Insulation Material Grade Requirements for High-Voltage Switchgear

1. Basic Insulation Material Requirements (Applicable to 10 kV / 35 kV Switchgear) Standards generally referenced: ...

1. Basic Insulation Material Requirements (Applicable to 10 kV / 35 kV Switchgear)

Standards generally referenced:

GB/T 11022, GB/T 3906, IEC 62271, DL/T 593, IEC 60085 (Thermal Classifications)

2. Solid Insulation Material Grade Requirements

FR4 / G10 / G11 Glass Fiber Reinforced Epoxy Laminates (Most Common)

Item Requirement
Thermal Class Class F (155°C) or Class H (180°C)
Dielectric Strength ≥ 10–15 kV/mm
Breakdown Voltage ≥ 40–50 kV (3–6 mm thickness)
CTI (Comparative Tracking Index) ≥ 175 V (minimum) / Recommended ≥ 300 V
Flame Retardancy UL94 V-0 required
Water Absorption ≤ 0.3%
Flexural Strength ≥ 300–450 MPa

Applications: barriers, busbar supports, insulating plates, truck isolation boards.

Epoxy Resin Cast Insulation (APG Process)

Item Requirement
Thermal Class Class F (155°C) / Class H (180°C)
Dielectric Strength ≥ 18–22 kV/mm
Partial Discharge Inception Voltage ≥ 15–20 kV
Volume Resistivity ≥ 10¹⁴ Ω·cm
Arc Resistance ≥ 180 s
Flame Retardancy UL94 V-0

Applications: solid insulated poles, bushings, switchgear castings.

DMC/BMC Molding Compounds

Item Requirement
Thermal Class Class F (155°C)
Dielectric Strength ≥ 8–10 kV/mm
Flame Retardancy Must reach UL94 V-0
Water Absorption ≤ 0.5%
Mechanical Strength Medium to high

Applications: operating mechanism insulators, structural supports.

SMC Composite Insulation Materials

Item Requirement
Thermal Class Class F or Class H
Dielectric Strength ≥ 8–12 kV/mm
Flame Retardancy UL94 V-0
Flexural Strength ≥ 170–200 MPa

Applications: compartment partitions, inner door insulation.

Silicone Rubber Insulation

Item Requirement
Dielectric Strength ≥ 20–25 kV/mm
Thermal Class Class H (180°C)
Hydrophobicity Class 1 (excellent)
Flame Retardancy UL94 V-0

Applications: cable terminations, busbar insulation sleeves.

Ceramic Insulators

Item Requirement
Thermal Resistance 200–300°C
Wet Power Frequency Withstand Voltage ≥ 10–30 kV/cm
Mechanical Bending Strength ≥ 70–100 MPa
Creepage Distance ≥ 25–31 mm/kV (for pollution class II–IV)

Applications: busbar support insulators, isolator supports.

3. Gas Insulation Requirements

SF₆ Gas
Item Requirement
Purity ≥ 97% (GB/T 12022)
Moisture Content ≤ 150 μL/L
Dielectric Strength About 9 kV/cm at 1 bar

4. Insulation Clearances (Important for Switchgear Design)

10 kV Switchgear
Item Minimum Distance
Phase-to-Phase Air Clearance ≥ 125 mm
Phase-to-Earth Air Clearance ≥ 125 mm
Creepage Distance (on solid insulation) ≥ 20–25 mm/kV
35 kV Switchgear
Item Minimum Distance
Phase-to-Phase Air Clearance ≥ 320 mm
Creepage Distance ≥ 31 mm/kV

5. Flame Retardancy Requirements

All insulation materials must meet:

UL94 V-0 (highest level)

Self-extinguishing within 10 seconds, no flaming drips.

Applicable to FR4, epoxy castings, SMC, DMC, silicone rubber, etc.

 6. Summary: Minimum Grade Requirements for High-Voltage Switchgear Insulation Materials

FR4 / Epoxy Laminates: Class F, UL94 V-0, ≥10 kV/mm dielectric

Epoxy Castings: Class H, UL94 V-0, ≥18 kV/mm

DMC/SMC: Class F, UL94 V-0, ≥8 kV/mm

Silicone Rubber: Class H, ≥20 kV/mm, UL94 V-0

Ceramics: High creepage, high wet withstand levels

SF₆ Gas: Purity ≥97%

Selection of insulation materials

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