vfd ??

[jimbo123]

We have a few 7.5 480 motors used with vfd . VFD don't seem to last very long before we have to replace the vfd . The vfd 's come up with a " 3 ground fault " and 41 IBGT CODE . Vfd won't reset reset to operate at all.

Will using load reactor help the vfd last longer in service ? Don't know if operator reset the vfd OL'S at all before calling for help. He said it tripped once and called repairs. The vfd is set for internal o l protection . Can't understand wHy they didn;t trip first. The motor has been megged and is ok.

These are C H svx9000 af drives. Any ideas to keep these units to last longer ?

 

[Jraef]

Without digging deeper into the specifics of that drive, it appears on the surface that you are blowing up the IGBTs, the main power output transistors that are the heart and soul of the VFD. That usually happens as a result of a severe and sudden fault on the output of the VFD, the main culprit usually is a defect in the motor lead insulation that is going to ground. It's rare that a VFD protection circuit can act fast enough to save the transistors themselves, but a load reactor may help in that regard because it adds an inductive time constant delay in the current rise. But there are other consequences to having a load reactor that must be weighed, and you also must consider that this does NOT solve the CAUSE of the problem, just one of the symptoms.

I have seen this in installations where the motor lead conduit gets filled with water and the cable insulation was either not rated for that, was damaged on installation, or someone hid an in-line splice and didn't say anything because of the cost of copper to replace the entire cable run (more common lately than it used to be). It could also be result of a termination problem in the motor peckerhead, i.e. someone used a split-bolt and didn't properly wrap it, so the vibration has worn through the tape and is shorting against the case. Another remote possibility is an insulation breakdown in the motor windings themselves, but that's more rare.

First step I would take (after visually inspecting the peckerhead) would be a proper megger test on the motor leads done from the VFD cabinet; disconnected from the VFD but with the motor still connected. If you see something when tested from that point, disconnect the motor and do it again. If the problem goes away, it's in the motor; if it's still there, it's in the cable.

 

[Besoeker]

Will using load reactor help the vfd last longer in service ?

In my experience, we usually fit load side reactors to help the motor, not the drive. The switching devices (IGBTs) have very fast switching rates and, if applied directly to the motor windings, can seriously reduce their life expectancy.

The motor has been megged and is ok.

At what voltage was the motor meggered?
And, as Jraef has pointed out, have the cables to the motor been tested?
What kind of location and ambient conditions? Wet, dusty, hot? Is there adequate ventilation?
More questions than answers......

 

[weressl]

We have a few 7.5 480 motors used with vfd . VFD don't seem to last very long before we have to replace the vfd . The vfd 's come up with a " 3 ground fault " and 41 IBGT CODE . Vfd won't reset reset to operate at all.

Will using load reactor help the vfd last longer in service ? Don't know if operator reset the vfd OL'S at all before calling for help. He said it tripped once and called repairs. The vfd is set for internal o l protection . Can't understand wHy they didn;t trip first. The motor has been megged and is ok.

These are C H svx9000 af drives. Any ideas to keep these units to last longer ?

You already got a slew of good suggestions. Couple of more questions:

1. How long are your motor leads?
2. Are the cables shielded?
3. Note the C-H warning on page 3-1 refering to minimum distances between the motor cables and 'other cables'.
4. Grounded or resistance grounded power supply to the drive?
5. Motor FLA vs. drive rating.
6. Variable or constant torque?

 

[jimbo123]

megged @1000vdc megged from drive to motor with motor leads connected.
constant torque
55' motor to drive
dry area 78*f
thhn wire
fla motor 11.1

thanks for all the good tips.

 

[SFBayVFD]

In my experience, we usually fit load side reactors to help the motor, not the drive. The switching devices (IGBTs) have very fast switching rates and, if applied directly to the motor windings, can seriously reduce their life expectancy.

I agree, load reactors will protect the motor from the drive; however 55' to the motor is usually not enough distance to warrant a filter.

What was the megger reading @ 1000vdc?
Was the motor replaced with the VFD? Or was a VFD added to an existing motor?
What is the insulation class on the motor? B, F, H?

 

[jdsmith]

What is the voltage rating of the motor windings? So-called "VFD-rated" motors are typically 1600V or higher winding insulation - the motors I use have 2200V insulation.

The insulation class (temperature rating) of the motor (B, F, H) shouldn't be relevant to this discussion, other than if it is class B it is also likely to have a low voltage rating. Class F is standard for modern motors, one manufacturer of IEEE 841 motors (high end TEFC, severe duty) is using class H insulation in the last few years.

I agree with SFBayVFD - if a filter solves the problem with 55 ft THHN motor leads it's only masking the problem and there's probably a better fix. Full magnitude reflected wave (2x the DC bus voltage) will occur above ~225 ft motor leads IIRC - 55 ft should result in a worst case reflected wave magnitude of 1000V or less.

 

[robbietan]

some of the cases I have seen involved the IGBT of the drive to burn out due to overcurrent when the drive was subjected to a voltage sag from the utility. and in some cases, the starting of a facility's large loads have been observed to affect drives.

it is because of these reasons that a line side reactor was recommended, load reactors only when motor damage is observed