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Topic Title: OHL Jumpers as isolation point for outages
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Created On: 08 January 2014 07:23 AM
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 08 January 2014 07:23 AM
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Badshah

Posts: 38
Joined: 22 July 2009

During Emergency or OHL tripping, we isolate section of the OHL by removing the jumper at OHL to identify the faulty section.

Can this Jumper be used as isolation point for planned outages?
 08 January 2014 09:19 AM
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Zuiko

Posts: 518
Joined: 14 September 2010

Is this 11 kV?


In principle, yes, and in practice, cut jumpers are often used a point of isolation.


How are you cutting them? Dead or live line working?


If live, how you acheive safety will depend on your company procedures (DSR 6.1.1).

Live, you are limited by the impedance of the line and the transformers connected to it that you are cutting (and the weather, you can't work live line in damp weather)

It is better practice to install a switch on the OH line and use that.

And it is better to install the switch dead, so this may mean extending the duration and size of your shutdown so you can do so. But at least you then have a permanant point of isolation on that line.

Edited: 08 January 2014 at 05:37 PM by Zuiko
 09 January 2014 10:35 AM
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Badshah

Posts: 38
Joined: 22 July 2009

Yeah for 11 kV OHL and to be isolated in dead condition only.
 09 January 2014 05:02 PM
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Zuiko

Posts: 518
Joined: 14 September 2010

If the line is to be dead, then you are going to have to have the circuit isolated and earthed, and issue a PTW to cut the jumpers.
 09 January 2014 08:41 PM
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Snips

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Joined: 01 April 2012

Or you could put the switch up Live using hot glove techniques.
 11 January 2014 06:10 PM
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neilmcd84

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Your language here is critically important. There is an enormous difference between 'cut' and 'removed'. The difference between life and death in fact. To act as isolation the jumpers must be fully removed, or some might allow them to be pulled back and secured. Just cutting them and bending them back is not enough for isolation, although this is enough for fault finding purposes when pressure testing fully isolated sections etc. I use 'removed and retained' jumpers for isolation up to 33kV, and my transmission colleagues use it up to 400kV.
 11 January 2014 09:21 PM
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Zuiko

Posts: 518
Joined: 14 September 2010

Of course, nobody cuts them and bends them back and leaves them flapping about in the wind! (that would not acheive isolation)


Cutting the jumpers is one thing; how isolation is acheived will be down to the company's interpretation of the DSRs and the SAP on-site. Removing, then replacing jumpers (live) may be more problematic than cutting them and securing them on the line (live).


The absolute best way to do this job is to exend the shutdown and put up a switch. It doesn't take long, it is the safest method, it increases the security of your network, and it saves a lot of hassle in the future.



Live working is a last resort -

"No person shall be engaged in any work activity on or so near any live conductor (other than one suitably covered with insulating material so as to prevent danger) that danger may arise unless -

(a)it is unreasonable in all the circumstances for it to be dead; and

(b)it is reasonable in all the circumstances for him to be at work on or near it while it is live;"

Edited: 12 January 2014 at 12:28 AM by Zuiko
 13 January 2014 10:10 AM
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acsinuk

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Joined: 30 June 2007

Zuiko
I has a SAP for most of the beginning of my working life and safety is paramount in my thinking but not unnecessary isolation and locking off just to satisfy lawyers. My time spent mostly in Africa was to make sure the supplies were restored with a minimum of delay.
My instructions to 11kV linesmen and switchmen operating in the bush were always the same. Test the line each side of the work position and apply a circuit main earth each side, issue permit to work, do repair, cancel PTW, remove earths and recommission. I did not insist on locking off everything along typically 10 km line with dozens of PMTs. No fatalities or electric accidents using this technique so far.
CliveS
 13 January 2014 05:10 PM
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Zuiko

Posts: 518
Joined: 14 September 2010

I've worked in Africa too (Uganda).

However, in the UK, to issue a PTW on an 11 kV circuit, the circuit must be isolated and earthed.



If your linesmen have tested not-live to apply the CME, then the circuit must have been switched off downstream. This is where the circuit shall be isolated. If you cannot be bothered to apply secure isolation, then that's African rules. This is totally unacceptable in the UK - and rightly so. I wouldn't accept a PTW from you without witnessing secure isolation. End of. There are cowboys in the bush!


The process involved prior to issuing a PTW is not to "make sure supplies are restored with a minimum of delay"; it is to acheive safety from the inherent dangers of the system.



Anyway, the point of cutting jumpers is so that the circuit can be energised up to that point, and that point used as a point of isolation.

Edited: 17 January 2014 at 08:24 PM by Zuiko
 15 January 2014 04:31 AM
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Badshah

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Joined: 22 July 2009

Hi, Thanks to all, Our plan is to remove jumper at one end and tie it with the line. This will cause any damage to the jumpers?
 15 January 2014 08:18 AM
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Zuiko

Posts: 518
Joined: 14 September 2010

Originally posted by: Badshah

Hi, Thanks to all, Our plan is to remove jumper at one end and tie it with the line. This will cause any damage to the jumpers?


Not if the linesman knows what he is doing!
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