the shaft current. When the currents generated by other high-frequency components work together, the shaft current will increase greatly, resulting in bearing damage. For constant power variable frequency motors, when the speed exceeds 3000 / min, special high temperature resistant grease should be used to compensate for the temperature rise of the bearing.

3. For ordinary asynchronous motors, the performance parameters mainly considered during design are overload capacity, starting performance, efficiency and power factor. The frequency conversion motor, because the critical slip rate is inversely proportional to the power frequency, can be started directly when the critical slip rate is close to 1, so the overload capacity and starting performance do not need to be considered too much, and the key issue to be solved is how to improve the motor Adaptability of non-sine wave power.