Under wet and dry installation categories covered by IEC 60502-1 and GB/T 12706.1, DJ210 is used as the extruded insulation layer in multi-core steel-wire armoured distribution cable rated 0.6/1 kV. The resin is charged at 100 phr, with dicumyl peroxide masterbatch metered at 1.8–2.0 phr and a hindered phenol antioxidant added at 0.2–0.3 phr; the lower peroxide addition relative to medium-voltage application is constrained by thin-wall residence-time uniformity and the need to limit retained peroxide by-products after dry-cure crosslinking. A 90 mm single-screw extruder with L/D 30:1 and a screen pack of 80/120/150 mesh feeds a dry-cure vulcanization tube at 180–220°C under 0.8–1.2 MPa nitrogen. The terminal products are single-core and three-core low-voltage power cables installed in conduit, tray, or direct-burial building distribution; insulation acceptance includes hot-set elongation below 175% at 200°C and 0.2 MPa load with permanent set below 15% according to IEC 60811-501. Operational boundaries for this grade include feed-stream moisture below 0.03 wt% and die temperatures not exceeding 125°C; moisture above this threshold generates steam channels in the insulation wall, while acid-functional fillers are not added because they interfere with peroxide free-radical cure and raise dissipation factor.

What controls hot-set margin in 6–35 kV dry-cure catenary extrusion?

In insulation layers rated 6–35 kV, DJ210 is processed through a triple-head extruder with 90 mm/120 mm/90 mm screw diameters and L/D 30:1; the conductor screen, insulation, and strippable outer stress-control screen are co-extruded. The insulation melt temperature at the die is held between 120°C and 130°C to suppress premature peroxide decomposition, while the dry-cure catenary tube is zoned from 180°C to 300°C and pressurized with nitrogen at 1.0–1.5 MPa to prevent microvoid growth. The governing standards are IEC 60502-2, GB/T 12706.2, and AEIC CS8; raw-material acceptance includes melt mass-flow rate according to ISO 1133-1:2022 at 190°C/2.16 kg and moisture content below 0.03 wt% before the feed throat. Production-scale failure modes on these lines are dominated by die-lip scorch when barrel temperatures exceed 130°C, by lumpy screen packs when gel fraction develops upstream, and by steam void formation when residual moisture is not lowered below the same threshold.

Formulation addition ratios are set with DJ210 at 100 phr, dicumyl peroxide at 1.8–2.2 phr, a hindered phenol antioxidant at 0.2–0.4 phr, and a copper deactivator at 0.1–0.2 phr where the cable carries a copper screen in wet service. The upper peroxide limit of 2.2 phr is dictated by scorch margin collapse at high line speed; the lower limit of 1.8 phr is set by hot-set margin and retained mechanical integrity after thermal ageing. The vulcanization kinetics are matched to the cure-tube profile by adjusting dicumyl peroxide concentration rather than by raising melt temperature, because increased temperature narrows the processing window before pre-cured particulate gels form in the high-shear dispersion zone. An on-line moving-die rheometer operating at 180°C, 1° arc, and 100 cpm verifies that the torque differential tracks the peroxide concentration within ±0.05 dN·m of the calibration curve; any excursion beyond this band triggers downstream hot-set inspection. The crosslinked insulation must exhibit hot-set elongation below 175% and permanent set below 15% under 0.2 MPa at 200°C for 15 min according to IEC 60811-501.

The downstream process uses conductor preheat at 80–110°C on copper or aluminium, followed by triple-layer co-extrusion and a dry-cure catenary section where the cable is held under nitrogen pressure to achieve crosslink density without steam quenching. Post-cure shrinkage is controlled by a water-free cooling stage and on-line diameter scanning; insulation eccentricity is held within ±0.1 mm for core sizes above 35 mm². Partial discharge testing is performed at 1.73 U₀, and any discharge cluster in the insulation body is traced back by microscopy to peroxide agglomerates, unfiltered gel particles, or steam voids rather than to global resin viscosity shifts. The terminal products are single-core and three-core medium-voltage distribution cables used in utility feeders, wind-farm collection circuits, and industrial ring mains.

Solar-array strings that operate at 1.5 kV DC and are exposed to 85°C/85% RH damp-heat cycles employ DJ210 as the crosslinkable polyethylene insulation inside a halogen-free flame-retardant outer sheath. The applicable standards are EN 50618, IEC 62930, and UL 4703; insulation formulation uses 100 phr DJ210, dicumyl peroxide at 1.8–2.0 phr, and a stabilizer package at 0.5–0.7 phr to address prolonged UV and damp-heat service. The production route uses a 60 mm single-screw extruder feeding a dry-cure tube at 200–250°C; conductor preheat is fixed at 80–90°C to maintain concentricity on fine-stranded tinned copper. Terminal products are single-core photovoltaic array cables, typically 4 mm² to 16 mm², with crosslinked insulation wall thicknesses specified by EN 50618, generally between 0.5 mm and 1.0 mm. The insulation layer is not filled with carbon black or mineral flame retardants because those additions raise dissipation factor and reduce volume resistivity; flame retardance is placed in the halogen-free sheath rather than in the XLPE insulation.

Because photovoltaic installations expose the insulation to reverse-current bias in fault conditions, wet junction boxes, and long DC run lengths, production lots are sampled for hot-set and volume resistivity after damp-heat aging. IEC 62930 requires long-term thermal endurance validation; published DJ210-specific aging data for this configuration is limited, so qualification is typically based on comparison of hot-set drift and tensile retention against unaged values on each production campaign. Pre-drying to moisture below 0.03 wt% is required when ambient relative humidity exceeds 60%. The boundary condition for processing is the scorch window at the die head; because the insulation wall is thinner than medium-voltage cable insulation, any melt temperature excursion above 125°C produces pre-cured gel that is visible as surface roughness and can fail the smoothness check in the finished cable.

When a thin-wall automotive primary wire must satisfy ISO 6722 Class B long-term thermal ageing

When a thin-wall automotive primary wire is specified for engine-compartment routing and must satisfy ISO 6722 Class B long-term thermal ageing at 100°C for 3,000 h, DJ210 is processed as the insulation resin with 100 phr base polymer, dicumyl peroxide at 1.6–1.9 phr, a phenolic antioxidant at 0.3–0.5 phr, and a copper deactivator at 0.1–0.2 phr when tinned fine-stranded conductors are used. The lower peroxide addition relative to medium-voltage cable is set by thin-wall flexibility and controlled strip-force retention, not by hot-set alone. The production line uses a 50 mm extruder with L/D 25:1, a pressure die, and a dry-cure tube at 200–230°C; the draw-down ratio is kept at 1.5–2.0 to avoid melt fracture on conductor sizes from 0.35 mm² to 6.0 mm². Terminal products include engine-compartment primary wire, battery cable, and sensor leadwire where the insulation wall may be as low as 0.25 mm. Published line-speed data for DJ210 in thin-wall ISO 6722 configurations is limited; line speed is established by hot-set sampling rather than extrapolated from thicker wall profiles. Pre-drying is required when ambient relative humidity exceeds 60% because thin-wall foam generation from dissolved water is visible as surface roughness and dielectric weakness. Installation plant experience shows that excessive crosslink density from dicumyl peroxide above 1.9 phr raises strip force above automatic harness cutting thresholds; the 1.6–1.9 phr band is therefore constrained by downstream wiring harness assembly as much as by electrical performance.

Heating-cable cold-lead insulation under repeated thermal cycling

Heating-cable cold-lead sections that connect the resistance element to thermostats and power terminations are insulated with DJ210 crosslinked polyethylene to meet IEC 60800 and the general construction requirements of IEC 60502-1 where applicable. The formulation is set at 100 phr DJ210, dicumyl peroxide at 1.8–2.0 phr, and a phenolic antioxidant at 0.2–0.4 phr; carbon black is not added to the insulation layer because the cold-lead dielectric must retain high volume resistivity under elevated floor-temperature conditions. The production line uses a 45 mm extruder with L/D 25:1 and a pressure die over solid conductors from 1.5 mm² to 2.5 mm², followed by a dry-cure tube at 200–240°C and water cooling after crosslinking. Terminal products include floor-heating cold leads, roof de-icing leadwires, and pipeline tracing cold sections. The main processing constraint is differential shrinkage between the copper conductor and the XLPE insulation during thermal cycling; permanent set below 15% on the hot-set test is used as a proxy for dimensional stability, and batch-to-batch moisture above 0.03 wt% is rejected before extrusion.

Surface discharge in aerial bundled cable depends on insulation morphology and screen adhesion

Aerial bundled cable installed in coastal and high-pollution corridors uses DJ210 as the extruded insulation over compacted aluminium phase conductors, with the complete assembly regulated by IEC 60502-1 for 0.6/1 kV service and by utility specifications such as GB/T 12527 where applicable. The insulation compound is mixed at 100 phr DJ210 with dicumyl peroxide at 1.8–2.2 phr and a hindered phenol antioxidant at 0.2–0.4 phr; no conductive carbon black is placed in the insulation, while track-resistant sheathing or surface treatment is used for outdoor exposure. The production route uses a 90 mm single-screw extruder with L/D 30:1 and a dry-cure line at 180–250°C; conductor preheating at 90–100°C improves adhesion to the aluminium and reduces longitudinal water ingress under wind-induced vibration. Terminal products are aerial bundled cable assemblies of two to five phase cores, strung on poles for rural and peri-urban distribution. The critical risk is partial discharge initiation at the insulation-sheath interface in saline fog conditions; surface contamination and poor interface adhesion generate boundary discharges that can erode the XLPE surface even when bulk dielectric strength remains high.

The processing limitation in coastal aerial bundled cable is not crosslink density but surface contamination during outdoor storage; the insulation surface must be free of silicones and low-molecular-weight amides that migrate to the surface after extrusion and reduce interface adhesion. Batches showing extrusion melt temperatures above 130°C at the screw tip are quarantined because pre-cured gel particles in the insulation create surface protrusions that become partial discharge initiation sites under salt fog. Pre-drying is specified when ambient relative humidity exceeds 60%; incoming granulate is conditioned for 4–6 h at 60°C in a desiccant-air dryer before being gravimetrically fed to the extruder. Migration kinetics of low-molecular-weight processing aids in the XLPE matrix must be considered in the downstream qualification plan because long outdoor aging can concentrate surface amides at the insulation-sheath boundary and reduce the interface discharge resistance measured after salt-fog exposure.