High Voltage Cable Termination Box Faults
reynolds
Has any body out there been doing or knows of research into faults in
compound filled high voltage cable termination boxes.
The company I work for operates a number of industrial plants, all of which
have a high voltage distribution network. The distribution networks are
mainly cable and although in recent times most new installations have used
XLPE, the majority of cable is still paper lead. Voltage levels are mostly
6.6 kV and 11 kV with some 3.3 kV.
Prior to 1970 most cable boxes were filled with bitumen compound. During
the early 70's Sefton Jelly was used because it was easier to decompound
than bitumen. Sefton Jelly was found to absorb moisture and was replaced
with a similar compound TA131. This was found to contain some potentially
carcenogenic compounds and since 1992 a wax oil compund called R4M has been
used for compound filled boxes.
Most new installations use XLPE cable with air insulated boxes and heat
shrink terminations.
The compound boxes currently fail short circuit in the crutch of the cable
at a rate of around two per year for a population of several hundred
termination boxes.
Or about ten years life out of boxes filled with Sefton Jelly or TA131.
Bitumen filled boxes seem to last longer but also fail.
I will be doing an on-line literature search which should pick up most of
the published literature such as IEEE Power Engineering Society. Is there
any unpublished information of this topic.
What are the failure mechanisms?
What maintenance procedures have other people used to prevent cable box
failures and do they work?
Any information on this subject would be appreciated either posted to these
newsgroups or e-mail me " reyn...@rivernet.com.au " or "
reynold...@bhp.com.au ".
Regards to all,
Ted Reynolds.
Do other operators of high voltage cable distribution networks have similar
problems?
rowbo...@telusplanet.net
In article <01bd0f93$6eb4e540$a36d6ccb@empire>, "reynolds"
<reyn...@rivernet.com.au> wrote:
We use 5 kV & 22.9 kV junction boxes. We also do 15 kV splices and
terminations. We used to use compound-filled plugs, vulcanized splices,
and poured splices, but have walked away from them in favour of
termination kits from the likes of 3M and their major competitors. (We
pretty much exclusively use XLPE cables.)
In our experience, we have found that the termination kits are all that
the manufacturers claim they should be, but the key thing is the initial
installation. We have had terminations fail, but only when the
termination was done by inexperienced contract labourers. In spite of
what the brochure with the kit says, training is necessary to properly
install a termination kit or splice. Without an understanding of WHY
details are requested, it is difficult to get consistant compliance. We
have had so many failures at our industrial site because we cannot control
the contract labour that we have dedicated a workforce of our own people
who have been properly trained (mostly by the termination manufaturer) in
how to install the terminations.
A local "competitor" had the same problem; they solved it in the same
way. Unfortunately, it is the CBLF Interface that causes problems.
Training and control is the only answer we have found.
If you want to discuss this further, please respond to me at:
THS,
HR.
--
wotthehell wotthehell archie wotthehell wotthehell
{Take the 3 *** out of my return address to reply. My version of a SPAM PILL.}
Kevin G. Rhoads
In addition to IEEE Power Engineering try
IEEE Trans. on Dielectrics and Electrical Insulation.
Valued Sony Customer
reynolds wrote in message <01bd0f93$6eb4e540$a36d6ccb@empire>...
>Has any body out there been doing or knows of research into faults in
>compound filled high voltage cable termination boxes.
I have third hand experience with a retrofit involving potted cable
termination kits. About three years ago a client of ours replaced all of
their lead paper cable with MV-90, XLPE. The existing termination boxes
were originally potted with bitumen. The installation was typically a 15 kV
multiconductor cable probably #2 to 2/0. The replacement XLPE cabled used
heat shrink termination kits in the original potted termination kits.
About 6 months after the retrofit was completed a phase to ground fault
resulted in the destruction of a cable termination box in the high voltage
section of a transformer. The results of the investigation showed that the
cable bus bar termination were uninsulated in the termination box. It was
thought that a voltage surge resulted in a flashover from phase to ground in
the termination box or the fault could have occurred due to long term corona
discharge. The investigation also showed that the phase to phase and phase
to ground spacing was less then in a typical air termination box, a fact not
discovered during the installation or design. The heat shrink termination
kits were installed correctly and were lugged to the bas bar pads.
The lesson learned stressed the importance of checking for design intent
when retrofitting equipment. The conductor to ground and conductor to
conductor spacing was adequate when the termination box was potted, but was
inadequate when used with uninsulated connections. This defect was hard to
detect during commissioning since the transformer termination point was the
break point in the retrofit. The original manufacture of the potted
termination boxes was no longer in business and engineering failed to
uncover this potential problem during design. The lead paper cables
required the potted connection box to prevent moisture from entering the
cable and for voltage stress relief. The heat shrink kits provide voltage
stress relief and seal the cable end, however they do not cover the
uninsulated lugs.
The fix was to tape insulate the connections which seems to have corrected
the problem.
Good luck in your research
Mike Dean P.E.