Case 3 - An 11kV Heat Shrink XLPE Straight Cable Joint Failure

By Chris Dodds on 3rd February, 2015

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Case 3 - An 11kV Heat Shrink XLPE Straight Cable Joint Failure

HV Heat Shrink Cable Joints & Cable Terminations. Fault Analysis.

T&D have an obligation to investigate any cable joint or cable termination product failure, but over the years we have been asked more and more to get involved in general cable failure analysis for high voltage HV networks.

This Blog is Part 3 in a series of 5 covering Cable Fault Analysis linked to the cable jointing and terminating of high voltage power cables.

Case 1 - An 11kV 3 Core Transition Cable Joint Which Was Audibly Discharging

Case 2 - High Voltage Cable Joint Failure On 11kV Trifurcating Transition Joint

Case 4 - Problems Of Cable Joint Earth Continuity On Low Voltage Feeder Cable

Case 5 - "Buzzing" 11kV Cable Box Terminations On XLPE 3 Core Cables

Case 3

An 11kV XLPE straight cable joint failed shortly after commissioning at a refurbished Irish factory. The heat shrink joint was cut out and forwarded to us for inspection. 

There was a massive amount of damage as a result of the 11kV cable joint failure. The heat shrink outer sleeve was severely damaged and the armour cage partly melted. Removing these exposed the 3 cores, one of which was completely destroyed.

The other two cores, though superficially affected by the blast, were electrically sound. Breaking down the two remaining 11kV cable cores showed the installer to have removed the screen correctly, jointed the cores and installed all stress grading material and tubing according to the JI provided.

For the amount of damage caused and only to one phase, we were at a loss to find a cause other than mechanical.

After receiving further information from site along with a picture, it appears ropes were attached over the armour removal area and the entire cable joint and cable winched into a new position. This had buckled the armour cage and forced one core into the sharp edge of the twisted cage piercing the core insulation heat shrink tubes.

Questions were also asked about the protection in place for there to have been this level of damage.

Invitation

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Discussion subjects include cable installations, cable jointing, electrical substation, overhead line and electrical construction at LV, 11kV, 33kV and EHV.

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Category:  HV Cable Jointing & Terminating

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