Electrical Design of 400 kV Composite Tower

Publikation: Bog/antologi/afhandling/rapportBogForskningpeer review


Overhead transmission line pylons are key components of high voltage power
systems. Traditional steel lattice pylons, which have been designed since 70 years
ago, have a negative visual appearance on landscapes, and for this reason, in recent
years general public oppose against the installation of such pylons for the extension
of power system networks. In order to get public acceptance, a fully composite pylon
design has been proposed in Denmark which has a better visual appearance with
respect to the old ones. The fully composite pylon design is a novel concept and
there is no enough information and practical experience regarding its electrical and
mechanical performance. In this book, the electrical performance of fully composite
pylon is investigated by using analytical and finite element methods and high voltage
experimental method.
The major challenges in the design process of fully composite pylon are addressed.
One of the challenges is the electrical dimensioning of the fully composite
pylon for which electrical clearances on the pylon should be determined. The electrical
air clearances on the pylon must be enough to withstand against power frequency,
switching and lightning overvoltages. The air clearances are calculated on
the basis of an extensive insulation coordination study.
Another challenge is the selection of the material of the composite cross-arm
core. In the book, two kinds of candidate fibre reinforced plastic (FRP) materials
are tested electrically and their important properties, including internal partial discharge
(PD) performance, dielectric permittivity and dissipation factor are evaluated.
Based on the test results, E-glass reinforced epoxy is recommended as the core
material of the composite cross-arm. Also, three manufacturing methods for fibre
reinforced plastic (FRP) materials are compared and the filament winding method
is recommended to the material supplier. As the fibre reinforced plastic (FRP) core
of the composite cross-arm is always stressed by electrical and mechanical loading
simultaneously, an electrical-mechanical combined setup that can apply high voltage
and dynamic tensile/compression forces to fibre reinforced plastic (FRP) materials
simultaneously is designed. With the combined setup, combined tests are performed
on fibre reinforced plastic (FRP) materials and effects of mechanical loading
on their electrical behaviors are investigated. Meanwhile, effects of the electrical
stress on the lifetime of fibre reinforced plastic (FRP) materials are studied.
Another challenge is the proper design of insulation for the unibody cross-arm
of fully composite pylon. In this regard, the application of different shed profiles
are mentioned and consequently, a small and large shed profile are assigned to the
shed housing on the unibody cross-arm. A major challenge in the design of pylon is
the electric field performance of fully composite pylon. Numerous finite element
analyses of the pylon are carried out to evaluate electric field and potential distribution
around and inside the unibody cross-arm. Two design scenarios of utilizing
internal or external ground connection for the shield wires are examined. Different
conductor clamp designs are considered for the attachment points between phase conductors and the unibody cross-arm. Electric field magnitudes in the different
regions of interest on the fully composite pylon are calculated and compared with
the threshold values.
In order to experimentally assess the electric field magnitudes on the unibody
cross-arm, a water-induced corona discharge setup is designed, with which a corona
test is performed on an equivalent full-scale composite cross-arm segment in wet
conditions. Artificial rain is applied to the cross-arm segment with an equivalent
phase-to-ground voltage. During this process, corona discharges from the cross-arm
segment are measured and observed. With a stringent corona inception criterion of
10 pC, it is found out that corona is triggered from the cross-arm surface under
nominal voltage in wet conditions. Thus, it is concluded that corona rings are necessary
for the fully composite pylon. Therefore, an optimization process is done by
using finite element method to find appropriate dimension and positions for the corona
rings at both sides of the conductor clamps to get a design scenario in which
fully composite pylon represents an acceptable electric field performance. Additionally,
the suitability of the initially designed unibody cross-arm inclined angle
from the ground plane is investigated. The water-induced corona discharge test and
scale model test are performed with different cross-arm inclined angles. Based on
test results, the initial inclined angle 30° is believed to be satisfactory if the electric
field on the cross-arm surface can be restrained to an acceptable level.
The next challenge is the lightning shielding performance of fully composite pylon
which is calculated and evaluated by different methods. The conventional
method of the electro-geometric model (EGM) is modified to be used for the assessment
of effectiveness of lightning shielding system for the fully composite pylon.
The feasibility of assigned negative shielding angle for the pylon is investigated
and the outage rate regarding its application is calculated. The protected and unprotected
zones on the fully composite pylon against vertical and possible horizontal
lightning strikes are visualized for different lightning stroke currents.
In order to experimentally evaluation of the lightning protection performance of
fully composite pylon, a scale model test is performed. It proves experimentally that
a shielding failure region exists at the center of the pylon and the experimental
shielding failure rate for an overhead line composed of fully composite pylons is
similar to that predicted by electro-geometric model (EGM). Based on the scale
model test, it is concluded that the shield wires arrangement in the fully composite
pylon is satisfactory.
Finally, the environmental aspects of fully composite pylon are calculated based
on analytical and finite element analysis methods. These aspects include radio interferences,
audible noises, corona losses and emission of electromagnetic fields at
the right-of-way of the lines. The calculated values are compared with the recommended
threshold values reported in related standards and literatures.
ISBN (Trykt)978-3-030-17842-0
ISBN (Elektronisk)978-3-030-17843-7
StatusUdgivet - apr. 2019
NavnLecture Notes in Electrical Engineering

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