The document discusses concepts for optimizing chainette towers and lattice towers. It describes the evolution of EHV structures used by Eskom in South Africa from self-supporting towers to various generations of cross-rope suspension towers. Potential efficiencies of third generation chainette towers are explored, including staggered bracing patterns, taller suspension heights, offset peaks, use of 60 degree hot-rolled angles, higher steel grades, and variable bracing intervals. The optimal base width is discussed as balancing superstructure needs versus total cost. Collaboration between different disciplines is emphasized for integrated tower designs.

1. Slide 1 of 32
3rd Generation
Chainette Towers
& Other Tower
Optimisation Concepts
2015 PLS-CADD Advanced Training & User Group Meeting
Pierre Marais

2. Slide 2 of 32
Optimisation of chainette towers
• Evolution of 400kV crossrope structures in South
Africa
• Chainette Tower Variants
• Understanding the performance
• Modelling in Tower
1st & 2nd generation Chainette towers
• Further potential efficiencies
3rd generation ideas
Optimisation of a narrow base 132kV lattice tower

3. Slide 3 of 32
100% Cost
Self - Supporting Suspension
Pre- 1985 1985
65% Cost
Guyed Vee Suspension
Evolution of EHV Structures in Eskom

4. Slide 4 of 32
2003
Evolution of EHV Structures in Eskom
55% Cost
1st Gen Cross-rope
Suspension
1995
50% Cost
2nd Gen Cross-rope
Suspension

5. Slide 5 of 32
Chainette Tower Variants
2005
50% Cost
Cross-rope
Suspension
1998
Compact Cross-rope
Suspension
“Flat Delta” Cross-
rope Suspension
Efficient Long Distance Transmission

6. Slide 6 of 32
Chainette Tower Variants
0-15 degree structures
R0
R75,000
R150,000
R225,000
R300,000
R375,000
R450,000
Misc Costs
Insulation
Hardware
Tower Erection
Tower Supply
Foundations
52%
Saving
• 0-15 Degree
guyed strain

7. Slide 7 of 32
Chainette Tower Variants
30m
50m
$0
$20,000
$40,000
$60,000
$80,000
$100,000
$120,000
Insulators
Conductor
Hardware
Cables & Stays
Tower Hardware
Foundation Cost
Tower Erection
Tower Supply
43%
Double Circuit 380kV

8. Slide 8 of 32
Chainette Tower Variants
970km 350kV DC line 2007

9. Slide 9 of 32
• Crossrope / chainette towers have the lowest
fault rate of any tower type on the Eskom grid
1 2 1 1 1 2
HYDRA HYDRA PEGASUS WITKOP VENUS VENUS
DROERIVIER DROERIVIER TUTUKA TABOR GEORGEDALE GEORGEDALE
1 2 1 2 1 1 2
VENUS VENUS MIDAS MIDAS PLUTO SPITSKOP SPITSKOP
MAJUBA MAJUBA MATIMBA MATIMBA MATIMBA MATIMBA MATIMBA
1 1 1
PEGASUS VENUS PEGASUS
MAJUBA ARIADNE ATHENE
1 1 1 1 1 3 1 1
KOKERBOOM MAPUTO SPITSKOP DUVHA EDWALENI HYDRA MAPUTO WITKOP
ARIES ARNOT BIGHORN CAMDEN CAMDEN DROERIVIER EDWALENI SPENCER
AVERAGE VALUE
275kV
Line
275kV
Line
275kV
Line
275kV
Line
MINIMUM PORTION OF
LINE FUALTS DUE TO
PIGYBACK FAILURE
SELF SUPPORTING GUYED VEE CROSSROPE
MIX
1
2
3
4
5
6
7
8
5.4
FAULTS/100KM/YEAR
3.0
FAULTS/100KM/YEAR
2.8
FAULTS/100KM/YEAR
1.2
FAULTS/100KM/YEAR

10. Slide 10 of 32
• A naturally high electric strength
HV Impulse tests confirm a higher electrical
strength compared to conventional towers
3.10 m

11. Slide 11 of 32
• Bird pollution flashovers virtually eliminated
Birds do not perch on crossrope
No possibility of nesting
No bird pollution on insulators

12. Slide 12 of 32
• Excellent shielding from Lightning Strikes
 Phases well protected against lightning strikes
NEGATIVE
SHIELDING
ANGE

13. Slide 13 of 32
• Multiple earth contacts produce lower
superior connection to earth
Reduced back-flashover rate
6 Earth
connections
over a large area

14. Slide 14 of 32
• Low weight
Rapid re-construction

15. Slide 15 of 32
• Compact phase
spacing is
electrically
efficient
Capacitance 
Inductance 
Lower losses 7m
7m
7m

16. Slide 16 of 32

17. Slide 17 of 32
60m
80m 40-50m
• Solution to wide tower footprint:
Standard right of way required for line (40-50m)
80x60m building restriction around every tower site

18. Slide 18 of 32
 Welding Eliminated
 Be careful to avoid eccentricities
Replicate the original Tower FEM model as far as possible
1st Generation 2nd Generation

19. Slide 19 of 32
• What is the optimal attachment height?
• Possibly taller than you think (Unless you have flat terrain)
– Taller suspensions can eliminate in line strain structures
– Optimum spotting will reveal the optimal height
33.4m
1st Generation
18.3m
20.0m
28.9m
2nd Generation
Optimal height
for flat terrain
Optimal height for
“normal” terrain

20. Slide 20 of 32
• Staggered bracing shown to be the most
effective bracing pattern
• Take note of RLX ratio (see also ex5.tow)

21. Slide 21 of 32
• Offset peaks can provide some structural efficiency
But also can induce torsional loads – choose extent
carefully
Heavily
loaded
mast
Lightly
loaded
mast
Wind
direction Bending
induced by
wind load
Bending
induced by
offset peak

22. Slide 22 of 32
• Hot rolled 60 degree angles
Hot rolled 60o angle “Schifflerized” 60o angle
• Potentially more cost effective material cost
• Lower drag coefficient
 SAPS wind used to benchmark current (square) design with proposed
(triangular) mast

23. Slide 23 of 32
• Compared to 90 degree angles of the same size:
60o angle
90o angle
 Ix, rx decreases
 Iz, rz increases
90o
ANGLE 60o
ANGLE % change
rx 21.3 19.1 -10%
rz 13.7 16.8 22%
• This impacts the relative efficiency of different bracing patterns
SECTION PROPERTIES OF
COMPLEX SHAPES CAN BE
DETERMINED IN AUTOCAD
USING “REGION” AND
“MASSPROP” FUNCTIONS

24. Slide 24 of 32
• 2 different bracing patterns investigated
Symmetrical bracing
(1.2L/rz controls)
• Staggered bracing still more efficient than Symmetrical bracing
L1
Staggered bracing
(2.4L/rx controls)
L2
10% Lighter
(L1 can = 1.75L2 for
same main leg size)

25. Slide 25 of 32
• Utilising higher steel grades (on main
legs) can produce further efficiency
• Gr. 450MPa compared with Gr.355MPa
steel
• Viability dependant on relative fabrication
costs Fy = 450MPa (65ksi)
Fy = 355MPa (51ksi)

26. Slide 26 of 32
• Combination of steel grade and 60o hot rolled
angles produce a 15% reduction in weight
• Alternatively structural efficiency can be translated
into increased strength
• Viability dependant on fabrication cost implications

28. Conventional Integrated
Hardware Design
Superstructure Design
Electrical Testing
Mechanical Testing
Electrical Design
Foundation Design
Electrical Testing
Mechanical Testing
Electrical Design
Collaboration with stakeholders
Insulation &
Hardware Design
Superstructure
Design
Foundation
Design
Suppliers Contractors End Users

29. Slide 29 of 32
Base width
OPTIMAL WIDTH
CONSIDERING
SUPERSTRUCTURE
ONLY
OPTIMAL WIDTH
CONSIDERING TOTAL
COST
Base width

30. Slide 30 of 32
Staggered
Bracing
Redundants
Staggered Bracing
with redundants X - Bracing
- Different bracing patterns
may have slightly
different optimal base
widths
- Minimal difference in
overall cost between
options
- For standard width
towers more significant
differences expected
2.5m 2.6m 2.5m

31. Slide 31 of 32
1. Determine load vs. position on main leg (max of all load
cases)
2. Determine compression load curve for main leg
3. Calculate bracing interval incrementally with successive
locations down the main leg
DISTANCE
BELOW
X-ARM
VARIABLE
SPACING
1M
SPACING
COMMON
BODY
BODY
&
LEG
EXTENSIONS
- Variable spacing on common body provides
additional efficiency

32. Slide 32 of 32
“Tusk Tower” 400kV Multi-Circuit
Sculpture Tower

33. Thank You
Questions?
pierrem@taprojects.co.za