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the article citations: time:2017-08-06 16:34:01
are induced because of the high frequency of the voltage pulses sent to the motor from the vfd. recall that a pulse-width modulated creates a synthesized sine wave by firing its output transistors many thousands of times per second. these pulses form high-frequency waves sent along the motor cable to the motor. since impedance is inversely proportional to frequency, the capacitances of the cable and motor present little or no impedance to these high-frequency pulses. as a result, can readily flow in the motor shaft. with sufficient magnitude, and in the absence of corrective measures, these shaft currents can pass through the bearings and races to the motor frame, causing bearing pitting or “fluting” – regular, tightly spaced grooves on the bearing races – via a process referred to as electric discharge machining (edm). ultimately, these irregularities will cause bearing failure.
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