Underground joint locator

[mjmarkey1979]

Morning gents (and ladies)

I have a job the now at a hydro power station where the client is experiencing a loss in production and believes this is due to moisture ingress into underound electrical joints along the 3km route of the 10core 5 pair BS5308 Type 2 Part 2 hill instrumentation cable. These are supposed to be epoxy scotch cast joints according to the as-builts, which have northing and eastings also kindly provided, however the client doesn't want to entertatin verifying the accuracy of the drawings by inputting the co-ordinates into a suitable GPS device and digging trial holes which I have previously suggested.

The electrical contractor has since went bust, and we have learned the complete route wasn't reticulated in ducting, obviously a £ saving measure on the contractors part.

I have tried the use of the Bicotest T625 time domain reflectometer on site to identify any changes of impedance at these joint locations but also had no joy. Loop continuity and megger testing was also carried out between cores and individual cores to earth and although IR ohmic values has degraded over time, all seems that it should still function as intended as a signal path.

Does any body else have any similar experiences to trying to locate such buried items or ideas how I can keep a diffulcult client happy?

Many thanks in advance.

 

[waross]

If enough power was being lost in cable connection to cause a noticeable drop in power production, the location would be readily visible due to the steam, smoke, fires and explosions. First verify ALL of the instrumentation used to monitor production. Then look at possible reductions in water flow or degradation of the turbine runners. Is the tailrace higher than normal?
Lost energy isn't "lost". it goes somewhere and any amount of energy dissipated at a connection will usually progress to a complete failure fairly soon.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[gattie]

Use of Time Domain reflectometer in the hands of an experienced engineer will accurately locate the position of all your joints.
Joints could then be examined externally for any possible ingress of moisture due to damage or poor jointing procedures.
All suspect joints could be cut out & replaced.

 

[mjmarkey1979]

Cheers Gattie, tried the TDR but for some reason I couldn't even see the upward curve of the open circuit for some reason at the end of the cable that had been OC at both ends?. Along this 3km route of cable there is 6 joint assemblies, some which the client have done themselves but cutting out a bad UG joint and replacing with 2 above ground IP65 assemblies. Being its a 10core cable and the number of joints involved, belling out could be an option where feasible to make sure corresponding cores are not cross conncted.

Way I look at it, the lient needs to trace and mark the complete cable route anyway for future fault finding purposes, it should have been done in the initial works. If it had been, along with joint markers, this job would have been a hell of a lot easier.

 

[gattie]

Greetings mjmarkey1979
I was called in to troubleshoot a 4kM long cable that was newly installed to remote control a Large Pump Station.
After locating under ground joints using as built drawings(???) & TDR I found a 300m middle section had been carefully joined to itself!!
The Company Consultant's excuse was that since the Installation Contractor's qualifications were scrutinised before contract was awarded, they did not consider that the installation should be checked or supervised!
Consultant & Contractor were stuck off bidding list.
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