Common Mode Overview and Reduction Guide

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Customer’s using Siemen’s VFDs Can Understand How to Reduce Common Mode

To start off, common mode is bad. Common mode voltage is created by Variable Frequency Drives (VFDs) that serve as a way of controlling the speed of AC motors by varying the frequency of the power source using pulse width modulation (PWM). This is done by switching the transistors, IGBTs, or thyristors, on and off continuously. The continuous generation of power pulses from VFDs prevents a smooth sinewave from being produced, which at any point is at a sum of zero. Instead, the waveforms produced result in a sum at any point that is not always zero. The result is damaging common mode over voltage, which can cause devastating effects to your equipment.

  • SP-003-E The dV Sentry™ is the only proven filter to provide common mode reduction, peak voltage protection, and rise time reduction – all in one unit.