For three-layer co-extruded medium-voltage distribution cables up to the 10 kV class, manufactured to IEC 60502-2 and GB/T 12706.2, Sinopec Qilu XLPE QHJ-01 is used as the undiluted insulation layer at 100 parts; no reactive let-down or additional peroxide concentrate is introduced because the pellet carries the peroxide curing system and antioxidant stabiliser in pre-dispersed form. The process window is set by the dry-cure continuous vulcanisation line: melt temperature at the crosshead is held between 112 °C and 124 °C, while the CV tube radiant zone operates at 350–420 °C under 1.0–1.2 MPa nitrogen pressure to suppress microvoids. On a 90 mm vented single-screw extruder with L/D 30:1, screw speed is limited to 40–60 rpm to keep melt residence time below the peroxide half-life boundary; at melt temperature above 128 °C, premature crosslinking generates hard XLPE specks that appear as lumps at the die and force line stoppage. Insulation thickness in this segment spans 2.5–5.5 mm; line speed is governed by heat diffusion through the insulation wall, with thick-wall designs below 12 m/min and thin-wall designs up to 35 m/min. Cure verification per IEC 60811-507—200 °C, 15 min—must show elongation under load ≤ 175% and permanent set ≤ 15%; the same lot is checked for gel content via xylene extraction, with typical acceptance ≥ 80%. Routine cable tests include partial discharge at 1.73 U₀ with sensitivity of 10 pC; no measurable discharge is permitted. Terminal product types include compacted circular copper or aluminium conductors with semiconductive conductor and insulation screens, aluminium-wire-armoured or unarmoured, with PVC or HDPE oversheath, deployed in 3.6/6 kV and 6/10 kV distribution networks. Hopper moisture above 0.02 wt% increases microvoid density and partial discharge background; pre-drying at 70 °C for 2–4 h is required when storage RH exceeds 60%.

Why Does Low-Voltage Insulation Extrusion Reject Repeated Batch-Change Scrap?

Low-voltage power distribution cables under IEC 60502-1, GB/T 12706.1, and national wiring rules such as BS 6004 are insulated with a 100-part undiluted QHJ-01 stream, but production conditions differ because the insulation layer thickness falls to 0.7–1.4 mm for 0.6/1 kV constructions. The preferred tooling is a pressure die with draw-down ratio 1.05–1.15:1 and die land length 8–12 mm; tubing tooling creates annular die-lip instability and periodic lump defects at line speeds above 300 m/min. A 60–90 mm single-screw extruder runs at 118–128 °C melt temperature, with compression ratio 2.8–3.2:1 and a breaker-plate screen pack of 60/80 mesh to trap occasional carbonised particles without generating excessive backpressure. If screw-pressure drift exceeds 25% over a four-hour run, the operator samples the die for gel specks before cable enters the CV tube because off-grade melt flow from contaminated regrind cannot be corrected by barrel temperature alone. Curing for smaller single-core conductors uses a hot-air atmospheric-pressure tunnel at 250–300 °C only where thin-wall construction permits; larger distribution feeder cables use the same dry-cure CV line as medium-voltage products. Batch-to-batch scrap rises when hopper moisture exceeds 0.02 wt%; pre-drying at 70 °C for 2 h is applied when storage RH exceeds 60%. Terminal product types include non-armoured building cables, conduit wires, and distribution feeder cables rated 90 °C continuous conductor temperature; because the QHJ-01 layer is not a flame-retardant barrier, finished cable flame performance is delivered by the oversheath and verified as a system to IEC 60332-1-2.

Across open-air aerial bundled conductor lines, the exposed insulation must survive ultraviolet radiation, dry-band tracking, and thermal cycling for service lives exceeding 30 years. For such lines aligned with HD 626 S2 and NF C 33-209, QHJ-01 is processed at 100 parts, with a separate carbon-black masterbatch dosed gravimetrically to achieve a final carbon content of 2.0–2.5 wt%; for a 40% carbon masterbatch this corresponds to 5.0–6.25 parts per 100 parts QHJ-01. Carbon loading above 3.0 wt% is avoided because it raises the 50 Hz dielectric loss tangent and reduces impulse breakdown margin under wet conditions. The downstream extrusion line uses a low-compression screw with 2.5–3.0:1 compression ratio to limit shear heating before the CV tube, and a screen pack no finer than 80/100 mesh prevents carbon agglomerate pressure spikes. A pre-heat zone at 140–160 °C conditions the outer surface before the CV tube radiant zone, and line speed is held between 80 m/min and 180 m/min depending on conductor diameter. Terminal product types are self-supporting aerial bundled cable assemblies with compacted aluminium phase conductors and black crosslinked polyethylene insulation, typically 0.6/1 kV service drop, street-lighting spans, and rural overhead feeder lines.

Control and Instrumentation Cable Insulation in Petrochemical Shutdown Loops

For control and instrumentation circuits in process plants, the insulation layer is thinner—0.3–0.6 mm—and must withstand repeated bending during marshalling cabinet termination. The construction standard for converter inspection documentation is typically EN 50288-7 or BS 5308-1, with insulation mechanical properties verified by IEC 60811-501. The compound is used neat at 100 parts; no plasticiser or processing lubricant is added because migration into the conductor can reduce adhesion and increase capacitance instability. Extrusion uses a 60 mm single-screw extruder at 112–120 °C melt temperature with a pressure die and 0.4 mm tip clearance; line speed is limited to 250 m/min to maintain capacitance uniformity below ±5% per unit length. Conductor preheat is held at 70–90 °C for tinned copper to prevent polymer skinning at the die exit. After extrusion, cure is selected according to wall thickness: below 0.4 mm a hot-air tunnel at 240–270 °C is preferred to avoid CV tube surface collapse; above 0.4 mm the dry-cure line is used. Terminal product types include 300/500 V twisted-pair instrumentation cables, individually or collectively screened, armoured with galvanised steel wire or braid, used in emergency shutdown loops, DCS analogue inputs, and analyser circuits.

When Solar Farm DC Feeder Insulation Is Crosslinked Without Halogenated Sheath Dilution

Solar farm direct-current feeders and photovoltaic array harnesses built to EN 50618 or IEC 62930 can use QHJ-01 as the primary insulation layer only when the outer jacket carries the low-smoke, halogen-free, flame-retardant function. The insulation addition ratio is 100 parts undiluted; no halogenated charring agents are added to this layer, which keeps insulation conductivity low under 1.5 kV DC wet ageing. The downstream process is dual-layer co-extrusion with dry-cure continuous vulcanisation at nitrogen pressure 0.8–1.0 MPa; line speed is adjusted so the insulation layer reaches the cure plateau before the outer jacket compound skins over. A production bottleneck observed on older CV lines is the need to purge the crosshead after carbon-black masterbatch campaigns because residual agglomerates contaminate light-coloured photovoltaic insulation and raise spark-test failure rates. The critical operational boundary is that the insulation must not be used as the sole flame-retardant barrier; the finished cable must be tested as a system to EN 60332-1-2 and, for larger arrays, EN 50399. Published third-party data for long-term DC wet ageing of QHJ-01 in this specific configuration is limited; qualification must be performed on the finished cable lot. Terminal product types are photovoltaic wire types PV1-F and H1Z2Z2-K, solar farm trunk feeders, and inverter-to-transformer DC links.