200 HP VFD Failure

Saturn_Europa said:
I dont think so. I will have to check with the operators to confirm but, the power is turned off after processing is done. The plant should be shut down with the SCADA system, then they turn off the disconnect.
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how frequently is power cycled? Seems I read precharge resistors will last longer the less you cycle power, if that is what is failing first then capacitor fails as a result.
 
kwired said:
how frequently is power cycled? Seems I read precharge resistors will last longer the less you cycle power, if that is what is failing first then capacitor fails as a result.
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The most its power cycled is once every 8 days for clean up. Then the VFD is turned back on after 2 days.
 
herding_cats said:
Hmmm that is weird. It's a buss failure? Is it violent when it dies? Like smoke or buning or a loud bang?
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Yes! Its a bang and a flash. The 400 amp OCPD at the switch board trips.

Both times it happened it was after the end of season clean up. Which is two days of hosing things out with salt water and using chemicals to clean the equipment in place (CIP). The motor is wrapped in plastic and both times the terminal box was dry.

That's why I am leaning towards water getting into the drive, even though its in a control room and a control panel.
 
tortuga said:
In the older days of telcom they used to run these pressurized cables, you can still find them in service, they run at at about 1-10 PSI. I always thought that was a cool system. If you ever see what looks to be a little propane tank next to some old phone equipment along side the road there is probably like a 2400 pair cable buried there and that device is probably a Pressure Transducer measuring pressure at that splice. I always thought pressurized electrical systems could be used more, there are some in hazardous location stuff in oil and gas work and MV and HV work but not as common as in telcom. I would think it would be especially well suited for aboard a ship in a area like you describe that gets washed down.
I know nothing about ship electrical or VFD's, but if you can pressurize it even to .3 PSI you'll know if you have a leak.
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Man, I haven't seen that type of setup in years....!
 
A 200 HP VFD may have SCRs in the rectifier bridge that are phase controlled to slow down the charging of the bus capacitors, instead of using a precharge resistor. Perhaps condensation has gotten on the control circuits for the SCRs and causing them to conduct when they should not and cause damage. Control circuits for SCRs and also for the VFD output IGBTs are relatively high impedance circuits, and therefore would be more susceptible to condensation on them.

There are VFDs that have conformal coatings on their circuit boards to help prevent condensation from causing problems.

For example, as mentioned here:

 
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