Data Sheet

Application: VSD failure

Introduction

• A variable speed drive on a critical system, the

fault indicator LED is on

• According to the VSD (variable speed drive), the

error code is F4; this is: the drive has detected an

“under voltage” condition and shuts down

How do you identify if the failure is in the drive,

in the motor or in a distorted supply voltage?

A typical industrial electrical distribution system

with non-linear loads

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Application: VSD failure Introduction • A variable speed drive on a critical system, the fault indicator LED is on • According to the VSD (variable speed drive), the error code is F4; this is: the drive has detected an “under voltage” condition and shuts down How do you identify if the failure is in the drive, in the motor or in a distorted supply voltage? A typical industrial electrical distribution system with non-linear loads
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Diagnosing VSD failure Using a DMM • Check the input line voltage (figure 1) – A typical multimeter will display either average or rms voltage values – Depending on the type of distortion, the rms or peak value may not reveal if a problem exists • Check the VSD dc bus voltage Figure 1.
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Diagnosing line voltage distortion.. Using an Oscilloscope • Check the input line voltage – Connect the oscilloscope to Phase and the ground lead to Neutral – The waveform reveals sine wave peaks that are rounded, almost becoming a “flat top” (figure 3) – When this occurs, the ratio between “peak” versus “rms” measured values is smaller than 1.
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Troubleshooting using an oscilloscope Conclusion • A DMM can display precise amplitude RMS or Peak values • An oscilloscope will graphically show amplitude (RMS or peak) as well as any distortion, disturbance and noise that may be present on the waveform A picture is worth more than a thousand words.