This chapter describes different aspects of overhead insulators. Properties of line insulators have been described. Materials used for manufacturing overhead line (OHL) insulators have been presented. Different types of insulators used in OHL application have been discussed. Requirement of string has been mentioned. Voltage distribution across different discs of string has been shown, and string efficiency has been derived. Design features of insulators for overhead application have been presented. Selection factors for insulator have been mentioned for transmission and distribution line applications. Fittings of insulator in OHLs have been described. Failure and testing of OHL insulator have been discussed. Different useful standards for this aspect have been referred.

Chapter Contents:

• 5.1 Introduction
• 5.2 Overhead line insulator
• 5.3 Common properties of line insulator
• 5.4 Material of overhead line insulators
• 5.4.1 Porcelain
• 5.4.2 Glass
• 5.4.3 Composite silicone
• 5.5 Classification of overhead line insulators
• 5.5.1 Pin-type insulator
• 5.5.2 Disc-type insulator
• 5.5.3 Shackle-type insulator
• 5.5.4 Stay-type insulator
• 5.5.5 Line-post-type insulator
• 5.5.6 Porcelain long-rod-type insulator
• 5.5.7 Composite silicone insulator for transmission line
• 5.5.8 Comparison of different types of insulators
• 5.6 Requirement of insulator sets
• 5.7 String of insulators
• 5.7.1 Suspension type string
• 5.7.2 Strain type string
• 5.8 Voltage distribution in string
• 5.9 Effect of unequal voltage distribution
• 5.10 String efficiency
• 5.11 Improvement of voltage distribution and string efficiency
• 5.11.1 Connection of parallel string
• 5.11.2 Connection of multiple parallel composite silicone insulators
• 5.11.3 Connection of grading for guard ring
• 5.11.4 Connection of arc horn
• 5.12 Selection practice for insulator
• 5.13 Associated design factors of insulators
• 5.14 Clamps
• 5.15 Nuts and bolts
• 5.16 Failure of insulator
• 5.16.1 Electrical causes
• 5.16.2 Mechanical causes
• 5.16.3 Thermal causes
• 5.16.4 Ageing effect
• 5.16.5 Other causes
• 5.17 Standards, test and practice
• 5.17.1 Electrical features
• 5.17.1.1 Capacitance
• 5.17.1.2 Insulation resistance
• 5.17.1.3 Dielectric dissipation factor and power factor
• 5.17.1.4 Time constant (discharging–charging property)
• 5.17.1.5 Partial discharge
• 5.17.1.6 Erosion resistance
• 5.17.1.7 Tracking resistance
• 5.17.1.8 Resistance to penetration of water
• 5.17.2 Mechanical features
• 5.17.2.1 Corrosion resistance
• 5.17.2.2 Tensile stress
• 5.17.2.3 Elongation
• 5.17.2.4 Ductility
• 5.17.2.5 Strain
• 5.17.2.6 Percentage of elongation
• 5.17.2.7 Elasticity modulus
• 5.17.2.8 Hardness
• 5.17.2.9 Impact strength
• 5.17.2.10 Yield point
• 5.17.2.11 Wear resistance
• 5.17.3 Thermal features
• 5.17.3.1 Thermal conductivity
• 5.17.3.2 Thermal resistance
• 5.17.3.3 Specific heat
• 5.17.3.4 Heat capacity
• 5.17.3.5 Thermal expansion
• 5.17.4 Routine test
• 5.17.5 Performance test
• 5.17.6 Power test
• 5.17.7 Practice tests
• 5.17.8 Effect of environment on leakage current
• 5.17.9 Ageing effect
• 5.18 Summary
• 5.19 Useful standards and guidelines for further study
• References

Inspec keywords: power distribution lines; insulators; power overhead lines; failure analysis

Other keywords: transmission line; OHL application; voltage distribution; line insulators; distribution line; overhead line insulator; design features; overhead insulators; OHL insulator; string efficiency

Subjects: Overhead power lines; Power line supports, insulators and connectors; Distribution networks