MV cable damage 5

[ziggyfrst]

I have the following Cable: Uniblend, Spec 6350, 250 kcmil: EPR/Copper Tape Shield/PVC, Medium-Voltage Power, Shielded 15 kV, UL Type MV-105. 1.25” overall nominal cable diameter. IAW NEC and mfgr specs the min bend radius is 15" It has been pulled through a Greenlee 9 ¾ radius sheave at ~4000 PSI, at a ~1300’ length with the sheave ~center of pull at 90 degrees. You can see where the shield ribbon pulled nearly apart on the outside and bunched bunched up when straightned. And on the sheave contact side is wrinkled. What does this do to the longevity?? Is there any danger ever?? Has this in any way degraded the performance of the cable???

 

[rcw retired EE]

IMHO - the cable might be serviceable but its longevity has been reduced. Possible damage includes cracked insulation, voids between adjacent layers of shielding tape creating HV stress points, conductor is no longer concentric in the insulation/shield, jacket damage leading to water intrusion, and several others.

You might be able to do a hi-pot test and verify some of the cable integrity. But that test will not find all of the possible failures. I am not sure if a partial discharge test could locate potential failure points.

 

[BJC]

If you mean 4,000 lbs tension not psi and you pulled the cable over a 9-3/4 inch sheave it's history.
The bending radius your referencing is static or traning radius.
The 9 -3/4 in sheave put about 4,900 lbs/Ft of side wall pressure on the cable. The usual limit is 300-900 lbs/Ft.
At the "To" end of a pull it's common to use a segimented sheave with a large effective radius.

 

[davidbeach]

DO NOT ENERGIZE the cable. It has been severely damaged. A properly pulled cable shows no distortion.

 

[apowerengr]

ziggy - tell the people who pulled the cable they can use the 9 3/4 sheave again to remove the damaged cable, then they can throw all of it away and start over. 250 CU MV105 at probably $20/ft. x 3900' = no profit on this job.

 

[jerryjointer]

hi
apart from the above points the damaged screen may not be able to deal with earth fault current so in the event
of earth fault current flowing through the damaged
section of screen you could get further faults on the cable
its scrap by the sounds of things.

 

[davidbeach]

The shield has been destroyed, and the insulation has been compromised. Once the contractor gets it all replaced at his cost, I'd be very leery of ever hiring that contractor again.