In developing countries, the demand for
electrical energy continues to rise, while
in developed countries, consumers seek higher
standards of system reliability and low-cost
energy. For instance, the European system,
which is regarded as one of the most powerful
systems in the world, now supplies more
than 400 million consumers who depend on
a reliable supply of electrical energy.
This article presents five projects in
which utilities in Northern Ireland, Mexico,
China, Australia and the Baltic states have
used or plan to use technology to address
transmission system interconnection needs.
Moyle Interconnector Links Northern Ireland
to European Network
In 1990, Northern Ireland Electricity (NIE),
the electricity transmission and distribution
company for Northern Ireland, signed agreements
with Scottish Power for the construction
of a high-voltage direct-current (HVDC)
interconnector between the companies' transmission
systems. It took nine years of planning
applications, public inquiries and environmental
statement procedures before NIE obtained
the statutory consents for the transmission
line, undersea crossing and converter stations.
Moyle Interconnector plc (Moyle), a member
of the Viridian Group, was established to
construct the link.
A New Source of Electricity Energy
Figures 2 and 3 show the geographical location
and schematic diagram of the Moyle Interconnector,
which will transmit power between the transmissions
in Northern Ireland and Scotland. The link
provides Northern Ireland with an important
new source of electricity supply, which
will promote competition in the emerging
markets in Northern Ireland and the Republic
of Ireland, as well as enhance security
and quality of supply. Turnkey contracts
for the Moyle Interconnector, which was
designed with specified power rating of
2 × 250 MW in either direction and
a December 2001 completion date, were awarded
to the following:
-
Nexans Norge AS for the supply,
installation and protection of the submarine
and underground cables. This included
the 8.5 km (5.3 miles) 250-kV dc cable
from each converter station to the coast
and the two 55-km (34-mile) 250-kV dc
submarine cable.
-
Siemens for the design, installation
and commission of the two HVDC converter
stations located at Ballycronan More
Island Magee, County Antrim in Northern
Ireland (Fig. 1), and at Auchencrosh,
Ayrshire, Scotland.
-
Balfour Kilpatrick constructed
the 275-kV single-circuit transmission
line [64 km (40 miles)] from the existing
Coylton Substation to the converter
station at Auchencrosh for Scottish
Power.
The estimated cost for the 500-MW link
— which was completed on schedule
and is now in service — was 234 million
euros (US$214 million), a total that included
a sponsored contribution of 83 million euros
(US$76.1 million) from the European Regional
Development Fund.
Technical Features of the Moyle Interconnector
The 250-kV 1000 mm2
(1.55 inches2) copper-conductored
dc mass-impregnated paper insulated dc cable,
rated at 250 MW, includes an integrated
return conductor (IRC). This innovative
design by Nexans has a metallic coaxial
layer integrated in the HVDC cable to form
the return path for the current and also
to form part of the torsion-balanced armoring.
A fiber-optic cable for control and communication
between the converter stations is integrated
into the polythene sheath of the IRC.
The submarine cables supplied in a continuous
length were laid 1 km (0.62 miles) apart
and then buried into the seabed by Nexan's
Capjet water-jetting system or protected
by concrete mattresses or rock dumping to
a nominal depth of 1 m (3.3 ft).
The converter stations are comprised of
two valve halls, one for each monopole constructed
on either side of the control building (Fig.
1). Adjacent to each valve hall is a dc
switchyard that includes measuring equipment,
smoothing reactor and cable terminations.
The two converter stations are the first
in the world to be completely equipped with
direct-light-triggered thyristors with integrated
overvoltage protection. Triggering is initiated
by light pulses generated at ground potential
and applied directly into the thyristor
gate through a set of fiber-optic cables.
The light pulses generated by laser diodes
have a life expectancy of more than 40 years.
Benefits of the Moyle Interconnector
The Moyle Interconnector is designed to
have low losses and low maintenance. In
addition, the Moyle Interconnector provides
enhanced security and improves supply quality.
The converter stations are designed for
a biannual scheduled maintenance with guaranteed
losses of less than 1.35% and guaranteed
energy availability of more than 99.6%.
Comision Federal de Electricidad Completes
Interconnection in Record Time
ALSTOM's Transmission & Distribution
Mexico Transmission Projects Business unit
completed the first phase of a US$45 million
turnkey project in the Mexican state of
Veracruz, linking the new Tuxpan II power
station to the country's national grid.
The Comision Federal de Electricidad (CFE)
in the Central American country invited
tenders for the erection of two 400-kV double-circuit
transmission lines with a total route length
of 111 km (69 miles), and two 400-kV switching
stations sited at either end of the 400-kV
lines. The most demanding feature of the
tender specification was that the contractors
had to commission the first phase of the
new transmission line and substation project
within 12 months. CFE awarded the contract
to ALSTOM's Transmission & Distribution
Mexico Transmission Projects business unit
on Nov. 1, 2000.
Transmission Line and Substation Specifications
The 400-kV, double-circuit transmission
lines will each include three ACSR conductors
(1113 kcmil) per phase, one OPGW and a guard
wire. The six-bay Tres Estrellas 400-kV
Switching Station also will be equipped
with six reactors (plus a spare unit). Figure
5 shows a schematic diagram of this two-phase
project.
Project Construction Phase One
The first new 400-kV substation, Tres Estrellas,
includes six 400-kV switch-bays and the
second existing 400-kV substation —
Poza Rica II — had to be extended
to install two additional 400-kV switch-bays.
This phase also included the erection of
a 55-km (34.2 miles) 400-kV double-circuit
transmission line undertaken by ALSTOM along
with Spanish contractors, Abengoa and Elecnor.
A contract of this nature normally would
take 15 to 18 months to complete. To meet
the demanding time schedule, ALSTOM sourced
products from its global manufacturing facilities.
For this project, the circuit breakers were
manufactured in France, isolating switches
in Italy and Mexico and the current and
voltage transformers in Mexico.
The site construction teams had to contend
with a month-long rainy season. However,
by ensuring that materials and personnel
were in the right place at the right time,
Phase One was commissioned in early September
2001, two months ahead of schedule.
Phase Two
The second phase of the project is currently
under construction with the erection of
an additional section of the 400-kV transmission
line, the 56-km (35-mile) section that will
link Tres Estellas 400-kV Substation to
the town of Poza Rica. This phase of the
contract has a completion date of April
2002.
Project Funding
The project was financed under the Pideregas
scheme, under which CFE, a wholly owned
Mexican state subsidiary, offers large tenders
for infrastructure work in the country,
which totaled US$800 million in 2000.
China's Electricity Travels East on Major
HVDC Link
The Tian-Guang HVDC power transmission
system delivers 1800 MW over 960 km (600
miles) from converter stations (Bipolar
2 × 900 MW) at Tianshengqiao (TSQ)
in Guangxi Province to the Guangzhou (GZ)
Converter Station in Guangdong Province.
The TSQ Converter Station is directly connected
to the substation of the hydropower stations,
and the GZ Converter Station to the existing
220-kV system and — via two autotransformers
— to the 500-kV system.
The HVDC transmission system forms an important
power link in the Southern China electric-power
network transferring bulk power to the Guangzhou
area operating parallel to the existing
500-kV ac transmission lines. A reliable
HVDC link among the ac-interconnected systems
increases the efficiency of the power-transmission
capacity between and within the two transmission
networks.
Tian-Guang HVDC scheme allows bi-directional
control of power interchange and improves
reliability and dynamic performance of both
ac-connected systems. Additionally, the
converter stations also can provide the
advantage to control the reactive power
exchange with the connected ac grids and
thus the ac system voltage. This HVDC link
will play a definitive role in the new national
power transmission strategy, West Electricity
Goes East.
Power Transmission Capacity
The 960-km (597-mile) long-distance HVDC
transmission system operates on a ±500-kV
bipolar scheme rated for a continuous power
of 1800 MW at the dc terminal of the rectifier
converter station. Figure 7 shows the schematic
single-line diagram of the Tian-Guang HVDC
project.
The converter stations (constructed and
equipped by Siemens Power Transmission &
Distribution) can transmit full-rated power
up to a maximum dry bulb temperature of
40°C (104°F) without a redundant
cooling system in service. With redundant
cooling, the same converter stations can
achieve a continuous overload of 110% of
rated load. Additionally, the dc transmission
permits a three-second overload of 150%
power (this overload rating being available
for use in all ambient conditions and in
all continuous overload previous operating
conditions). Such short-time overload capabilities
are important for some contingencies, such
as power modulation after ac system faults.
The HVDC interconnection scheme is capable
of continuous operation at a reduced dc
voltage of 400 kV (80%) and 350 kV (70%)
from minimum current up to the rated dc
current of 1800 A with all redundant cooling
equipment in service. To optimize the filter
and converter transformer design, valves
to operate at high firing angles combined
with an extended range of the tap changer.
Performance Requirements
The energy availability and combined operational
availability for the two converter stations
is guaranteed to be more than 99.5%, or
alternatively, a forced energy unavailability
of less than 0.5%. The forced outage rate
should be less than six outages per pole
per year.
The utility operators specified performance
requirements for audible noise, electrical
noise, and radio and noise interference
that were incorporated in the scheme at
the design stage. Noise filter equipment
provided for the ac switchyard and the dc
line damps the interference between the
thyristor valves and the PLC equipment.
Low loss design was of central importance
for technical and economical optimizations.
This resulted in converter station designs
with total losses (excluding dc lines) of
approximately 12 to 13 MW per station at
1800 MW of transmission power. At rated
transmission capacity, the converter transformers
(about 50% of the total losses) and the
converter valves (about 35% of the total
losses) cause the main losses.
Reactive Power Requirements
The hydropower generators partly cover
the reactive power demand of the TSQ converters
(up to 330 MVAr) 0.9 × 80 MVAr Q-elements
balance the reactive flow to the TSQ AC
system at rated power. These Q-elements
in three filter banks with individual switching
capability connect to the station bus bar.
The reactive power supply equipment is capable
of regulating the reactive power interchange
with the ac system from -80 MVAr (supply)
up to +80 MVAr (absorption) in whole power
range and with one sub-bank out of service.
The GZ Converter Station is connected to
the 220-kV substation with a design of 100%
redundancy of reactive power requirement
that can be met with one sub-bank out of
service. Installing 11 sub-banks, rated
at 100 MVAr will meet this requirement.
The total reactive power supply divided
into three banks is capable of regulating
the reactive power interchange with the
ac system from -100 MVAr (supply) up to
+100 MVAr (absorption) in whole power range.
Future Transmission System Development
in China
The Tian-Guang HVDC Interconnector was
commissioned in June 2001. With the growing
demand for power in this region, the State
Power Corporation of China in Guangzhou
awarded contracts for the construction of
a 3000 MW, ±500-kV HVDC transmission
line (940 km [585 miles] long), due for
commissioning in October 2004, from the
hydro and coal-fired power plants in the
west of China to the rapidly developing
areas in the southeast, around Guangzhou
and Shenzen.
TransGrid (Australia) Provides New Supply
to Sydney's CBD
Electricity demand in the Central Business
District (CBD) of Sydney and the surrounding
suburbs has been growing at an average of
4% per year over the last four summers.
Predictions state that electricity demand
will continue to grow at this strong rate
because of new commercial and residential
developments. Studies indicate utilities
will no longer be able to meet existing
reliability standards for Sydney's CBD and
inner suburbs from the summer of 2003 onward.
Existing Supply System
The electricity supply to Sydney's CBD
and surrounding suburbs is sourced from
TransGrid's main grid of 330/132-kV substations
where 132-kV capacity is available to Energy
Australia (EA). EA owns and operates the
132-kV network that interconnects these
substations and supplies the major sub-transmission
substations in the metropolitan area. This
arrangement permits the sharing of capacity
between the source substations.
TransGrid and EA decided the most cost-effective
and achievable solution was to install and
commission a 330-kV underground cable between
the Sydney South 330-kV Substation and a
new CBD 330-kV Substation with associated
132-kV works prior to summer 2003 (Fig.
10).
The Sydney CBD project consists of the
following major components:
-
A new 330/132-kV substation at Haymarket
adjacent to the CBD
-
A single-circuit 330-kV cable with
a route length of 28 km (17 miles) from
Sydney South Substation to Haymarket
Substation
-
Extensive 132-kV developments including
a new inner-city substation.
Haymarket Substation
Haymarket Substation will be a new 330-kV
substation adjacent to Sydney's CBD. It
will be predominantly underground with provision
for a “high rise” commercial
development on site. The site location is
adjacent to public areas that link commercial,
tourism and university districts.
Fire and other electrical failures were
major factors in the development of this
substation concept. The transformers were
the critical components of the design. Because
of the possibility of catastrophic failures
of conventional transformers on the Haymarket
site, gas-insulated transformers were selected.
Toshiba will supply three 400 MVA 330/132-kV
gas-insulated transformers and one 100-MVA
gas-insulated reactor with cooling systems.
These will be the highest-rated gas-insulated
transformers in the world to date.
Siemens won the contract for the substation
building and the balance of the substation
plant, which includes five bays of 330-kV
gas-insulated switchgear and 23 bays of
132-kV gas-insulated switchgear. Again,
innovation will be a major feature of the
design. The substation plant and environment
will be highly monitored and will include
a gas management strategy to ensure there
is no significant loss of SF6 to the substation
environs.
330-kV Cable Circuit
The 28-km (17-mile) single circuit that
will supply Haymarket Substation will be
one of the longest high-voltage ac cable
installations. The first 24 km (15 miles)
of the cable will be direct buried in public
streets with some directional drilling.
The last 4 km (2 miles) of the route to
the Haymarket Substation will be in a deep
tunnel.
A pre-qualification process allowed the
offering of any technology to meet the needs
of the project, of which 29 offers were
received from 13 applicants. Sumitomo offered
the best cable, a paper-polypropylene insulated
cable. The high levels of cable monitoring,
which include a dynamic rating system based
on integrated optical-sensing fiber, is
an important feature of the design. The
low magnetic field design for sections of
the route in residential streets is another
key feature.
In parallel with these works, TransGrid
and EA are pursuing investigations about
using DSM or embedded generation to defer
future network augmentation.
Baltic States Upgrade Interconnected Power
Systems
Historically, the Soviet Union's northwestern
regional planning strategy lead to concentration
of the thermal power plants in Estonia while
more than 70% of the installed capacity
in Latvia was hydropower. The installed
capacity at the Ignalina Nuclear Power Plant
in Lithuania produces the majority of the
state's power requirements. The structure
of the generation capacity within the Baltic
Interconnected Power System (IPS) is very
diverse, and to optimize the power balancing
on the Baltic IPS, each state's power system
requires support and cooperation from the
neighboring states to supply base and peak
demands. Figure 13 details the annual electrical-energy
interchange among the Baltic and neighboring
power systems.
The three Baltic states-Estonia, Latvia
and Lithuania — are located on the
eastern coast of the Baltic Sea and have
a combined population of about 8 million.
The Baltic IPS was established in 1992 following
independence from the Soviet Union. Baltic
IPS operates in parallel with Russia's Unified
Power System (UPS) and the Belarus IPS via
an “electrical ring” of 330-
to 750-kV transmission lines, which were
constructed in the northwestern part of
the former Soviet Union in the 1960s and
1970s. The power plants and power systems
in each Baltic state operate independently.
However, the operation is coordinated by
the Dispatch Center of the Baltic IPS (DC
Baltija), which is located in Riga, Latvia.
To improve operational control, GE Harris
SCADA systems have been installed in the
Lithuanian and Estonian National Control
Centers. Work is currently in progress to
install similar equipment in DC Baltija
and the Latvian National Control Center.
The Baltic IPS
The Baltic IPS has a current total installed
capacity of 11,490 MW and includes a wide
spectrum of generation types: nuclear plant
(Ignalina NPP), combined heat and power,
thermal, hydro and pumped storage power
plants. The annual peak demand in 2000 on
the Baltic IPS was 4551 MW (Lithuania 1910
MW, Estonia 1469 MW and Latvia 1172 MW).
The transmission network of the Baltic IPS
consists of 330-kV transmission lines with
a total length of 4137 km (2571 miles) based
upon January 2001 data.
DC Baltija
Following independence from the Soviet
Union, each power system of the Baltic states
operates independently, though DC Baltija
coordinates the operations. DC Baltija in
Riga was founded on the basis of the former
North-West Dispatch Center, a facility installed
on Russia's UPS. DC Baltija's principle
role and main tasks include:
-
The reliable operation of the Baltic
IPS 330-kV network and tie lines with
Russia UPS and Belarus IPS in close
cooperation with dispatch centers of
respective power systems
-
Efficient power and energy balance
planning and realization for the Baltic
IPS.
The regional operational control takes
into account the generation structure of
each country to deal efficiently with demand
or generation deviations from planned values.
To improve operation control, GE Harris
SCADA systems were installed in Lithuanian
and Estonian National Control Centers; in
2002, the SCADA systems will be fully installed
in DC Baltija and Latvian National Control
Center.
Currently, the Ignalina NPP generates energy
from two 1300-MW RBMK-type reactors manufactured
in the Soviet Union. The Lithuanian government
has decided to shut down the first reactor
in 2005 and the second reactor in 2010.
This decision will lead to serious changes
in the power balance in Lithuania and in
the whole Baltic IPS as Ignalina NPP produced
35% of the total Baltic IPS electrical energy
production during 2000, (8419 million kWh).
Figure 14 shows the emergency protection
scheme installed to safeguard the IPS in
the event of the loss of the power in-feed
from Ignalina NPP.
Research Activities of DC Baltija
Since DC Baltija was established, engineers,
scientists and specialists from power companies
and universities of the Baltic states have
performed field tests to verify appropriate
relay protection and to establish the power/frequency
characteristics and regulating capability
of Baltic IPS.
A series of field tests raised concerns
about the performance of the speed governors
providing unstable operation as a result
of out-of-date fuel and steam supply systems
of the power plants. These factors made
it necessary to carry out wide-scale field
tests with isolated operation of the whole
Baltic IPS. This is an urgent issue. Presently,
there is serious discussion about implementation
of the Automatic Generation Control in Baltic
IPS, and therefore, it is necessary to determine
all requirements and measures for the primary
control. Though there have been several
attempts to complete the field tests, they
continue to be deferred because of disagreements
among Baltic IPS, Russia UPS and Belarus
IPS on the basis of the electrical ring
security and the provision of commercial
contract fulfillment among these power companies.
In addition to the research activities,
successful black start tests on the Ignalina
NPP's two main circulation pumps (5.6 MW
each) were conducted using two generators
at the Pljavinas HPP supplying energy via
three 330-kV transmission lines.
Future Development of Baltic IPS
The effect of the decommissioning of the
Ignalina NPP on the Baltic states is the
subject of the report “Baltic Regional
Energy Development Program” prepared
by Latvian, Estonian and Lithuanian power
systems in cooperation with Electrotek Concepts
Inc. USA.
This regional development analysis confirmed
that to re-establish the energy balance
of the Baltic states after the decommissioning
of the Ignalina NPP would require the construction
of the new power plants having a total generation
capability of 700 MW. The location of these
power plants will have to take into account
economical and political considerations
in addition to optimizing their location
to ensure siting in close proximity to the
existing 330-kV transmission network of
the Baltic IPS. Furthermore, an additional
factor is the possible future power system
connection development with UCTE and NORDEL
systems.
In 1998, the Baltic Ring project provided
development scenarios of new electrical
connections, such as a 400-kV ac link between
Lithuania and Poland, and a 400-kV dc link
connecting Estonia with Finland. Currently,
the respective countries are studying the
economic effectiveness of these links, taking
into consideration the results of the project
“Synchronous Interconnection of TESIS
and UPS Networks,” prepared by experts
of European Union countries within the framework
of EC TACIS.
The accumulated experience of Baltic IPS'
joint operation with neighboring countries
and well-developed relations with power
companies from the United States and Eastern,
Central and Western European countries will
be used by the governments of the Baltic
states to create a common Baltic electricity
market.