Did a bit of digging today.

[Bobster]

Anyone seen a joint like this before? I certainly haven't.

400mm 3core going into it. 6 x 630mm singles coming out (2 per phase) @11kv

Found a short to earth on two phases.

 

[Knobhead]

It’s an 11KV trifurcating joint.

Will try to find the details of why there used now, it’s down to how switchgear manufacturer make the terminal boxes for single core cables only. I’ve got a PDF of the methods and standards.

 

[Bobster]

Never seen one like it before. Almost looks like its been a home made job. Fibreglass filled with tar or pitch.

Will be spiked on Monday ready for the jointers.

 

[Knobhead]

Have a look at http://www.sppowersystems.co.uk/newconnections/pdf/CAB-04-009%20Issue%202%20-%20Policy%20&%20Application%20Guide%20for%2011kV%20Pol.pdf

 

[Knobhead]

Have fun spiking the polymeric cables.

The lecy boards have had trouble with them, the spike fires in OK, now try getting the bugger out! It grips the spike.

 

[Bobster]

I've had to spike quite a few de-commissioning a substation on site. I diddnt have too much trouble with them... Was a lot more difficult inside the cable trenches. Not to mention having to fill in confined space permits and special risk assessments.

 

[Knobhead]

Just been thinking about this, 400mm in and 6 x 630mm out? Seems a bloody funny set up to me! I can see the singles, but 6 of them?

 

[ACDC]

Wow, that is a impressive joint! wish i had opportunities to get involved with HV. espeically the spiking part

 

[Bobster]

It is a funny set up, was peiced together from what was already laid. As for 6 coming out as you said earlier it's how the terminations in the switch gear is set out.

Ill get more photos on Monday if you wish of the switchgear or of the joint as a lot more has been dug out.

 

[rfears]

Call The Time Team? :wacko:

 

[Bobster]

Call The Time Team? :wacko:

Felt like someone from timeteam digging round the singles with a trowel.

Was lucky really there are 4 of them joints right next to each other and the thumper only gives a rough location of the fault.

 

[Engineer54]

I thought i could see evidence of another similar joint in your photo's. Those thumpers normally give a pretty clear indication of where the faulty cable is...lol!! So are you involved with the cutting out this exposed joint and replacing it with a new one?? ...Fun and games that should be...lol!!

I'm sure others, like myself would very much appreciate a photo or two of the new joint prior to being filled, ie...showing the connection arrangement(s) between the multi core and single core cables etc...

 

[Engineer54]

Have a look at http://www.sppowersystems.co.uk/new...- Policy & Application Guide for 11kV Pol.pdf

I don't think some of those joints shown in this guide are up too much. I like to see a good 4 to 6 inches of adhesive heat shrink going back onto the cable sheath at each end, especially when being direct buried, rather than just a couple of inches shown here...

Another thing i noticed, there doesn't seem to be any armouring on these HV/MV direct buried cables, only the copper screen. I'm basically used to seeing the screen around each of the cores of MV multi core cables, in the form of a thin copper steamer tape, against a semi conductive outer layer of the cores... But there are i know, many different cable make-up arrangements out there...

 

[Bobster]

I'll only be in charge of proving dead and making it safe for the jointing team to come in. I will try and get photos.

There are 4 identical joints right along side one another (can just see the edges of two of them in the photo).

The reason I think the thumper wasn't as accurate as normal was the fact 2phases were hard down to earth, so it wasn't producing much of an audible arc. The fact there was 8 foot of soil above the concrete protection flags probably didn't do much to help.

 

[SPARTYKUS]

Great thread, would love to see more piccys too!

 

[Knobhead]

How did you go on with this escapade? Everything back to normal yet?

 

[Bobster]

Well the fault wasn't in the joint box (unsure why the thumper detected a fault now. Will investigate later)

I have got pics of the cable cut after spiking and the terminations in the switch gear I will upload when I get a min.

Thats as far as this jobs gotten so far It's fallen by the wayside a bit. Monday we had a peice of brand new 11kv switch gear explode so I've been investigating that. Fingers crossed it hasn't damaged our 12MVA transformer.

I have pics of this I will upload at the same time. I'll start a new thread with it though.

 

[SPARTYKUS]

Well the fault wasn't in the joint box (unsure why the thumper detected a fault now. Will investigate later)

I have got pics of the cable cut after spiking and the terminations in the switch gear I will upload when I get a min.

Thats as far as this jobs gotten so far It's fallen by the wayside a bit. Monday we had a peice of brand new 11kv switch gear explode so I've been investigating that. Fingers crossed it hasn't damaged our 12MVA transformer.

I have pics of this I will upload at the same time. I'll start a new thread with it though.

The City & Guilds 6037 ​looks an interesting one!

 

[Bobster]

 

[Bobster]

Just to explain the pictures. The terminations that are unbolted are the faulty cable. The terminations behind these are the cable to the right of the one that's been cut in the picture above.

We have the two cables in parallel.

 

[Bobster]

The City & Guilds 6037 ​looks an interesting one!

Bloody long exams. 4hour written 4hour practical.

 

[mogga]

where are you from ROB??

 

[Bobster]

From the north west near Blackburn.

 

[Engineer54]

Just to explain the pictures. The terminations that are unbolted are the faulty cable. The terminations behind these are the cable to the right of the one that's been cut in the picture above.

We have the two cables in parallel.

I've never seen so much copper showing on 11KV cable lug terminations. I always like to see, and insist on the lug butting up to the insulation, and at the very least heatshrink upto the bolted section of the lug. All our MV cable terminations are fully booted after all testing has been completed, but that wouldn't be possible with this termination arrangement.

The photo maybe deceiving, but the distances between those termination plates seem awful close to me for 11KV, especially when bare, (un-booted or insulated)

 

[SPARTYKUS]

Bloody long exams. 4hour written 4hour practical.

Closed book I expect as well. Proper exam.

 

[Knobhead]

Got to agree with E54, there’s far to much bare copper for my liking. Plus all the corners of the link plates should be rounded.
What’s the transformer rating 11/3.3KV maybe? Even 3.3 would need some hellish switch gear. 12MVA @ 3.3 = 2099A

 

[Bobster]

There insulated with a very viscous oil. This is why the gaps are so close. That what the brown liquid is at the bottom.


Answer to the other question yes closed book exam.

Edit: Tony it's an 11/3.3 the fault occurred on the secondary side. We dipped peoples lights at home up to 13miles away when the fault occurred. Glad I wasn't there.

 

[Knobhead]

One thing I do like is the lugs are sweated brass. It’s awhile since I’ve done them!

 

[Knobhead]

Just had a real close look at the terminal box. They look like PILC screened cables. To me the stress relief is no where near long enough, but it’s not failed there so must have been OK. I would normally take the stress relief about 60mm beyond the lead.

 

[Bobster]

To be honest Tony I haven't ever worked with oil filled termination boxes before. These have been installed 20years according to documentation I've found and has never been a problem.

With this switchgear fault we have had on site the cable fault discussed above has been put on the back burner for the time being.

I'd like to share more information about the switchgear fault but the cause still hasn't been identified and this is a public forum, I wouldn't feel right posting what could turn out to be fairly sensitive information.