11

High Voltage Braced High Voltage Braced Insulator Insulator

AssembliesAssemblies Design & ApplicationDesign & Application

Panel Session PN23Panel Session PN23

2008 IEEE Transmission & Distribution 2008 IEEE Transmission & Distribution Exposition & ConferenceExposition & Conference

April 24, 2008 Chicago, ILApril 24, 2008 Chicago, IL

22

High Voltage High Voltage Braced Braced

Insulator Insulator AssembliesAssemblies

Design & ApplicationDesign & Application

A. C. Baker: A. C. Baker: Overview & general Overview & general commentscomments

R. A. Bernstorf: R. A. Bernstorf: Strength ratingsStrength ratings

D. G. Powell: D. G. Powell: Horizontal Vee stabilityHorizontal Vee stability

R. K. Kihara: R. K. Kihara: ConstructionConstruction

33

Armless ConstructionArmless Construction

44

Load Capacity Load Capacity ImprovementImprovement

Maximum Allowable Vertical (Weight) Load

REFERENCES: 1) ANSI C29 STANDARDS, (C29.2, 29.7, C29.12, & C29.17) 2) IEEE STANDARD 987, “IEEE Guide for Application of Composite Insulators” 3) NEMA STANDARD PUB. HV-2, “Application Guide for Ceramic Insulators”

Conventional Vertical String

Horizontal Line Post

Braced Post

Assembly

Porcelain

RTL

( RTL = 0.5 M&E)

RCL

(RCL = 0.4CS)

For α = 45º

For α = 30º Polymer

RTL

(RTL = 0.5 SML)

RCL

(RCL = 0.5 SCL)

.707 RTL .500 RTL

RTL range

RCL range

VMAX

range

7,500 – 25,000 lbs. 650 – 1,900 lbs. 2,500 - 14,000 lbs.

d

d θ

α

55

Braced Insulator Braced Insulator AssemblyAssembly

66

Vertical Load Carrying Capacity vs. Transverse Loading for a Typical 230 kV Horizontal Vee

0

1000

2000

3000

4000

5000

6000

7000

8000

0 500 1000 1500 2000 2500 3000 3500 4000

Horizontal Load H, lbs.

Ver

tical

Lo

ad V

lbs.

230 Kv Horizontal Vee

Post: Max Working Loads Cantilever = 1,000 lbs. Tension/Compression = 7,500 lbs

Brace: Max .Working LoadTension = 12,500 lbs.

77

Unbalanced Unbalanced Longitudinal LoadsLongitudinal Loads

LL1 1 ≠≠ LL22

T = (V sin θ – H cos θ) tan ω

88

Horizontal Vee Horizontal Vee Longitudinal Longitudinal DisplacementDisplacement

L1 L2

99

HorizontalHorizontal Vee Lines Vee Lines • Wind stability limit can be lower than Wind stability limit can be lower than

maximum wind speed usually considered.maximum wind speed usually considered.

• HV assemblies subjected to unbalanced HV assemblies subjected to unbalanced longitudinal loads will be displaced in longitudinal loads will be displaced in direction of higher load.direction of higher load.

• Changes in sag will counteract the Changes in sag will counteract the unbalancing load, establishing new unbalancing load, establishing new equilibrium at each support point.equilibrium at each support point.

• Iterative solution needed.Iterative solution needed.

1010

Horizontal VeeHorizontal Vee Wind Speed Wind Speed StabilityStability Limit Limit

0

50

100

150

200

250

300

350

0 10 20 30 40 50 60 70 80

Number of Spans

Win

d S

tab

ility

Lim

it, k

m/h

r

1111

230 kV Horizontal Vee 230 kV Horizontal Vee LineLine

Ref. INMR Quarterly Review Quarter 1 2004

1212

Rotated Horizontal VeeRotated Horizontal Vee

Ref. INMR Quarterly Review Quarter 1 2004

1313

Braced Post Used as a Braced Post Used as a Longitudinal Restraint Longitudinal Restraint

PointPoint

Ref. INMR Quarterly Review Quarter 1 2004

1414

Tripod Longitudinal Tripod Longitudinal Restraint Restraint AssemblyAssembly

1515

Other Loading Other Loading ConsiderationsConsiderations

• Suspension insulators: tension loads only.Suspension insulators: tension loads only.

• Brace: no compression loadsBrace: no compression loads..

• Polymer posts: combined loading effects Polymer posts: combined loading effects

• Some Porcelain posts designed for Some Porcelain posts designed for tension /compression only. tension /compression only. Do not use for Braced Post Assemblies.Do not use for Braced Post Assemblies.

• Posts : consider buckling strengthPosts : consider buckling strength

• These subjects will be covered in detail in These subjects will be covered in detail in later presentations.later presentations.

1616

Electrical Design Electrical Design • Brace and Post insulator components Brace and Post insulator components must be properly coordinated.must be properly coordinated.

• Individual components must be Individual components must be adequate to withstand the power adequate to withstand the power frequency and impulse electrical frequency and impulse electrical stresses in service.stresses in service.

• Assembly Leakage Distance.Assembly Leakage Distance.

• Assembly Dry Arc Distance.Assembly Dry Arc Distance.

• Manufacturers should be consulted Manufacturers should be consulted concerning need for corona rings.concerning need for corona rings.

1717

SummarySummary • Two types of Braced Insulator Assemblies: Two types of Braced Insulator Assemblies: Braced Posts & Horizontal Vees Braced Posts & Horizontal Vees (fixed or articulated posts)(fixed or articulated posts)

• Different mechanical characteristics.Different mechanical characteristics.

• Braced Posts primarily polymer.Braced Posts primarily polymer.

• Consider Horizontal Vee wind stability limits. Consider Horizontal Vee wind stability limits.

• Longitudinal restraint assemblies can Longitudinal restraint assemblies can increase the wind stability limit for a increase the wind stability limit for a Horizontal Vee line.Horizontal Vee line.

• Installation of some Horizontal Vees may Installation of some Horizontal Vees may require special construction techniques. require special construction techniques.