Dielectric strength at temperature
Breakdown voltage falls as temperature rises. Specify the class at the working temperature, not the catalogue value at 23 °C.
Application · Transformer
Transformer Insulation
Transformer lead insulation is a thermal and dielectric problem at the same time. The sleeve must hold breakdown voltage at the operating temperature, survive potting or oil immersion, and stay flexible enough to route around the bobbin without cracking.
Application challenges
Where transformer insulation fails
Continuous vs peak temperature
Class 155 and Class 200 constructions behave differently under cyclic peaks. Match the class to the measured winding hot spot.
Oil immersion and potting
Resin and oil attack some coatings. Confirm compatibility with the actual medium, cure cycle and cleaning solvents.
Import replacement validation
Replacing a specified brand requires dimensional, dielectric and thermal evidence. Plan sample validation before the change is released.
Recommended materials
Material by insulation position
Silicone resin fiberglass sleeving
Class 200 dielectric sleeve for lead exits and winding ends.
View detailsAcrylic coated fiberglass sleeving
Class 155 general-purpose insulation with good flexibility.
View detailsHigh breakdown voltage sleeve
7.0 kV and 4.0 kV grades for high-voltage windings.
View detailsPTFE heat shrink tubing
Chemical and oil resistant protection at high temperature.
View detailsOil-resistant sleeving
For oil-immersed and potted assemblies.
View detailsSelection checklist
Confirm before quoting
Working voltage: System voltage, test voltage and required breakdown margin
Temperature class: Class 155 / 200, hot spot and peak excursion
Medium: Air, oil, potting resin, cleaning solvents
Dimensions: Lead diameter, sleeve ID, wall thickness, cut length
Flammability: VW-1 or equivalent requirement
Approval: UL file, RoHS / REACH and replacement validation plan
Catalogue values describe the product direction we can supply. Confirm final drawing, grade, tolerance and test method before mass production.
FAQ
Common questions
Class 155 or Class 200 - how do I decide?
Start from the measured hot spot at rated load plus margin, then check the peak excursion. If the hot spot is close to 155 °C, Class 200 usually gives the safer long-term margin.
Is the sleeve suitable for oil-immersed transformers?
Oil-resistant constructions are available, but compatibility depends on the oil type, temperature and any additive package. Confirm with an immersion sample test.
Can you match an existing part number?
Yes. Send the drawing or the specified part and we will propose an equivalent with dimensional and dielectric data for your validation.
What is the typical lead time for samples?
Standard constructions are usually shipped within 3-5 working days; custom cut lengths and special grades depend on the quantity.
Quote and samples
Send the winding data and working conditions
Working voltage, temperature class, medium, lead diameter and annual volume are enough for a material proposal and sample plan.