| Scenario: An application requires the use a VFD to drive a 460 VAC three- phase geared motor. (Motor FLA = 3.5 amps). Other than the overload in the drive, one overload relay in the output on the inverter is also used. Problem: motor trips frequently due to the overload relay (output). The measured drive current shows less. A clamp-on meter shows only 0.2 amps and roughly 700 volts. What's problem? At which current should the overload relay be set at? |
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Measuring voltage and current on the output of a drive is often presents problems. Most meters read incorrectly because the output is PWM output (pulse-width modulated) rather than a clean sinewave.
Some overloads may also have problems with the output of a drive. Be certain that the overload that being used is not an electronic type -- use bimetal only, and set the trip current to the motor rating.
If you liked the "At which current should the overload relay be set at?" article above, you may also be interested in the rest of the articles in our comprehensive series on: Variable Frequency Drives (VFD) Or, browse through our categorical or master article archive to see a listing of all main topics. |
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