pwr_june-2024 - 29

GRID MANAGEMENT
Global Problem
As the world pushes for more and more
renewables, the issues of grid stability
and system strength are becoming more
apparent. As a country's percentage of
renewables rises, these problems become
sharply evident. Here are a couple
of extreme examples from South America
and Australia, though the same issues
arise in North America and Europe.
Chile plans to close 28 coal plants
and add 15 GW of renewable energy
by 2025, according to BNamericas. And
that is just the beginning. From 13% today,
the country is fast tracking renewable
energy to supply 70% of its total
energy by 2030. This headlong charge is
running into problems. Chile's Coordinador
Eléctrico Nacional (CEN) issued an
international tender for complementary
voltage control services via the installation
of synchronous capacitors or the
conversion of power plants into synchronous
condensers.
As CEN said, " According to the studies
that have been carried out, the exit of
coal-fired power plants and the greater
penetration of variable renewable energies
can reduce the short-circuit power
of the system, making it more fragile,
especially in the north of the country
where there is a greater presence of this
type of generation. There, in the event of
a failure in the system in a decarbonization
scenario, some solar or wind farms
may be disconnected due to the lower
short-circuit power, which is insufficient
to avoid this risk. In this way, it is concluded
that the installation of synchronous
capacitors, which are equipment
capable of controlling the voltage in the
system, is essential to maintain safe and
economical operation. "
Meanwhile, in Australia, 32% of the
total
country's
electricity generation
came from renewable energy sources in
2022. By 2027, the International Energy
Agency forecasts Australia's renewable
energy capacity will expand by 85% and
reach 40 GW. Simultaneous efforts to
phase out local diesel generators and
coal plants as part of grid modernization
initiatives are running into a variety of
grid challenges.
The Australian Renewable
Energy
Agency (ARENA) published a report highlighting
requirements for system strength
and inertia services to manage power
system security. It said: " Retirement of
fossil-fuel generation, particularly large
coal-fired power stations, is projected to
reduce both system strength and inertia.
The international energy transition and
June 2024 | POWER
3. 765-kV shunt reactors. Courtesy: GE Vernova
adoption
of more inverter-based renewable
generation is driving international
demand for large synchronous condensers
(SCs). One possible solution is to
convert existing fossil-fueled generators,
which are synchronous machines, into
SCs. At face value, this should provide
a cost-effective way of providing the required
security services. "
Grid Solutions
As mentioned previously, there are a
series of traditional and advanced ways
of dealing with grid stability and reactive
power issues. Capacitor banks,
SVCs, and STATCOMs have been used
for these functions for decades, though
the technology continues to evolve. Capacitor
banks (or shunt capacitors) are
low cost and widely used. They have a
relatively large footprint and other limitations:
they supply reactive power but
can't absorb it and struggle when faced
with major load or voltage drops. Meanwhile,
GE Vernova's Grid Solutions business
is supplying Power Grid Corp. of
India (PGCIL) with a series of 765-kV
shunt reactors (Figure 3) for its Rajasthan
and Karnataka regions to help maintain
voltage levels and improve grid stability.
" This equipment plays a crucial role
in enhancing grid stability and efficiency,
especially in the context of integrating
large-scale renewable energy
projects, " said Eric Chaussin, Power
Transmission Business Leader of Grid
Solutions, GE Vernova.
SVCs can be regarded as switches
composed of shunt capacitors and other
electrical equipment that are designed
to provide a high level of voltage control
and lower reactive current demand
on the transmission system. While they
can both absorb and supply reactive
power, they sometimes struggle due
to sudden changes in the grid. But the
technology is growing in sophistication.
The likes of Hitachi Energy and GE Vernova
have developed SVCs that can be
customized to grid condition and control
external shunt banks.
STATCOMs take things to another
level by leveraging power electronics.
www.powermag.com
They cost more than SVCs but deliver
response times of a few microseconds.
American Superconductor's Dynamic
VAR (D-VAR) system can scale from 2
MVAR and up, and has overload capabilities
of three times their rated capacity
for up to three seconds. Hybrids of
SVCs and STATCOMs are also available.
Hitachi Energy's SVC Light Enhanced
combines power quality and grid stabilization
technologies as well as reactive
power support. It incorporates supercapacitors,
which store hundreds of
megawatt-seconds of energy and automatically
release it within milliseconds
when disturbances occur.
Synchronous Condensers
Synchronous condensers are large pieces
of spinning machinery composed of
a generator. They are often paired with
a flywheel to provide rotating
inertia
without generating any power. These
machines spin at grid frequency and contribute
to system stability by dampening
frequency fluctuations and providing
voltage stability through reactive power.
" Synchronous condenser is the name
given to a synchronous machine that is
connected into an electrical network to
help in maintaining the system voltage, "
said Dr. James F. Manwell, a professor
and director of the Renewable Energy
Research Laboratory at the University of
Massachusetts. " The synchronous machine
is essentially a motor to which no
load is connected. "
There are several approaches to synchronous
condensing from the likes of
GE Vernova, Siemens Energy, and Hitachi
Energy. GE Vernova offers a synchronous
condenser and flywheel combo that is
air cooled and rated up to 300 MVAR to
be used for reactive power compensation,
voltage support, and system inertia.
Siemens
Energy's
horizontal
synchronous
generator connects to the
high-voltage transmission network via
a step-up transformer. It is started and
stopped with a frequency-controlled
electric motor (pony motor) or a starting
frequency converter. When the
generator reaches synchronous speed,
it provides reactive power to the transmission
network, as well as inertia and
active power injection or absorption during
sudden load unbalance events.
Quinbrook Infrastructure Partners is
installing four synchronous condensers
in Scotland as part of the UK National
Grid's Stability Pathfinder Program. The
sites chosen near Gretna, Neilston,
Rothienorman, and Thurso are largely in
29
http://www.powermag.com
pwr_june-2024

Table of Contents for the Digital Edition of pwr_june-2024
