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| Construction of the Poulaphouca Dam. Image courtesy O'Dea Photograph Collection, The National Library of Ireland. Photographer James O'Dea |
The
Liffey Reservoir Bill was signed into law and became an act in 1936.
Construction of the dam commenced in 1937 with flooding of the Liffey
Valley beginning in 1940. The hydroelectric power station was finally
commissioned in 1947.
How Does the Dam Work?
The dam simply builds up a pressure head,
similar to that produced by the weir that used to be located north of
the bridge in Kilcullen, water being kept at a high level so it gains potential energy and can release that energy to do useful work as it falls. Work
has a specific meaning in physics and is defined as "when a force moves
a body through a distance". In this case, work is done when water
loses momentum and creates a force as it decelerates on hitting turbine
blades (just like a hammer head hitting a nail). Water is carried from the dam, under the N81, to the power house of the Poulaphouca Hydro Station, located several hundred metres away, via a 400 m long, 4.8 m diameter pressure tunnel and then via two penstocks or intake tunnels to the turbines.
Two 15 MW Kaplan turbines at the generating plant produce electricity
which is stepped up to a high voltage for transmission to a 110 kV
substation near Stratford-on-Slaney.
How Does Kilcullen Get Its Power?
The
Stratford substation, along with a 110 kV station near Walshestown in
Newbridge supply electricity at 38 kV to the substation in Kilcullen.
From this station, power is then distributed at a lower 10 kV to
pole-mounted transformers (or cabinets in newer housing estates) around
the town which finally reduce voltage to 230 V for domestic use. The
idea of an electricity grid is to build redundancy into the system so
power can find its way around "holes" in the grid (analogous to a
fishing net). So if for instance Poulaphouca hydroelectric station
becomes non-functional, the transformer station at Stratford is fed
from elsewhere. Similarly for the Newbridge station. If the line from
Stratford to Kilcullen breaks, or Stratford substation goes out of
service, power is still fed to Kilcullen from Newbridge. Eirgrid, who
control the transmission network for lines of 110 kV and over, can
switch and sync generating stations into and out of the grid as demand
rises and falls.
This is a map of the high voltage transmission network (high voltage being anything greater than 20 kV)
Image courtesy O'Dea Photograph Collection, The National Library of Ireland. Photographer James O'Dea