Fiberglass Rods for Modern Composite Insulators TONY BAKER 2015 - - PowerPoint PPT Presentation

Fiberglass Rods for Modern Composite Insulators

TONY BAKER

Fiberglass Rods for Modern Composite Insulators

2015 INMR WORLD CONGRESS

Fiberglass Rods

• Modern composite high voltage insulators
• Mechanical characteristics
• Electrical characteristics

– Design tests – Routine tests

• Brittle rod fractures

– Causes & prevention – Verification of solution

Modern Composite Insulator

Elastomeric Outer Housing

One-piece injection molded Silicone Rubber

Pultruded Resin Reinforced Fiberglass Rod

Epoxy or polyester resin E-Glass

Alumino-borosilicate electrical glass

ECR-Glass (boron-free)

Alumino-lime silicate electrical/chemical resistance glass

Compressed-on End Fittings Extruded 6061-T6 Aluminum Galvanized Ductile Iron Moisture-proof Interfaces All rubber/rod/hardware interfaces

Defined in ANSI C29 & CSA C411 Insulator Standards

Primary Mechanical Loads

Suspensions / Dead-ends Line Posts

Tension Torsion Cantilever

Rod Strength Characteristics

RESIN Strength POLYESTER EPOXY Tension 110,000 psi 110,000 psi Torsion 11,100 psi 12,700 psi Bending 120,000 psi 130,000 psi

Rod Torsion Strength

Diameter Ratio Torsion Strength Ratio 1/2 in. 1.00 1.00 5/8 in. 1.25 1.95 3/4 in. 1.5 3.37

Polyester resin Epoxy resin ~ 15% inc ncrease in n torsio ion str trength 5/8 in. rod 3/4 in. rod ~ 73% inc ncreas ase in n to torsio ion strength 20% inc ncrease in n diam ameter

Rod Dielectric Strength Tests

Test Detail Pass Criteria Dye Penetration 1% dye solution wick test > 15 min for 10 mm thick rod section Water Diffusion 30 mm rod section boiled in 1% salt water for 100 hrs. Withstand 12 kV for 1 minute

ANSI, CSA, & IEC Design tests

to demonstrate a rod has sufficient dielectric strength for use in high voltage insulators

Routine Electrical Test

Distance through solid dielectric material > half the dry arc distance

Not specified in composite insulator standards

Routine Electrical Test

One Manufacturer’s Routine Electrical Tests on Fiberglass Rods

• 100 kV /lineal foot along the

rod and circumferentially to it.

• Pass/fail leakage current

criteria varies with rod diameter.

Brittle Rod Fracture

Brittle rod fracture : 345 kV Suspension insulator with epoxy cone end-fittings

• Ref. M. Kumosa, et al “Failure analysis of non-ceramic insulators Part I: brittle fracture characteristics”, IEEE Electrical

Insulation Magazine, May/June 2005, Vol. 21, No. 3

Brittle Rod Fractures

• Ref. M. Kumosa, et al “Failure analysis of non-ceramic insulators Part I: brittle fracture characteristics”, IEEE Electrical

Insulation Magazine, May/June 2005, Vol. 21, No. 3

Stress corrosion cracking of the glass fibers in the rod due to:

• I. Exposure of the rod to water and mechanical stress.
• II. Associated with an acid , derived from the hardener, combined

with water ingress and mechanical stress .

• III. Nitric acid formed in service and mechanical stress.

Fiberglass rods must not be exposed to water or acids

Resistance to Nitric Acid Attack

19,430 psi 4-Point bending tests

• n fiberglass rods exposed to 1.2 pH Nitric acid

Fiberglass Resin AE events E-glass (boron ) polyester 43,699 E-glass (boron) epoxy 1,435 ECR-glass (boron free, high seed) polyester 328 ECR-glass (boron free, high seed) epoxy 136 ECR-glass (boron free, low seed) epoxy 3.5

• Ref. L.S. Kumosa, et al, “Resistance to brittle fracture of glass reinforced polymer composites used in composite

(non-ceramic) insulators”, IEEE Trans on Power Delivery Vol. 20, No.4, Oct. 2005

Fiberglass Electrical Strength

E-glass ECR-glass - high seed count

• Ref. M. Kumosa, et al “Failure analysis of non-ceramic insulators Part II: The brittle fracture model and failure

prevention”, IEEE Electrical Insulation Magazine, July/August 2005, Vol. 21, No. 4

Thermo-mechanical Load Temperature Cycle Test

CSA C 411.4 Composite Suspension Insulator Standard

Moisture Proof Design

High pressure washing composite transmission suspension insulator.

Long-term Immersion/Load Test

Suspension insulator with encapsulated end-fittings subject to continuous 400 hour tension load at 50% SML .

Long-term Immersion/Load Test

Suspension end-fitting encapsulated in liquid fuchsine dye

Long-term Immersion/Load Test

Interfaces after 400- hour tension-dye encapsulation tests showing no dye in seal area.

Summary

• High inter-laminar shear stress applications

Epoxy resin fiberglass rods.

• Torsion loading

Diameter more important than resin type.

• Rod dielectric strength

Tests are indirect, but routine electrical tests possible.

• Brittle rod fractures

Stress corrosion cracking of small diameter fiberglass rods from exposure to nitric acid formed in service.

• Prevention of brittle rod fractures:
• Entire composite insulator assembly must be moisture proof in service.
• Boron –free ECR-glass, epoxy resin fiberglass rods required.
• But must also be low-seed ECR glass.
• Moisture-proof tests:
• Thermo-mechanical load temperature cycle test.
• Long-term immersion/load test.