High Voltage Insulating Varnish: 5 Selection Checks Beyond Dielectric Strength
When selecting a high voltage insulating varnish, dielectric strength is an important specification, but it cannot alone demonstrate that a grade is suitable for your high-voltage equipment. The dielectric strength stated in a material TDS, insulation coordination for the equipment, winding structure, curing condition and actual voltage tests represent different levels of verification.
This guide establishes a selection route through five checks and compares the confirmed TDS specifications for Changxian E962, E57A, E57-81H and E57-89H. No rated operating voltage is inferred for any grade. Final suitability should be based on the applicable standards, insulation system design and tests on your actual workpiece.
1. Check 1: Define the Voltage Conditions and Applicable Standards First
Before comparing materials, organize your design and test conditions:
| Item to Confirm | Information to Record | Why It Cannot Be Omitted |
| Application | Motor, transformer, coil, reactor or another type of equipment | Different equipment may be subject to different product standards and validation conditions |
| Voltage conditions | Operating voltage, test voltage and applicable overvoltage conditions | A single reference to “high voltage” cannot replace the design input |
| Insulation structure | Solid insulation, air gaps, insulation surfaces and the corresponding structure | Material specifications cannot replace equipment insulation design |
| Environmental conditions | Pollution, humidity and the actual service environment | Surface insulation and long-term reliability need to be evaluated in relation to the environment |
| Applicable standards | Product standards, insulation system requirements and test methods | These determine the actual verification items and acceptance criteria |
If these conditions have not yet been defined, you should not place an order based on a single TDS specification. First establish what the material needs to satisfy according to your design and test requirements, then compare grades.
2. Check 2: Interpret Dielectric Strength Data Correctly
The dielectric strength of a high voltage insulating varnish is commonly expressed in kV/mm or MV/m. One kV/mm is numerically equivalent to one MV/m. However, this does not mean that values from different TDS documents can be ranked directly while ignoring their test conditions.
When making a comparison, check:
- The test method corresponding to the value.
- Specimen condition and test conditions.
- Whether the data comes from the TDS for the specific grade.
- Whether the insulation structure and process in your actual workpiece match the test specimen.
- Which additional equipment or insulation system tests are required.
Do not divide the equipment operating voltage by the TDS dielectric strength to infer the required film thickness. Laboratory dielectric strength should also not be presented directly as the equipment’s rated withstand voltage. Actual insulation design also involves the structure, process and applicable standards.
3. Check 3: Separate Material Specifications from Insulation Coordination
The application guide in the IEC 60664 series covers the dimensioning of clearances, creepage distances and solid insulation, while emphasizing evaluation of safe equipment use under foreseeable environmental conditions. High-voltage insulation therefore cannot be assessed through the coating material alone.
Reference document: IEC/TR 60664-2-1 public preview.
During selection, confirm the following separately:
- Solid insulation: The candidate material and its validation within the actual structure.
- Clearances: Determined by the equipment structure and applicable standards rather than replaced by the TDS dielectric strength.
- Creepage distances: Evaluated according to surface paths, environmental conditions and applicable standards. They cannot be omitted from the structural review merely because an insulating varnish is used.
- Test requirements: Determine withstand-voltage, partial-discharge or other necessary tests according to the product standards.
This article does not extend the scope of IEC 60664 to every type of high-voltage equipment. Your equipment should still be evaluated according to its corresponding product standard and the standards applicable to its voltage level.
4. Check 4: Review Thermal Class and Curing Process Together
Even when a material has the required electrical specifications, it cannot be treated as production-ready if its thermal class or curing process does not match your requirements.
| Product | Thermal Class | Primary Process Route | What to Confirm |
| E962 | Class B | Air drying | Complete drying condition, electrical properties and actual application conditions |
| E57A | Class B–F | Baking | Dilution ratio, baking conditions and suitability for the actual workpiece |
| E57-81H | Class H | Confirm using the complete TDS and actual process | Class H requirements, refrigerant resistance needs and other actual validation |
| E57-89H | Class H–C | Curing after vacuum or trickle impregnation | Impregnation, curing, bonding strength at elevated temperatures and thermal requirements |
The thermal class should be confirmed together with the insulation system design. IEC 60085 provides a reference for the thermal evaluation and designation of electrical insulation: IEC 60085 official page.
The thermal class stated in a material TDS does not automatically demonstrate that the complete equipment insulation system has received the same thermal classification. For an air-drying product, a surface that feels dry to the touch should not be used as the basis for energization.
5. Check 5: Complete Final Validation on the Actual Workpiece
Final validation of a high voltage insulating varnish should cover the material, process and workpiece rather than testing only a liquid sample.
Retain the following records:
- Application, operating voltage and test voltage conditions.
- Workpiece structure, dimensions and insulation system requirements.
- Product grade and sample batch.
- Application viscosity, impregnation and draining conditions.
- Curing method and actual curing conditions.
- Appearance, coverage and visible abnormalities.
- Electrical tests performed according to the applicable standards.
- Partial-discharge, thermal-aging or other reliability tests added according to your design requirements.
- Process confirmation on production equipment.
Whether partial-discharge or other specialized tests are required should be determined by the actual voltage, structure, frequency and applicable standards. A single requirement is not assigned to every application in this guide.
6. TDS Comparison of the 4 Candidate Products
The following high voltage insulating varnish comparison is intended for initial screening. It does not demonstrate that any grade has passed validation in your high-voltage equipment. Unlisted items are marked “—.”
| Comparison Item | E962 | E57A | E57-81H | E57-89H |
| Resin system | Modified polyester | Alkyd-amino | Unsaturated polyester | Solventless epoxy-polyester |
| Thermal class | Class B | Class B–F | Class H | Class H–C |
| Primary process route | Air drying | Baking | Confirm using the complete TDS | Curing after vacuum or trickle impregnation |
| Dielectric strength | ≥40 kV/mm | ≥60 kV/mm | ≥22 MV/m | ≥24 MV/m |
| Solid content / active ingredients | — | 45–55% | — | 100% active ingredients |
| Rotational viscosity | Approx. 145–230 mPa·s | Approx. 150–235 mPa·s | — | Approx. 165–355 mPa·s |
| SG | 0.95 | 0.98 | — | 1.075 |
| Volume resistivity | ≥1×10¹² Ω·cm | — | — | — |
| Bonding strength at room temperature | — | — | — | ≥140 N |
| Bonding strength at 180°C | — | — | — | ≥50 N |
| Thermal conductivity | — | — | — | ≥0.4 W/m·K |
| Refrigerant resistance | — | — | Excellent performance in the 96-hour test | — |
| Rated equipment operating voltage | — | — | — | — |
The final row remains “—” because the dielectric strength in a product TDS cannot be converted directly into a rated equipment operating voltage. Selection requires further validation against your structure and applicable standards.
7. How to Narrow Your High Voltage Insulating Varnish Candidates
Use your thermal, process and performance requirements to narrow the high voltage insulating varnish candidate range before sample testing.
When You Need an Air-Drying Class B Option
Evaluate E962. Its TDS provides dielectric strength and volume resistivity data and lists applications including inductive coils. Complete drying and electrical performance on the actual workpiece still need to be confirmed.
When You Need a Class B–F Baking Option
Evaluate E57A. Its TDS lists dielectric strength of ≥60 kV/mm. Whether it suits your application also depends on the baking conditions, workpiece structure and applicable standards.
When You Need Class H and Refrigerant Resistance Evaluation
Evaluate E57-81H. Its confirmed specifications include Class H, dielectric strength ≥22 MV/m and excellent performance in the 96-hour refrigerant resistance test. Other unlisted items should be supplemented through the complete TDS or testing.
When You Need Class H–C Solventless Impregnation and Elevated-Temperature Performance Data
Evaluate E57-89H. Its TDS provides vacuum and trickle impregnation routes and lists bonding strength at elevated temperatures and thermal conductivity data, allowing you to establish a corresponding verification checklist.
8. Related Selection Guides
Class H Insulation Varnish Guide
Motor Winding Insulating Varnish Selection Guide
Transformer Insulating Varnish Selection Guide
Electrical Insulating Varnish Manufacturers Guide
Electrical Insulation Paint Guide
9. Frequently Asked Questions
Q1: Does higher dielectric strength make a product more suitable for high-voltage equipment?
Not necessarily. A high voltage insulating varnish should also be evaluated according to its test conditions, the equipment insulation structure, applicable standards, production process and tests on the actual workpiece.
Q2: Can you calculate the required equipment film thickness from the TDS dielectric strength?
A simple division calculation is not recommended. Actual insulation design involves specimen conditions, workpiece structure, curing condition and applicable standards. Determine the design through engineering evaluation and actual testing.
Q3: Can clearances and creepage distances be ignored after applying an insulating varnish?
No. Material selection and equipment insulation coordination are different levels of assessment. Confirm them separately according to the applicable product standards.
Q4: Which Changxian product can be labeled directly as dedicated to high-voltage equipment?
This guide does not add a “dedicated to high-voltage equipment” claim to any grade based on a single specification. You can screen candidates according to voltage conditions, thermal class and process, then determine suitability through validation on the actual workpiece.
Q5: Why is every rated equipment operating voltage marked “—” in the table?
The reviewed TDS specifications cannot be converted automatically into a rated equipment operating voltage. Retaining “—” prevents material dielectric strength from being misrepresented as an equipment-level rating.
10. Conclusion
The correct sequence for selecting a high voltage insulating varnish is to define the voltage conditions and applicable standards first, then review dielectric strength, insulation coordination, thermal class and curing process, and finally complete validation on the actual workpiece.
E962, E57A, E57-81H and E57-89H provide different thermal classes, resin systems and process routes. Our engineers can provide TDS documents, selection comparisons and free samples for testing based on your application, voltage conditions and production process, without replacing equipment-level validation with a single material specification.
About Changxian
Zhuhai Changxian New Material Technology Co., Ltd. has specialized in electronic chemicals for more than 30 years. Changxian is listed on China’s National Equities Exchange and Quotations (stock code: 831323) and recognized as a national-level Specialized, Sophisticated, Distinctive and Innovative “Little Giant” enterprise. Our approximately 40,000 m² production base in Zhuhai’s Gaolan Port area includes in-house resin synthesis capabilities. We have achieved ISO 9001, ISO 14001 and ISO 45001 management system certification, together with IATF 16949 certification. Relevant insulating varnish and conformal coating products are covered by UL files; specific grade coverage is subject to the applicable certification.
Changxian’s position is straightforward: specifications benchmarked item by item against international brands, with factory-direct pricing — Equal Quality, Factory Price. If you need insulating varnish TDS documents, selection comparisons for high-voltage applications or free samples for testing, contact our engineers. We will provide targeted support based on your design conditions and validation requirements.
Source basis for this article: The public preview of IEC/TR 60664-2-1, the official IEC 60085 page, product TDS documents for E962, E57A, E57-81H and E57-89H, and confirmed technical records. Test items not listed in the applicable TDS are marked “—” and have not been estimated.
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