The difference between repairing variable frequency motor and repairing ordinary motor
4. Do a good job of matching between the inverter, cable and motor, and limit the length of the cable between the motor and the power supply.
Due to the mismatch of the impedance of the power line, as the cable length between the inverter and the motor increases, the amplitude of the overvoltage at the motor end increases, which is prone to partial discharge. To this end, according to the specific characteristics of the variable frequency power supply and actual needs, the length of the connecting cable should be shortened as much as possible to reduce the overvoltage amplitude and partial discharge of the motor end and prolong the life of the motor.
The variable frequency motor power cable generally uses a professional cable, also called a symmetrical conductor frequency conversion cable, which is a 3P+3N/E series, that is, the original 3+1 is divided into three.
The difference between variable frequency motor and ordinary motor
The variable frequency motor can meet the required speed requirements by changing the frequency of the motor according to the needs of the work. Of course, a strong cooling fan is added to ensure the cooling of the motor at low speed.
Variable frequency motor features
1, electromagnetic design
For ordinary asynchronous motors, the main performance parameters considered during design are overload capability, startup performance, efficiency, and power factor. The variable frequency motor, because the critical slip ratio is inversely proportional to the power supply frequency, can be directly started when the critical slip rate is close to 1. Therefore, the overload capability and the starting performance are not required to be considered too much, and the key problem to be solved is how to improve the motor pair. The ability to adapt to non-sinusoidal power supplies. The method is generally as follows:
1) Reduce stator and rotor resistance as much as possible
Reducing the stator resistance reduces the copper loss of the fundamental wave to compensate for the increase in copper consumption caused by higher harmonics.
2) In order to suppress higher harmonics in the current, it is necessary to appropriately increase the inductance of the motor. However, the rotor slot leakage resistance is large, and the skin effect is also large, and the high-order harmonic copper consumption is also increased. Therefore, the size of the motor leakage reactance should take into account the reasonableness of the impedance matching in the entire speed range.
3) The main magnetic circuit of the variable frequency motor is generally designed to be unsaturated. One is to consider the higher harmonics to deepen the saturation of the magnetic circuit, and the other is to increase the output voltage of the inverter in order to increase the output torque at low frequencies.
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