Composite InsulatorsComposite insulators are typically non ceramic insulators have different chemical compositions

typically fibreglass rod with rubber (EPDM or silicon) sheath and weather sheds.

They are use in HDPE line insulator applications. Cycloaliphatic (epoxies) station applications.

Metals components normally crimped.

There are following types of composite insulators .

Silicon rubber (SR) – Room temperature vulcanizing (RTV), High temperature vulcanizing

and liquid rubber (LSR).

1.

Ethylene Propylene rubber (EPR) , Ethylene Propylene Monomer (EPM), Ethylene Propylene

Dien Monomer (EPDM).

2.

Epoxy Resin – Bisphenol, cycloaliphat3.

Polyurethene4.

Polufluor carbons – Teflon, PTFE5.

Manufacturing

Design

First we have to design the insulators according to our needs.

22kV 2 Sisk Equivalent Composite Suspension/Strain Insulator Socket/Ball

22kV Composite Suspension/Strain Insulator Clevis/Tongue

11 To 44kV 40kN Composite suspension/Strain Insulator Socket/Ball

66 To 132kV 40kN Composite Suspension/Strain Insulator Socket/Ball

Moulding

After designing we have the different moulding methods in which we mould the insulators using

different moulding materials .There are three types of moulding.

Compression moulding1.

Transfer moulding2.

Injection moulding3.

Materials for Housing

Silicone Rubber HTV, RTV, LSR1.

Ethylene Propylene Rubbers: EPDM, EP

silicone alloys

2.

Epoxies: Cycloaliphatic epoxies3.

Polyolefins : Ethylele Vinyl Acetate (heat shrinkable)4.

Hydrophobicity

Ability of surface to prevent water filming – water drops beading.

Often misunderstood property

Hydrophobicity loss does not mean failure.1.

All polymers are initially hydrophobis2.

Hydrophobicity is reduced during service3.

Dirt, UV, Corona , Discharges4.

For EPs , Epoxy, the above will eliminate hydrophobicity5.

For silicones, only excessive corona and strong discharge can destroy hydrophobicity

locally.

6.

Recovery

Desireable as high surface resistance restored

Mainly due to diffusion of LMW polymer chains from bulk to surface

Recovery ability different for polymers, Silicones highest – high surface resistance obtained even

before visible recovery accurs.

Recovery ability lost for EP, epoxy when dirty.

Difference between Porcelain andComposite Insulators

Porcelain

They are brittle and require careful handling.1.

Materials very resistant to UV,contaminant degradation,electric field degradation.2.

Materials strong in compression,weaker in tension3.

High modules of elasticity – stiff4.

Havier than NCIs5.

Limited flexibility of dimensions6.

Process limitations on sizes and shapes7.

Applications/handling methods generally well understood.8.

Surface of these insulators are hydrophilic. i.e continuous film of water form leads to the

increase in leakage current.

9.

Composite

Hydrophobic materials improve contamination performance.1.

Strong in tension ,weaker in compression.2.

Deflection under load can be an issue.3.

Lighter – easier to handle4.

Electric field stresses must be considered5.

Material properties have been improved e.g standardized product lines now exist.

Balancing act – leakage distance/field stress – take advantage of hydrophobicity.

Application parameters still being developed. Line design implications(lighter weight,

improved shock resistance).

6.

90% weight reduction7.

Reduce breakage8.

Lower installation costs9.

Aesthetically more pleasing10.

Improve resistance to vandalism11.

Improved handling of shock loads12.

Improve power frequency insulation13.

Improved contamination performance14.