Motor stator winding protection
When the length of the cable exceeds 30 meters, the modern inverter will inevitably generate a spike voltage at the motor end, shortening the life of the motor. To prevent damage to the motor, there are two ideas. One is to use a motor with higher insulation resistance than the winding insulation (generally called a variable frequency motor), and the other is to take measures to reduce the peak voltage. The former measure is suitable for new projects, and the latter measure is suitable for retrofitting existing motors.
At present, there are four common motor protection methods:
1) Install a reactor at the output of the inverter: This measure is most commonly used, but it should be noted that this method has a certain effect on a shorter cable (less than 30 meters), but sometimes the effect is not ideal, as shown in Figure 6 (c ) shown.
2) Install the dv/dt filter at the output of the inverter: This measure is suitable for the case where the cable length is less than 300 meters, and the price is slightly higher than the reactor, but the effect is obviously improved, as shown in Figure 6(d). .
3) Install a sine wave filter at the output of the inverter: this measure is ideal. Because here, the PWM pulse voltage is changed to a sine wave voltage, and the motor operates under the same conditions as the power frequency voltage. The problem of the spike voltage is completely solved (the cable is long and the peak voltage does not occur) .
4) Install the peak voltage absorber at the position of the cable and motor interface: The disadvantage of the previous measures is that when the power of the motor is large, the reactor or filter has a large volume and weight, and the price is high. In addition, the reactor Both the filter and the filter will cause a certain voltage drop, affecting the output torque of the motor. The inverter spike absorber can overcome these shortcomings.
The SVA spike voltage absorber developed by the Aerospace Science and Industry Group Second Hospital 706 is an ideal device for solving motor damage by using advanced power electronics technology and intelligent control technology. In addition, the SVA spike absorber protects the bearings of the motor.
Compared with the motor protection methods such as the du/dt filter and the sine wave filter described above, the peak absorber has the advantages of small size, low price, and easy installation (parallel installation).
Especially in the case of high power, the advantages of the peak absorber in terms of price, volume and weight are outstanding. In addition, since it is installed in parallel, there is no voltage drop, and there is a certain voltage drop on the du/dt filter and the sine wave filter. The voltage drop of the sine wave filter is close to 10%, which will cause the torque of the motor. reduce.
