EirGrid plc is the independent electricity Transmission System Operator (TSO) in Ireland and the Market Operator in the wholesale electricity trading system. EirGrid’s role is to deliver services to generators, suppliers and customers across the high voltage electricity system, and to put in place the grid infrastructure needed to support Ireland’s economy. EirGrid develops, maintains and operates a safe, secure, reliable, economical and efficient transmission system. Electricity is an essential and convenient service provided to two million electricity consumers, including domestic customers, small and medium industry, farms and agribusiness, and large high-technology industrial customers. This illustrates the vital nature of the service EirGrid provides.

1. N A T I O N A L C O N T R O L C E N T R E
www.eirgrid.com
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2. 1500
2000
2500
3000
3500
4000
MEGA-WATTS(MW)
QUARTER-HOUR TIME INTERVALS
4500
00:00 04:00 08:00 12:00 16:00 20:00 00:00
4 Aug 2013
22 Jan 2013
System Load Curves
Forecasting electricity demand during the day or year can
utilise the fact that normally demand follows the pattern
of similar conditions on the same day in previous years.
For instance, winter demand adopts the following pattern
normally: demand reaches its lowest level, or trough, in
the early hours of the morning, before rising sharply as the
population wakens. It then rises again over the lunchtime
period, and finally increases to its winter evening peak,
due to lighting, heating and cooking needs of consumers
returning home. In summertime, demand is far lower and
due to brighter conditions in the evening, the daily peak
is at lunchtime, rather than during the evening.
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3. EirGrid
EirGrid plc is the independent electricity Transmission System
Operator (TSO) in Ireland and the Market Operator in the
wholesale electricity trading system. EirGrid’s role is to deliver
services to generators, suppliers and customers across the
high voltage electricity system, and to put in place the grid
infrastructure needed to support Ireland’s economy. EirGrid
develops, maintains and operates a safe, secure, reliable,
economical and efficient transmission system.
Electricity is an essential and convenient service
provided to two million electricity consumers, including
domestic customers, small and medium industry, farms and
agribusiness, and large high-technology industrial customers.
This illustrates the vital nature of the service EirGrid provides.
The Power System
The power system consists of the transmission grid, along
with power generators (using gas, coal, oil, peat, wind or
hydro-power as their fuels) and the distribution system.
The transmission system is operated at the voltage levels of
400kV, 220kV and 110kV. An analogy can be drawn between
the transmission system and the national road network.
The 400kV system can be likened to the major inter-urban
motorways, the 220kV system to the dual carriageways and
the 110kV system to the national roads serving every county
and linking every town. It is the backbone which supports
electricity supplies to industry, offices, shops, schools, farms
and homes and all other users.
All-Island Fuel Mix 2013
400kV 3 440
220kV 19 1830
110kV 81 3850
Summary of Transmission Plant
Figures are indicative.
STATIONS CIRCUITS
(km approx)
Notes:
· Renewable % = Wind + Hydro + ½(Waste)
· These are preliminary percentages obtained from SCADA.
SONI will provide more accurate data for NI from meter readings and SEAI will add small scale renewables which are not visible to us,
so the final renewable figures are likely to be higher but probably by a small amount (in the order of 1%).
Renewable:
17.8%
Gas:
39.7%
Peat:
7.0%
Coal:
19.8%
Imports:
10.6%
CHP:
3.8%
Other:
1.3%
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4. The National Control Centre (NCC)
The system is operated from EirGrid’s National Control Centre
(NCC) in its role as Transmission System Operator. The EirGrid
NCC is located in Dublin and exercises energy management
functions over the generation and transmission system.
The objective of the NCC is to operate the generation and
transmission system for maximum economy, consistent
with safety, security, continuity, quality and environmental
standards. It provides high quality delivery to all customers,
through maintaining this essential service, 24 hours a day,
every day of the year.
The NCC was originally opened in April 1987 and moved
to its current location in 2006. Previous to the NCC, a centre
called the Load Dispatch Office (LDO) carried out similar, but
not identical roles. This was superseded by the NCC, which
introduced the use of modern IT systems, replacing previous
systems which relied heavily upon telephone communications
between station operators and control centre personnel.
On 27th April 1995 the system was interconnected with the
Northern Ireland system via two 275/220kV links. The system
in Northern Ireland is operated by SONI, the System Operator
for Northern Ireland. The advent of the Single Electricity
Market on the island in November 2007 has emphasised the
requirement for, and major advantages of, close co-operation
in the operation of the power systems in both jurisdictions.
The EirGrid East West Interconnector (EWIC), a direct
current (DC) cable linking the Irish Transmission System to
the UK National Grid, commenced commercial operation in
December 2012. EWIC is approximately 260km in length and
has the capacity to transport 500 megawatts – enough energy
to power 300,000 homes. The NCC engineers are responsible
for the operation of EWIC and do so by controlling the flow of
power on the interconnector while simultaneously monitoring
conventional generators, wind generation levels and demand
fluctuations.
Critical to the work in the EirGrid NCC are all generators,
the Hydro-Electric Control Centre in Turlough Hill and the two
Distribution Control Centres (DCCs) which are operated by ESB.
The DCCs are located at the major load centres of Dublin and
Cork and have responsibility for distribution of power within
their regions. Distribution networks are at a medium and lower
voltage and link most customers to the National Grid.
To ensure the secure minute-to-minute operation of the
system, continual monitoring is essential. To facilitate this,
the NCC requires a substantial quantity of on-line information.
This information is collected by remote terminal units (RTUs)
which are located in each transmission station around Ireland
and transmit the information to the NCC computer system.
There is a simulator in the NCC which enables instructors
to provide challenging training scenarios in a real-time
environment. Operators are all highly-trained engineers having
spent extensive periods working alongside experienced grid
controllers and also undertaken a certification process prior to
assignment to the NCC.
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5. The basic generation function of the NCC is to ensure enough
power is produced to meet customer demand.
This function must be carried out in a fair and transparent
manner while the supply-demand balance must be maintained
on an instantaneous basis in order to keep the frequency of
the system stable at 50Hz. The NCC engineers determine which
generation will be required throughout the day and schedule
and dispatch the appropriate generation units accordingly.
This generation schedule is influenced by the Single Electricity
Market (SEM). The NCC engineers must also allow for unforeseen
events, such as a greater demand than expected, the loss of
a generator from the system or damage to a piece of equipment
on the system.
Unusual events – such as football matches – can cause
changes in the operation of the system if demand deviates from
normal patterns. When one million people switch on their kettles
at half-time, the combined effect is a significant increase in
demand. NCC engineers are aware of the need to be prepared for
these events, as well as other normal fluctuations in demand on
a daily or seasonal basis.
Operation of the
Generation System -
second by second
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7. The purpose of the transmission system is to facilitate
the bulk transfer of electrical energy from generators to
demand centres. This power transfer is carried out at high
voltages so as to minimise transmission losses. The control
engineers’ function is to ensure that voltages and flows on
the system are within acceptable limits at all times. System
stability and safety of the public and those working on the
system are key priorities. Significant changes in demand can
cause both the voltage and frequency to change; they must
therefore be monitored constantly. Changes in demand for
power nationally, therefore, must be anticipated and timely
action taken. This is primarily accomplished by continually
monitoring and controlling generators’ power production
and by managing the topology of the transmission system.
Stormy weather can cause problems on the transmission
system. To cope with the challenging conditions created by
high winds and lightning, the control centre engineers must
quickly decipher what has happened and act swiftly. In most
cases, this is achieved without any consumer being affected,
although major incidents can affect customers. The priority
is to restore the network as quickly as possible in a safe
manner. A lightning detection system is available to the
control engineers to assist with operating the system during
storms and Met Éireann is contracted to provide special
alerts and forecasts to the NCC in relation to upcoming
weather events. The engineers must be prepared to deal with
all unforeseen events. To assist them in this regard they
utilise powerful software tools such as Contingency Analysis,
Loadflow and State Estimation programmes.
Operation of the Transmission System
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9. Map of Transmission
and Generation
System
Transmission Connected Generation
400kV Lines
275kV Lines
220kV Lines
110kV Lines
220kV Cables
110kV Cables
HVDC Cables
400kV Stations
275kV Stations
220kV Stations
110kV Stations
Hydro Generation
Thermal Generation
Pumped Storage Generation
Wind Generation
Transmission System
400kV, 275kV, 220kV & 110kV
The system in the Republic of
Ireland is operated by EirGrid.
The system in Northern Ireland
is operated by SONI.
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