VLF Dead break terminations - 21.1kv test voltage recommendations

[tcoupekyle]

We are out on a solar farm testing 35kv cable with Dead break terminations. The termination is 21.1kv rated but 35kv class. Cable is 35kv xlpe cable.
Neta says test at 44kv VLF for 35kv cable but there seems to be a gray area in the termination.
Any experience or recommendation on test voltage? Or test procedure?
When we try to test at 44kv vlf the set is arcing across the body.
So the plan as of now is to test at 22kv for 15 minutes and step the voltage to 44kv after that 15 minutes.

[SecondGen]

We are out on a solar farm testing 35kv cable with Dead break terminations. The termination is 21.1kv rated but 35kv class. Cable is 35kv xlpe cable.
Neta says test at 44kv VLF for 35kv cable but there seems to be a gray area in the termination.
Any experience or recommendation on test voltage? Or test procedure?
When we try to test at 44kv vlf the set is arcing across the body.
So the plan as of now is to test at 22kv for 15 minutes and step the voltage to 44kv after that 15 minutes.

You may need to reduce the voltage to match the rating of the termination. Where do the cables land? If they connect to a switch that you can isolate you might be able to get some more voltage with the cables terminated.

[tcoupekyle]

You may need to reduce the voltage to match the rating of the termination. Where do the cables land? If they connect to a switch that you can isolate you might be able to get some more voltage with the cables terminated.

So we brought that issue to engineering that the term is only rated for 21.1kv and at first they said test at 26kv. But then (after testing) they said no they wanted to re-test at 44kv and they couldn't find any literature to back up the test voltage one way or the other. So they decided to re-test at 44kv.

The cables terminate on an inverter so we can't jump through.
We are using a dead break connecting cap to input the voltage into the cable. And dead end caps screwed together on the other side.

We have gotten the cable to test in the last hour. We covered the exposed end of the connecting cap with 130c tape. It's also hotter and drier now this morning was 99 percent humidity.
It's probably 95% humidity now. So somewhere between the tape on the connecting cap and the humidity drop we have been able to get a complete test on 1 single conductor.

I am still curious about others opinion on the test voltage though.

[tcoupekyle]

525Trying to attach picture

[SecondGen]

525Trying to attach picture

That is a sweet looking setup, I'd still be worried about overstressing the term but it sounds like that burden is on engineering now. Is this a new install? Obviously cables should have been tested at 44kV prior to terminating and then re-tested at the term voltage but that's not possible now.

[tcoupekyle]

Yes. You're exactly right. New installation, acceptance testing.

Cable were not tested prior to the termination being built.

And yes, we recommended not testing at full voltage because the term is the weak link in the chain. But got over turned after the fact. So yes the burden of liability is on the engineers in the office.

[tcoupekyle]

So today we came back out and continue testing. The first cable we've tried to test today fails at 44kv within the first minute.
No progress as of today.

[TestTech]

So today we came back out and continue testing. The first cable we've tried to test today fails at 44kv within the first minute.
No progress as of today.

Your technically Testing a "Half a Splice" connected to your cable. Why would you expect it to hold the voltage?

Why not simply finish making the splice correctly, add some cable and test away?

See attached (I hope) picture (Stolen from CBS Field Services post on Linkedin without permission)

It shows a 200A elbow but the concept is the same.

526

[tcoupekyle]

Hey! Yeah that's what we decided to do build another and a stress cone to try it.
That's exactly what we been looking for. Is that how you normally test these?
I've always just used the half splice and hadn't had issue until now. But maybe in the past it was all lower voltage. In Maintenance situations.

[Kalbi_Rob]

So we brought that issue to engineering that the term is only rated for 21.1kv and at first they said test at 26kv. But then (after testing) they said no they wanted to re-test at 44kv and they couldn't find any literature to back up the test voltage one way or the other. So they decided to re-test at 44kv.

The cables terminate on an inverter so we can't jump through.
We are using a dead break connecting cap to input the voltage into the cable. And dead end caps screwed together on the other side.

We have gotten the cable to test in the last hour. We covered the exposed end of the connecting cap with 130c tape. It's also hotter and drier now this morning was 99 percent humidity.
It's probably 95% humidity now. So somewhere between the tape on the connecting cap and the humidity drop we have been able to get a complete test on 1 single conductor.

I am still curious about others opinion on the test voltage though.

35KV terms are actually rated maximum phase-to-ground 21.1 KV and stamped on the side of the termination. If you read the literature, you will find they are actually rated for up to 38kV class operating voltages, see link:

https://www.eaton.com/content/dam/eaton/products/medium-voltage-power-distribution-control-systems/line-installation-and-protective-equipment/600a-35kv-class-bol-t-deadbreak-connector-catalog-ca650008en.pdf

I agree with the above comments, since it looks like your trying to test a cable using pass-thru bushings with insufficient insulation and corona suppression (that bushing is technically uninsulated unless installed inside the t-body). This would be possible at lower voltages (still not recommended), but at higher voltages, you must fully insulate the test specimen and suppress the corona. Damage to cables comes from discharge of voltage, which means your non-destructive test has now become a potential destructive test due to insufficient tools. This is common practice, since management typically doesn't want to spend the money to make a adequate test rig, typically or just lack the knowledge to properly test cables.

[Kalbi_Rob]

Hey! Yeah that's what we decided to do build another and a stress cone to try it.
That's exactly what we been looking for. Is that how you normally test these?
I've always just used the half splice and hadn't had issue until now. But maybe in the past it was all lower voltage. In Maintenance situations.

We found around 37-42 KV (based on weather) open Pass-Thru Bushings start to arc. That was before we learned (like you are now) that we needed to produce a proper rig to test.
We contracted a MV splicer to create 3 ft t-body cables and put lug terminals at the other end for our cable connections, since we could easily attach corona suppression balls on the end along with our test cable.

[TestTech]

We found around 37-42 KV (based on weather) open Pass-Thru Bushings start to arc. That was before we learned (like you are now) that we needed to produce a proper rig to test.
We contracted a MV splicer to create 3 ft t-body cables and put lug terminals at the other end for our cable connections, since we could easily attach corona suppression balls on the end along with our test cable.

Exactly.

In addition, its important to keep the various test rigs that you make clean and in good shape. You dont want to remove a customers new clean silicone coated T-Body and plug in a test jig that has been rolling around the back of your van for a month with dirt and sand stuck in the used silicone. It may pass the your VLF test but certainly wont last as long at it should when you plug the now dirty new T-Body into the transformer or switch after your done.

[tcoupekyle]

We found around 37-42 KV (based on weather) open Pass-Thru Bushings start to arc. That was before we learned (like you are now) that we needed to produce a proper rig to test.
We contracted a MV splicer to create 3 ft t-body cables and put lug terminals at the other end for our cable connections, since we could easily attach corona suppression balls on the end along with our test cable.

Thanks!

[tcoupekyle]

We built a test rig similar to what you pictured. And testing went ultimately very well.
Thank you all so much.

[ericnessl]

So we brought that issue to engineering that the term is only rated for 21.1kv and at first they said test at 26kv. But then (after testing) they said no they wanted to re-test at 44kv and they couldn't find any literature to back up the test voltage one way or the other. So they decided to re-test at 44kv.

The cables terminate on an inverter so we can't jump through.
We are using a dead break connecting cap to input the voltage into the cable. And dead end caps screwed together on the other side.

We have gotten the cable to test in the last hour. We covered the exposed end of the connecting cap with 130c tape. It's also hotter and drier now this morning was 99 percent humidity.
It's probably 95% humidity now. So somewhere between the tape on the connecting cap and the humidity drop we have been able to get a complete test on 1 single conductor.

I am still curious about others opinion on the test voltage though.

Hey bud, I've been doing acceptance testing at 44kV on solar farms in NC (high humidity) and I've found that I can overcome the arcing at 44kV by cutting the end off of a rubber boot from a sectionalizer and fitting it snugly over a deadbreak connecting plug with stud.

Attaching a photo...

This also works in mild rain that has occurred in the middle of testing.

535

I wouldn't test those terminations (in your case) at 44kV either. We often see 15kV elbows on 25kV cable. Not sure why it's built that way (the drawings usually call for 15kV cable in those cases), but whatever. We treat it like 15kV.

I'm curious to know what inverter type has MV cable terminations. Are you sure it wasn't a skid with an integrated MV transformer?

[Kalbi_Rob]

Hey bud, I've been doing acceptance testing at 44kV on solar farms in NC (high humidity) and I've found that I can overcome the arcing at 44kV by cutting the end off of a rubber boot from a sectionalizer and fitting it snugly over a deadbreak connecting plug with stud.

Attaching a photo...

This also works in mild rain that has occurred in the middle of testing.

535

I wouldn't test those terminations (in your case) at 44kV either. We often see 15kV elbows on 25kV cable. Not sure why it's built that way (the drawings usually call for 15kV cable in those cases), but whatever. We treat it like 15kV.

I'm curious to know what inverter type has MV cable terminations. Are you sure it wasn't a skid with an integrated MV transformer?

Actually think he has 35kV connectors.

It is common to have 15kV terminations placed on Higher rated (35kV or 25kV) cable, as some customers wish to oversize the cable capabilities for future applications, thus only having to replace the terminations versus the entire cable run. You are correct to treat the cable as 15kV since your terminations are the weakest link, and you cannot exceed the voltage specs for the weakest linked component on the cable.

But the termination he described are 21.1kV to ground standard 35kV rated 600A dead-break terminations as noted in the below link document below. The termination is rated up to factory test voltage of 50kV or 70kV depending on the BIL rating, thus Acceptance test voltages of 44kV are required per IEEE 400.2. See table 1 of the attached document linked below:

https://www.eaton.com/content/dam/eaton/products/medium-voltage-power-distribution-control-systems/line-installation-and-protective-equipment/600a-35kv-class-bol-t-deadbreak-connector-catalog-ca650008en.pdf

[ericnessl]

Actually think he has 35kV connectors.


But the termination he described are 21.1kV to ground standard 35kV rated 600A dead-break terminations as noted in the below link document below. The termination is rated up to factory test voltage of 50kV or 70kV depending on the BIL rating, thus Acceptance test voltages of 44kV are required per IEEE 400.2. See table 1 of the attached document linked below:

https://www.eaton.com/content/dam/eaton/products/medium-voltage-power-distribution-control-systems/line-installation-and-protective-equipment/600a-35kv-class-bol-t-deadbreak-connector-catalog-ca650008en.pdf

Yep... good point. I didn't read that carefully enough and thanks for pointing that out.