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Old 07-09-2018, 12:24 PM   #1
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Default 5kv epr hi pot voltage

133% insulation 115 wall-mils EPR shielded, Raychem Terms DC Hi-Pot initial acceptance test. what voltage do you all normally go up to. i know okonite says 35kv 15 min, NETA max is 36, IEEE 576-2000 max is 36, IEEE 400 is 28kv. but what do you all do and how long?

thank you very much.

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Old 07-09-2018, 12:29 PM   #2
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You asked. I answered .........
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Old 07-09-2018, 12:37 PM   #3
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Going off memory, the NETA spec was square root of 2 times the RMS voltage of the cable.
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Old 07-09-2018, 12:40 PM   #4
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This new cable or an aged install?
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Old 07-09-2018, 12:44 PM   #5
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Quote:
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This new cable or an aged install?
new.

i edited my origianl post with the NETA, Okonite and IEEE stuff. i'm interested in what you all are actually doing though, i have heard much lower. 12.5kv.

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Old 07-09-2018, 12:45 PM   #6
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Old 07-09-2018, 01:15 PM   #7
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DC Hipot will only find gross installation errors. Pretty worthless test for an acceptance test. VLF or Tan Delta is what most test companies will do.
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Old 07-09-2018, 01:17 PM   #8
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DC Hipot will only find gross installation errors. Pretty worthless test for an acceptance test. VLF or Tan Delta is what most test companies will do.
Not only that, I don't have the nerve to hipot anything that's not brand new. I'm not interested in creating scrap wire.
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Old 07-09-2018, 03:26 PM   #9
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Quote:
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Not only that, I don't have the nerve to hipot anything that's not brand new. I'm not interested in creating scrap wire.
https://www.okonite.com/media/wysiwy...er/Tech_31.pdf

EPR insulation doesn't break down like XLPE, if you don't go over voltage
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Old 07-09-2018, 03:38 PM   #10
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Quote:
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DC Hipot will only find gross installation errors. Pretty worthless test for an acceptance test. VLF or Tan Delta is what most test companies will do.
thanks, i'll look into those.
i thought VLF was similar to dc-hi pot, just ac and lower voltage? this is epr insulation too if it makes a difference to you
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Old 07-09-2018, 05:06 PM   #11
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for acceptance only.....no higher than 36KV for 5 minutes.

you can increase treeing channels if you do it on old cables.
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Old 07-09-2018, 10:07 PM   #12
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IEEE 400 is the standard for AC hi pot, VZlF, and DC hi pot. It specifically tells you very bluntly that since it doesnít show anything and was designed for PILC, and causes cable damage, it is no longer recommended.

Second the acceptance test is for manufacturing as in Factory Acceptance Test, not a field test. You are supposed to use the maintenance voltage for field acceptance unless you are extruding cable in the field. I donít care if NETA is a large consortium of testing companies that spec out all kinds of irrelevant and pointless tests for the sake of driving up testing profits.




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Old 07-10-2018, 06:44 AM   #13
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Quote:
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IEEE 400 is the standard for AC hi pot, VZlF, and DC hi pot. It specifically tells you very bluntly that since it doesn’t show anything and was designed for PILC, and causes cable damage, it is no longer recommended.

Second the acceptance test is for manufacturing as in Factory Acceptance Test, not a field test. You are supposed to use the maintenance voltage for field acceptance unless you are extruding cable in the field. I don’t care if NETA is a large consortium of testing companies that spec out all kinds of irrelevant and pointless tests for the sake of driving up testing profits.




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the manufacturer says something a little different, and like i said in previous posts this is EPR not XLPE (the insulation everyone had problems with back in the day with DC Hi-Pot)


"Okoguard is not affected by the application of a DC potential at factory testing and subsequent
tests prior to energizing or after many years of operation. In fact, it is customary in industrial
installations to DC Hipot an Okoguard cable including:
• When first received at the installation site,
• Prior to pulling the cable,
• After pulling the cable,
• After splicing and final terminating the cable,
• As a final system test prior to turning it over to the end user.
Thus, it is acceptable to apply a DC Hipot to Okoguard insulated cables as many times as
needed without the consequence of damaging the insulation
"


https://www.okonite.com/media/wysiwy...er/Tech_31.pdf


"VLF (Very Low Frequency) and field partial discharge tests have been developed over recent
years to provide an option to DC Hipot testing for XLPE cables"


we have found bad cables with dc-hi pot, 5kv cables and they've shown bad at like 7kvdc (new, never energized cables, straight from factory)

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Old 07-10-2018, 06:51 PM   #14
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i found an old thread from another forum i think Zog was apart of back in 09' LOL, i guess He's been here before. lot's of good info, thanks for the old posting Zog. whats your thoughts on PD?


DC Field Test for Medium-Voltage Cables: Why Can No One Agree?, IEEE Transactions on Industry Applications, Vol. 34, No. 6, Nov/Dec 1998,
the authors indicate that the EPRI tests were limited to XLPE cable and that the recommended tests on EPR cable were stopped due to lack of funds. The lack of evidence of damage to EPR may not mean there is no damage.


does anyone have any information on whether EPR was ever fully tested? and shouldn't be tested like okonite says after put into service?

what do you all think of the okonite info i posted, i thought okonite was a very respectable company, there engineering handbook seems well thought out.


by the way. i understand and agree there are better tests for determining cable condition, my original post is just for a pass fail initial acceptance test, just a withstand test, i know i get know useful data other than pass or fail and i'll look into that for future but for now we're just doing dc hi-pot so any advice on doing dc hi-pot is especially appreciated right now, info on other test is appreciated to but i can look into those myself later, i'm just not finding a ton on dc

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Old 07-10-2018, 07:05 PM   #15
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paulengr whats 400 recommend using, whats it say about Partial Discharge, that's whats looking best to me?

an IEEE guy said this back in 09'
"An off-line PD test detects on the order of 99% of defect in cable systems if.... administered properly."

thanks
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Old 07-10-2018, 07:30 PM   #16
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Quote:
does anyone have any information on whether EPR was ever fully tested? and shouldn't be tested like okonite says after put into service?
No. EPRI is very open. You can look up all their projects and you can read any report over 10 yeas old. It's all posted publicly on their web site. Buying current (<10 years) reports if you're not a member is pricey ($10,000 per report) though. Sometimes they go ahead and release some of them early.

EPRI has basically a catalog of research ideas. Their members (nuclear power utilities) basically put down funding on as many projects as they are interested in. When one reaches full funding status, they do it. Kind of like a very private version of "Go Fund Me".

]quote]what do you all think of the okonite info i posted, i thought okonite was a very respectable company, there engineering handbook seems well thought out.[/quote][/quote]

All well and good but when on the one hand we have a consensus safety standard that says that essentially DC hi potting is a waste of time compared to other better tests and one company that says "OK you can do it", it really doesn't matter. And yes Okonite is just about the most expensive medium voltage cable on the market (Essex is worse) and it's some good stuff, and their technical guides are really good..

I look at DC hi pot this way. The best use for it is not so much testing the cable but the connections at the end. Occasionally you have a termination that fails for whatever reason whether installation error or manufacturing defect, and any of the IEEE 400 tests (PD, VLF, AC hi pot, DC hi pot) can find it, and the others either eliminate stress on the system or greatly reduce it (VLF), and are accepted and recommended. DC hi potting certainly tests something but it's not really testing legitimate conditions on the cable...it's inducing polarization, so what. We don't do that when we put AC on the cable. So that's why the other tests in my mind are vastly more beneficial. AC hi pot has the big problem that the tester weighs a lot. I know...we have one. In fact we don't even have a DC hi pot.

Put it another way...I was just at a customer's site in the Outer Banks (oh please don't send me out there...) a couple weeks ago. They had 3 pumps. The pump vendor tested all three motors with a multimeter and determined they were good. All three pumps didn't work when the customer wired them in. I've got a pretty high range multimeter and sure enough, one motor tested around 20+ Megaohms. Then on the same motor I stuck my megger on it and hit it with 500 V. It measured about 0.1 megaohms. With another recent known probably burned up motor I meggered it and got 90 megaohms but it shot right up to that number and then flatlined...classic bad insulation. PI test was 1.0. It also failed on milliohm testing on the coils...everything pointed to a burned up motor, confirming the PI test.

The point of this is that I'm sure something out there says that ohming a motor is a great test and I'd agree that as a first pass, the same motors that fail a megger test can't pass a simple ohm check either. But there are plenty of marginal cases where it passes the multimeter testing but fails as soon as we bring out the big guns and test with meggers and milliohm testers. IEEE and EASA recommend using not just those two tests but also some sort of inductive measurement (surge testing or MCA). The reason is that the megger (never mind the multimeter) have limited ability to detect motor defects. The other tests work to detect the cases that the megger misses to the point where the few marginal issues that the full MCA (megaohms, resistive imbalance, and inductive imbalance) is the best and most comprehensive test to use, given a choice. Like I tell my customers if all you have is a multimeter, use it. But you ar going to catch a lot more problems with a megger, and if you can afford it get a milliohm meter too. If you are not funding limited you can get an MCA tester but you need the week long training that goes with it and paying for calibrations every so often. By that point paying me once in a while to check it for you is cheaper.

Same thing is true with high voltage testing. Definitely need to do it especially for medium voltage installs the first time. If you only have a DC hi pot then be careful but use it. But if you are paying someone else to test or you have the money to get a better tester, by all means get a better tester and fleabay the DC hi pot. It's outdated and there are far better tests on the market that are less expensive if you are buying instead of renting or contracting out.

And yes...I'm qualified to do and have the equipment to do DC and AC hi potting, and all the tests I mentioned. And I'm quite up front with the customer. I had one today and we started with do we do MCA only or MCA and MCSA. Customer wanted MCA so that's what they're getting. I explained what MCSA does and we agreed with the trouble they are experiencing that there's no reason to do the test so I just did MCA.
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Old 07-12-2018, 11:17 AM   #17
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The thing about PD testing is all about data. Not so much the data gathered during the test but the data the company has doing the testing has to compare it to. You can have 3 companies come do a PD test on the same cable and have different interpretations of the same data. So I'm not a big advocate.
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Old 10-19-2018, 07:32 AM   #18
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Quote:
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The thing about PD testing is all about data. Not so much the data gathered during the test but the data the company has doing the testing has to compare it to. You can have 3 companies come do a PD test on the same cable and have different interpretations of the same data. So I'm not a big advocate.
have ever heard anything good or bad about polarization/depolarization current analysis using DC hi pot?

it's described IEEE 400 6.2.4, sounds like if you would build up a data library of cables you test and test them when they are new you may be able to do some productive analysis on aged cables with dc hi pot.
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Old 10-19-2018, 10:26 AM   #19
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Also i have an odd question, do you have an opinion or answer on if you need to completely make up a stress cone to do a quick dc hi pot before pulling a cable. i would imagine you would need to prep the ends like you would with a stress cone, stepping the semi con and shield, clean cable and possibly apply stress reducing tape at semi-con, temporary the shield braid. but would you need to apply the moisture seals and outer boot?

thanks
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Old 10-19-2018, 11:59 AM   #20
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I found a resource that says you can, thanks if anyone was looking. you just strip out the cable like you were going to terminate.
Attached Files
File Type: pdf DC+High+Potential+Testing southwire.pdf (213.3 KB, 59 views)

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