Transformer insulation paper and pressboard

Electrical insulation paper and pressboard provide dielectric and mechanical functions in an insulation system. Select cellulose-based components with the transformer design, insulating liquid, drying process and service conditions. Sheet properties alone do not qualify a complete transformer.

General technical information published by PAXOMER Inc. to support preliminary material evaluation. It is compiled from the sources cited on this page and has not been independently reviewed or certified by a professional engineer, laboratory or certification body. Values marked typical, illustrative or requiring confirmation are not specifications. Confirm properties, standard editions, regulatory status and suitability for your specific application with the manufacturer and, where the use is regulated or safety-related, with a qualified professional or the relevant authority.

1. Quick answer

Electrical insulation paper and pressboard provide dielectric and mechanical functions in an insulation system. Select cellulose-based components with the transformer design, insulating liquid, drying process and service conditions. Sheet properties alone do not qualify a complete transformer.

2. What is the product, and what function does it perform?

Electrical insulation paper and pressboard provide dielectric and mechanical functions in an insulation system. Select cellulose-based components with the transformer design, insulating liquid, drying process and service conditions. Sheet properties alone do not qualify a complete transformer.

3. What types, constructions and grade distinctions are available?

4. Which properties and measurement conditions should the specification include?

5. How is the material manufactured and converted?

Pulp preparation, sheet forming, pressing and drying produce different paper and board constructions. Subsequent cutting, forming and machining introduce component geometry and edge-quality requirements. Supplier processing and cleanliness matter alongside the nominal material designation.

Transformer manufacture includes controlled drying and impregnation within a larger insulation system. Re-exposure to ambient moisture can change the condition achieved by drying. Packaging, transport, storage and the time between unpacking and assembly therefore belong in the procurement requirement.

6. Which applications and end-use boundaries should be defined?

Applications include defined conductor insulation, barriers, spacers and formed components in compatible liquid-filled transformer designs. A component must match its electrical and mechanical role. Do not substitute a generic packaging paper or board on the basis of thickness or appearance.

7. Which quality controls support qualification?

Identify the applicable material standard and current edition with the transformer designer. IEC 60554 and IEC 60641 are candidate paper and pressboard families to verify; this guide does not claim review of their full texts or compliance of any product. Agree incoming moisture, dimensions, cleanliness and mechanical checks, followed by the designer’s dried/impregnated and system qualification. Confirm compatibility with the actual mineral or alternative insulating liquid.

8. How should production problems be investigated?

9. What limitations and tradeoffs affect selection?

Cellulose offers established processing options but is sensitive to moisture and thermal ageing. Paper and pressboard serve different geometries and mechanical duties. Alternative high-temperature materials require system redesign and compatibility assessment rather than a presumed equal-thickness replacement.

10. Which market developments require current evidence?

Weidmann’s public material portfolio distinguishes insulation-paper constructions. For procurement, liquid compatibility, moisture control and documented processing are useful evaluation axes. No transformer efficiency gain, service-life extension or market growth rate is asserted here without system-specific evidence.

11. Prepare a PAXOMER technical enquiry

PAXOMER is a Canadian technical-supply, manufacturer-development and market-development company. Submit the intended application, current material or construction, process, acceptance criteria, destination and sample requirements. We can assess the technical requirement and potential development path. This guide does not establish stock, a manufacturer appointment or a supply commitment.

12. Primary references and evidence boundary

References establish material-family or test-method scope. They do not establish PAXOMER representation, exact-product performance or suitability of a finished system. Full paid standards have not been reviewed.

Weidmann insulation paper (opens in a new tab)

13. Separate incoming sheet condition from the dried insulation system

An incoming moisture result and the condition achieved after transformer drying describe different stages. Specify how the sample was handled before measurement and how delivered material remains protected before assembly. An analytical result without exposure history can obscure a logistics or handling issue.

Paper and pressboard dimensions and mechanical response may change with moisture, pressure and thermal history. Compare the specimen state used for the requirement with the state used for the test. Do not convert one dielectric value into a service-life or system-clearance rule.

Any change in insulating liquid, cellulose treatment, component geometry or drying cycle needs review by the responsible transformer designer. A familiar material family does not justify an untested process change. Preserve lot and component traceability through machining and impregnation.

14. How should an application trial establish acceptance?

15. Agree paper and pressboard acceptance in the state that matters

Insulation paper and pressboard have different flexibility, geometry and mechanical roles. Paper wrapping, barriers and machined structural components should not share a single thickness-only purchase description. Identify fibre-based construction, treatment, density and the required component form.

Moisture-related condition and insulating-liquid impregnation influence electrical and mechanical evidence. A supplied dry sheet, a laboratory-conditioned sample and a dried/impregnated component are different states. Record the state used for every result rather than combining unmatched data into one design claim.

Dimensional and mechanical checks should represent machining, compression and assembly. The exact liquid and process need compatibility review with the responsible equipment designer. A material-family test cannot establish clearances, loading or expected service life for an unreviewed transformer design.

Manufacturer development should address cleanliness, packaging integrity, opening/storage control and traceability through conversion. Agree relevant current paper/pressboard specifications and methods with the designer; this guide does not declare product compliance from a standard-family name.

16. Agree paper and pressboard acceptance in the state that matters: specification and investigation

17. Why must paper moisture and impregnation history stay traceable?

State paper construction, thickness, preparation and the insulating liquid with the evidence. Measure moisture using an agreed method and preserve handling history after preparation. A paper description cannot establish finished-transformer dielectric or thermal performance. Do not transfer aramid-paper claims to cellulose paper or treat their families as interchangeable.

18. How should paper evidence be separated from transformer-system evidence?

Use this comparison record to make an enquiry or trial interpretable. It is a buyer worksheet, not a set of material acceptance limits. Agree the exact grade, procedure and decision criteria with the responsible technical team.

Supporting reference — Insulation-paper portfolio context; no drying recipe, moisture limit or transformer approval inferred. (opens in a new tab)

19. How should moisture content identify its wet or dry mass basis?

A moisture percentage needs a defined denominator and an agreed measurement method. Wet-basis and dry-basis percentages are different even when they describe the same hypothetical sample. For electrical insulation, preserve sampling, sealing and handling history with the result; an exposed sample may not represent the condition of material inside the assembly.

Hypothetical arithmetic only: a sample comprises 100 g dry material and 2 g water. Moisture on a dry basis is 2 ÷ 100 × 100 = 2.00%. On a wet basis it is 2 ÷ 102 × 100 = 1.96%. These values demonstrate denominators and are not acceptable moisture limits, a drying endpoint or a test procedure for transformer insulation.

20. Which records should accompany an insulation-paper moisture result?

Use the following application-specific comparison record to make the enquiry and qualification decision explicit.

21. How should conflicting insulation-paper moisture reports be reconciled?

If moisture reports disagree, first reconcile sampling locations, exposure and the analytical basis. Do not average incompatible measurements into an apparent pass. Review the result with the responsible electrical-insulation team before choosing drying or assembly actions; this guide provides no energization, drying or high-voltage operating procedure.

22. Frequently asked questions

23. References

Links inside sections are supplier or standards-body context for the statements they accompany.

Last revised 2026-10-27.

Related guides

• Battery separators and ceramic coatings
• Copper Magnet Wire & Electrical Winding Materials
• Switchgear & Electrical Assembly Insulation Materials

Explore further

Product and material pages

• Industrial Electrical Insulation
• Transformer Insulation Paper & Pressboard

Material card: Transformer insulation paper and pressboard (listed in Products & Solutions).

Glossary terms

Insulation pressboard · Insulation impregnation · Thermally upgraded paper

Tools

Manufacturer Finder · RFQ brief