TVSS Failure

[Panelman01]

On a 3Ph 480V delta ATS with TVSS's supplied line side.... what could cause the TVSS's to fail only once load is applied? All the loads ( mix of lighting and motor loads ) have not been verified for proper wiring, manufactured defects, etc.... Just looking for where to start the process.

 

[GoldDigger]

I would start by putting a transient voltage recorder and or a scope on the lines.
Once you see what the disruption is you have a better chance of identifying and finding the source.
Possibly extreme load harmonics could cause peak voltages above the max of the TVSS without affecting the RMS values much.
Possibly aided by a resonance problem on the line side or even POCO primary?

 

[petersonra]

did you check the TVSS to see if it is rated for delta? maybe you have a wye unit installed.

 

[Panelman01]

did you check the TVSS to see if it is rated for delta? maybe you have a wye unit installed.

I didnt think that TVSS's were uniquely constructed for wye or delta use. I assumed they only had an L-L or L-N voltage rating based
on how they were wired. Can you explain this?

 

[Jraef]

I didnt think that TVSS's were uniquely constructed for wye or delta use. I assumed they only had an L-L or L-N voltage rating based
on how they were wired. Can you explain this?

The term TVSS is no longer used by the way, its now SPD = Surge Protective Device

An SPD intended for use in a Grounded Wye system will use devices expecting to never see more than the Wye voltage reference to ground, because the maximum potential energy in that device is lower, so the components cost less. The MOVs (typically) used inside will also often be configured in a Wye themselves, sometimes with a 4th device from the Wye point to ground as well. When you connect that to a delta system, the line to ground voltage potential is the line to line potential, so you immediately exceed the ratings of the devices inside and they pop the first time there is a grounded circuit below them. Then if the unit has the 4th device, it attempts, very briefly, to become the Wye point for your entire system and pops immediately!

 

[meternerd]

In my POCO experience, I have seen surge supressors fail fairly often. Most are just varistors and a cool indicating light. They are kind of a one time feature. If they fail, they're useless. We, as a POCO, used to sell whole house surge suppressors, but the failure rate was so high, we quit. I'm not convinced they do much good. I can't speak for the more sophisticated ones, but I remain a skeptic.

 

[ATSman]

SPD Theory

SPD Theory

On a 3Ph 480V delta ATS with TVSS's supplied line side.... what could cause the TVSS's to fail only once load is applied? All the loads ( mix of lighting and motor loads ) have not been verified for proper wiring, manufactured defects, etc.... Just looking for where to start the process.

This subject has always been an interest to me. Attached is an email I sent to two EE's for answers to the effectiveness of SPD's installed in switchgear with regard to placement next to components in control circuits, specifically ATSs.
Although it does not directly address your question which others have mentioned may be related to voltage ratings and connection configuration, I think it warrants posting again because of the general information on the subject.
I will try and find the pics of the blowup.
Forgot, it is an email thread so read from the bottom up.

 

[ghostbuster]

The term TVSS is no longer used by the way, its now SPD = Surge Protective Device

An SPD intended for use in a Grounded Wye system will use devices expecting to never see more than the Wye voltage reference to ground, because the maximum potential energy in that device is lower, so the components cost less. The MOVs (typically) used inside will also often be configured in a Wye themselves, sometimes with a 4th device from the Wye point to ground as well. When you connect that to a delta system, the line to ground voltage potential is the line to line potential, so you immediately exceed the ratings of the devices inside and they pop the first time there is a grounded circuit below them. Then if the unit has the 4th device, it attempts, very briefly, to become the Wye point for your entire system and pops immediately!

We had this exact type of failure occur at several of our customer's sites that had a delta system that suddenly flashed over to ground on 1 phase.They all lost their SPD"s plus lots of other failed equipment.The SPD's were all Y connected at this reduced component voltage level.

 

[big john]

We had this exact type of failure occur at several of our customer's sites that had a delta system that suddenly flashed over to ground on 1 phase....

That's exactly what I'm thinking.

Very common to see "ungrounded" systems that have been running for years with a faulted phase because of poor maintenance. If the SPD runs fine until loads are energized then I would bet even money that there's ground fault on one of the branch circuits. When energized that phase zeros out, and the other two phases are now full line-voltage relative to ground, which is over the clamping voltage of the SPD.

 

[ghostbuster]

That's exactly what I'm thinking.

Very common to see "ungrounded" systems that have been running for years with a faulted phase because of poor maintenance. If the SPD runs fine until loads are energized then I would bet even money that there's ground fault on one of the branch circuits. When energized that phase zeros out, and the other two phases are now full line-voltage relative to ground, which is over the clamping voltage of the SPD.

New code provisions in our country are now forcing customers to install grounded phase detection (lights) and annuciation on delta systems.Utility supplies the same (common) delta system to many customers on the same street.These new detection systems are constantly in alarm from a grounded phase from some other customer on this street.Utility refuses to investigate and find the offending cusomer.

 

[GoldDigger]

New code provisions in our country are now forcing customers to install grounded phase detection (lights) and annuciation on delta systems.Utility supplies the same (common) delta system to many customers on the same street.These new detection systems are constantly in alarm from a grounded phase from some other customer on this street.Utility refuses to investigate and find the offending cusomer.

My reaction, for what it is worth, would be that if the utility contracted to furnish you with an ungrounded delta system, then they are in breach of their contract unless they disconnect the customer who is grounding your service.

If all their tariff gives you is a delta system with grounding not specified, then I guess you are more likely to be SOL.

 

[ghostbuster]

My reaction, for what it is worth, would be that if the utility contracted to furnish you with an ungrounded delta system, then they are in breach of their contract unless they disconnect the customer who is grounding your service.

If all their tariff gives you is a delta system with grounding not specified, then I guess you are more likely to be SOL.

Utility specs are strictly for phase to phase voltages.According to them they are not responsible for a grounded phase (even if it is their own equipment (cables ,transformers etc.) that is causing this problem).I have 5 different locations --so far---across this city where this same situation exists.Lawyers have been hired.

 

[Sahib]

The same SPD, now sacrificial, may also be designed to protect the downstream equipment for any increase in voltage due to phase to ground fault, IMO.