Toughened Glass And Porcelain Insulators Compared

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The practical difference between the two on an overhead line is not dielectric strength. It is what happens when one fails, and whether your patrol can see it.

The Failure Mode Is The Real Difference

When a toughened glass disc is punctured the glass shatters and the shell falls away, leaving the cap and pin holding the string. That is visible from the ground and from a helicopter. When a porcelain disc is punctured it usually still looks intact, and finding it means testing the string unit by unit. On a long line this single difference decides the maintenance budget.

U70B Toughened Glass Disc Insulator For 33kV Lines

Mechanical Ratings

Both materials are used across the same range of duties. Our toughened glass discs run from 40kN on the U40B through 70kN, 100kN and 120kN to 160kN on the U160B, with a mechanical routine test applied to every disc from 20kN up to 80kN. Porcelain pin and post insulators cover cantilever ratings from 4kN through 16kN depending on the pattern.

U40B Toughened Glass Disc Insulator 40kN

Creepage Per Unit

Glass discs contribute a fixed creepage per unit and the string length sets the total: 185mm on a U40B, 320mm on a U70B through U120B and 400mm on a U160B. A porcelain pin post carries its whole creepage in one body, from 450mm on the ALP22-450 up to 1015mm on the ANSI 57-14. Which approach fits depends on whether the design has room for a swinging string.

ANSI 57-14 Line Post Porcelain Insulator 1015mm Creepage

Where Porcelain Still Wins

Porcelain is the established material at the transformer tank interface, where the part has to be both a mechanical fixing and a seal. It also holds its surface in UV and heat without the ageing behaviour a polymer housing can show. For bushings below 40kV it remains the default, which is why our transformer bushing range is porcelain throughout.

DIN 24kV 630A Transformer Bushing CD525

Choosing For A Dusty Line

On a dusty line the profile matters more than the material. Aerodynamic glass discs are shaped so wind carries deposits off rather than letting them settle. In porcelain the equivalent move is to a long creepage pin post such as the ZS-770 with 770mm of leakage path.

Aerodynamic Toughened Glass Suspension Insulator XYAY Series

Products Referenced In This Guide

Glass Suspension Insulators

U40B Toughened Glass Disc Insulator 40kN

Glass Suspension Insulators

• Creepage Distance 185 mm
• Socket Coupling 11 mm
• Wet Power Frequency Withstand Voltage 25 kV

U70B Toughened Glass Disc Insulator For 33kV Lines

Glass Suspension Insulators

• Diameter 255 mm
• Creepage Distance 320 mm
• Socket Coupling 16 mm

Aerodynamic Toughened Glass Suspension Insulator XYAY Series

Pin Type Insulators

• Rated Mechanical Failing Load 120 kN
• Nominal Creepage Distance 365 mm
• Power Frequency Puncture Voltage 130 kV

ZS-770 Pin Post Porcelain Insulator 770mm Creepage

• Creepage Distance 770 mm
• Rated Electromechanical Failing Load 16 kN
• Lightning Impulse Withstand Voltage 190 kV

Related Ranges And Applications

Glass Suspension Insulators

Pin Type Insulators

Overhead Line Contractors

Power Utilities And Substations

Selecting Creepage For The Pollution At Your Site

Questions About This Topic

Apply This To Your Own Project

Send the drawing or describe the site and we will recommend a pattern and a creepage class.