Network Development Statement 2010/11 to 2019/20 - Gaslink

7. Networks Asset Management &
Development continued
7.2 AGIs & DRIs
The network consists of a number of Above Ground Installation
(AGI) assets, on the transmission system where the pressure
of the gas in the system is controlled and delivered to large
consumers such as power stations or reduced to be put
through the distribution system for delivery to domestic end
users. The complexity of these systems varies. In the intricate
interconnector stations, gas passes though filtering systems
to remove any particulate matter and capture any liquids prior
to metering. Once metered the gas is heated to overcome the
Joules-Thompson effect of pressure reduction this is carried out
in stages and via multiple streams.
A further refinement in the Interconnector sites is the ability
to control both gas flow and pressure so as to allow load
balancing across the network; this is carried out via an on-site
station control system. The on-site control system accepts
set point commands from the national grid control centre.
This is particularly important to facilitate the gas market in
accommodating Shippers’ instructions.
Fig. 7.3: Gormonstown IC2 Landfall AGI
On the distribution systems further pressure reduction occurs
to supply high density locations such as those found within
city and town centres. In these District Regulating Installations
(DRI’s) gas pressure is further reduced via regulating stream(s) to
domestic inlet pressures.
AGI’s supplying a regional town or city gate also consist of
filtering, heating and gas pressure reduction via multiple
streams to a fixed value for imputing in to the transmission and
distribution systems.
The redundancy of the pressure reducing streams is a critical
factor in all AGI’s as it allows for the continuous supply of gas
while servicing and inspections are carried out, or in the event
of a fault developing on a stream. These individual streams also
contain many important safety elements to ensure that pressure
is maintained and delivered safely and within pre-prescribed
limits, the SCADA system continually monitors these limits to
ensure the correct pressures are maintained.
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