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sidhu16
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India - Member - New Member Engineering Fields - Electrical Engineering - New Member Technical Fields - Technical Writing - New Member

Join Date: Feb 2010
Location: India
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Armour Shunting of Single Core Cable

02/26/2010 11:38 PM

One of our 33KV outgoing feeder failed in e/f indication. After checking it is found that flash mark in cable chamber of the breaker and Y phase was bursted just below the termination. Y phase cable bursted from the position where earth shunt connected to armours. Other phases also had flash mark near shunt connection spot. There are two per leg cables and all are single core. All cable's armours are connected to earth at both end. Termination maker and cable supplier visited the place and told that there was no problem in cable or termination. This cables one end is GIS and other end is VCB. Both end is at 33KV.

Pls help me to find out the probable cause of failure.
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raju11
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Join Date: Dec 2008
Posts: 6
#1

Re: Armour Shunting of Single Core Cable

02/27/2010 11:28 PM

Two possiblities for the problem. Maximum field stresses happen where the fault happend and therefore it could have failed due to workmanship, not following procedure per manufacturer of termination, material defect etc. The other issue is circulating current through the sheath as both ends grounded. The circulating current depends on cable current(main conductor), length of cable. If it is short length of cable such as within a substation, you may try single point grounding and open end of sheath connected to SVL (Sheath voltage limiter)
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sidhu16
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#4
In reply to #1

Re: Armour Shunting of Single Core Cable

02/27/2010 11:37 PM

Can you provide me the detail of SVL? Then I may suggest it to management.
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raju11
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Posts: 6
#5
In reply to #4

Re: Armour Shunting of Single Core Cable

02/28/2010 12:22 AM

Please check the following web site to get more information.

http://www.areva-td.com/solutions/US_1031_RNL+&+Varisil%99+HC+Sheath+Voltage+Limiters+(Varisil).html

http://www.akpowersolutions.com/uploads/pres/cable_sheath_voltage_limiters_presentation.pdf
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amitbhatia
Active Contributor

Join Date: Feb 2010
Posts: 18
#7
In reply to #1

Re: Armour Shunting of Single Core Cable

02/28/2010 2:44 AM

As a thumb rule, less than 1 km can be considered for single point bonding.

Indian standard for earthing calls for the voltage rise on the floating end should not exceed 65 Volts.

Regards

Amit Bhatia

Raychem
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CR44
Member

Join Date: Feb 2010
Posts: 8
#2

Re: Armour Shunting of Single Core Cable

02/27/2010 11:31 PM

If the cable was terminated properly & passed all the test prior to keep in service or it was in service since long time then let me know that is there are surge arreasters/surge suppressor installed at this feeder???

If,not then there is a major possibility of insulation break down on heavy surge voltage due to the switching.
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sidhu16
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#3
In reply to #2

Re: Armour Shunting of Single Core Cable

02/27/2010 11:36 PM

But CR44, we have others out going feeders also which are being fed by same bus. Voltage surge could harm other fdrs also.
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Dickson
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Location: Abuja, Nigeria.
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#6

Re: Armour Shunting of Single Core Cable

02/28/2010 1:24 AM

There is no use deceiving our selves and wasting too much time on the issue. ur problem is termination or cable failed.

Was there any test carried out when the supplier brought the cable?

Was there any test carried out after completing termination?

Can I see the reading?

Pls. in all make sure u don't frustrate the efforts of the supplier since u may not have done ur job from the on set.

Dickson.

__________________
 There is peace in silence and achievement in plans.
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amitbhatia
Active Contributor

Join Date: Feb 2010
Posts: 18
#8

Re: Armour Shunting of Single Core Cable

02/28/2010 2:51 AM

I know of this. Your feeder length is 3.7 kM's and grounded at both ends. It has circulating current flowing through the armour and it is causing localised heating at the points of high contact resistance.

What is needed is a proper sheath bonding system.

For details you may contact us
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Anonymous Poster
#9

Re: Armour Shunting of Single Core Cable

02/28/2010 11:08 AM

If this cable is an underground feeder, I would say that the fAilure is due to water getting under the cable jacket, then wicking it's way up under pressure then realeasing the vapor causing the short at the termination
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shaw
Participant

Join Date: Feb 2010
Posts: 2
#10

Re: Armour Shunting of Single Core Cable

02/28/2010 12:26 PM

Dear Mr.Sidhu 16

The flashing of the single core cable is due to the earthing of the cable on either side. Single core cables shall be earthed at one end only, remove the earthing from one end the problem will be solved.

Any further clarification are required please let me know.

Regards

J.L.Shaw Sumanam

Consultant
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amitbhatia
Active Contributor

Join Date: Feb 2010
Posts: 18
#11
In reply to #10

Re: Armour Shunting of Single Core Cable

02/28/2010 9:21 PM

It shall depend upon the feeder length. As described earlier, the sheath standing voltage on the floating end should not exceed 65 Volts under full load conditions.

Mr Sidhu16, please confirm the feeder length and the current rating of the cable
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sidhu16
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#12
In reply to #11

Re: Armour Shunting of Single Core Cable

03/01/2010 4:26 AM

Fdr length is 3km and capacity is around 800A.
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Users who posted comments:

amitbhatia (3); Anonymous Poster (1); CR44 (1); Dickson (1); raju11 (2); shaw (1); sidhu16 (3)

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