“As the country
continues to
decarbonise,
Cruachan Power
Station’s exibility
has never been more
113MW. When
reversed, they
generate power
at 120MW (units
1&2) and 100MW (units
3&4). In other words, the
power station is an overall net
consumer of electricity, with an overall
round-trip mechanical e ciency of 75%.
Turbines were upgraded along with plant
instrumentation in 2005.
Cruachan’s overall utilisation factor,
de ned as the station’s total activity,
averages out to about 40-50% of the
day, according to Colin MacFarlane,
EC&I engineer at Cruachan Power
Station, although he adds that
activity varies depending on market
conditions, contracts and time of year.
In generation mode, water ow
from the dam is used to run the
machine up to speed. It can reach
full generating load in less than two
minutes. In pumping mode, the
station uses a pony motor to run
the turbine up to speed within six
minutes. The station can switch
between generating and pumping
modes in 10-15 minutes.
MacFarlane explains that the
system controls the di erent items
of plant required to spin in either the
generation or pumping direction.
That includes switching phases on
high-voltage 16kV connections to the
generator via a forward/reverse isolator
arrangement.
In addition, they can be switched to
inertial mode to absorb grid instability.
This function did not require much
upgrading, apparently. MacFarlane
says: “Operation in stability
mode involves operating
in either spin generate
or spin pump mode,
providing reactive
power (voltage
control), inertia and
fault ride-through
capability without
exporting load.
This is a standard
operating mode, so the
turbine control system
did not require signi cant
modi cation to provide this.
important”
However, some minor software changes
to optimise governor and AVR automatic
voltage regulator settings, and a suite
of proving tests, were required to ensure
contract speci cations were met.”
MRO
CONTROL
The upgrade contractor has a long
history with Cruachan. ITI is the new
name for Servelec Controls, the systems
integration company that installed the
current PLC control systems in 1987,
which replaced the hardwired relay
controls originally installed in the 1960s.
It also built the control system which
allows the Lanark and Galloway Hydro
Schemes to be remotely managed when
needed from Cruachan’s underground
cavern, from a single interface. Apart
from the turbines, other systems
control cooling water pumping systems
and cavern ood protection, ventilation
and re systems.
Bryn Thomas, sales director for
power and infrastructure at ITI, says:
“We’ve been working at Cruachan
Power Station for over 30 years now,
and in that time have developed a deep
understanding of its assets, its systems
and its operational requirements.”
The turbine control upgrade is part
of a larger station-wide programme
initiated because the current PLC
systems are no longer fully supported
by the OEM. Phase 1 of this four-to-
ve-year plan was completed in 2020
with the successful upgrade of the
station and alarm PLCs. Phase 2 involves
Winter 2021 www.operationsengineer.org.uk 47
/www.operationsengineer.org.uk