HighLight 55 - DNV Kema

Innovative pylons on test
Figure 1. Suspension tower braced V.
(with C-frame)
Figure 2. Angle tower jumpers.
Apart from its aesthetic quality, the
Wintrack design has two key benefits.
Firstly, the closeness of the conductors
minimizes the electromagnetic field
(EMF). As a result, there is only a
narrow corridor of 50 m either side
of the centre line where the magnetic
field exceeds the Dutch government’s
recommended limit of 0.4 µT for ‘sensitive
locations’. Furthermore, it reduces space
requirements, while the unique suspension
arrangement allows for tight turns – all
of which simplifies siting towers, even in
crowded urbanized areas.
Fine-tuning the system
DNV KEMA worked closely with TenneT
in the development of Wintrack, which
included innovative steps such as
employing architects to design the poles.
The entire system was also tested at DNV
KEMA’s High-Power and High-Voltage labs
in Arnhem, the Netherlands. And as this
experience shows, even if all the individual
components are fully proven, testing them
together can help fine-tune the design
before it goes into production.
The test set-up consisted of over 100 m
of power line and several reduced-height
Wintrack-like tower arrangements,
including an angle mast with its unique
horizontal C-frame suspension. Using this
configuration, DNV KEMA experts ran a
full range of short-circuit and dielectric
withstand tests, including corona, radio
interference voltage and audible noise
tests.
During one of the dielectric tests, hot spots
appeared on the tips of the insulators of
the jumper loop. “At this stage, the issue
was quickly and easily remedied by simply
adding an extra corona ring,” explains
Peter Kolmeijer, who manages the TenneT
account for DNV KEMA. “But imagine
if you had to replace all the corona
rings once you had tens or hundreds of
kilometres of transmission line installed
in the field. That’s a far more complex
operation.”
The ultimate test
Above all, system testing is the key to
proving that a new design meets – or
even exceeds – the reliability and safety
of traditional towers. This is particularly
important as many new designs feature
advanced materials such as polymer
composites. These offer greater design
freedom, but they also generate completely
different behaviour than traditional steel,
glass and porcelain.
“Modelling allows you to see how
innovative designs stand up in theory,
but ultimately the proof of the pudding
is in the eating,” says Andre Lathouwers,
Head of DNV KEMA’s High-Voltage Lab
in Arnhem. “Testing is the only way to
see what will actually happen under the
extreme stresses of major electrical or
mechanical faults.”
Testing can also help TSOs understand
how designs will behave under different
weather conditions. As transmission lines
move into new geographies and climates,
that’s invaluable knowledge. Even within
a small country like the Netherlands, the
wind and icing conditions vary between
the western coastal strip and the northern
provinces.
In short, system testing transmission
towers offers multiple benefits. And DNV
KEMA has a lot of experience to share.
We have been working with customers on
developing and testing pylons for decades.
Today, that experience is being put into
the service of the very latest innovations,
so TSOs can expand capacity with safe,
aesthetically-pleasing pylons that reduce
space requirements and environmental
impact.
HighLight | August 2013 | 5