Ecmweb 7408 Quiz 0
Ecmweb 7408 Quiz 0
Ecmweb 7408 Quiz 0
Ecmweb 7408 Quiz 0
Ecmweb 7408 Quiz 0

Electrical Troubleshooting Quiz - May 19, 2015

May 19, 2015
How can you eliminate restart problems?

Inside your plant is a complex process machine that includes a variety of loads supplied by its own branch circuit panel that is, in turn, on its own feeder. Among the loads are about a dozen motors under 2 HP, three 200 HP motors, four resistive barrel heaters, two ultraviolet lights, and a forced draft fume hood.

This machine runs on three shifts, but sometimes it must be shut down for order changes, maintenance, or other purposes. Starting it is always problematic. It invariably takes several attempts and involves replacing fuses on those small motors and on some of the other loads. How can you eliminate these restart problems?

Use a recording digital multimeter (DMM) or power analyzer on the feeder serving this machine. The fact this system blows small fuses so dependably tells us those 200 HP motors are starting across-the-line and creating voltage dips followed by voltage spikes. A new fuse might handle an instance or two of this abuse, but after a few rounds it’s going to be toast.

This system was probably designed with starting capacitors for the larger motors. The cheapest solution is to replace any failed ones. A better solution is to replace them with variable frequency drives (VFDs). VFDs will have correction for power factor and harmonics plus provide a soft start function.

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