Medium Voltage XLPE Insulated Power Cable YJLV

Triple Extrusion Eliminates Partial Discharge

The conductor screen, XLPE main insulation, and insulation screen are extruded simultaneously through three concentric dies in a single production pass — not as separate layers applied sequentially. The three layers bond together without interfaces, voids, or contamination that would otherwise initiate partial discharge under voltage stress. Partial-discharge tests at factory acceptance verify the cable has zero detectable discharge above background noise — the test that separates real MV cable from poorly-made imitations.

90°C XLPE = 30-40% Higher Ampacity vs PVC

XLPE insulation rated for 90°C continuous conductor temperature, 130°C emergency overload (typically 100 hours per year), and 250°C short-circuit for 5 seconds. The thermal headroom over the 70°C PVC insulation in low-voltage NYY translates to roughly 30-40 percent higher steady-state ampacity at the same cross-section. For utility distribution networks where conductor cost is dominant, that ampacity advantage justifies the premium for XLPE construction.

Voltage Classes 3.6/6 kV Through 26/35 kV

The full IEC 60502-2 voltage range available from a single product family: 3.6/6 kV (light industrial), 6/10 kV (urban distribution), 8.7/15 kV (the most popular global MV class), 12/20 kV (utility primary distribution), 18/30 kV (sub-transmission, wind farms), 21/35 kV and 26/35 kV (higher utility distribution). Each voltage class has specific insulation wall thickness and screen specifications per the IEC table — specify the project voltage class precisely, not a generic “MV cable”.

Copper Screen for Earth Fault, Not EMI

The copper tape or copper wire screen over the insulation is sized to carry the network earth-fault current for the specified clearing time (typically 1 to 3 seconds at 10 to 25 kA depending on the network design). This is fundamentally different from the EMI-rejection screen in control cables — the MV cable screen is a fault-current path that operates the upstream protection during an insulation failure, not a noise-rejection layer. The screen cross-sectional area is project-specific; specify the fault-current rating at order so the screen is sized correctly.

Red Sheath = International MV Identification

Standard outer sheath colour is red for medium-voltage cable across all major international markets — the universal visual identification that distinguishes MV cable from the black low-voltage NYY/NAYY that shares the same cable trenches and trays in many installations. The colour convention prevents catastrophic misconnection where a low-voltage circuit would be wired into a medium-voltage termination by mistake. Other colours (black, blue, grey) available on quotation for projects with specific identification requirements.

IEC + BS + VDE + HD + AS/NZS Multi-Market Certified

Production certified to IEC 60502-2 as primary international reference, plus BS 6622 (UK 6-33 kV), BS 7835 (UK 11-33 kV LSZH), DIN VDE 0276-620 (Germany), HD 620 S1 (CENELEC harmonised European), AS/NZS 1429.1 (Australia/NZ). KEMA, BASEC, CESI, and SGS test reports available for utility-acceptance qualification. For projects exporting across multiple regulatory regimes, dual or triple certification on a single physical cable production run is straightforward — specify all target markets at order.

MV cable terminations and joints require specialised tools, training, and quality control beyond what general electrical contractors typically have. Use only jointers with manufacturer certification for the specific termination kit and cable type, working in clean conditions (covered work area, no dust, no humidity), with proper stress-cone preparation and semi-conducting screen termination. Most MV cable failures in the field trace back to defective terminations or joints, not to the cable itself.

Pre-energisation testing for MV cable includes both insulation resistance (megger at 5 kV DC, expected > 1000 MΩ) and partial discharge measurement at AC voltage above the rated U₀. The PD test is specific to MV cable and detects insulation defects that megger testing alone misses. Document the PD test results in the project handover. Cables with detectable PD above background noise have insulation defects that will fail within months to years; replace before commissioning rather than energising a known defect.

For short cable runs (under a few hundred metres), bond the copper screen to earth at both cable ends — provides the lowest-impedance fault current path. For long single-core cable runs, use cross-bonding (screen continuity at intermediate joints with phase rotation) to control the standing voltage that would otherwise develop on the screen from the AC magnetic field. The bonding scheme is project-specific and should be designed in advance by the network engineer — do not leave it to installation discretion.

MV cable minimum bending radius is 15× OD for single-core and 12× OD for three-core (per IEC 60502-2). Tighter bends during cable pulling damage the XLPE insulation and the semi-conducting screen interfaces invisibly from outside but cause partial discharge initiation over months in service. Use proper cable rollers at corners during pulling, never manual force around tight bends. For very large cables (300 mm²+), use cable-pulling equipment with calibrated tension monitoring — over-tension stretches the conductor and damages the insulation.

For three single-core cables forming a three-phase circuit, route them in equilateral trefoil formation (the three cables touching at the centre of a triangle) rather than flat side-by-side spacing. Trefoil minimises the AC inductance, reduces the cable losses, balances the impedance between phases, and keeps the magnetic field cancellation effective at the cable group radius. Flat formation works but requires phase rotation along the run and produces higher losses. Strap the trefoil bundle at regular intervals (typically 1-2 m) to maintain the formation under thermal cycling.

Water ingress is the primary long-term failure mechanism for MV cable. The water-blocking semi-conducting tape inside the cable is the last line of defence, not a substitute for proper end sealing. During construction, always cap cable ends with heat-shrink end caps immediately after cutting and before backfilling trenches. For cable runs awaiting termination, apply waterproof end caps and elevate the cable ends above ground level. Moisture trapped inside the cable during construction sits there for years and slowly degrades the XLPE insulation from the inside, causing water treeing and eventual breakdown.