Using “Heat Shrink Wraparounds” To Repair High Voltage Transmission Cables In Underground Cable Vault

Published 21 Jan 2019

uploaded by Chris Dodds - Thorne & Derrick Sales & Marketing Manager

Heat Shrink Wraparounds

During an annual inspection of the High Voltage Cable (Transmission & Distribution) Network at a power grid located in Thailand the following cable damage was witnessed to the high voltage underground cable sheath, note the “cracking” effect to the jacket.

Installed in 1996 and originally manufactured by Phelps Dodge the 66kV/115kV high voltage distribution cable was of single core construction with XLPE insulation, lead sheath (Alloy E) and compact copper conductor with 800sqmm cross section area – the cable specification and project record book noted a nominal overall diameter of the complete cables at 113mm.

The client was concerned about the potential threat of water ingress seeping into the inner cable construction and causing electrical fault breakdown overtime.

Heat Shrink Wraparounds

Under consideration to reinstate the cable sheath damage was a wraparound heat shrink cable repair system – the cable repair sleeve consists of a raised rail profile with interlocking stainless steel channel and thick wall adhesive lined heat shrink tube to wraparound the section of damaged cable to reinstate the electrical insulation to the CABLE sheath/jacket. The “wraparound solution” could be used if the underlying layers of the cable construction had not been damaged. The “wraparound” would be provide excellent moisture sealing and defence against water contamination into the high voltage cable.

Proposed Solution: Heat Shrink Wraparound Cable Repair System

Cable Type: 115kV HXLP-LS 800sqmm (Spec IEC 840)

Cable Sheath Damage

The cable oversheath manufactured from polyethylene material with a nominal thickness of 4.75mm and minimum thickness of 3.73mm incurred jacket damage in service and required repair to prevent potential outage to the high voltage power cable system.

The following Comments from the cable manufacturer were noted with respect to the site condition of the cable and the proposed repair using “heat shrink wraparounds”:

From your pictures, it is difficult to express the root cause of the oversheath crack. It may cause from many factors such as hitting by external force, long time immerse in oil or chemical water, age of cable, etc.
From the cable construction, the cable has lead alloy sheath which is the perfect barrier for water, oil and chemical. Therefore, the water cannot ingress into the XLPE insulation unless the lead alloy sheath is damaged. The cable is still safe for operation.
One concern is the copper wire screen and copper contact tape under the oversheath. Since the oversheath is cracked, the water can come in under the oversheath and cause the corrosion to the copper wire screen. The function of this copper wire screen is to carry the single line to ground fault current in case of fault occur. If the copper wire screen is completely corroded, only the lead sheath is used for carrying the single line to ground fault current. From my rough calculation, the lead sheath alone can carry the earth fault around 23kA for 1 second. You can check the corrosion of the copper wire screen by measuring its resistance and comparing its value with their previous measurement.
Since the oversheath is already cracked and water already come in, you may consider in the worst case that the copper wire screen is completely corroded and consider if the earth fault current carrying capacity of lead sheath of 23kA for 1 second is enough for your system or not. If it is okay, you still can use this cable.
Please also check with the cable splice supplier if the water leak under the oversheath can cause any harm to the cable splice or not.
Periodic maintenance and test to see the trend is recommended such as insulation resistance test of XLPE insulation, on-line or off-line partial discharge test, resistance of copper wire screen and lead sheath test, etc.

Phelps Dodge

HV Cables

Phelps Dodge International (Thailand) Limited (PDITL) was established in 1968 as a joint-venture between an existing Thai firm and Phelps Dodge Corporation – PDITL are pioneers in the local industry and were the first company to introduce the majority of new processes, products and technology related to wire and cable manufacturing. PDITL is the only supplier in Thailand with complete in-house facilities for testing power cable up to 400kV.

PDITL has got its certification type test from International Independent Laboratories such as KEMA, Cable Technology Lab, etc. for LSHF cable, Fire resistant cable, Medium voltage, High voltage and Extra high voltage XLPE cables up to 245kV cables.

PDITL manufactures world-class quality wire and cable, not only for the local market but also for international markets, complying with strict international standards. It is proud of its customer services and long term relationships. PDITL has a team of over 700 employees, which are most important assets.

Bare Copper Conductors
Low Voltage Power Cables (XLPE, PVC, PE, EPR Insulation)
Control Cable & Instrumentation Cables
Lead Sheathed Cables
Fire Resistant & LSHF Cables
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High Voltage Power Cables (69kV | 115kV XLPE Cable)
Extra High Voltage Power Cables (230kV XLPE Cable)
Aluminium Conductor (AAC)
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Aluminium Alloy Conductor (AAAC)
Weather Proof Cables (WPC)
Service Entrance Cables (SEC)
Service Drop Cables (SDC)
Spaced Aerial Cables (SAC)

High Voltage Cable Manufacturer – PDIT

Thorne & Derrick

T&D are Specialist Distributors to UK Distribution Network Operators (DNO’s), NERS Registered Service Providers, ICP’s and HV Jointing Contractors of an extensive range of LV, MV & HV Jointing, Earthing, Substation & Electrical Eqpt – this includes 11kV/33kV/66kV joints, terminations and connectors for both DNO and private network applications.