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

By Chris Dodds on 3rd February, 2015

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

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

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

T&D undertake to make an un-biased investigation into any failure involving high voltage cable joints and cable terminations regardless of manufacturers or whether heat shrink or cold shrink type.

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 3 - An 11kV Heat Shrink Transition Cable Joint Failure

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

Case 5

An 11kV HV cable box in the basement of a London news organisation was reported as "buzzing".

The HV cable box contained 2 x 11kV XLPE high voltage heat shrink terminations entering from the side. Both 11kV terminations were removed and sent to us for investigation.11kV XLPE High Voltage Terminations

Both cable terminations had crossed cores and the spacing between cores was less than ideal. On the first 11kV termination the investigation showed the high voltage insulation to have been damaged when removing the "peelable" extruded screen. However, this did not show signs of activity and although this was a potential problem, it was unlikely to be the cause of the noise in the HV cable box.

Examining the red anti tracking heat shrink tubing on the second 11kV termination showed signs of erosion on two of the cable cores above the stress control area. These lined up and it would appear the two 11kV copper conductor cores were in contact with each other whilst in service.

The cause of the "buzzing" in the 11kV cable box was due to the cores in intimate contact with each other in an unscreened area, this would in time have eaten through the tubing and possibly caused the heat shrink termination to fail.

An interview with the HV cable jointer revealed, at the time of installation, there was more than sufficient clearance, but over time the cable had sagged and the gap closed.

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Category:  HV Cable Jointing & Terminating

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