200 HP VFD Failure

Saturn_Europa

Saturn_Europa

Senior Member
Location
Fishing Industry
Occupation
Electrician Limited License NC, QMED Electrician
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?
 
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).
 
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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.
 
S_E

What seemed to blow up? The capacitors? The rectifying IGBTs? The inverter IGBTs? The charging resistor? Large fuses? Maybe a circuit board, and a small arc flash got to the main busses causing a big arc flash? Have you talked to AB?

If there is a maintenance schedule from AB, such as testing the IGBTs, you could go through that before powering up.
 
Did you replace the drive or have it repaired? If repaired hopefully whoever repaired it can give some clues as to what causes were? Small drives (maybe under 100 hp) not worth repairing as a general rule unless they have somewhat abnormal characteristics about them but this one maybe can be repaired for less than a new drive.
 
kwired said:
Did you replace the drive or have it repaired? If repaired hopefully whoever repaired it can give some clues as to what causes were? Small drives (maybe under 100 hp) not worth repairing as a general rule unless they have somewhat abnormal characteristics about them but this one maybe can be repaired for less than a new drive.
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Even if it's dead you can do a postmortem and look for signs of liquid infultration
 
Joethemechanic said:
Even if it's dead you can do a postmortem and look for signs of liquid infultration
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Or at least confirm what component failed which could give clues as to why.

This would likely have pre charge resistors on the capacitors, maybe those failed for some reason and the capacitors ruptured from charging to rapidly? Which may also take out front end rectifier? If same thing happened both times---why becomes the question.
 
kwired said:
This would likely have pre charge resistors on the capacitors, maybe those failed for some reason and the capacitors ruptured from charging to rapidly? Which may also take out front end rectifier? If same thing happened both times---why becomes the question.
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That’s an important point. For example, if there is a starter or contactor on the line side of this drive, so it is being powered on and off multiple times per day, that will stress the pre-charge resistor and either short them out or cause the bypass contact for it to weld. Without the resistor in series, the caps can destroy themselves on power up.
 
Jraef said:
That’s an important point. For example, if there is a starter or contactor on the line side of this drive, so it is being powered on and off multiple times per day, that will stress the pre-charge resistor and either short them out or cause the bypass contact for it to weld. Without the resistor in series, the caps can destroy themselves on power up.
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Its a very simple control cabinet. A disconnect, line reactor , control transformer off of 2 legs, then the VFD.
 
kwired said:
Or at least confirm what component failed which could give clues as to why.

This would likely have pre charge resistors on the capacitors, maybe those failed for some reason and the capacitors ruptured from charging to rapidly? Which may also take out front end rectifier? If same thing happened both times---why becomes the question.
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I will try to take the failed VFD apart when I get back to the boat. The VFD that failed most recently was in service for about 6 months, than powered down for around 3 or 4 days.
 
kwired said:
Did you replace the drive or have it repaired? If repaired hopefully whoever repaired it can give some clues as to what causes were? Small drives (maybe under 100 hp) not worth repairing as a general rule unless they have somewhat abnormal characteristics about them but this one maybe can be repaired for less than a new drive.
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The first VFD that failed was in service for around 10 years. I replaced it with a brand new drive and threw the failed one out without much investigation. The most current one failed after only 6 months in service, but was purchased more than 3 years ago. Do you know of a company that refurbishes drives?
 
synchro said:
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.
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Thats a good question. We megged out the cable and the motor, both times the VFD failed, both times the cable and the motor passed. Its a mil spec shipboard rated cable. But honestly, I think I only megged the cable to ground and didnt disconnect the cable at both ends and meg it phase to phase.

Honestly, I checked the load side of the VFD just to be thorough. I thought there are protections in the VFD that will protect it from a Ground Fault or Phase to Phase fault causing internal damage to the drive?

I will hand over hand the cable when I get back to the boat and see if there is any physical damage. The cable is wire tied to a wire way and not in any protective conduit.
 
Saturn_Europa said:
Do you know of a company that refurbishes drives
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There likely some place in your area that sells and services motors, drives and other industrial electrical and mechanical equipment or at least has someone they get to work on these if they don't have anyone within their own organization. Places that rewind motors have some chance of having this kind of service as well which is the kind of place i have had this done at before.

First time I figured out they could do this I had a somewhat specialty drive that failed. It was 240 single phase in but 480 three phase out (but no step up transformer, not sure how that is done electronically but apparently can be done) and driving a 20 HP submersible well motor. I initially was looking for a possible replacement drive. They told me they could repair the old one not only faster than they could get a replacement and for less cost as well. I don't recall what failed, probably either front end rectifier or capacitor(s). Otherwise most the business I previously done with them was new motors, motor rewinds, or VFD/soft starter purchases.
 
These VFDs are $21,000. After two failures in less than a year, I need to pin down the root cause. Thanks everyone for the feed back and let me know if you think of anything else to check.

TLDR: 2 VFD failures in a year after factory clean up with salt water.

Motor and cable passed megger test phase to ground.
No visible water in the control cabinet.
All components in the control cabinet are fault free and functional.

To do:

Inspect the drive to see what failed.
Inspect the cable to the motor to look for damage.
Meg cable phase to phase after disconnecting motor and vfd.
 
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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