#epoxybushing

Railway rooftop bushing manufacturer in India | radiantenterprises

Railway Rooftop Bushing Manufacturer in India – Radiant Enterprises is a leading railway bushing and epoxy bushing manufacturer in India, specialising in high-performance insulation solutions for electric traction systems. As a trusted railway roof feedthrough 25 KV bushing manufacturer in India and High current bushing manufacturer in India, we design and deliver precision-engineered bushings that ensure safety, reliability, and long-term performance under demanding operating conditions. Our products are widely recognised for their rugged construction, superior dielectric strength, and compliance with international railway standards. As an established railway rooftop bushing exporter and supplier in India, we cater to OEMs, rail network operators, and global partners with customised solutions backed by expert technical support. Partner with Radiant Enterprises for top-quality railway insulation components that you can trust.

12 kV & 24 kV Epoxy Resin Bushing Insulation Distance and Creepage Requirements

Epoxy resin bushings are widely used in medium-voltage switchgear, transformers, and power distribution equipment due to their compact structure, high mechanical strength, and good dielectric performance. However, correct insulation distance and creepage distance design is essential to ensure long-term reliability, especially for 12 kV and 24 kV systems.

This article explains how insulation clearances and creepage distances are determined for epoxy resin bushings, referencing common industry practices and IEC principles.

1. Key Definitions

Before reviewing numerical requirements, it is important to clarify two fundamental concepts.

Insulation Distance (Clearance)

Insulation distance, also known as clearance, is the shortest distance through air between two conductive parts or between a live part and earth.

Clearance is mainly influenced by:

Rated voltage

Overvoltage level

Altitude

Insulation coordination level

Creepage Distance

Creepage distance is the shortest path along the surface of an insulating material between two conductive parts.

Creepage is strongly affected by:

Pollution level

Humidity

Surface material properties

Environmental conditions

For epoxy resin bushings, creepage distance is often the limiting design factor, especially in indoor substations with condensation risk.

2. Applicable Standards and References

Although exact values vary by application, most designs follow principles from:

IEC 62271-1 (High-voltage switchgear and controlgear)

IEC 60071 (Insulation coordination)

IEC 60815 (Selection of insulators for polluted conditions)

Manufacturers may also apply internal design margins above minimum IEC requirements.

3. Typical Insulation Clearance Requirements

12 kV Epoxy Resin Bushings

For 12 kV systems (rated voltage 12 kV, highest voltage for equipment 12 kV or 12.5 kV):

Phase-to-earth clearance: Typically ≥ 125–140 mm

Phase-to-phase clearance: Typically ≥ 160–180 mm

These values assume:

Indoor installation

Normal altitude (≤ 1000 m)

Controlled environment

24 kV Epoxy Resin Bushings

For 24 kV systems (highest voltage for equipment 24 kV):

Phase-to-earth clearance: Typically ≥ 220–250 mm

Phase-to-phase clearance: Typically ≥ 260–300 mm

At higher altitudes or with higher lightning impulse requirements, additional correction factors apply.

4. Creepage Distance Requirements

Creepage distance depends mainly on pollution class. Epoxy resin bushings generally use the specific creepage distance (mm/kV) approach.

Typical Specific Creepage Distance Values

Pollution LevelSpecific Creepage DistanceLight16 mm/kVMedium20 mm/kVHeavy25 mm/kVVery Heavy≥ 31 mm/kV

12 kV Creepage Distance

Using common medium pollution conditions:

12 kV × 20 mm/kV ≈ 240 mm

Heavy pollution may require 300 mm or more

24 kV Creepage Distance

For medium pollution:

24 kV × 20 mm/kV ≈ 480 mm

Heavy pollution conditions often require 600 mm or higher

Epoxy bushings used in coastal or high-humidity regions typically adopt higher creepage margins.

5. Influence of Epoxy Resin Material

Epoxy resin offers several advantages:

High dielectric strength

Good mechanical rigidity

Molded surface geometry for extended creepage paths

However, epoxy resin is not hydrophobic, unlike silicone rubber. Therefore:

Surface contamination and moisture can reduce insulation performance

Proper shed design and surface profiling are critical

Periodic inspection is recommended in humid environments

6. Indoor vs Outdoor Applications

Most epoxy resin bushings are designed for indoor switchgear. If used in semi-outdoor or poorly ventilated areas:

Creepage distance should be increased

Surface tracking resistance must be verified

Condensation control becomes important

Outdoor applications typically prefer composite or porcelain bushings with higher pollution resistance.

7. Altitude Correction Factors

At altitudes above 1000 m, air density decreases, reducing dielectric strength.

Typical practice includes:

Increasing clearances by ~1% per 100 m above 1000 m

Creepage distance usually remains unchanged, but safety margins are often added

8. Practical Design Considerations

When specifying epoxy resin bushings for 12 kV and 24 kV systems:

Always confirm the highest voltage for equipment (Um)

Match creepage distance to actual pollution level

Consider installation environment and ventilation

Apply additional margin for long-term aging

Coordination between bushing design and switchgear layout is essential to avoid insulation bottlenecks.

9. Conclusion

For 12 kV and 24 kV epoxy resin bushings, correct insulation distance and creepage design is critical to ensure safe and reliable operation. While typical clearance and creepage values are well established, real-world conditions such as pollution, humidity, and altitude must always be considered.

Partial discharge (PD) testing is a critical quality and reliability check for 12 kV epoxy resin busbar bushings used in medium-voltage switchgear. Even when insulation meets power-frequency withstand requirements, localized defects such as voids, cracks, or interface gaps can lead to partial discharge, accelerating insulation aging and increasing the risk of in-service failure.

This article explains why PD testing matters, the standard test methods, and practical procedures for testing partial discharge in 12 kV epoxy resin busbar bushings.

1. Why Partial Discharge Testing Is Important

Epoxy resin bushings are solid insulation components. Unlike air-insulated parts, defects inside epoxy cannot be seen or corrected after manufacturing.

Partial discharge may occur due to:

Internal voids or porosity in epoxy resin

Poor bonding between epoxy and embedded conductors

Sharp edges or stress concentration points

Surface contamination or moisture ingress

Even low-level PD can cause:

Progressive insulation degradation

Treeing and erosion inside epoxy

Reduced service life

PD testing helps identify hidden insulation weaknesses before installation or commissioning.

2. Applicable Standards for PD Testing

PD testing of 12 kV epoxy resin bushings generally follows principles from:

IEC 60270 – Partial discharge measurement

IEC 62271-1 – High-voltage switchgear and controlgear

IEC 60060-1 – High-voltage test techniques

Manufacturers often define internal acceptance limits that are stricter than minimum IEC requirements.

3. Test Setup for 12 kV Epoxy Busbar Bushings

Basic Test Arrangement

A typical PD test setup includes:

High-voltage AC test transformer

Coupling capacitor

Measuring impedance (quadrupole)

PD detector and data acquisition system

Shielded test environment

The bushing under test is mounted in a configuration representative of actual installation whenever possible.

Grounding and Shielding

Proper grounding is essential to avoid external noise interference:

All non-energized conductive parts must be grounded

Test cables should be shielded

The test area should be free from corona sources

Background noise level should be verified before testing.

4. Test Voltage Levels for 12 kV Bushings

For 12 kV systems, the highest voltage for equipment (Um) is typically 12 kV or 12.5 kV.

Typical PD Test Voltage

PD measurement voltage: 1.2 × Um

Common test value: ≈ 14–15 kV AC

The voltage is raised gradually to the test level and held long enough to observe stable PD behavior.

5. Partial Discharge Measurement Procedure

Step 1: Background Noise Measurement

Before energizing the test object:

Measure system noise

Ensure background PD level is sufficiently low (typically < 2–5 pC)

Step 2: Voltage Ramp-Up

Increase voltage smoothly from zero

Observe PD inception voltage (PDIV)

Note any sudden PD activity

A higher PDIV generally indicates better insulation quality.

Step 3: PD Measurement at Test Voltage

At the specified test voltage:

Measure apparent charge in pico-coulombs (pC)

Monitor PD magnitude and stability

Record phase-resolved PD patterns if available

Step 4: Voltage Reduction

Reduce voltage slowly and observe PD extinction voltage (PDEV). A significant gap between PDIV and PDEV may indicate internal defects.

6. Typical Acceptance Criteria

While exact limits depend on manufacturer and application, common acceptance values for 12 kV epoxy resin bushings are:

PD magnitude ≤ 5–10 pC at test voltage

Stable PD behavior with no increasing trend

No sudden discharge bursts

High-quality APG-produced bushings often show PD levels below 5 pC.

7. Common Causes of Excessive PD

If PD exceeds acceptable limits, common causes include:

Internal voids from poor casting process

Inadequate pressure control during curing

Sharp conductor edges inside epoxy

Poor surface finish or contamination

Such defects are usually not repairable, and the bushing should be rejected.

8. Factory Test vs Field Test

Factory PD Testing

Controlled environment

Low noise level

More accurate PD measurement

Preferred for quality control

Field PD Testing

Influenced by environmental noise

Often limited to trend monitoring

Useful during commissioning or diagnostics

For epoxy resin bushings, factory PD testing provides the most reliable results.

9. Practical Recommendations

Always perform PD testing on critical 12 kV epoxy bushings

Combine PD testing with power-frequency withstand tests

Record PD patterns for future reference

Ensure test personnel are trained in noise discrimination

Proper PD testing significantly reduces early-life failures in medium-voltage switchgear.

10. Conclusion

Partial discharge testing is a vital quality assurance step for 12 kV epoxy resin busbar bushings. By following IEC-based procedures and applying appropriate acceptance criteria, manufacturers and users can detect internal insulation defects before service, ensuring long-term reliability and safe operation.

Customized insulator and bushing manufacturers in India | radiantenterprises

Radiant Enterprises is one of the leading customized insulator and bushing manufacturers in India, offering reliable solutions for electrical and railway applications. We specialize in surge counter bushing and disconnectors, custom made support insulators, monoblock bushings, and epoxy pole housing designed for superior performance and durability. Our products are engineered to meet international quality standards, ensuring safety and efficiency in power distribution and transmission systems. With years of expertise and advanced manufacturing capabilities, we deliver tailor-made electrical insulation components that match your project requirements perfectly.

They may look small, but epoxy resin bushings are essential to electrical reliability. These components provide insulation and stability for transformers, switchgear, and breakers — ensuring smooth operation even in tough environments. Degatech’s epoxy resin bushings combine durability, thermal resistance, and flawless insulation quality.

Behind every high-voltage system lies a network of precision components — and epoxy resin bushings play a key role. They insulate electrical connections, withstand extreme temperatures, and prevent current leakage, ensuring long-term system stability.

At Degatech Electric Co. Ltd, our epoxy resin bushings are crafted with high-quality materials and rigorous testing. They provide excellent insulation and mechanical strength for transformers, switchgear, and substations.

Epoxy Resin Bushings in Power Systems

Epoxy resin bushings safely transfer electricity through grounded barriers. Lighter, stronger, and more resistant than porcelain, they excel in transformers, switchgear, and RMUs. Maintenance-free and reliable, they’re perfect for industrial and utility applications.