Cable bending damage ?

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Lossless

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Hi
I have a situation where 33kV XLPE copper armoured cables has been installed exceeding the manufacturers bending radius by between 10 to 20%.

Whilst the manufacturer states that this voids the warranty the installer argues the the cable passes all test. ie hypot

How can the possible damage be quantified?

I can find no references to what exactly are the effects of exceeding the mf bending radius other than that it may effect longevity.

My position as PM is that the offending areas be cut out and new section added re dress and join.

Any input would be appreciated Thanks
 
Lossless said:
My position as PM is that the offending areas be cut out and new section added re dress and join.
Click to expand...


The problems ussually occur at splices. So while I agree with you, the bend may cause a longevity prolem. Splices may make it worst. You would want to use the least amount of splices as neccessary.
 
Lossless said:
Hi
I have a situation where 33kV XLPE copper armoured cables has been installed exceeding the manufacturers bending radius by between 10 to 20%.

Whilst the manufacturer states that this voids the warranty the installer argues the the cable passes all test. ie hypot
Click to expand...

Do you mean that the installation radius was 10-20% _smaller_ than that recommended by the manufacturer? Because if the radius is 10-20% larger, than that is just fine. The bending radius is a _minimum_ value.

-Jon
 
It does not matter what the installer says, the cable has been compromised, and it is why the manufacturer will supply no warranty. The installer should be required to replace the cable at his expense.

Check the construction documents/contract for wording pertaining to warranty, replacement/repair of damaged equipment and materials, etc. Replacement of the compromised section, where the splices can be done in a manholes or junction boxes, may be a viable solution depending on contract requirements.
 
buckofdurham said:
The problems ussually occur at splices. So while I agree with you, the bend may cause a longevity prolem. Splices may make it worst. You would want to use the least amount of splices as neccessary.
Click to expand...

Good point, I couldnt agree more .
 
Lossless said:
Hi
I have a situation where 33kV XLPE copper armoured cables has been installed exceeding the manufacturers bending radius by between 10 to 20%.

Whilst the manufacturer states that this voids the warranty the installer argues the the cable passes all test. ie hypot

How can the possible damage be quantified?

I can find no references to what exactly are the effects of exceeding the mf bending radius other than that it may effect longevity.

My position as PM is that the offending areas be cut out and new section added re dress and join.

Any input would be appreciated Thanks
Click to expand...

What IS the manufacturer's warranty? The Contractor is liable ONLY for the manufacturers warranty. That should be easy.
 
Thanks for all your responses

Just to clarify
The cables installed exceed the manufacturers recommended bending radius.
The manufactures warranty is 12 months for manufacturing defects and installation in accordance to installation pull and bending limitations
Tests used are VLF HV AC

My question remains how can the effects of exceeding the bending radius be demonstrated. What would be the physical indications. would there be a gradual change to the insulation properties ie leakage.
Would there be a visable change to the insulation material such as stress fractures.

I believe that the cables be replaced.
 
If a smaller radius bend was installed then there is a good chance the the maximum sidewall pressure of the cable was exceeded during the install. If the cable was compromised then I would replace it. There are formulas for figuring out the sidewall pressure, check Southwire's or Okonite's web site. Ask the contractor to provide you with the pulling calculations.

Jim
 
I believe that these are questions that you need to ask the manufacturer directly in order to obtain the nominal characteristics of the cable. Whether or not damage can be determined may not be possible without destructive testing. Was the bending radius exceeded mid span or just at terminations ? How was it determined that bending radius was exceeded. what is the application ? (just curious)
 
nakulak said:
I believe that these are questions that you need to ask the manufacturer directly in order to obtain the nominal characteristics of the cable. Whether or not damage can be determined may not be possible without destructive testing. Was the bending radius exceeded mid span or just at terminations ? How was it determined that bending radius was exceeded. what is the application ? (just curious)
Click to expand...

If the bending radius extension was toward the end I would only replace the portion of the cable that was subject to the damage, eg. the portion that experienced the extra bending. If it is close to the pulled end then the user maybe lucky. I would only do that if the cable test shows damage. Otherwise I would relieve the extra bend back to the maximum allowed bend BEFORE the test.
 
Lossless said:
Hi
I have a situation where 33kV XLPE copper armoured cables has been installed exceeding the manufacturers bending radius by between 10 to 20%.

Whilst the manufacturer states that this voids the warranty the installer argues the the cable passes all test. ie hypot

How can the possible damage be quantified?

I can find no references to what exactly are the effects of exceeding the mf bending radius other than that it may effect longevity.

My position as PM is that the offending areas be cut out and new section added re dress and join.

Any input would be appreciated Thanks
Click to expand...

a couple things come to mind.... splices will be more problematic than
decreased pull radius over a long period of time. if splicing was indicated,
i'd repull instead.

a megger that shows the applied voltage as well as the megohm reading
could be placed on a similar length of cable that was not subjected to excessive bending, and voltage and meggage noted. then the questionable cable could have the same test done, and readings compared. fluke makes
a megger that does that, but only up to 1 kvdc, and that isn't enough
for a valid test of your cable.

however.... you can rent a meter that can do it at:

ProTec Equipment Resources, Inc.
1250 Post n Paddock, Suite 400
Grand Prairie, TX 75050
(866) 352-5550
ProTec Meter Rental (support@protecequip.com)

cost is $37.50 a day, and it'll put out up to 75kvdc.
that'll be enough dynamite to get the job done, butch.

as for reduction in life of the cable, they do not rent
crystal balls, but if there is no loss in IR at load at
the current time, all should be well.


Randy
 
Fulthrotl said:
a couple things come to mind.... splices will be more problematic than
decreased pull radius over a long period of time. if splicing was indicated,
i'd repull instead.
Click to expand...

Wow, pretty free flowing with the cash arent we, how about a good analysis of the installed cables condition before we go to that extreme?


Fulthrotl said:
fluke makes
a megger that does that, but only up to 1 kvdc, and that isn't enough
for a valid test of your cable.
Click to expand...

I have a 10kV megger in the trunk of my car

Fulthrotl said:
however.... you can rent a meter that can do it at:

ProTec Equipment Resources, Inc.
1250 Post n Paddock, Suite 400
Grand Prairie, TX 75050
(866) 352-5550
ProTec Meter Rental (support@protecequip.com)

cost is $37.50 a day, and it'll put out up to 75kvdc.
that'll be enough dynamite to get the job done, butch.
Click to expand...

Enough to cause treeing and premature failures in XLPE cable according to EPRI and IEEE also.

Fulthrotl said:
as for reduction in life of the cable, they do not rent
crystal balls,
Click to expand...

No but they do rent Tan Delta test sets that is a good test to do for condition assesment and recommended by IEEE, EPRI, BETA , and the ICEA for XPLE cable condition assesment.
Randy[/QUOTE]
 
Was the tight bend inside a conduit or is it at the terminations where the cable had to bend to meet termination fittings? The condit bend is the greater evil due to additional side wall pressure casued by pulling as mentioned before.

What can happen on a tight bend? If there is spiral wrapped copper tape shielding, the spirals get crimped on the inside of the bend and oepned up on the outside. Voids can occur between successive wraps leading to corona discharge and eventual failure. With enough sidewall pressure, voids can appear at the insulation to conductor interface, again leading to corona and failure.

A VLF highpot probably won't find those voids. Jsut because the cable passed the test doesn't mean some damage did not occur.

The cable is maybe good for 1 or 5 or 10 years. Unless the cable was severely damgaged, it probably has a better chance of surviving than does a field splice at 33 kV.
 
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