200 HP VFD Failure

[Saturn_Europa]

I work on a fishing boat. We had a 200 HP VFD fail for the second time in similar circumstances. The VFD is an AB PowerFlex 753. It is housed in a standalone control panel with a line reactor, control transformer, and disconnect. Its supplied by a 400 amp breaker. 480v 3 phase. The control panel is in a control room that is conditioned and has a watertight bulkhead and hatch.

After the end of the season there is extensive clean up in the process area with large volumes of sea water spraying down equipment. The control room watertight hatch is supposed to be closed and dogged down. During clean up the 200 HP VFD is locked out and tagged out.

Last year, after end of season clean up, the operator powered up the drive with the local disconnect and he heard a big bang. The 400 amp breaker tripped and you could see that smoke and dust and soot was blown out the side of the VFD. Before replacing the VFD, I megged out the motor and made sure there was no water in the motor termination box. I megged out the line reactor and checked for a short circuit in the control transformer. I also verified that the disconnect had no resistance when closed and verified that I was getting 480/277.

This year, after end of season clean up, the operator powered up the drive with the local disconnect and he heard a big bang. The 400 amp breaker tripped and you could see that smoke and dust and soot was blown out the side of the VFD. The electrician onsite, checked the same things I did and did not find a problem with anything.

The control panel has a 120-volt ventilation fan and an air inlet. The fan is powered by the control transformer, and the cabinet was powered off so the fan was not running. The operators admitted to leaving the watertight hatch open, during cleaning so it's likely that some saltwater mist got in the control room. But the cabinet with the VFD was locked shut. There are computers and workstation in the same area and everything else was ok.

The going theory right now is that the VFD got wet and blew up when powered up, twice. However, I did not see any water damage last year and neither did the electrician this year. But what else would cause a VFD to fail on power up after only being locked out for a few days? I cant think of anything else.

To remedy the situation, we are going to start taping plastic over the fan vents in the cabinet. I am also going to install a separate 120v circuit to power a heater in the cabinet. I am going to run this off of a NC relay on the drive to close a contactor that will power a small heater with a thermostat so that when the drive is off or powered down the heater will be on. I am also going to start putting my lock on the cabinet and inspecting it for water intrusion before it is powered on.

Other than water damage, what else would cause a VFD to fail on power up after being locked out for a few days?

How effective have you seen control panel heaters in prevented VFD failures in water mist environments?

 

[DBill64]

It may be corrosion damage overtime from salt in the air. Salt will do all sorts of unwanted things to shipboard electronics (corroding solder joints, degrading insulation, etc.). My radar control cabinets in the Navy were essentially all IP 67/NEMA 4X enclosures, all entry points into them were filled with goop, and they were all liquid cooled via demineralized cooling loops from external skids. This was all to avoid any ambient air from infiltrating the enclosure. Perhaps the VFD enclosure needs to be changed out to one with better ingress protection.

Also, do you have any compressed air onboard? You could look into conditioning some air with a desiccant drier, fine particulate filter, and regulating it down for a vortex cooler for the cabinet (also if it isn't oil-free air then you'll want something to catch the oil too). This will positively pressurize the inside and keep outside stuff from getting in. You only need the pressure inside to be ever-so-slightly higher than ambient (like 0.1 - 0.3 PSI higher.). If you do this, you'll also want to make sure you have a means of keeping the door shut while the air is on so no one can open the door while pressure is present or else they may receive a knock to the noggin.

I have never used a heater for shipboard use or for mitigating ingress, but I have used them for controlling internal condensation inside of cabinets in cold & humid environments. A heater wont stop water mist getting in (only your enclosure's ingress rating & the quality of the penetrations into the enclosure will do that).

 

[synchro]

Could their be any water that has gotten into the wiring between the VFD and the motor? Salt water may have enough conductivity to create a L-L or L-G fault and cause excess current to be drawn on one or more of the IGBT output devices in the VFD, causing failures.

 

[jim dungar]

Is the VFD being fed from shore power or from the onboard generator(s)?