Page 46 - Energize April 2021

TECHNICAL

The electrical benefit of the compact configuration is reduced
inductance and increased capacitance which results in higher surge
impedance loading (SIL). By bundling three sub-conductors per
phase, the SIL capacity increases and electric stress decreases to
achieve desired corona and audible noise performance. A 345 kV
double circuit 3-bundled conductor design offers a 43% improved
surge impedance loading over a traditional double circuit 2-bundled
conductor design of the same voltage class. 8
The development also considered aesthetics and structural
Figure 14: Conductor suspension system (INMR)
optimisation to support the delta configured phase conductors in a
visually appealing way. The compact delta conductor configuration
is attached to a curved arm which also offers geometric benefits by
minimising the structure height.
The result is a highly efficient line operating on shorter structures
with less visual impact. The system has been developed for 345 kV
tubular and lattice designs and current efforts are underway to fully
develop 230 kV and 138 kV designs.

9
400 kV compact line (Germany )
Developed by a team from industry and institutes in Germany, this
innovative compact line solution reduces the ground clearance and Figure 15: V string attachment (INMR)
sag problem by creating a suspension structure of two steel cables
from which the four conductors are suspended in a catenary fashion. in a lower overall sag for the conductors and the required ground
The steel rope has a 26 mm diameter and consists of stranded, clearance can be achieved with lower masts.
hot-dip galvanized steel wire having an overall tensile strength rating The tower is a conical solid wall monopole with an innovative
of 791 kN. These ropes are installed under high tension, while phase suspension of the conductors. The basic compact line has a tower
conductors hang, like garlands, beneath. The resulting sag in each height of 30 to 36 m and a corridor width of 55 to 60 m. Distances
span is therefore no longer being defined by the conductors but between compact line towers will reach up to 400 m, just as for
rather by the steel ropes to which they are attached. conventional overhead lines. The final distance depends on the
The conductors are attached to the suspension cable at intervals terrain and the corridor route.
of 20 m, and sag only occurs in the length of conductor between Special insulator string sets and fittings also had to be developed
the attachment points. Steel suspension cables carry a small for both suspension and tension towers. Among the benefits of the
percentage of the overall current and the temperature is affected steel support rope is reduced lateral movement of conductors due to
less by the level of current than are the conductors. This results wind. To take advantage of this benefit, a rigid V string arrangement
was selected for suspension insulators to withstand increased
compression and tensile forces. Tension insulator sets must be able
to handle the high tensile forces from the steel support ropes, and
insulators were designed for tensile forces up to 1320 kN.
The use of composite insulators and monopole masts allows
a wide variety of compact transmission line designs, all of which
can achieve the goal of reducing the overall height and width of
transmission line corridors while improving the visual impact. n

References
Figure 12: Comparison with conventional lines (AEP) 1. M Ntuli et al: “Increasing the capacity of transmission lines via
current uprating: An updated review of benefits, considerations and
developments”, AUPEC 2016.
2. H Devaserie: “Co-existing with Transmission Lines: Engineering
Considerations”, http://www.planning.org.au/documents/item/3201
3. SM Rowland: “Developing Composite Insulating Cross-Arms for 400 kV
Lattice Towers”, INMR, July 2, pp 86-90, (2104).
4. K Sharma: “Polymeric insulators”, http://www.appstate.edu/~clementsjs/
surfaceflashover/insulatortesting.pdf
5. Sediver: “Composite line post insulators”, http://sediver.cn/transmission_
lines/composite/Sediver_line_post_insulators.html
6. Pfisterer: “Insulator sets for high voltage applications”, www.pfisterer.com
7. E Miller: “Breakthrough Overhead Line Design (BOLD)”, AEP 2016.
8. INMR: “Implementing a Compact 400 kV Line”, www.INMR.com, 2021.

Figure 13: 400 kV compact system (INMR) Send your comments to rogerl@nowmedia.co.za

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