Jiangsu Dewei YJWTR-35 is a fully formulated, peroxide-curable, water-tree-retardant XLPE insulation compound supplied as pellets for medium-voltage cable insulation. The following entries are restricted to production-scale wire and cable routes where wet electrical ageing, semi-conductive layer adhesion, and continuous vulcanization control dominate acceptance. Each entry identifies the applicable compliance standard, feed ratio, downstream process parameters, and terminal cable type.

Wet-Ageing Compliance Boundaries for 35 kV Direct-Buried Distribution Cables

Compliance testing of direct-buried 26/35 kV cable insulated with YJWTR-35 is anchored to GB/T 12706.3-2020 for construction and routine electrical tests, with cross-reference to IEC 60502-2:2014 for wet-ageing and mechanical property requirements where the rated voltage falls within the standard’s scope. The insulation is processed as a 100 wt% undiluted pellet stream; line-side addition of external peroxide masterbatch is set at 0 phr because the crosslinking system is already pre-dispersed. For a 1×240 mm² compacted copper conductor, the nominal insulation wall is 8.0 mm, with a conductor shield at 0.8 mm and insulation shield at 0.6 mm, giving a radial layer ratio of 0.8:8.0:0.6. The wet-ageing test method is ASTM D6097-16, with acceptance based on relative ranking against a non-water-tree-retardant XLPE control because absolute tree-length limits are not fixed in cable type tests.

The downstream process uses a 150 mm single-screw extruder with L/D 25:1 and compression ratio 2.5:1, feeding a triple-layer crosshead. Melt temperature is held in the 118–122°C band at the head to avoid measurable dicumyl peroxide decomposition in stagnant flow regions, since peroxide half-life at 120°C is approximately 10 h and decreases sharply above 130°C. Continuous vulcanization is conducted in dry nitrogen at 320–350°C and 10–15 bar, with residence time adjusted to achieve gel content of at least 80% when checked by xylene extraction per ASTM D2765-16. Insulation-wall eccentricity is monitored by on-line X-ray scanning and held below 10% for the full reel. Terminal product is a longitudinally water-blocked, copper-wire-screened, PE-sheathed 26/35 kV medium-voltage power cable for direct burial in wet underground routes.

In wind farm collector cable production, moisture penetration occurs not only through jacket defects but also through radial water migration in metallic screens, making insulation-layer water-tree resistance the primary long-term reliability variable. The 35 kV collector cable is built to GB/T 12706.3-2020 and IEC 60502-2:2014, with wet electrical ageing assessed by ASTM D6097-16 relative ranking against a control insulation. YJWTR-35 is used at 100 wt% compound basis; no silane coupling agent or antioxidant masterbatch is added on the line because the water-tree-retardant package is already dispersed in the pellet. For a 3×95 mm² aluminium conductor, insulation wall thickness remains 8.0 mm, and the conductor shield and insulation shield are co-extruded at 0.8 mm and 0.6 mm. The production line typically pairs a 90 mm shield extruder, 150 mm insulation extruder, and 90 mm shield extruder in a triple-head configuration. Conductor pre-heating to 60–70°C before entry into the crosshead reduces stress-induced shrinkback at the conductor shield interface. Curing takes place in a dry-nitrogen continuous vulcanization tube at 10 bar and 320–340°C, with cable exit temperature below 85°C before cooling water. The finished product is a water-blocked 26/35 kV wind farm collector cable with copper tape screen and flame-retardant outer sheath where specified.

What Limits Line Speed During Triple Extrusion of 8.0 mm Wet-Ageing-Resistant Insulation?

For 18/30 kV industrial feeder constructions with an 8.0 mm nominal insulation wall, the line speed ceiling is set by cure-tube residence time rather than extruder throughput. At a 60 m dry-cure tube length and 340°C nitrogen temperature, the cable must remain above 150°C internal cure temperature for at least 5 min to drive peroxide decomposition and crosslinking beyond the gel point; this corresponds to a practical line speed range of 2.5–4.5 m/min on many production lines. The compound is fed at 100 wt% as-supplied pellet form, and no external peroxide masterbatch is dosed because YJWTR-35 already contains the crosslinking system. The downstream process uses triple-layer co-extrusion with a 150 mm insulation extruder at L/D 25:1 and screw compression ratio 2.5:1; melt temperature is controlled to 118–122°C at the head, and melt pressure is maintained below 250 bar to avoid screen pack blinding from gel accumulation. Finished product is an armoured 18/30 kV industrial motor feeder cable with copper wire screen and flame-retardant outer sheath.

Production-scale observations on triple-extrusion lines indicate that melt pressure instability exceeding ±15 bar over a 30 min window is an early indicator of pre-cured gel formation in the die land, and it is corrected by reducing head temperature rather than increasing screw speed. Because water-tree-retardant additives can alter melt viscosity relative to standard XLPE, the insulation extruder’s screw cooling is run 10–15°C lower than conventional grades to maintain pellet conveying stability. Terminal acceptance criteria include insulation wall eccentricity below 10% measured by on-line X-ray scanning, and peel strength between insulation and semi-conductive shields above 8 N/25 mm when checked by established cable plant methods. This scenario is process-confined because published water-tree length data for this specific industrial feeder configuration is limited; performance is demonstrated by type testing rather than absolute tree-length thresholds.

Screen pack selection interacts with the water-tree-retardant formulation because fine-mesh layers can accumulate gel particles and increase head pressure. A 40/60/80 mesh pack is typically used, and pack replacement is scheduled when head pressure rises by more than 15% from the stable value at start-up. If the pressure rise is ignored, the resulting stagnation zones at the entrance to the metering section generate local peroxide decomposition, which then contaminates the insulation wall as visible 10–50 µm gel protrusions at the outer surface. These protrusions are detected in the final cable during routine voltage testing per IEC 60502-2:2014 and by surface inspection on the jacket line, but detection is not guaranteed if the gel remains embedded within the insulation layer.

Substation egress cable manufacturing in below-grade vaults imposes simultaneous wet immersion and high short-circuit mechanical stress on insulation, so acceptance testing includes both laser micrometer wall eccentricity and water-tree length after 500 h in saline solution per ASTM D6097-16. The cable is built to IEC 60502-2:2014 for 12/20 kV or 18/30 kV designs, with insulation wall of 5.5 mm or 8.0 mm depending on voltage class. Addition ratio is 100 wt% YJWTR-35; regrind from the insulation layer is not permitted, and the conductor shield and insulation shield are co-extruded at 0.7 mm and 0.5 mm nominal thickness for the 12/20 kV case. The downstream process involves conductor pre-heating to 70°C, triple-layer extrusion with melt temperature at 120°C maximum, and dry-cure vulcanization under 10 bar nitrogen. After curing, the cable enters a degassing chamber for 72 h at 70°C to reduce methane and acetophenone byproduct concentration before screen application. Terminal product is a substation interconnecting cable with aluminium foil-laminated water barrier, copper wire screen, and flame-retardant sheath.

Because these egress cables are often pulled through conduits with short bend radii, the insulation must be evaluated for hot-set elongation after degassing rather than immediately after cure. The hot-set test is run at 200°C under 0.2 MPa load, and the elongation is recorded only after the sample has equilibrated. If the cable has been degassed for less than 48 h, residual peroxide byproducts can produce low hot-set values that pass but do not reflect the final crosslink network. Batch-to-batch variation in this grade is most readily observed in hot-set elongation before the degassing cycle; values exceeding 175% on un-degassed samples typically indicate under-cure or wrong temperature profile rather than raw material variation.

When Cable Ducts Remain Continuously Flooded and Ammonium Sulfate Contamination Is Present

When urban 6/10 kV distribution feeders are installed in continuously flooded concrete duct banks, ammonium sulfate contamination from soil and groundwater can accelerate water-tree growth in conventional XLPE. YJWTR-35 is applied in this scenario because the water-tree-retardant formulation provides a relative improvement in vented water-tree length when tested under ASTM D6097-16. The construction follows IEC 60502-2:2014 for 6/10 kV, with an insulation wall of 3.4 mm for a 1×240 mm² conductor. The compound is used at 100 wt% without dilution; external antioxidant masterbatch addition is 0 phr. Triple-layer extrusion is conducted with a 120 mm insulation extruder at L/D 25:1, melt temperature 120°C, and dry-cure vulcanization at 320–340°C under 10 bar nitrogen. Post-cure degassing is set at 72 h at 70°C to reduce peroxide decomposition byproducts below cable acceptance thresholds before sheathing. The terminal product is a longitudinally water-blocked 6/10 kV urban underground distribution cable with copper tape screen and HDPE outer sheath. Published water-tree length data for this specific ammonium sulfate contamination level is limited; acceptance is therefore based on comparative ASTM D6097-16 ranking against a non-water-tree-retardant control sample.

In flooded duct applications, the radial water barrier is not absolute, and water can enter the insulation shield interface through mechanical damage during cable pulling. To reduce this risk, the insulation shield is specified with hot-strippable semi-conductive compound and extruded with a dual-layer head that permits separate temperature control from the insulation stream. Peel force between insulation shield and insulation is checked in the plant at 8–20 N/25 mm to ensure the shield strips cleanly during joint preparation without leaving carbon residue on the wet-aged insulation surface. Field failure modes in conventional XLPE often localize at shield-insulation interfacial voids where tree initiation begins; this grade is processed to minimize interfacial micro-voids by maintaining melt temperature stability within ±2°C at the die lip.

Industrial plant 6/10 kV motor feeder cables routed through cooling water trenches require insulation that retains dielectric strength after prolonged water uptake, a condition conventional XLPE is not designed to withstand beyond 1,000 h of wet electrical testing without water-tree mitigation. YJWTR-35 is processed at 100 wt% compound feed, with no let-down ratio and no post-compounding addition of crosslinking agent. For a 6/10 kV cable, insulation wall is 3.4 mm nominal; conductor shield and insulation shield thicknesses are 0.6 mm and 0.5 mm, giving a 0.6:3.4:0.5 radial layer ratio. Extrusion is run on a 120 mm single-screw line at L/D 24:1 with a triple-layer crosshead, head temperature 120°C, and melt pressure capped at 200 bar to avoid premature crosslinking induced gel formation in the screen pack. The cable is dry-cured under nitrogen at 10 bar and then degassed at 70°C for 72 h before armouring. Terminal product is a galvanized steel tape-armoured 6/10 kV motor feeder cable with PVC or low-smoke zero-halogen outer sheath as specified by plant fire codes.