ABB ACS 880 VFD Varistor Phase to Ground Screw Removal

[Saturn_Europa]

I work on a boat with an ungrounded 480v wye system. I am installing a replacement drive for a system we have had in place for 5-6 years. The model number is ACS880-01-040A-5

We usually remove the jumper/screw for the phase to ground varistors on VFDs that come equipped. In the manual for the drive it says:


""￭Frame R4
For disconnecting the EMC filter and removing the ground-to-phase varistor screw, contact
ABB Service.""

Does anyone have a good contact number for ABB Drive Service. I called a number I found the ABB website on Friday and couldnt get anyone on the phone to help.

The screw is clearly marker and easy to access. I am also wondering why they want me to call in before removing.

The drive I am replacing has the ground to phase varistor screw in place and worked for 5-6 years.

 

[coop3339]

Just curious, is there a reason why the boat uses an ungrounded system? I have never worked on a large boat electrical system... Is it to help prevent electroless on the hull?

 

[Saturn_Europa]

Just curious, is there a reason why the boat uses an ungrounded system? I have never worked on a large boat electrical system... Is it to help prevent electroless on the hull?

I honestly dont know. I just know that it can cause problems with drives with varistors.

 

[GoldDigger]

I honestly dont know. I just know that it can cause problems with drives with varistors.

A corner grounded delta is pretty much assured to cause problems with excessive voltage on some of the varistors if the connection is not removed.
An ungrounded delta may not immediately cause problems, because incidental capacitances and the varistor network itself will tend to cause the lines to have symmetrical voltages to ground. But any ground fault, which will convert it to and effectively corner grounded system and not immediately cause any OCPD tripping, will cause the varistor network to fail just as with a solidy corner grounded source.

 

[ptonsparky]

A corner grounded delta is pretty much assured to cause problems with excessive voltage on some of the varistors if the connection is not removed.
An ungrounded delta may not immediately cause problems, because incidental capacitances and the varistor network itself will tend to cause the lines to have symmetrical voltages to ground. But any ground fault, which will convert it to and effectively corner grounded system and not immediately cause any OCPD tripping, will cause the varistor network to fail just as with a solidy corner grounded source.

OP indicated an ungrounded wye is in use. How does that change things?

Would the questioned "screw in" essentially make it grounded?

 

[coop3339]

I was thinking about this and wondering if there is a way to use surge suppression on an ungrounded system? All of the supressiors I'm aware of require a ground to shunt the overvoltage to. The first thought I had was maybe just join the varisters together making a kind of wye connection. As long as this connection is isolated you wouldn't have any issues with a ground fault or corner grounding because the voltage line to line would not be affected. This would still provide protection by shunting the overvoltage across the other phases.

 

[GoldDigger]

OP indicated an ungrounded wye is in use. How does that change things?

Would the questioned "screw in" essentially make it grounded?

The fact that the source is a wye does not really alter anything if no connection is made to the wye point.
Putting in the screw connects the wye point of the varistors to EGC, not to the wye point of the source and so does not alter the ungrounded nature of the source.
If there were a compliant way to connect the varistor wye point to the source wye point, the situation would be different. But the VFD design probably does not allow for that.