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Three Core 21/35KV Medium Voltage Unarmored Cable
Voltage: 21/35kV (Um=42kV)
Conductor: Copper or aluminum, compacted circular Class 2
Conductor Screen: Extruded semi-conductive compound (per core)
Insulation: XLPE, 9.3mm per core
Insulation Screen: Extruded semi-conductive compound + Cu tape screen
Assembly: 3 screened cores + filler + binder tape
Outer Sheath: PVC Type ST2, PE, or LSZH (BS 7835)
Product Overview
Three Core 21/35kV (Um=42kV) Medium Voltage Unarmoured Cable is a sub-transmission-class XLPE-insulated power cable operating at the highest commercially available three-core voltage level. At 21/35kV with 9.3mm of XLPE insulation per core, this cable crosses the threshold from IEC 60502-2 (power cables up to 30kV) into IEC 60840 (power cables 30kV to 150kV) — the standard governing high-voltage cable design and testing. Three individually screened cores are assembled with non-hygroscopic filler and binder tape within a common PVC Type ST2 outer sheath. The 9.3mm insulation is 16% thicker than the 18/30kV class (8.0mm), providing the dielectric strength required for a maximum system voltage of 42kV. This cable serves as the inter-substation backbone in 35kV-class utility networks — the dominant primary distribution voltage in China, Russia, and parts of the Middle East — and as the collector cable in large-scale wind and solar farms stepping up to 35kV for grid connection.
IEC 60502-2 vs IEC 60840: Crossing the 30kV Threshold
Cable Construction
1. Conductor — Stranded compacted circular copper or aluminium
2. Conductor Screen — Extruded semi-conductive compound
3. Insulation — XLPE, 9.3mm, 90°C rated
4. Insulation Screen — Extruded semi-conductive compound
5. Metallic Screen — Copper tape
6. Binder Tape — Non-hygroscopic
7. Filler — Non-hygroscopic
8. Outer Sheath — PVC Type ST2 (PE or LSZH)
Technical Characteristics
| Rated Voltage U₀/U (Um) | 21/35kV (42kV maximum system voltage) |
| Governing Standard | IEC 60840 (cables 30kV to 150kV) — NOT IEC 60502-2 |
| Insulation Thickness | 9.3mm per core (all cross-sections) |
| Max. Conductor Temperature | 90°C (continuous), 250°C (short-circuit, max 5s) |
| Min. Bending Radius | 15 × overall diameter |
| Core Identification | Red, Yellow, Blue tape between insulation screen and metallic screen |
| Sheath Options | PVC Type ST2, PE, or LSZH (BS 7835) |
| PD Test Voltage | 1.5U₀ (31.5kV) per IEC 60840 with extinction voltage measurement |
Applicable Standards
| Standard | Scope |
|---|---|
| IEC 60840 | Power cables with extruded insulation for rated voltages above 30kV up to 150kV. 21/35kV (Um=42kV) exceeds IEC 60502-2 scope and is governed by IEC 60840. |
| GB/T 12706.2 | Chinese national standard for power cables 6kV to 35kV. 21/35kV is the highest voltage in this Chinese standard. YJV/YJLV designations apply. |
| BS 6622 | British standard for XLPE insulated cables 3.8/6.6kV to 19/33kV. 35kV class is at the upper boundary of this standard's scope. |
| BS 7835 | LSZH sheathed power cables for fire-sensitive indoor installations. |
| IEC 60228 | Conductors — Class 2 stranded copper and aluminium, compacted circular. |
Technical Specifications — Three Core 21/35kV
XLPE insulation: 9.3mm (all cross-sections). Ampacity values pre-calculated for three-core bundled configuration. Air: 30°C. Soil: 20°C, 2.5 K·m/W, 0.7m depth.
| Cross Section (mm²) | Conductor Dia. (mm) | Insulation (mm) | Sheath (mm) | Overall Dia. (mm) | Weight Cu (kg/km) | Weight Al (kg/km) | Ampacity Air Cu | Al (A) | Ampacity Soil Cu | Al (A) |
|---|---|---|---|---|---|---|---|---|
| 3 × 25 | 6.0 | 9.3 | 3.1 | 67.5 | 4,637 | 4,170 | 125 | 96 | 135 | 105 |
| 3 × 35 | 7.0 | 9.3 | 3.2 | 69.9 | 5,153 | 4,500 | 150 | 115 | 160 | 125 |
| 3 × 50 | 8.4 | 9.3 | 3.3 | 73.2 | 5,887 | 4,954 | 175 | 135 | 190 | 145 |
| 3 × 70 | 10.0 | 9.3 | 3.4 | 76.8 | 6,772 | 5,466 | 220 | 170 | 230 | 180 |
| 3 × 95 | 11.5 | 9.3 | 3.5 | 80.3 | 7,803 | 6,031 | 265 | 205 | 275 | 215 |
| 3 × 120 | 13.0 | 9.3 | 3.6 | 83.7 | 8,802 | 6,563 | 305 | 235 | 315 | 245 |
| 3 × 150 | 14.5 | 9.3 | 3.7 | 87.1 | 10,009 | 7,211 | 345 | 270 | 355 | 275 |
| 3 × 185 | 16.2 | 9.3 | 3.9 | 91.0 | 11,361 | 7,910 | 390 | 305 | 400 | 310 |
| 3 × 240 | 18.4 | 9.3 | 4.0 | 96.1 | 13,380 | 8,903 | 450 | 350 | 455 | 355 |
| 3 × 300 | 20.5 | 9.3 | 4.1 | 99.9 | 15,380 | 9,784 | 520 | 405 | 515 | 405 |
| 3 × 400 | 23.5 | 9.3 | 4.4 | 108.0 | 19,082 | 11,621 | 590 | 465 | 585 | 460 |
DC Conductor Resistance & Short-Circuit Withstand at 20°C
| Cross Section (mm²) | Cu (Ω/km) | Al (Ω/km) | Cu Short-Circuit 1s (kA) | Al Short-Circuit 1s (kA) |
|---|---|---|---|---|
| 25 | 0.727 | 1.20 | 3.69 | 2.42 |
| 35 | 0.524 | 0.868 | 5.15 | 3.37 |
| 50 | 0.387 | 0.641 | 7.31 | 4.79 |
| 70 | 0.268 | 0.443 | 10.2 | 6.68 |
| 95 | 0.193 | 0.320 | 13.8 | 9.03 |
| 120 | 0.153 | 0.253 | 17.4 | 11.4 |
| 150 | 0.124 | 0.206 | 21.7 | 14.2 |
| 185 | 0.0991 | 0.164 | 26.7 | 17.5 |
| 240 | 0.0754 | 0.125 | 34.6 | 22.6 |
| 300 | 0.0601 | 0.100 | 43.1 | 28.2 |
| 400 | 0.0470 | 0.0778 | 57.4 | 37.65 |
Packaging & Delivery
Heavy-Duty Iron-Reinforced Drum
Massive wooden or steel drums. 3×400mm² Cu cable weighs 19+ tonnes per km. Crane offloading mandatory. Drum flange diameter ≥25× cable OD.
Triple-Layer Moisture Protection
Per-core heat-shrink sealing + overall sheath end sealing + dual-layer caps with desiccant. UV-resistant drum wrap. Extended outdoor storage: up to 12 months.
IEC 60840 Documentation Package
Per-core PD certificate (31.5kV test with extinction voltage), AC voltage test (52.5kV/30min), DC resistance, material traceability, drum loading certificate.
Typical Applications — Three Core 21/35kV
Chinese 35kV Utility Networks
35kV is a primary distribution voltage throughout China. Three-core 21/35kV cables form the backbone of urban and industrial 35kV distribution rings.
Large Wind Farm Collection
35kV collector circuits in 200MW+ onshore wind farms. 3×400mm² cable carries 585A in soil at 35kV — equivalent to ~35MVA per circuit.
Substation Interconnection
132/35kV or 110/35kV primary substation to 35/10kV secondary substation interconnectors. Highest power density three-core cable available.
Heavy Industry 35kV Networks
Chinese and Russian industrial parks, steel mills, and aluminium smelters operating 35kV private distribution networks with dedicated MV/HV switchgear.
Solar Farm Grid Connection
GW-scale solar farms aggregating inverter output at 35kV for step-up to 110kV or 220kV at the grid connection point.
Russian & CIS 35kV Networks
Standard primary distribution voltage in Russian and CIS utility networks. 35kV three-core cables form regional distribution rings from 110/35kV substations.
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Frequently Asked Questions
As a factory, we offer flexible MOQ depending on the cable type. For standard stock items, MOQ is low; for customized specifications, please contact our sales team for a detailed quote.
Yes, Qiangli cables are manufactured in compliance with international standards such as UL, CE, TUV, and VDE. We provide full test reports and certificates upon request.
Absolutely. We have a dedicated R&D team that can customize cable structure, material, color, and printing to meet your specific project needs.
For standard products, lead time is usually 7-15 days. For large-scale project orders or customized products, it typically ranges from 20 to 30 days.
Yes, we provide free samples for most standard cables. You only need to cover the international courier costs. Contact us to arrange your sample shipment.