Introduction
Cable installation of EHV (Extra High Voltage) cable is one of the most critical phases of any power transmission project. It demands the same level of care, knowledge and discipline as the manufacturing of the XLPE insulated cable itself.
Regardless of the installation method — direct burial trench, duct laying, or trenchless HDD — the handling of the cable at every stage is paramount. Work must be carried out by a trained crew under close supervision.
Cable Storage, Site Conditions and Safe Handling of Cable Drums
- Inspect cable drums for physical damage and check visible cable ends on arrival from the manufacturer.
- Verify all cable end caps and seals are intact — missing or loose caps must be replaced immediately.
- Load and unload drums using a crane of appropriate capacity only.
- Stack cable drums in rows grouped by section-wise laying requirements to streamline site logistics.
Storage of Cable Accessories
- Store cable accessories strictly as per the cable accessory supplier's recommendations.
- Mark the expiry date on any shelf-life accessory kit and ensure kits are used before expiry.
- Keep all accessories in a single designated area, segregated by type to prevent mix-ups during jointing.
Site Inspection, Survey and Trial Pits
- Survey the complete proposed cable route before any excavation work commences.
- Excavate trial pits along the route to identify and map existing underground utilities.
- Prepare route drawings and pucca trench design drawings based on survey findings.
- Obtain all necessary approvals from the Competent Authority before commencing work.
Cable Path Preparation
All permissions must be obtained from Local Civic Agencies and the Police Department before any trenching work begins.
HDD (Horizontal Directional Drilling) Process:
A. Pilot Hole Drilling — A small diameter pilot hole is drilled along the predetermined path using a surface-launched drilling rig.
B. Reaming — The pilot hole is progressively enlarged to accommodate the cable or conduit.
C. Pulling HDPE Pipes — The requisite number of HDPE pipes are pulled through the enlarged borehole.
Cable Laying Work
This is the central phase of the installation. A motorised winch machine is essential for controlled cable pulling at EHV voltage levels.
- Confirm the trench is dry, clean and dressed. Deploy pumps to drain any standing water before laying begins.
- Position the motorised winch machine at the far end of the section.
- Thread the winch sling rope back to the cable drum location and attach the cable pulling eye via a D-shackle arrangement.
- Pull the cable slowly, keeping it on top of the rollers throughout. Maintain specified bending radius at all points.
- Visually inspect the outer sheath for damage while still on rollers. Mark and repair any damaged sections before backfilling.
Sheath Testing and Repair
For cables with graphite-coated outer sheaths, a sheath integrity test must be carried out before primary backfill.
- Test the cable at 5 kV to 12 kV DC for one minute (typically 10 kV DC for one minute on newly installed cables).
- If the outer sheath fails, locate the fault and repair the faulty portion. Repeat the DC high voltage test after repair.
Testing and Commissioning of Feeders
- Measure and record the Insulation Resistance of each cable feeder using a 5 kV Megger.
- Check and confirm the Phase Sequence of each feeder before energisation.
- Connect both cable ends at the feeding point and at the receiving end substation.
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