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Anonymous Poster #1

Joints on Buried 220KV 630mm2 Single Core XLPE Cables

01/30/2017 8:41 AM

What is the minimum distance to be maintained between joints on buried 220KV 630mm2 single core XLPE cables?

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#1

Re: joints on buried 220KV 630mm2 single core XLPE cables

01/30/2017 8:44 AM

It will depend upon the dimensions of the joint assembly being installed, which cannot be seen from here:

  • It would not be possible to install a piece of cable that were of shorter length than the joint assembly unit, as the adjacent joint assembly units would clash with each other.
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#2
In reply to #1

Re: joints on buried 220KV 630mm2 single core XLPE cables

01/30/2017 9:11 AM

thx PWSlack.

however, what i required is the minimum distance between joints on the same cable assuming that the cable was severed during construction and requires to be jointed. for example, the distance between normal joint stations is 300m and the severed section occurred some 120m away from the next normal joint: would it be possible to install a joint or it would require changing the entire cable?

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#3
In reply to #2

Re: joints on buried 220KV 630mm2 single core XLPE cables

01/30/2017 9:15 AM

<...possible...require...>

Of course it is possible. However, any requirement would be contained within the local Client's standard, which cannot be seen from here.

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#4
In reply to #3

Re: joints on buried 220KV 630mm2 single core XLPE cables

01/30/2017 9:31 AM

the client is asking to change the entire cable. this decision is not substantiated by contractual specification but rather by an imposed solution (preference) from thepart of the client. i could not locate any document/article that states the minimum distance to be maintained between jointing, but factually that joints are normally more resilient than the cable itself. is there an document/article to that effect?

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#5
In reply to #4

Re: joints on buried 220KV 630mm2 single core XLPE cables

01/30/2017 9:35 AM

Yes. The Client's variation order in response to the change in value of the contract presented under the contact terms.

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#8
In reply to #4

Re: joints on buried 220KV 630mm2 single core XLPE cables

01/30/2017 11:16 PM

It is too late to ask, "is there an document/article to that effect"?

These documents should have been identified and invoked during contract negotiations.

Do what is best for your customer and your reputation.

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#9
In reply to #4

Re: joints on buried 220KV 630mm2 single core XLPE cables

01/31/2017 7:58 AM

If this is a new cable the client has every right to have a new cable section installed on a 220Kv cable run. Do your sums. By the time you have finished peeing about and hoping you only need to install one new joint it will have been quicker, safer and break even to pull the damaged cable out, install the new section and 2 joints, and reinstate all the cross bonding at the existing joint bays. Also I assume the cable is ducted and not direct buried, so where is the hassle to haul it out. Is it in trifoil, in one duct or buried in a sand bed in a trench? Laid flat?

Depending on the damage depends on how much the insulation has carbonised or allowed water to ingress. Trust me in this, your guarantee will be used for ever and cost you a small fortune later on. Be smart, replace the cable if insulation damage has occurred.

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#7
In reply to #2

Re: joints on buried 220KV 630mm2 single core XLPE cables

01/30/2017 3:47 PM

Unless the client's contract specified that cables should not have joints at less than 300m intervals, he does not have an argument. The damage to the cable was an unforeseen event, no doubt subject of someone's insurance. What does contract say about remedies for defects? Does it say "repair or replace" or "replace" in case of defect or damage?

I suggest you consult cable maker/installer for their experience/practice & your insurer.

Note that replacing all the cable involves 2 new (buried?) joints compared to one for repair, with attendant failure risk.

Digging up & replacing 300m of cable, replacing, backfilling is obviously far more costly in time delay & money compared to a joint. Is there any contract penalty for lateness which will multiply your loss? Forcing you to replace this, rather than a repair looks like an unfair cost, especially if it hits you with time penalties.

Give the client the option of a repair joint at your cost or replacement at price quoted by you, which can be "at cost" - he can have what he wants, but not for free!

The buried electrical system of the country is full of joints where new consumers have been spliced-in or repairs made. Joints usually have more metal and insulation than the equivalent length of cable & less volt drop/temperature rise.

300m interval just reflects the practical maximum length for drum size/weight.

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#6

Re: Joints on Buried 220KV 630mm2 Single Core XLPE Cables

01/30/2017 11:45 AM

The distance will depend on the voltage, the environment and the isolation of the cables.

Adding the cross section and the insulation material makes me feel like you do not really know what you are doing.

Anyhow, answering your question, I would leave about 2 times what you would leave in air. So let's make it 20m (but this is just a guess, buy some standards to know the exact value).

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#10

Re: Joints on Buried 220KV 630mm2 Single Core XLPE Cables

01/31/2017 3:42 PM

One thing to consider when jointing cables after a fault is the distance flashover has driven carbon in to the cable structure. For 11kV, I would chop out 6 metres each side of the point of failure.

As for the distance between joints, it should equal the spacing of the main cable run.

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#11

Re: Joints on Buried 220KV 630mm2 Single Core XLPE Cables

02/05/2017 4:20 AM

Distance between two joints in H.V.&E.H.V. joints depends on various factors likes type of cable, cable joint, and most predominantly the surge impedance/ characteristic impedance of the cable as because when any voltage surge is travelling through the cable at the joints or in termination point there is change of surge impedance and part of the surge voltage is transmitted and rest is reflected back with doubling effect and additional voltage stress is developed. To avoid this phenomenon sufficient distance is maintained. The distance can be calculated from various data as mentioned above including length of the cable

Manindra

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#12
In reply to #11

Re: Joints on Buried 220KV 630mm2 Single Core XLPE Cables

02/05/2017 5:20 AM

Manindra, I am looking forward to your supporting information on your input.

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#13
In reply to #12

Re: Joints on Buried 220KV 630mm2 Single Core XLPE Cables

02/05/2017 7:20 AM

I add, there is a common perception that this site can just 'know' and answer questions as factual when the posters provide zip information. So how you got your answer is puzzling without knowing the damage further details. We all know about assumption.

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