Repetative cable failure 1

[H1H2N3F4]

Helo every one:
We have around 500m cable that are connecting and backing up ( during maintenance or interruptions) two 4.16 KV systems. This is a BILCA cable that is rated for 5KV and always energized from one side and open in the other side. It is rarely used, however it fails many times in different locations.
I need your help in investigating and analyzing the cause of such failures if it is related to a phenomena that I am not aware of.

Thanks in advance for the time and advice.


H1H2N3F4

 

[VEBill]

Can you provide a link to the cable spec?

I tried Googling it and nothing obvious popped up on page 1.

 

[hacksaw]

how is it installed, moisture intrusion is a common cause

 

[IRstuff]

What's the exact failure mechanism?

TTFN
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[VEBill]

This is unlikely, but I might as well throw it out there:

"...4.16 KV [RMS?, 5.9Kv peak?]... ...rated for 5KV [peak?]..."

I think it's unlikely because some? many? most? voltage-rated items are proofed to twice their rating.

 

[ScottyUK]

What is the quality of the installation, i.e. is it bedded on and covered in sifted sand, or in a trench backfilled with soil and rubble? The latter happens more often than it should.

 

[H1H2N3F4]

Sorry all I was out of country on a business trip and was not able to see your valuable input.

The cable is 3 core armored manufactured in 1961, 5/phase and length around 800 meters. It is laid in a bed of sweet sand direct buried and well protected.



H1H2N3F4

 

[IRstuff]

But, how is it failing? Buried cables tend to die from corrosion; things get wet, then... I was without one phase of 3 for a couple of sweltering days one year. It was traced to an underground vault that had gotten flooded and killed only one phase. Was particularly annoying because my A/C would only partially work, given that the compressor was on one phase, and the blower on another. And, of course, some lights and some sockets worked, while others did not.

TTFN
faq731-376

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[hacksaw]

the cure to your problem get an engineer involved or listen to the ones you have...

 

[waross]

What is a BILCA cable??
Is the cable rated for 5 kV to ground or 5 kV phase to phase?
Have there ever been lightning strikes in the area? I once saw a 5 kV conductor in PCV conduit buried in the earth. One end of the cable took a lightning strike and the conductors were damaged in multiple locations. After the third failure the conductors were pulled out. The many damaged locations were readily visible. The conductors were replaced.

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

 

[resqcapt19]

The cable was manufactured in 1961? I would think that it is at the end of its life.

 

[7anoter4]

I agree with Irstuff,waross and resqcapt19 ,of course. Insulation material –as PVC- uses stabilizers in order to keep their properties and the stabilizer is leaving the insulation in time. A life time for this kind of cable was –designed-40 years only.
However,-I guess-the cable was very high overloaded –once or more-by short-circuit current not cleared in time or by a long lasting overload of 50% or more.
I think you have to check the protection setting.