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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 powerhouse of the Poulaphouca Hydro Station, located several hundred metres away, via a 400 m long, 4.8 m diameter pressure tunnel and then through 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 supplies 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. 10 kV lines can be radial but sometimes travel out in an open ring from a substation. So if there's a fault or break in a line, one part of the line can be isolated in order that other houses on the ring can still be supplied with electricity. (The open ring is closed.) At a transmission level (110 kV and higher) the
idea of an electricity grid is to build redundancy into the system so that 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, Kilcullen is connected to the Newbridge 110 kV station via the Athgarvan 38 kV Substation. Normally, this connection is open to reduce fault currents propagating through the grid. However, if Stratford can't supply, it's switched out of the system and Newbridge is connected to the Kilcullen station. 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. ESB Networks meanwhile are responsible for the distribution network of 38 kV and lower.
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
