The motor shaft voltage and bearing current reason and harm of formation

In the motor running, settle, or around the axis of phase current in the rotor magnetic circuit any imbalance can cause spinning system flux. When the shaft rotates, the flux can be produce potential difference on both ends of the shaft, the potential difference is called shaft voltage. Can pass on both ends of the bearing on the shaft and shaft voltage loop formed by the case ( Closed circuit) Inspire a loop current, the current is called shaft current. As shown in figure a. In addition, the remanent magnetism of rotor core is more, for wound rotor motor, in case of winding on the rotor core or two or more axis of short circuit and so on, also can produce the shaft voltage and shaft current. The size of the bearing current and motor structure, the power of the motor, the driving voltage amplitude, pulse rise time, cable length and other factors. The power of the motor, the driving voltage is higher, the greater the driving voltage rise along the steep, the shorter the cable, the bearing, the greater the current. Frequency converter drive motor contains abundant high frequency PWM voltage ( Up to several thousand Hertz) Composition, high frequency stray capacitance of electric current through bearings through the bearing, bearing current, the current is greater than the ordinary numerical when sinusoidal ac power supply, its destructive will be very big, of course. When the motor shaft voltage reaches a certain degree, will cause the motor bearing rolling body ( Ball or child) With raceway arc discharge, produce the dot or the shape of washboard injury ( As shown in figure b) , and can produce fine metal particles into the bearing grease ( Oil) , the rolling resistance increases, lead to bearing overheating or even burning.