The world's longest undersea cable reaches
July 20, 2007 - Asia Pulse
The world's longest undersea cable is
bringing energy generated from renewable sources on
the island of Tasmania to the Australian continent.
If necessary, the link, which was built by Siemens,
will work in the opposite direction as well.
for the interconnector between Australia and Tasmania.The
290-km link carries 600 MW of power.
Eucalyptus trees, green pastures, blackberry
hedges and thistles dominate the hilly countryside of southeastern
Australia. Shy koala bears hide in trees, while curious
kangaroos explore a nearby open-pit lignite mine.
White steam rises from the cooling towers
of the Loy Yang power plant, where lignite is fired to generate
electricity for the Melbourne area some 165 km west of the
plant. Since the spring of 2006, that lignite power has
been supplemented by a green source of energy produced on
the island of Tasmania.
There, the license plates bear the slogan "Your natural
state"—which is not surprising, as Tasmania is rich in forests,
large ferns, marshes and canyons. What's more, Tasmania,
which is around the size of Ireland, covers 90 % of its
energy needs from hydropower, and is now providing some
of that power to neighboring Victoria. The power is carried
by a 290-km undersea interconnector cable 70 m beneath the
Alternating current (a.c.) was not an option
here, as transmission losses would have been too great.
Instead, the "Basslink," as the interconnector is known,
uses high-voltage direct-current transmission, or HVDC (see
Pictures of the Future, Fall 2003,? Power Transmission).
"This is the only way to economically transmit large amounts
of electricity over great distances," says Erwin Teltsch,
an HVDC expert at Siemens Power Transmission and Distribution
(PTD). "HVDC begins to pay off when above-ground lines reach
a length of 600 km; with undersea cable, the threshold is
The cable being used for the Basslink is 15 cm thick.
It resurfaces on Ninety Miles Beach in Victoria. There,
it runs through a duct under the beach, continues for a
few kilometers as an underground cable, and finally emerges
as an above-ground line running 70 km to Loy Yang. There,
the d.c. is converted into a.c. with the help of power converter
valves. "Only then can it be fed into the three-phase power
system," says Dr. Günther Wanninger. "On the other side,
in George Town, Tasmania, a similar station transforms the
a.c. generated there into d.c." Wanninger is an electrical
engineer at PTD and head of the Basslink project, for which
Siemens supplied the rectifier stations and overhead lines.
Consortium partner Prysmian Cables & Systems, a former Pirelli
subsidiary, provided the undersea cables.
makes it possible to send up to 600 MW of power from Tasmania
to Victoria. Transmission works in the opposite direction
as well, however, which means Tasmania is able to tap into
the continental power grid during dry periods when its rivers
do not contain enough water to fill its dams. Another advantage
of HVDC systems is that they require only two cables as
opposed to the three needed for three-phase current transmission.
As a result, an HVDC overhead line also requires less space.
Basslink is not only the world's longest HVDC undersea cable
link; it also has several other impressive features. For
example, semiconductor elements—thyristors—act as power
converters, which are controlled by 10-mW laser flashes
via glass fibers. These thyristors, which have a diameter
of 100 mm, were produced by Infineon, and are made of silicon,
molybdenum and copper. To achieve a d.c. voltage of 400
kV, several dozen thyristors per converter valve are connected
in series and suspended from the ceiling of an 18-m-high
hall to secure them against earthquakes. All of these thyristors
must trigger within 1 µs in order to ensure that none are
overloaded or damaged.
Siemens is the only HVDC supplier
to use such laser-controlled converters. Conventional technology
relies on electrically-triggered thyristors, which require
a pulse with a power of several watts. The pulse is generated
by a complex electronic system located at each thyristor.
"You don't need such a system with the direct light pulse,"
says Teltsch. "As a result, the control electronics for
the thyristor valves requires around 80 % fewer components.
That not only saves on space; it also increases reliability."
And there's another benefit for National Grid Australia,
which operates the system. "The customer also gets to work
with our new Win-TDC control technology," says Wanninger.
"This system displays a high degree of integration, which
means the hardware takes up less space in the converter
station." Whereas the switchgear cabinets used in previous
control systems were 20 m long, today's cabinets have a
length of only around 10 m. All control, regulation and
protective functions are carried out by a Simatic-TDC system
that has already proved itself in rolling mills. What's
more, the Simatic WinCC visualization system simplifies
operation. For example, if the user wishes to change a setting,
this can be done easily using the Windows user interface.
"The standardized software and hardware platform reduces
the number of spare parts needed, but that's not all," says
Wanninger. "It also simplifies troubleshooting."
cables are also being used for a similar Siemens project
on the other side of the world—but one where curious kangaroos
are unlikely to be seen, as the location is in the New York-New
Jersey metropolitan area. The project involves an HVDC link
between Sayreville, New Jersey and Long Island that will
be used for power transmission starting in mid-2007. Siemens
is supplying the rectifier stations, and Prysmian is again
providing the 105-km-long power cable, through which 750
MW of electricity will flow at a direct voltage of 500 kV.
That should certainly be enough power to help Long Island
cope with hot summer months.
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