Voltage Detector for Underground Cable 2

[LDG0926]

Hi

Is there anyone can help me fine a tool/equipment that can detect the Ring Main Unit underground cables? Other RMU's has capacitive test point and this will be determine by using the voltmeter. But other RMU's dont have and the termination is not elbowed rather lug type connection.

I am going to open the kiosk switchgear and earthed the cables. This determing the cable is dead because it is earthed. What I will do next is to unearthed the cable becasue I am going to test it. In order for me to test the cable is to unearthed the cable again.But I want to have a double check that the volatge (11KV,22,33KV) is not present on the cable "test before you touch" anybody?

Thanks.

 

[Zogzog]

What type of test do you plan on doing to your cables?

I am asking because one who is qualified to do MV cable testing should know how to and have the equipment to verify the cable is not energized. You might want to consider hiring a qualified testing company to do this testing if you have to ask questions like that.

 

[Marmite]

You shouldn't need to test it. If the design of the RMU permits, then make the test connections before you open the earth switch. If its of the design where opening the test access removes the earth then you know its dead and earthed immediately prior to opening the test access so there's no danger. The riskiest part of testing is making sure the charge you have applied has dissipated from the cable before manipulating connections. Use a discharge stick and a test set with integral discharge resistors.
All the HV voltage testers I've come across are designed for direct contact. To start removing cable box covers and sliding down insulating boots to make a test connection to the studs is increasing the risk of inadvertently opening the wrong box and risks damaging the termination in some way. If you have to slide the boots down by hand anyway then you have defeated the object of the test.
Regards
Marmite

 

[Zogzog]

"You shouldn't need to test it."

OSHA and NFPA 70E would disagree with that statement. So you are saying you can bet your life that an interlock has never and will never fail?

Tif and Salisbury make non contact voltage detectors for those voltage levels, I have never seen a person work on MV cables without owning and using a non contact detector before.

 

[slavag]

I'm totally agree with ZogZog. Not double check, ten times check before touch!!!!! Once I touched, enough.
I would like recommend you ( It's not sale and not marketing) some intresting device from Poland. I think use it as standard device in several projects. Please see attached.

http://library.abb.com/GLOBAL/SCOT/...716C003BD8E4/$File/VisiVolt-Catalogue_EN.pdf.

I know it's not exctly answer to OP, but it's important for safety.
Regards.
Slava

 

[Marmite]

I stand by what I said. In the UK the national safety rules say that to make a high voltage system safe for work or testing, it must be first made dead, then isolated (safety locks, caution men working labels), earthed and screened from any live parts that may come into contact. If you follow these steps then there is no possibility of something being live because you have applied an earth immediately prior to issuing either a permit to work or a sanction for test safety document. With a ring main unit the earthing is integral to the switchgear and everything is interlocked, so you would need the failure of the main contacts to open, the failure of the earthing switch to operate and the failure of the test access interlock before you get an unsafe condition. Thats three different mechanical interlocks on one switch that need to fail. Plus then you have another switch at the other end of the feeder you are testing which would need to experience identical failure. There is no requirement to test in the UK safety rules once you've gone through the make dead, isolate, earth steps, and it would be physically impossible to make a meaningful test on most types of non isolatable switchgear. An oil filled ring main unit with compound filled cable boxes is a perfect example. Most require the insertion by hand of test bushings into the switch. The test access won't open until the earth has been applied, but there is no way of testing anything before you insert the test bushing. I accept that if you can make a meaningful test then you should do, but the original post referred to a ring main unit, and was not a general point of principle question.
Regards
Marmite

 

[davidbeach]

Gee, no induced voltages on cables in the UK, how nice. Not something I'd bet my life on, thanks.

 

[Zogzog]

My problem isnt that you are betting your life that the interlocks will never, ever fail, but rather than you are recommending someone else bets thier life too.

"With a ring main unit the earthing is integral to the switchgear and everything is interlocked, so you would need the failure of the main contacts to open, the failure of the earthing switch to operate and the failure of the test access interlock before you get an unsafe condition."

or.. the switchgear was never grounded properly in the first place or a loose/corroded ground connection. Those who do acceptance testing on MV switchgear have all found this condition more than once.

 

[slavag]

Dear Marmite.
Isn't important were are you: UK, US or USSR, isn't important what is a national safety rules, isn't ipmortant
swg RMU, primaty, 400V or 400kV. Don't think about it, you need think about your life or your team life.
We told about additional check before touch and additional
eq., it's all, it's nothing. Not requested time, not so much money. If will happend something, someone add to national safety rules new rows, but it isn't help to family.
Sorry for patetic.
Regards.
Slava

 

[Marmite]

Any testing to check that there is an unsafe voltage on high voltage apparatus is done before the application of earths. Once the earths have been applied the apparatus is released for work. If you can't accept that fundamental principal that something is safe once its properly isolated and earthed then no work would ever be able to be carried out on HV apparatus. There is no betting of life.
Regards
Marmite

 

[slavag]

Hi Marmite.
Only in theory and only in HV or EHV, but not in distribution grids. I try explain two cases in the last tree years in our area, same cases and cubicles RMU in small contries. In both cases, maintanance team open all disconectors and CB's and puted moving earthing condactors. Provided maintanance, open earthing and.. in one case one person was dead in second several months in hospital.
Reason:
1. Head of team not check all 400V CB's in whole area.
2. Fail of ATS interlocks on one of 22/0.4kV xfr.
3. Standbay generators start work on the 3-phase short-circuit w/o problem after some delay.
Result is clear.
Regards.
Slava

 

[LDG0926]

Hi Guys- Thank you very much for your discussion. I do not make any testing, but I am looking for this kind of tool that would safely secure the worker/lineman on field. What he will do is to test the cables using the megger (insulation test). Before this is done, the cables were attached to the RMU's. Steps:

1. De-energize two RMU's that are connected(one to test)
2. Earthed the cable by turning the earthing switch
3. Open the lid tank/panel.
4. Unearthed the cable by manipulating the interlocks

> The cable now is unearthed and now ready for insulation test of the cable.
BUT..before the test is done the cable now is floating and unearthed because we cannot test it, if it is earthed.

Now it now address the "test before you touch". Modiewark cannot be used at all RMU's since different RMU's have different termination type (Elbow,Lug Type etc.)

Thanks.

 

[Zogzog]

"Any testing to check that there is an unsafe voltage on high voltage apparatus is done before the application of earths"

Thats not what you stated earlier, you said "you shouldn't need to test it"

 

[Marmite]

Zogzog, you should try reading the posts before replying to them. Right at the very beginning of this thread LDG0926 stated
"I am going to open the kiosk switchgear and earthed the cables. This determing the cable is dead because it is earthed. What I will do next is to unearthed the cable becasue I am going to test it. In order for me to test the cable is to unearthed the cable again"

This is perfectly acceptable and consistent with normal HV safety rules with will not allow the release of apparatus for work or testing until it has been earthed.

My point right through this thread was that once the earths have been applied you shouldn't need to test the cables for unsafe voltages. The earthing switch applies a three phase short to earth.

The thread turned into a general philosophical argument about whether you should test before touching. I don't have a problem with that, it makes perfect sense.
The problem is that the design of ring main units, unless they have capacitively coupled test points or elbow type cable connections generally precludes such testing without dismantling or infringing safety clearances to make the test.

I have considerable experience in this situation as the vast majority of UK distribution substations are equipped with ring main units.

Regards
Marmite

 

[davidbeach]

The problem, Marmite, is that the grounds are removed and the cable is then worked on live. Equipment is either live or visibly grounded, there are no other states, no such thing as "deenergized" at the voltages mentioned in the original post. The presence of other energized conductors will ensure that there is some voltage on the conductors as soon as the grounds are removed. You want to kill your self messing about with live conductors that is your business, but I find it highly inappropriate that you recommend others do so.

 

[burnt2x]

LDG0926,
Back to OP, you simply need to get yourself an MV Voltage proximity tester. Looks like a stick with a shrouded tip, lits up when cable is energized. Just be sure to test at terminals where the grounding shield is laid back. Google it.

Additional comments: You may want to refer to 29CFR 1910.269 for guidance on making sure you don't get torched! There's a saying "TBT easier said than done" (Test Before Touch = TBT).

Peace man!

 

[Marmite]

Davidbeach, I really don't understand your comments and can only assume that there are major differences in either the terminology we use, or the working practices, or both. I would be genuinely interested in a step by step explanation of how you would go about this testing.
I have been a senior authorised person in the UK utility industry, which is the level of system authority required to put people to work on HV systems since 1990, and have not recommended any practice in this thread which is not routine or fully compliant with the UK Distribution Safety rules.
Regards
Marmite

 

[slavag]

Hi Folks.
I checked this points with our utilities ( power generation sector) and them saied me same as Marmite. " After disconnect earthing/grounding you don't need check again voltages". What is a difference in my understanding and may be it's our misunderstanding of Marmite position: don't connect any test devices to cable/motor/xfr w/o earthing/grounding, that mean you connect your device, other person disconnected earthing/grounding, after test again same person connect grounding and only after this you can disconnect your tester. This procedures also include many additional check points.
I would like check this issue also with our transmission and distribution sector. Actually, it's not my field, but I think safety it's very important issue in our job.
Regards.
Slava

 

[slavag]

OOOOHHHHHHH.
David , Zogzog, we are not right!!!!!.
I read again first post of Marmite, he wrote, make your test connection before open earthing.
Marmite, sorry!!!!!!.
Best Regards.
Slava

 

[Zogzog]

Here is the issue,

"If its of the design where opening the test access removes the earth then you know its dead and earthed immediately prior to opening the test access so there's no danger."

This is an assumption that an interlock did its job, right before this you said "you shouldnt need to test it"

Now I do agree with you that after TESTING the cable you can apply grounds without doing a voltage test if your test set has an internal discharge feature.

Maybe there is a language barrier here, maybe our OSHA requirements are different in the US than the UK, maybe we have different opinions on what football is (Wait, got off track there), but you should NEVER assume that a system is de-energized until you do a voltage test (Live-Dead-Live, verifing the detector works befotre and after the test on a known live source), even if it is interlocked.

Have you ever seen the aftermath of applying grounds to an energized circuit? Its ugly, several OSHA incidents (fatalaties) can be found on

http://www.osha.gov

on this paticular accident.