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400kv MCC Room cable pits
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Fisher900116  
#1 Posted : 08 January 2014 20:28:25(UTC)
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Fisher900116
I am wondering if anyone has any advice or procedures for cleaning of cable pits in an MCC room. The cable pits have become contaminated with water and is now causing issues with smelling badly and also fly issues. However the cables have 400kv cables that run in the pits and then connect into the control panels, the buzz bars are located at the top of the control panels. The issues are confined space but also cleaning the pits.
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paul.skyrme  
#2 Posted : 08 January 2014 21:23:24(UTC)
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paul.skyrme
Are you SURE these are 400kV cables?
If so then, if they are your responsibility then you should have an SAP on site, ask them, they must know what to do, it's the law.
400kV cables are VERY unusual on consumer sites as consumer responsibility, these are normally National Grid cables, so they would normally have responsibility for them, so you can just get NG to turn them off for you to clean out if it is your property and they are causing you issues, but you would loose all power to your site, and I suspect quite a large area around your site, possibly several square miles.
So it may need to be a planned shutdown.
Also NG may wall be interested in their 400kV cables being contaminated in this way by your site, so you could get into bother from NG.
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Jane Blunt  
#3 Posted : 09 January 2014 08:29:08(UTC)
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Jane Blunt
I would go along with what Paul says - check that they really are 400kV and what they are for.

I have worked in places where there are very high voltage cables which have nothing to do with the National Grid (electron beam equipment). For an example see
http://en.wikipedia.org/.../Electron_beam_machining

Fools rush in on these. If they have insulators, they do not necessarily become 'dead' when isolated from the energy source. You need someone who knows how to render them safe.
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jontyjohnston  
#4 Posted : 09 January 2014 11:34:38(UTC)
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jontyjohnston
Fisher

Are you sure they are not 400V? What diameter are they roughly?

400kV cables would only ever go into a transformer not a control panel. 400kV is transmission voltage only and is normally stepped up from the generation source (txs) and stepped down (txs) as it enters the distribution network.

That said you need a competent person to assess them and advise you of an appropriate safe system of work.
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Jane Blunt  
#5 Posted : 09 January 2014 13:30:37(UTC)
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Jane Blunt
jontyjohnston wrote:
Fisher

Are you sure they are not 400V? What diameter are they roughly?

400kV cables would only ever go into a transformer not a control panel. 400kV is transmission voltage only and is normally stepped up from the generation source (txs) and stepped down (txs) as it enters the distribution network.

That said you need a competent person to assess them and advise you of an appropriate safe system of work.


While they probably are 400V rather than 400kV, I would not completely rule out the possibility that they are what is stated. There is at least one 600 kV electron microscope in existence. The design of the power room is amazing.

http://www-g.eng.cam.ac.uk/oatley/hires.html

These forums are used by people from a very wide ranging background.


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paul.skyrme  
#6 Posted : 09 January 2014 16:16:21(UTC)
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paul.skyrme
Jane,
Whilst I appreciate your point fully.
The OP has stated that this is a Motor Control Centre, MCC.
I really doubt that the cables are 400kV TBH.
It is possible but doubtful, after all this is classed as EHV >132kV IIRC, shame on me not knowing off the top of my head I know, but I don't "do" HV, it's not that common really outside Heavy Industry, the NG & DNO, allowing for other "special" areas obviously!
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Zimmy  
#7 Posted : 09 January 2014 18:20:16(UTC)
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Zimmy
400kv? MCC room? Not a hope in hell...
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Zimmy  
#8 Posted : 09 January 2014 18:22:06(UTC)
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Zimmy
and... it is BUS bars not Buzz :-)
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Zimmy  
#9 Posted : 09 January 2014 18:24:16(UTC)
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Zimmy
400,000 V would need a lot of room in an MCC panel, give it a go. See how far you can hold an earthed steel rod away from them before they blow you away.
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Jane Blunt  
#10 Posted : 09 January 2014 19:26:46(UTC)
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Jane Blunt
Zimmy wrote:
400,000 V would need a lot of room in an MCC panel, give it a go. See how far you can hold an earthed steel rod away from them before they blow you away.


Why? I would expect these to be insulated.
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paul.skyrme  
#11 Posted : 09 January 2014 19:35:10(UTC)
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paul.skyrme
Jane,
What I & Zimmy understand of an MCC panel with buss bars being in the industry seems different to your understanding.
Buss bars are uninsulated.
The insulation between them is by air separation, so @ 400kV, this is going to be considerable, the control gear for the motors is also going to be huge.
It is always possible to bypass interlocks and often it is the only way to accomplish the work.
However, with HV, it is a no-no.

TBH, we are now speculating, we need more info from the OP.
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Fisher900116  
#12 Posted : 09 January 2014 20:46:30(UTC)
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Fisher900116
Apologies the cables are 400v still large enough to cause issues though, I want to carry this work out when it can be fully isolated. I've completed the risk assessment today and the only thing I'm concerned with is having people in the pit while the cables are still live!!!
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paul.skyrme  
#13 Posted : 09 January 2014 20:54:54(UTC)
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paul.skyrme
Why are you concerned about the cables being live?
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Fisher900116  
#14 Posted : 09 January 2014 21:58:25(UTC)
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Fisher900116
I'm concerned the people carrying out the cleaning will be entering the pits when the electrical is still live as its been discussed not to switch off and isolate then to carry out the task. The electrical cables enter the bottom of the electrical panels and also they will be working very close to the cables when inside the pits to be able to get them cleaned out. The electrical competent person on side has there is little risk to coming into contact with the cables as they are insulated and if they were damaged then would show faults.
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paul.skyrme  
#15 Posted : 09 January 2014 22:06:20(UTC)
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paul.skyrme
Are they SWA?
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johnmurray  
#16 Posted : 09 January 2014 23:02:27(UTC)
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johnmurray
¨400,000 V would need a lot of room in an MCC panel, give it a go. See how far you can hold an earthed steel rod away from them before they blow you away¨

My Paschens is a little rusty now....but that would be about 500mm in dry air at 1 bar?
Mind you, the one holding the steel bar would just not exist for long..
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Fisher900116  
#17 Posted : 09 January 2014 23:16:42(UTC)
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Fisher900116
Yeah they are SWA.
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Jane Blunt  
#18 Posted : 10 January 2014 07:28:45(UTC)
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Jane Blunt
paul.skyrme wrote:
Jane,
What I & Zimmy understand of an MCC panel with buss bars being in the industry seems different to your understanding.
Buss bars are uninsulated.


I know that bus bars are uninsulated. If you read the original post, they are described as above, and the other cables as beneath.

MCC panel is not my area, however, with at least one rather incongruous part of his post, there was a fair chance that we were not dealing with a bog standard situation and, until otherwise notified, it is wise to take it at face value on the one hand, but expressing our concerns on the other.

paul.skyrme wrote:
The insulation between them is by air separation, so @ 400kV, this is going to be considerable, the control gear for the motors is also going to be huge.
It is always possible to bypass interlocks and often it is the only way to accomplish the work.
However, with HV, it is a no-no.

TBH, we are now speculating, we need more info from the OP.


I agree, and we now know that our suspicions were correct. However, as above, when a post does not make sense, it is wise to think around the problem to other areas perhaps where such voltages are encountered, albeit in insulated cables. The 100kV cable on the electron beam gun does not 'blow you away', but you mess around with it after it has been disconnected from the energy source at your peril, as it retains considerable stored energy, to be released on the unwary later.

Some of the users of this forum work in interesting places.
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paul.skyrme  
#19 Posted : 10 January 2014 08:29:14(UTC)
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paul.skyrme
TBH then Fisher, I don't see for the life of me what you are worried about.

If your description is correct.

Yes you have 400V phase to phase rms.

You have 230V phase to earth rms.

Your flex on your kettle or toaster has 230V phase to earth, and the conductors on that are a lot more vulnerable than those in an SWA cable.

The SWA has a layer if insulation over the conductors, then a layer of polymeric bedding, which has insulating properties, but is not officially an insulator, then an earthed steel wire armour then a layer of polymer sheathing, which also has insulating properties, but again is not officially an insulator.
Plus they could have 2 earthed conductors under the bedding as well.

IF the cables have been installed correctly then working around them, water or no is fine, your electrical person on site was quite correct.

You do however, know that the cables are not damaged don't you? After all you should be maintaining the installation in accordance with EAWR, thus compliance with BS7671 should be assured, thus, your last periodic inspection (PIR/EICR) should show that the cables are fine.

The confined space bit I can't comment on as I've not seen it, not my speciality either.


Jane, I agree, that is the thing with HV stuff, the stored energy in the cables after isolation can be considerable due to the cable capacitance, many don't realise this.
It's one of the reasons the DNO's spike HV cables before jointing.
If the OP had not described the situation in the way they did then I would not have taken the route that I did with my answers.
In a lab environment, as you say, possibly very different, again in Heavy Industry, & Electrical Distribution, but in the latter two, you will have SAP's who know their stuff in charge of the HV if it's their responsibility.
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Fisher900116  
#20 Posted : 10 January 2014 14:24:59(UTC)
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Fisher900116
Thanks Paul for your information, I have inspected the cable and cant see any damage I will ensure that I check when these were last inspected.
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Zimmy  
#21 Posted : 10 January 2014 16:12:40(UTC)
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Zimmy
This is fun :-)
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John M  
#22 Posted : 10 January 2014 16:48:32(UTC)
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John M
400 kv? Transmission lines surely!

Distribution lines?

Seek EXPERT advice my good man!

Jon
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Zimmy  
#23 Posted : 11 January 2014 15:41:58(UTC)
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Zimmy
Thanks for the input Jon, most informative :-) I'll be sure to add you to my 'electrical expert list'
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tony.  
#24 Posted : 13 January 2014 21:05:00(UTC)
Rank: Forum user
tony.
Get a sump pump to pump out the water. Wet vac for all the sludge and crap that will collect in the trench
Get a mixture of bleach and water and apply in the trench and brush about.
Get ducts sealed to prevent water ingress. Try rise kits.

Before all of the above, write ms/ra and obtain permit from AP if required.

Bottom of MCC may not be ip rated so dont spray water about, but if your sensible I wouldnt see a problem.
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johnmurray  
#25 Posted : 14 January 2014 07:29:43(UTC)
Rank: Super forum user
johnmurray
Presumably a non-sodium hyperchlorite bleach one hopes?
Otherwise the operative could find him/her/it self breathing chlorine,
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