MTE Sets The Benchmark For Power Quality Take Advantage of Our Expertise Running a motor directly from the power source produces uniform, sinusoidal waveforms but wastes energy due to continuous speed operation regardless of the load. To enhance efficiency, Variable Frequency Drives (VFDs) control motor speed, reduce energy consumption, and minimize equipment wear. However, VFDs use pulse-width modulation (PWM) to supply electrical pulses instead of a true voltage waveform, generating harmful harmonics that can damage motors, cables, and bearings when the VFD-to-motor distance is significant. Harmonic issues between the VFD and motor are often related to differential mode or common mode voltage and current. Differential mode voltage is the voltage that energizes the motor. Increased differential mode voltages can cause premature failures in both the motor and the cable. As the motor is farther from the VFD, the adverse effects worsen due to increased cable resistance. This leads to a surge in peak voltage and rise time, known as the reflective wave, amplifying the impact. Common mode refers to the voltage or current that appears between all conductors and ground in an electrical system. It can cause interference, damage to components, and unexpected behaviors. VFDs generate power pulses that can introduce common mode voltage and current issues, such as premature motor failure, cable degradation, and electrical fluting, pitting, and frosting of bearings. These must be properly managed to ensure the reliable and efficient operation of the motor and associated equipment. What Effect Does a VFD Have on a Motor? Understanding Differential Mode and Common Mode 2
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