High Voltage Braced
Insulator Assemblies
Design & Application
Panel Session PN23
2008 IEEE Transmission & Distribution
Exposition & Conference
April 24, 2008 Chicago, IL
1
High Voltage Braced
Insulator Assemblies
Design & Application
A. C. Baker: Overview & general comments
R. A. Bernstorf: Strength ratings
D. G. Powell: Horizontal Vee stability
R. K. Kihara: Construction
2
1
Armless Construction
3
Load Capacity Improvement
α
d
θ
d
Maximum Allowable Vertical (Weight) Load
Conventional
Vertical String
Porcelain
Polymer
Horizontal
Line Post
RTL
RCL
( RTL = 0.5 M&E)
(RCL = 0.4CS)
RTL
RCL
(RTL = 0.5 SML)
(RCL = 0.5 SCL)
RTL range
7,500 – 25,000 lbs.
RCL range
650 – 1,900 lbs.
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”
Braced Post Assembly
For α = 45º
.707 RTL
For α = 30º
.500 RTL
VMAX range
2,500 - 14,000 lbs.
4
2
Braced Insulator Assembly
5
8000
7000
230 Kv Horizontal Vee
Vertical Load V lbs.
6000
Post: Max Working Loads
Cantilever = 1,000 lbs.
Tension/Compression = 7,500 lbs
5000
4000
Brace: Max .Working Load
Tension = 12,500 lbs.
3000
2000
1000
0
0
500
1000
1500
2000
2500
3000
3500
4000
Horizontal Load H, lbs.
Vertical Load Carrying Capacity vs. Transverse Loading
6
for a Typical 230 kV Horizontal Vee
3
Unbalanced
Longitudinal Loads
L1 ≠ L2
T = (V sin θ – H cos θ) tan ω
7
Horizontal Vee
Longitudinal Displacement
L1
L2
8
4
Horizontal Vee Lines
• Wind stability limit can be lower than
maximum wind speed usually
considered.
• HV assemblies subjected to unbalanced
longitudinal loads will be displaced in
direction of higher load.
• Changes in sag will counteract the
unbalancing load, establishing new
equilibrium at each support point.
• Iterative solution needed.
9
Horizontal Vee
Wind Speed Stability Limit
Wind Stability Limit, km/hr
350
300
250
200
150
100
50
0
0
10
20
30
40
50
Num ber of Spans
60
70
80
10
5
230 kV Horizontal Vee Line
Ref. INMR Quarterly Review Quarter 1 2004
11
Rotated Horizontal Vee
Ref. INMR Quarterly Review Quarter 1 2004
12
6
Braced Post Used as a
Longitudinal Restraint Point
Ref. INMR Quarterly Review Quarter 1 2004
13
Tripod Longitudinal Restraint
Assembly
14
7
Other Loading Considerations
• Suspension insulators: tension loads only.
• Brace: no compression loads.
• Polymer posts: combined loading effects
• Some Porcelain posts designed for
tension /compression only.
Do not use for Braced Post Assemblies.
• Posts : consider buckling strength
• These subjects will be covered in detail in
later presentations.
15
Electrical Design
• Brace and Post insulator components
must be properly coordinated.
• Individual components must be adequate
to withstand the power frequency and
impulse electrical stresses in service.
• Assembly Leakage Distance.
• Assembly Dry Arc Distance.
• Manufacturers should be consulted
concerning need for corona rings.
16
8
Summary
• Two types of Braced Insulator Assemblies:
Braced Posts & Horizontal Vees
(fixed or articulated posts)
•
•
•
•
Different mechanical characteristics.
Braced Posts primarily polymer.
Consider Horizontal Vee wind stability limits.
Longitudinal restraint assemblies can increase
the wind stability limit for a Horizontal Vee line.
• Installation of some Horizontal Vees may
require special construction techniques.
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