Are Epoxy Transformer Bushings Better Than Porcelain?

When it comes to power systems, the performance and reliability of components often come down to material choices. Among the most critical components in any transformer are its bushings—responsible for safely conducting current between the internal winding and the external circuit. While the transformer bushing itself may appear simple from the outside, the choice between epoxy transformer bushings and porcelain transformer bushings plays a major role in operational safety, longevity, and overall system cost. At NJREC, we provide both material types—engineered and certified for high-voltage, medium-voltage, and demanding environments. But which one is better? Let’s examine the differences.

What Materials Are Used in Transformer Bushings Today?

Understanding Common Bushing Insulation Materials

Transformer bushings are generally categorized by the insulation material used in their construction. Three primary materials dominate the market today: porcelain, epoxy resin, and composite resin materials.

Porcelain: A traditional ceramic material used for over a century in high-voltage systems. Porcelain offers excellent outdoor durability and high resistance to UV rays, making it a top choice for external environments and long-term outdoor installations.

Epoxy Resin: A synthetic polymer that offers electrical insulation, mechanical strength, and the flexibility of complex shapes. Epoxy is commonly used in modern epoxy transformer bushings, especially in compact or enclosed transformers.

Resin or hybrid composites: These include glass-fiber-reinforced epoxy or silicone rubber-based materials that offer improved resistance to cracking, hydrophobic performance, and lighter weight.

Each material brings its own set of advantages, and the decision on which to use depends on voltage level, installation location, and performance expectations.

How Do Mechanical and Dielectric Strengths Compare?

Physical Properties and Performance in Harsh Conditions

Mechanical and dielectric strength are two of the most important criteria for selecting a transformer bushing. Let’s break down how epoxy and porcelain compare:

Weight and Handling

Epoxy bushings are significantly lighter than porcelain equivalents. This makes them easier to install, transport, and mount—especially in compact substation environments or on pad-mounted transformers.

Porcelain bushings, while heavier, offer excellent structural rigidity. They are less susceptible to surface erosion or UV degradation but can crack or break upon impact during transport or in seismic conditions.

Stress and Vibration Resistance

Epoxy materials have better resistance to mechanical shock, vibrations, and flexural stress, especially beneficial in mobile substations or urban grid networks.

Porcelain is brittle by nature and may fracture under extreme mechanical loads or installation errors.

Dielectric Performance

Both materials provide high dielectric strength, but epoxy can be molded into complex internal capacitive structures for graded insulation, especially in medium voltage transformers.

Porcelain remains preferred for very high-voltage outdoor transformers, thanks to its proven external insulation capabilities under heavy pollution or long creepage distance requirements.

NJREC manufactures transformer bushings using advanced epoxy casting techniques and high-purity porcelain forming, ensuring both categories meet stringent standards for mechanical and dielectric integrity.

Which Type Suits Which Application?

Application-Based Recommendations

The choice between epoxy transformer bushings and porcelain transformer bushings often comes down to where and how the bushing will be used. Here's how they typically align with application needs:

High-voltage outdoor transformers (e.g., 52 kV)
→ Best matched with porcelain bushings due to long creepage requirements, robust outdoor weather resistance, and mechanical rigidity.

Indoor dry-type transformers or compact switchgear (1–36 kV)
→ Ideal for epoxy bushings, offering lower weight, better integration in confined spaces, and simpler mounting.

Pad-mounted distribution transformers
→ Epoxy bushings are often preferred for these due to vibration resistance and insulation customization.

Polluted, coastal, or desert areas
→ Porcelain bushings with RTV coating or specialized hydrophobic glazes provide superior resistance against salt fog, dust, and acid rain.

NJREC provides both epoxy and porcelain bushing designs, available in ANSI, DIN, and EN standard configurations. Custom solutions can be developed depending on the pollution class, voltage range, and space constraints of the application.

What Are the Maintenance and Lifecycle Costs?

Longevity, Inspection, and Replacement Considerations

While the initial cost of a transformer bushing is important, lifecycle costs can significantly impact long-term operational budgets. Material choice plays a key role here.

Maintenance Frequency

Porcelain bushings generally require less frequent inspections, thanks to their hard surface and durability. However, once damaged, porcelain units typically need full replacement.

Epoxy bushings may require more regular inspection for surface degradation, discoloration, or micro-cracking, especially in harsh UV or thermal cycling environments. However, minor surface issues may be remediated without full replacement.

Damage and Replacement

Porcelain bushings, once chipped or cracked, cannot be repaired and must be replaced to ensure safety.

Epoxy bushings are more impact-tolerant and may continue functioning even after surface abrasion, although internal defects (like voids or bubbles) must be tested for dielectric failure risk.

Expected Service Life

Both epoxy and porcelain bushings can offer over 20 years of service life under proper conditions. Environmental fit and correct voltage rating are more predictive of failure than the material itself.

NJREC offers performance-tested bushings with documentation on expected lifespan under different conditions, helping clients plan preventive maintenance and minimize total cost of ownership.

How Do Certifications and Testing Figure In?

Third-Party Tests and Compliance Assurance

At NJREC, all our transformer bushings—whether epoxy or porcelain—are subjected to rigorous mechanical, thermal, and electrical tests to validate their performance under various environmental and operating conditions.

Certified testing includes:

Full Type Test Reports: Covering lightning impulse, power frequency withstand voltage, partial discharge, and temperature rise.

Pollution & salt fog testing: Simulating long-term exposure to contaminants.

UV resistance validation: Especially for epoxy bushings in outdoor use.

ISO 9001 and TUV quality assurance for material consistency and factory control.

SGS and CNAS lab verifications for international trade compliance and reliability evaluation.

Each NJREC product is traceable and comes with documentation for utility compliance, helping project developers and OEMs meet international procurement and installation standards.

Conclusion

There is no one-size-fits-all answer when comparing epoxy and porcelain transformer bushings. Each offers distinct advantages depending on your operating environment, voltage class, and long-term cost considerations. For compact, indoor, or vibration-sensitive systems, epoxy transformer bushings provide flexibility and lightweight durability. For outdoor, high-pollution, or high-voltage applications, porcelain transformer bushings remain the benchmark for rugged reliability. At NJREC, we help customers assess their technical requirements and supply fully certified transformer bushings tailored to their application. Contact us today to discuss your needs or explore our full range of epoxy and porcelain solutions.