Transformer winding insulation rarely fails in the middle of the winding — it fails where the lead exits the overhang, at terminations, and wherever heat, oil and mechanical movement concentrate. This page maps each failure mode to the sleeving construction that survives it.
Start from the failure mode, not the catalogue. Each card below is a failure point we see again and again in transformer plants.
Dielectric breakdown and creepage tracking start where the winding lead exits the overhang toward a bushing or terminal. Silicone fiberglass sleeving with 4–20 kV dielectric strength (up to 50 kV on selected constructions) gives the lead a tracking-resistant, flexible barrier.
Class H (180 °C / 356 °F) insulation systems need sleeving that stays flexible after years of thermal cycling. Silicone fiberglass sleeving is rated −60 ~ +200 °C (−76 ~ 392 °F), with 220 °C (428 °F) peak on selected constructions.
In oil-filled transformers the sleeving is permanently submerged. Acrylic-coated fiberglass (ARG) holds its dielectric and mechanical properties in oil where many coatings swell or extract — the grade behind our UL UZFT2 / CUL UZFT8 recognition.
Tap-changer connections and control wiring routed through the tank see abrasion, crush and vibration. Woven fiberglass distributes point loads where a solid extruded wall can be nicked through.
Every row pairs a real transformer position with the working condition at that spot and the WCW construction we recommend for it.
| Position | Working Condition | Recommended WCW Material | Key Rating |
|---|---|---|---|
| Lead exits & terminations | Dielectric stress, flexing at the exit | SGS / SRS silicone fiberglass sleeving | 4–20 kV · −60 ~ +200 °C (−76 ~ 392 °F) |
| Winding overhang & interleave | Class H heat, thermal aging, batch consistency | SGS / SRS silicone fiberglass sleeving, high-breakdown grades | Class H 180 °C (356 °F), 220 °C (428 °F) peak selected |
| Oil-filled transformers | Continuous oil immersion, dimensional change | ARG acrylic fiberglass sleeving | UL UZFT2 / CUL UZFT8 · −60 ~ +155 °C (−76 ~ 311 °F) |
| Leads needing a tough outer surface | Abrasion at the exit, handling damage | GS sleeving — inside rubber / outside fiber | 7000 V avg / 6000 V min · UL 1441 E233804 (GS-WCW-70) |
| Tap changer & control wiring | Crush, chafe, vibration through the tank | PET expandable braided sleeving | −60 ~ +155 °C (−76 ~ 311 °F) · cut & abrasion resistant |
| Positions near heat sources above 200 °C | Radiant heat, routing near hot sections | TGS-1W-600C high-temperature fiberglass sleeving | −60 ~ +600 °C (−76 ~ 1112 °F) |
Six constructions cover every position in the unit — from the lead exit to the control wiring.
The transformer workhorse: silicone-coated fiberglass, flexible at −60 °C, 4–20 kV standard (up to 50 kV selected), UL 1441 with UL VW-1.
Smooth silicone-rubber outer skin over a fiberglass core; the E233803 style for lead protection where a sealed feel matters.
Rubber inside, braid outside: a tough outer surface for leads that get handled during assembly. 7000 V avg / 6000 V min, UL 1441 E233804 (GS-WCW-70).
The oil-filled transformer grade. Holds dielectric and mechanical properties under continuous oil immersion — UL UZFT2 / CUL UZFT8.
Bundling and cut protection on tap-changer and control wiring; expands over connectors, cuts cleanly.
For zones no silicone can reach — routing near hot sections up to 600 °C (1112 °F).
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