Global electric "power highways" could
become a force for peace
day there will be a global electricity network that links all countries
of the world. It will take decades to complete but the first steps have
already been taken and the principle is deemed workable.
A key benefit will be a reduction in the number of power stations that
are needed globally. During night time, for example, any given
country’s generators can be kept running efficiently by supplying the
extra needs of other countries during their working hours further round
the globe. It will also help balance the different types of power
generation indigenous to different countries. Nuclear power stations
can take several days to switch on or off, so they are best at
providing continuous base-load electricity.
But a hydropower generator can be started in minutes, making it ideal for meeting surges.
example, Switzerland imports base-load electricity from French nuclear
power plants, but exports power from its Alpine dams in short bursts to
meet France’s peak needs. Any one country does not have to cater for
all contingencies because it can use resources from elsewhere.
global network will enable easier access to major sources of energy
that are uneconomical to reach just now. The Himalayan kingdom of
Nepal, for example, is a remote region with a large hydroelectric
potential. The capacity of the national system is about 300MW,
according to its Water and Energy Commission, but it could generate
more than 40GW of hydroelectricity in its steep valleys.
grid will increased security of supply, reduce the need for new power
plants and cut back on the primary electricity reserve requirements
within each country. This includes the use of spinning reserve where a
station is semi-powered so it can take over very quickly if another
station fails or if demand rises sharply.
Union for the Co-ordination of Transmission of Electricity (UCTE) is
the association of transmission system operators in continental Europe.
It provides a reliable market base by creating efficient and secure
electric power highways. It has 50 years of experience in the
synchronous operation of interconnected power systems and its networks
supply some 500million people in 22 countries from Portugal to Romania
and from The Netherlands to Greece with about 2300TWh of electricity.
Part of its network is the Baltic Ring, recently developed by the
Baltic Ring Electricity Co-operation Committee (BALTREL) which has
created a common electricity market in Latvia, Lithuania, and Estonia.
It expects this will strengthen economic development in the region,
increase reliability of supply and help the environment.
UCTE is investigating the feasibility of a synchronous interconnection
between the Baltic States, Russia and many countries of eastern Europe
as far as Mongolia. This would create an electricity system with an
installed generation capacity of some 800GW, spanning 13 time zones and
serving about 800million people.
Today, Europe is linked to North
Africa by ac cable between Spain and Morocco, Algeria and Tunisia –
known as the Maghreb, or western, countries. Further interconnection
will bring in Tunisia and Libya, already forming a synchronous block
with Egypt, Jordan and Syria – known as the Mashreq, or eastern,
This is the basis of the Mediterranean Ring, which could eventually include Turkey.
project will increase energy security in the entire region, and enable
more efficient power flows at lower costs. It will also reduce the need
for more power plants to meet rapidly increasing demand for electricity
in the southern and eastern Mediterranean regions. From Turkey the ring
would then link back into the European grid via Greece or through the
newly interconnected Eastern European country grids.
the economic and technical hurdles to be overcome, there are two quite
different outlooks to reconcile. European networks are highly meshed,
consisting of high voltage lines, with high consumption and high
density of consumers, and predictable load patterns. But grids in the
Southern Mediterranean region are typically lower voltage grids,
non-redundant, serving fewer loads, concentrated in highly urbanised
areas, and strung out through the countryside at lower voltages.
Power Transmission and Distribution Group is one company keeping an eye
on these developments. As one of the two world-leading suppliers in the
HVDC market, it expects to contribute to discussions regarding
technical realisation of the project.
The group is already very
active in HVDC around the world. Currently, it is working with local
companies to construct a link in southeast China. The US$121million
contract was awarded by China Southern Power Grid Company in Guangzhou
and the project is expected to be connected in 2007. The new HVDC
transmission line will eventually provide electricity from the hydro
and coal fired power plants in the west of the country to the
industrial districts in Guangdong.
India’s largest power
transmission project, the East-South HVDC Interconnector II, was
completed by Siemens PTD Group ahead of schedule. It links the states
Karnataka and Orissa over a distance of 1450km – the second longest
HVDC link in the world – with a bulk power of up to 2000MW.
says HVDC is the only technically and economically feasible solution
for interconnection of asynchronous grids and for power transmission
over large distances between generation and load centres.
although most grids are ac, more dc lines are being installed and the
backbone of a global grid will probably be HVDC. Such links are less
costly than ac versions because they need only two main conductors
while an ac line needs three. And the losses are lower. But HVDC
converter stations cost more than the ac terminal stations so HVDC may
not be economical over short distances, unless earth return can be used
to further reduce transmission line costs.
The major advantage of
HVDC is its controllability. There is no need to synchronise power
stations and grids with each other and there are no problems with phase
change over distance, so stability is no problem.
The basic power
control is achieved trough a system where one of the converters
controls its dc voltage and the other converter controls the current
through the dc circuit. The control system acts through firing angle
adjustments of the thyristor valves and through tap changer adjustments
on the converter transformers.
A back-to-back HVDC station can be
used to link two ac grids. This system isolates each grid from fault
conditions and disturbances on the other and eliminates the need for
synchronisation while allowing two-way power transmission.
latest from ABB is its HVDC2000 system, based on thyristor-switching at
converter stations. Its key feature is the use of capacitor commutated
converters (CCC) in conjunction with its development of continuously
tuned ac filters (ConTune). These filters can be built to generate
small quantities of reactive power but still provide good filtering.
capacitors are connected between the thyristor valve bridge and the
converter transformers. With a CCC there is no need to switch filter
banks or shunt capacitors banks in and out to follow the reactive
consumption when the active power is changed.
The ConTune AC
filter has electromagnetic tuning that adjusts to the inherent
frequency variations and temperature variations of the filter
components. It uses a filter reactor with variable inductance based on
an iron core with a control winding round it.
By feeding a
corrective direct current into the control winding, the total magnetic
flux in the reactor is influenced, so changing the inductance, which
tunes the filter to the correct frequency of the harmonic.
converters produce current harmonics on the ac side and voltage
harmonics on the dc side. For good performance, low impedance tuned
filters often need to be provided for the lowest characteristic
harmonics. Detuning of conventional filters is caused by network
frequency excursions and component variations such as capacitance
changes due to temperature differences.
The outdoor air-insulated
thyristor valve is a new component, made possible by the development of
high power thyristors. It gives increased flexibility in the station
layout; eliminates the need of a valve hall, including its subsystems;
reduces the equipment size; and makes it easier to upgrade existing
stations. Future relocation of an HVDC station will also be simpler
when outdoor HVDC valves are used.
All functions for control, supervision and protection of the stations are implemented in ABB’s MACH2 fully digital software.