Cable fault location meters , anyone used them before ?

[JD6400]

We had a break down call out on Thursday to a stable yard we have just completed , it turned out that the 500m 95mm three phase sub main that was installed as a single phase for the time being until they can afford a three phase meter upgrade has been compromised on the currently used brown phase and also on the black phase which is dormant at the moment !
The grey phase and neutral bell out fine .
So we have got the yard up and running at the moment , but we need to go back and locate the problem now !
Have any other forum members had dealings with cable fault location gear and can you recommend which is best ?
We have been quoted around £550 + to hire some , but i always prefer to look at buying reconditioned kit at a all be it higher cost rather than pay a dead loss hire fee .
It would not be so bad but the run was moled under two private tarmac roads and strait across the main access yard and lorry park park for the whole complex , without being ducted ( clients request to keep cost down along with using their own labour to lay it ) , BUGGER !!!!!!!!!!!!

 

[lamb]

Good private job for a BT engineer, they all carry TDR's.

 

[JD6400]

Hi Lamb , thanks for the fast reply !
Would this work on a 95mm , have started looking on flee bay for stuff and have come across these but it only seems to mention for telecoms ?

 

[lamb]

Yes, a TDR will work on any cable that has two cores, eg L1 + N, L3 + SWA etc.
For each cable size/conductor type you need to find the signal transfer rate and set this on the machine.
The machine then tells you the distance (roughly) from the test point to each anomaly in the conductor (cable joint, termination, cable break etc), you then have to interpret the signal to work out where your fault may be.
So if it bounces back 70m, 250m and 500m, and you originally put a joint half way along the run, disregard the 250m (joint) and 500m (termination) and investigate the 70m reading first.
Using a cat and genny find the 70m from test point (will probly be +/- 2m or 3m), dig up and have a look.
Other methods include wheaton bridge but you need a degree to interpret the results (too complicated for me) or old school cut into cable half way, test each half, cut bad section in half again, etc, until you get down to last 20m eg. then just overlay new cable on that section.

 

[lamb]

Forgot to say, you can also use a cable thumper, again it's specialist to set up, pumps mega volts through the cable at regular intervals, you then walk along the run and listen for the bang as the cable fail point flashes over.

 

[La Poste]

Forgot to say, you can also use a cable thumper, again it's specialist to set up, pumps mega volts through the cable at regular intervals, you then walk along the run and listen for the bang as the cable fail point flashes over.

Great stuff, I'd like to have a go or at least see it in action.

 

[JD6400]

Forgot to say, you can also use a cable thumper, again it's specialist to set up, pumps mega volts through the cable at regular intervals, you then walk along the run and listen for the bang as the cable fail point flashes over.

This is the one that we were looking to hire if we can not find anything else , but at £550+ it is some what pricey !

 

[lamb]

TBH by far the best method is common sense - are there any joints in the run, has the ground been disturbed eg other trenches/ demolition works, can be a lot cheaper to ask these questions than hire in specialist equipment and specialists to interpret the results.

 

[Knobhead]

How good is the fault? Dead short or high resistance?
A dead short can be found if you have access to a ductor by measuring the resistance between the faulty cores from each end. This will give you a ratio that you transpose on to the cable length.
R2+RF+R4/R1+RF+R3

View attachment 11974

 

[JD6400]

Have walked the run and nothing obvious , it only went in a couple of months ago !
My gut feeling is it is at the furthest end of the run through the yard , as the we were not on site when this was back filled and it was some what a hostile environment in that part of the trench !
The black phase has been so badly damaged and because the run is up a fair slope , there is actually water running out of it !

 

[JD6400]

Sorry my thanks button has now disappeared , No Tony only ever herd of them and never seen one in real life , and it is a dead short .

 

[Knobhead]

Try it with any low resistance meter. It’s cheaper than hiring equipment. I will admit it’s donkeys years since I’ve used it.

We always had access CAT detectors or if neaded the group engineering pulse reflection gear and the dreaded thumper.
Be warned with a thumper it’s not something to be used unless you’re trained. Last time I had anything to do with one we ended up with two faults, the thumper blew an 11KV joint.

 

[JD6400]

This is what worries me the most Tony , i do not really no what to expect with the thumper and as the owner of the yard is up at the top of his game , there are a lot of very , very expensive four legged friends about that have a bit of a aversion to getting a lick !

 

[UKMeterman]

If there are four legged friends about forget the thumper and just hire in a TDR.

 

[Mark_Burgess]

Would be a TDR for me, just input the cables velocity of propagation and test, just as lamb suggested.

 

[i=p/u]

sounds intersting , im fed up installing 10A light switches and doing domestic, i kn ow already

 

[Heisenberg]

Just out of curiosity, who's gonna be paying for all this? As it was only installed a couple of months ago, is the client blaming you and expecting you to cover the cost?
Sounds like the sort of job that could turn a profitable year into a not very profitable one if that's the case :dead:

 

[lamb]

If there is water running out of the cable, there could be a lot more to chop out than just the damaged section.
If any joints or terminations are lower than the cable fail point, they will keep getting damp.

 

[Knobhead]

The outer sheath is compromised so the armours are at risk. I know it’s late now but this is where testing the armouring to earth pays off, proves the outer sheath isn’t damaged.
DP, what tests were done on the cable before putting in service?

Sorry but the more I think about it this cable is going to be a write off.

 

[lamb]

Agreed, a large section will need to be cut out at least.
Steel has a co-efficient of expansion of 6:1 when oxidised, so when the armour rusts it will further ruin the sheath and pierce/compromise the bedding and insulation.
I would still try to salvage any good part of the cable if it is dry and sheath not leaking to earth.

 

[WPD Lad]

I'll have a Kelvatek Reflekt in around 3 weeks if you can wait, failing that I've got a boggo cat and genny

 

[Knobhead]

Nice bit of kit.

 

[JD6400]

Right then first off , thanks for all of the replies and apologies for not getting back until now ( just getting over a second bout of tonsillitis in the last two weeks, so had a lay in ).

Richard / UK Meter , this seems the way to go but from what you have mentioned it sounds a bit like rocket science ?

Heisenberg , as far as we are concerned it has nothing to do with us but the client also thinks the same for him self !
This is how it has developed so far - To save money we sourced and specked the cable from our usual wholesalers and the client payed for it direct , one of our apprentices then subbed direct to the client and hired a digger to lay the sub through the fields and borrowed one of our moles to go under the roads , this was direct to the client .
The client also employed the chap building one section of the complex to go through the yard at the top and back fill it ( which is where i think could be the problem ).
All we did was connect both ends , i know our man had gone direct but we still feel some responsibility .
It will be around a £20,000 hit if it all goes pair shaped ! ( job had already over ran the budget by £12,000-£13,000 and cost us several £0000 more than the original quote so not impressed at the moment !!!!!!!!!)

Tony , it was megged out and at the time all was good but it was very dry at that point and had been since it had gone in the hole .

WPD Lad , thanks for the offer maybe we could hire your service's if that would work as if we do not buy one then i would far more prefer to give the money to some one from the forum !

 

[Knobhead]

I’ve fallen for clear tests before, about a mile and a quarter of 70mm, so there were a couple off joints in it. Perfect readings. And then the rains came. Oh dear!
It took me weeks to find where one of our wonderful process guys had been cleaning up with the aid of a front-end loader.

It would be good if you can get WPD Lad on side.

 

[UKMeterman]

Hi,
A TDR for power cables can be hired here biotest T625 cable fault locator | hire | inlec They are quite easy to use, they just need connecting up and details of the type of cable in use.

 

[UKMeterman]

Next time you install a cable like this, don't use a standard megger use megger MIT520/2 5KV diagnostic insulation resistance tester | hire | inlec this can detect a whole host of insulation problems, before the insulation suffers total failure. A TDR can also spot some subtle changes as well so it may be an idea to do both.

 

[UKMeterman]

As regards faulty underground power cables and horses remind your customer about the newbury racecourse incident. Two horses were electrocuted...

 

[mogga]

google RADIO DETECTION their RD400 with a GENNY can be used for fault location practice with a dod laid on top of the ground get to know what to listen for then follow the cable sound along the route WATCH for inducted sound on any gas/water pipes tho If used correctly this could assist you

Vhttp://www.inlec.com/electrical-tes...etection-rd400pxl-cat-genny-cable-locator-p33

 

[mogga]

SRC training center use to have some crackin specialist fault locating kit and as Tony says clear cable can turn into down all over the place when the rain hits the ground as for crossing the yard we had this when they decided to lay tar on a yard and the pressure pushed a brick through a 75mm4 core that was my first big joint

 

[Engineer54]

None of these cable fault detectors are easy to use, ...well they are if you know how to interpret the signals the machine is showing you. I've seen experienced operators totally flummoxed at times!!

Your best bet is to get a recognised company in to find this fault, they will generally guarantee the location of the fault to within a metre of where they say it is. Other than that, you could end up digging down in umpteen locations if your not experienced in using these fault locators... lol!!

What the betting that either the floor of the trench wasn't cleared of sharp protruding stones and debris, or that this trench was backfilled without the correct sand bedding....

 

[JD6400]

Hi again ,

UKMeterman , It has megged out ok at 1000v on the blue and grey so is safe for the short term .
I have swapped out the incomer for a 30ma at the moment as well , the yard is TT anyway as we had existing barns already on site and it was going to be a absolute no no to get a tied grid in under the new indoor menage !

Engineer54 , i think this will be exactly the problem as to why we now have the damage but i had absolutely no jurisdiction on certain parts of the cable run and only limited on the other parts , and the part where i think the damage is was laid when we had not been on site for a fortnight .
I do think that getting in a specialist in is a sound idea , but we may yet get lumbered with the costs ? Added to this is the fact i personally have all the plant needed (apart from the fault finding gear ) for the job back at my home , so i have the ability of keeping nearly all the costs in house .

Mogga , we brought a RD2000+ and genny a couple of months ago , would this model do the same as i have not found any information yet saying it will ?

 

[Engineer54]

The specialised fault finding company would only be used for finding the location of the fault, the subsequent excavation and repair to the cable you can do in house, along with the back filling....

 

[JD6400]

I have to admit i think you are right and this may be the best option , i am just worried that after we have sorted one fault then there will be subsequent faults further along that may be missed while they are there .
But i think we will just have to risk it , unless they have the ability to pick up multiply faults in one pass ?

 

[Engineer54]

An experienced operator with the right equipment, can probably tell you if there are further weak spots in the cable run, or indeed if your going to be dealing with multiple breaks as it stands at the moment... Fingers crossed for you!! ...lol!!

 

[mogga]

As enginer says EXPERIENCED Operator is realy required to use the equipmwent as the readings are whats needed to interpret
havent used the rd200 the 400 we followed the cable till lost signal DIG there sorted 9 out of 10 times we got it spot on even depth
I have seen S.P. use a "Thumper" god thats a fantastic bit of kit One goy at cable end with thumper other guy walking down cable route listening for THUMP again normaly SPOT on with experienced guys using it

 

[Knobhead]

Give the RD2000 a go on the faulty cores.
I don’t know what model we had at work but it must be 30odd years old, got my arse out of the fire plenty of times. I used to set the geny up at one end and trace to where the signal vanished, then do the same from the other end.

 

[JD6400]

Hi Tony , I will give it a whirl , but i think we are looking at getting in the big guns .
The cable has not been sheared just compromised so i think the cat will just trace as normal , unless i am missing some other way of doing it ?
I think all in all it's a feeling of :frown2: at the moment !

 

[WPD Lad]

Where is the job?

Have the brown and black gone open circuit or phase to phase or phase to E?

Reflekt is here!

 

[JD6400]

South Warwickshire , brown is flat to earth and black is also flat to earth with the added bonus of water running out of the copper cores !
Never bothered to try phase to phase / brown to black as was feeling rather despondent by that point , but would say it will be flat to earth .

Where are you based ?

 

[Knobhead]

Hi Tony , I will give it a whirl , but i think we are looking at getting in the big guns .
The cable has not been sheared just compromised so i think the cat will just trace as normal , unless i am missing some other way of doing it ?
I think all in all it's a feeling of :frown2: at the moment !

Signal will end at the short.

But it look like WPD may come to your rescue

 

[mogga]

IF WPD comes to your rescue we DEMAND PHOTOS !!!!!!!

 

[WPD Lad]

South Warwickshire , brown is flat to earth and black is also flat to earth with the added bonus of water running out of the copper cores !
Never bothered to try phase to phase / brown to black as was feeling rather despondent by that point , but would say it will be flat to earth .

Where are you based ?

Solihull/Birmingham, doesn't sound too far

 

[Knobhead]

Good to see people helping each other out.

 

[mogga]

cooperation WPD remember and PM DP what your fav bikkies and takeaway meal are before assisting lol

 

[JD6400]

Mogga , what would you like me in for pict's leather or silk ?:ihih:

WPD Lad , sounds like a plan ! I will pm you my details now , thank you !!!

 

[mogga]

Preferably you NOT in the photos But if there happens to be a young lady with a bikini and ampple cleavage passing this may be appropriate

 

[JD6400]

:35:And i was just going through the other half's wardrobe as well !