Application of FR4 Epoxy Sheet in GIS Circuit Breakers

Application of FR4 Epoxy Sheet in GIS Circuit Breakers Gas-insulated switchgear (GIS/RMU) is widely used in medium-v...

Application of FR4 Epoxy Sheet in GIS Circuit Breakers

Gas-insulated switchgear (GIS/RMU) is widely used in medium-voltage distribution systems due to its compact structure, high insulation strength, and excellent operational reliability. As one of the critical insulation and structural materials inside GIS circuit breakers, FR4 epoxy sheet ( fr4 fiberglass epoxy laminated sheet) plays an essential role. Its outstanding mechanical strength, dielectric performance, and moisture resistance ensure stable operation in sealed SF₆ environments.

This article analyzes the key application scenarios, performance requirements, and selection guidelines for FR4 epoxy sheets in GIS circuit breakers.

1. Main Applications of FR4 Epoxy Sheet in GIS Circuit Breakers

Insulating Barriers for Operating Mechanisms

Used to isolate mechanical components from live parts

Ensures reliable operation in SF₆ or dry-air environments

High dielectric strength (≥20 kV/mm) prevents electrical breakdown

Structural Supports and Fixing Components

Provides support for metal fittings and moving parts

Maintains dimensional stability with minimal water absorption

Suitable for vibration-prone operating mechanisms

Auxiliary Insulation in Arc Chambers and Contact Areas

Used as insulation rings, positioning plates, and structural inserts

Withstands short-term arc heat and mechanical shocks

FR4 typically meets Class F (155°C) thermal rating

Insulation for Secondary Wiring and Terminal Blocks

Protects control wiring from the influence of strong electric fields

Serves as terminal support plates and isolation panels

Enhances reliability of protection and control systems

Additional Applications

Insulation gaskets, spacers, and mounting brackets

Partition boards inside SF₆ tanks

Component alignment and reinforcement

2. Key Performance Requirements for FR4 in GIS Operating Conditions

GIS circuit breakers operate in fully sealed chambers with long service life (20–40 years). Therefore, FR4 sheets used in these environments must meet higher standards.

Electrical Properties

Dielectric strength: ≥20 kV/mm

Surface resistivity: 10¹²–10¹⁴ Ω

Maintains insulation stability in SF₆ environments

Mechanical Properties

Flexural strength: ≥300 MPa

Compressive strength: ≥350 MPa

Good impact resistance for dynamic mechanism loads

Thermal and Arc Resistance

Temperature rating ≥ Class F (155°C)

Tolerates localized heating and mechanical shocks

Good long-term thermal stability, preventing micro-cracks

Dimensional Stability and Moisture Resistance

Low moisture absorption is essential due to GIS airtightness:

Water absorption ≤0.2%

Minimal warping or expansion with temperature/humidity changes

SF₆ Chemical Resistance

Excellent resistance to SF₆ and decomposition byproducts (SOF₂, SO₂F₂)

No delamination or material degradation over time

3. Selection Guide for FR4 Epoxy Sheet in GIS Applications

Selection should be based on usage position, mechanical load, and thermal conditions.

Based on Thermal Environment

 Recommended Thickness

Structural supports: 8–20 mm

Insulation barriers/terminal plates: 3–10 mm

Gaskets/small insulation parts: 1–5 mm

Processing Requirements

GIS requires high-precision machining:

CNC precision milling

Chamfered edges to avoid partial discharge

Clean surfaces with no fiber burrs

For live areas, moisture-proof coating is recommended.

Quality Standards & Certifications

Choose FR4 products meeting the following standards:

IEC 60893 (industrial laminated sheet standard)

UL 94 V0 (flame retardancy)

RoHS / REACH environmental compliance

Mechanical, dielectric, and thermal properties should be supported by third-party reports.

4. FR4 vs. G10 vs. G11 for High-End GIS Equipment

For premium SF₆ GIS equipment, G11 or high-performance FR4 is often recommended.

5. Conclusion

FR4 epoxy sheet performs critical insulation, support, separation, and structural functions inside GIS circuit breakers. Its high dielectric strength, mechanical performance, thermal stability, and moisture resistance make it suitable for long-term use in sealed SF₆ environments.

Proper material selection must consider:

Installation location

Thermal class

Mechanical load

Electrical insulation requirements

Machining precision

For high-temperature zones near arc chambers, G11 or high-temperature FR4 is recommended to ensure long-term reliability.

If you are looking for FR4 epoxy fiberglass sheets, Please contact Xujue Electrical and provide the product specifications, thickness and purpose you need, you can get detailed product information and quotation, and also send samples free of charge