Essay: Structure Of The National Grid

 

Chapter 1

Introduction

The National Electric Grid, also referred to as the Transmission System, is effectively an infrastructure for the distribution of electricity around the country. It is a highly sophisticated system, consisting of approximately 6,500km of high voltage (110kV, 220kV and 400kV) overhead lines and 100 transmission stations. The grid is the backbone of the electricity system and commands around the clock monitoring to balance supply and demand and to control flow of power on the network. The system is an interconnected network used to transport electricity from supplier to the customer.

Figure 1.1- Ireland’s transmission system (www.eirgrid.com)
The grid is made up of the power station, step up transformer, transmission lines, Pylons, step down transformer, distribution lines and control and monitoring systems. Power stations are ideally located in remote areas, due to possible noise generation and poor aesthetics, and near a fuel source or in a location which can take advantage of natural renewable energy sources. Examples of such sources range from oil, coal, bio fuel, natural gas and nuclear to the renewable sources such as wind, hydro, ocean, tidal, pumped storage etc, many of which will be discussed later in this report. Once the electricity has been generated by any of the aforementioned methods a step up transformer steps the voltage from approx 10kV up to approx 110kV/220kV/400kV before connection to the transmission lines. The purpose of the step up in voltage is to reduce the current, thereby reducing heat and also allowing for smaller size cabling to be used on the transmission lines. In fact power wasted by heat loss can be reduced by a factor of 75% for each doubling of the transmission voltage. The pylons are simply a name given to the tall structures used to support the transmission lines/cabling and ensure these transmission lines are of a safe distance above ground level. The transmission network moves the power over long distances, until it reaches the local distribution network’s substation. A step down transformer is then used to step the voltage back down from 110kV/220kV/400kV) (transmission level) to 10kV (distribution level), and a second step down then is required from 10kV to 240V (service voltage) which is then supplied to the customers homes and businesses.

The transmission system is managed by ESB Networks Limited and operated by an independent state company called EirGrid. EirGrid is responsible for operating and developing the national electricity grid or transmission system in Ireland. The transmission system is operated and controlled from the National Control Centre (NCC), which is located in Dublin.
As mentioned previously power is generated by power plants and renewable methods such as wind farms throughout the country. The majority of these generating power plants feed into the national grid and some are used as back up. In the event of the national grid encountering an unexpected increase in demand, failure, or maintenance to another generating plant, these reserve plants will be called upon. The major generating plants feed into the national grid and this power then flows freely to wherever it is needed around the country.
The demand for electricity varies greatly from morning to evening, weekday to weekend, summer to winter etc. To best forecast the expected demand of electricity statistical information is used. This allows the National Control Centre (NCC) to predict the amount of electricity that will be in demand. Some periods can easily be predicted such as high demand in the mornings and evenings, cold winter days, long bright sunny days, Christmas day, All Ireland Final day etc. The job of the NCC controllers is to inform the various generators to increase or decrease power to keep in line with demand. Too much or too little power may result in power loss.

Figure 1.2-Typical winters day demand for power (www.eirgrid.com)

In a synchronous grid all the generators run at the same speed and in phase, each generator maintained by a local governor that regulates the driving torque. The generation and consumption of power must be balanced across the grid. Failure to one part of the grid requires immediate compensation; failure to achieve this may result in insufficient capacity to other areas of the grid resulting in further failures. This can lead to a cascading effect and lead to power failure across the country. This explains the necessity for 24 hours a day monitoring of the national grid by a central authority that would have protocols in place should a situation described above happen.
The importance of the electrical infrastructure cannot be taken for granted. A highly efficient and dependable electrical transmission and distribution system is vital to this country’s economy. The reliability of the power supply in Ireland proves a major attraction for multinational companies and in particular high-tech companies. This reliable and sustainable power supply is essential for the operation of computer servers, power machinery, hospitals etc.
EirGrid’s primary purposes are the daily management of the Irish national grid, the operation of the wholesale power market, and the development of high voltage infrastructure to serve Ireland’s economy. Up to recently European Law stated Ireland must supply 40% of its energy demand via renewable sources. However recently this rule has changed and this is no longer an obligation. Ireland has invested heavily in wind farms across the country in a bid to reduce its reliance on fossil fuels and reduce its carbon footprint. However some of the most suitable locations are in areas huge distances from transmission lines meaning the need for expansion to the current transmission system. This will involve the erection of pylons to transport the electricity generated at these wind farms and also involve connections to the grid.

Throughout this report various aspects of the National Grid will be discussed such as the different types of generating methods with particular emphasis places on renewable methods. In addition, this report will look at other aspects such as the capacity of the National Grid, the various forms of metering and protection, and also the concept of the smart grid will be discussed.

History

The ESB was established in 1927 and given the responsibility of managing Ireland’s electricity supply. The ESB quickly realised the need for additional power, which led to the development of Ireland’s first hydroelectric plant at Ardnacrusha. It was during the development of Ardnacrusha that the ESB began to build the electricity grid. Ireland’s first transmission line was built between Ardnacrusha and Dublin in 1930, which liked up with the first part of the distribution grid which was built around the then outskirts of the city.
At the time of completion, Ardnacrusha was the largest hydroelectric station in the world, proving Ireland to be global leaders in sustainable energy at that time. Ardnacrusha remains Ireland’s largest hydroelectric station to this day. Ardnacrusha, and upon completion had the capabilities of generating 86MW of energy, enough to provide electricity for the entire country. However, Ardnacrusha today generates 92MW of electricity and amazingly accounts for only 2% of the countries demands. By 2010 14 hydroelectric generators were connected to the transmissions system. SEAI report Ireland has in the region of 660MW of hydro systems contributing to our TPER, with a total of 212MW connected to the transmission systems which accounts for 2.8% of the total connected generation capacity.

Figure 1.3-Ardnacrusha
By 1937, the need for more hydroelectric plants was realised and plans were in place for their construction at various sites around the country such as Poulaphouca, Golden Falls, Leixlip, Clady, Cliff and Cathleen’s Fall, Carrigadrohid and Inniscarra. By 1949 construction had been completed and the combination of these new plants together harnessed approximately 75% of Ireland’s inland water power potential. Many of these plants are still in operation today.
1947 saw the construction of the North Wall station in Dublin as a result of the continuing growth in demand for electricity. There were also further additions including peat fire stations at Portarlington in Laois and also Allenwood in Kildare. Lanesboro power station was constructed in 1958 and Shannonbridge was added seven years later in 1965.
Energy demand is normally low at night time and high during day time. In order to prevent the waste of night time capacity, the ESB commissioned a new pumped storage hydroelectric station to be constructed at Turlough Hill (Figure 2.2) in 1968. Located in County Wicklow, Turlough Hill has two reservoirs with the upper reservoir lying 370m above the lower reservoir. Water is pumped uphill to the upper reservoir at night, utilising the surplus energy on the grid. The water is then released downhill during the day and this water drives the turbines to generate power. The plant generates up to 292 MW of power ‘ but output is limited in terms of hours because of the storage capacity of the reservoir.

Figure 1.4-Turlough Hill

Ireland’s industrialisation continued to grow in the 1970’s and as a result the demand for energy grew also. To meet these demands the construction of the country’s two largest power plants were sanctioned-Poolbeg in 1971 with a capacity of 1015MW, and Moneypoint in 1979 which remains Irelands only coal burning plant with a capacity of 915MW.
2002 and 2003 saw new independent stations constructed at Huntstown Power and Dublin Bay Power. Amazingly, up until 2003, there were still areas in Ireland who remained without power. However in September of that year Inishturbot and Inisturk islands were finally connected to the national grid.
In July 2006, EirGrid was established under Irish and European Law to enable competition to enter the Irish power sector. EirGrid is responsible for the operation and development of the national grid, and also the balancing of electricity generation and electricity demand. It is also responsible for the security of the national grid and to facilitate the market for renewable electricity in Ireland. In the same year statistics showed 60 wind farms with connections to the national grid. These wind farms have the capacity to generate 590 MW of power, depending on wind conditions. These wind farms are mainly owned by independent companies and landowners.
On 27 March 2008, the ESB announced a ’22bn capital investment programme in renewable energy technologies in a bid to half carbon emissions by 2020, and then achieve zero emissions by 2035.
In October 2008, EirGrid launched a long-term strategy for developing the transmission system, entitled Grid25. The strategy proposes doubling the capacity of the transmission grid, to support economic growth, integrating more renewable energy and regional development.
In August 2008, EirGrid secured a deal to purchase System Operator Northern Ireland, and in 2012 completed the 500MW East-West Interconnector submarine cable between Ireland and Britain.
The grid today comprises of two types of networks, transmission lines which carry very large amounts of electricity long distances connecting power stations to local transformer stations and local distribution grids which carry electricity from the transformer stations into individual consumers’ premises.
As a general rule, the transmission grid is carried on large metal pylons or wooden portal frames, two high poles with a connecting metal crossbar on the top and it operates at very high voltages. The distribution grid is carried on single wooden poles and uses lower voltages.
In towns and cities the distribution grid is sometimes placed underground. However, it is extremely expensive to build underground AC transmission lines and the technology is at a very early stage of development.
Today there are a number of ongoing developments to the grid and they include The Grid Link Project, The Grid West Project and The North South Project. These will be discussed later in this report.

Location Plant Fuel Year commissioned Generation Capacity(MW)
Cork Aghada Natural Gas and distillate 1980 963
Clare Moneypoint
Coal or Oil 1985 915
Dublin Poolbeg
Natural gas with distillate as an emergency back-up 1971 470
Wicklow Turlough Hill
Pumped storage hydroelectricity 1968 292
Dublin
North Wall Natural gas or distillate
1947 262
Offaly
West Offaly Power Peat
2004 150
Longford
Lough Ree Power
Peat
2004 100
Cork
Marina Natural gas and distillate
1954 96
Clare
Ardnacrusha
Hydroelectricity
1929 86
Donegal
Erne (Cathaleen’s Fall and Cliff) Hydroelectricity
1950 65
Wicklow
Poulaphouca
Hydroelectricity
1938 30
Cork
Inniscarra Dam
Hydroelectricity
1957 19
Cork
Carrigadrohid Hydroelectricity
1957 8
Kildare
Golden Falls Hydroelectricity
1938 4
Kildare
Leixlip Hydroelectricity
1938 4
Donegal
Clady Hydroelectricity
1959 4
Table 1.1- Various power stations, their location, fuel, capacity and year of commissioning.

 

Chapter 2

Capacity

Electricity is essential in every aspect of everyday life. Its importance is continually growing over time, one such example being the transport sector which has seen an increase in sales in electric vehicles. This will result in an increase in demand on the national grid due to the charging of such vehicles. The recent downturn in the economy has led to many business closing down which in turn has led to a decrease in demand on the national grid. Given this decrease in demand, the national grid is capable of meeting the current demands for the short term future. However with a forecasted slow but steady increase in demand on a yearly basis, and with 2020 obligations, Ireland will have to make changes to increase and improve the national grid. The past ten years has seen an additional 4500 MW added to the system, of which 2570MW was as a result of combined cycle gas turbine (CCGT) and combined heat and power (CHP), and 1180MW from wind generation. However it is still recommended improvements is made to accommodate further wind generation and the replacing of old power stations.

EirGrid, as part of their ‘Grid 25’, plan to invest an estimated 3.2 billion euro in the national grid by 2025 which will see the capacity doubled. The investment is proposed to provide a secure, competitive and sustainable supply for the future. Under this planned investment 4000km of lines will be upgraded and a further 800km of new lines are to be built. However the building of these new lines is causing much controversy and there remains strong opposition to overcome at the time of writing this report. Ireland currently has approximately 6500km of overhead lines; however EirGrid predict an increase in demand of up to 60% over the next ten years which will require an increase in capacity, resulting in the construction of wind farms and associated new infrastructure to provide connection to the grid.
‘We are forecasting growth in electricity demand of 60% over the period to 2025. Our role is to ensure that electricity infrastructure does not become a barrier to the social and economic development of any region or county. Grid25 is our strategic response to this challenge.’ (EirGrid Chief Executive Dermot Byrne, www.eirgrid.com )
The national grid has a current capacity of approximately 7.4GW which needs to be significantly increased to accommodate this predicted 60% increase in demand but is currently hindered by an infrastructure unable to deal with increasing amounts of intermittent power.

‘Reliable and cost-effective electricity transmission infrastructure underpins inward investment, regional economic development and allows us to harness indigenous sources of renewable energy, such as wind and wave. The EirGrid strategy clearly illustrates the need to put in place the infrastructure needed to meet these ambitions.’

“Transmission infrastructure is critical for business, which accounts for 62.5% of the total energy consumption in the electricity retail market. In difficult economic times it is vital that this infrastructure is delivered quickly and cost effectively’ (IBEC Director of Policy Danny McCoy, www.seai.ie )

Ireland also has an obligation which required 40% of total electricity consumed to be generated from renewable sources by 2020(A recent change in EU Law means this target is no longer an obligation). This will be achieved primarily via wind generation, but other renewables will also be implemented. Ireland has one of the strongest wind regimes in Europe with wind generation, prior to March 2013, already accounting for a total of up to 1.8GW. In order to meet 2020 targets wind energy will need to account for between 3.5 and 4GW capacity of the grid, meaning the addition of approximately a further 2.8GW will be required. However, its limited grid capacity and domestic demand is insufficient to absorb the large wind production, which is leading to curtailments.

Outlined below are some of the various projects being developed at the moment and also some closures planned over the next ten years.

The connection of various wastes to energy projects over the next few years will add a further 77MW to the grid.
The East-West Interconnector is the second transmission cable connecting Ireland to England and is expected to provide an additional import or export of up to 500MW at any given moment.
The addition of a second North-South tie line will improve the security of the grid on both sides of the border. However this line will not be in operation until 2017. In recent times there has actually been a decrease in demand but this is predicted to rise with any upturn in the economy
In Northern Ireland there are also a number of renewable generation projects both under construction and planned over the next ten years. This will lead to a total capacity of 2.1 GW in Northern Ireland by the year 2022. This 2.1 GW includes 1.1GW from onshore wind, 600MW by offshore wind, 200MW of tidal energy and large scale biomass generating a further 45MW. These figures have been taken from various sources including Strategic Environmental Assessment (SEA), the Onshore Renewable Electricity Action Plan (OREAP) and the Strategic Energy Framework (SEF) produced by the Department of Enterprise, Trade and Investment (DETI). There has also been an announcement from Crown Estates, giving authorisation for the development of a 600MW offshore wind farm and two 100MW tidal sites in Northern Ireland’s coastal waters.

Closures of heavy oil units across the country including those at Tarbert and Great Island will lead to a reduction of 802 MW in capacity.

Individual jurisdictional studies show Northern Ireland to have an adequate capacity up to 2015. The closure of Ballylumford in late 2015 and changes to the operations at Kilroot in early 2016 will see any surplus in capacity in Northern Ireland reduced to a dangerously low figure of around 200MW. This means Northern Ireland will be at risk should a problem occur at one of the larger generating plants or the Moyle Interconnector. Further changes at Kilroot due to further restrictions on emissions will put Northern Ireland into deficit by the year 2021, meaning the North-South is seen as crucial to help alleviate this deficit.

Irelands forecast is more positive, however the closure of older plant will cause a reduction in surplus capacity from 1600MW to 600MW by 2022. The introduction of the additional North-South tie line will see the ‘All-Ireland grid’ have a combined surplus of 700MW available to both jurisdictions.

A recent study by EirGrid examined the estimates of demand during a period from 2013-2022 and the generation capacity available to meet this demand. The table below is taken from the ‘All Island Generation Capacity Statement 2013-2022′ which can be found on their website at the link below.
http://www.eirgrid.com/media/All-Island_GCS_2013-2022.pdf
This table also serves as a summary of the information given above of the various capacities predictions over the next ten years.

Table 2.1-Expected All Island changes in capacity over the next ten years.

Prime Mover Classification

The previous section of this chapter looked at the national grid in terms of capacity. It outlined the current capacity and the predicted demand over the next ten years, including any expected additional plants to be added to the grid, as well as any closures, over the same period. This section of the chapter will look at the various types of prime movers contributing to the overall capacity of the grid.
A prime mover, also referred to as turbines or engines, are mechanical machines used in the conversion of a fuel such as oil, or natural resource such as wind, into mechanical energy, which in turn is converted into electrical energy in the shape of an alternating current (AC). The fuel is burned in a combustor which produces thermal energy; this is then turned into mechanical energy in the prime mover.
Prime movers operate on a number of different fuels such as coal, gas, oil or nuclear, however these are becoming less popular due to their carbon emissions. Ireland has an obligation to generate 40% of its total capacity through renewable sources by 2020 with a long term objective to reach 100% and zero carbon emissions. The most popular type of renewable source is wind, however there are many others including tidal, hydro, solar etc.

Fuel Working Fluid Power Range Main Applications Type Observation
Coal or nuclear fuel Steam Up to 1500 MW/Unit Electric Power systems Steam Turbines High Speed
Gas or Oil Gas(oil) and air From Watts to hundreds of MW/Unit Large and distributed power systems. Automotive applications(vessels, trains, highway and off-highway vehicles), autonomous power sources Gas turbines , diesel engines, Internal combustion engines , Stirling engines With rotary but also linear repricocating motion
Water energy Water Up to 1000MW/Unit Large and distributed electric power systems, autonomous power sources Hydraulic turbines Medium and low speeds >75rpm
Wind energy Air Up to 5 MW/Unit Distributed power systems, autonomous power sources Wind or Wave turbines Speed down to 10 rpm
Table 2.2-Prime mover classification.

This chapter will take a look at some of the various methods used today by generating plants with more emphasis places on modern methods employed to reduce carbon emissions.

Thermal Units
Thermal units are still the most common types used by plants today. These are driven by prime movers which convert the fossil fuels such as coal, oil, peat and gas into steam energy. The fuel is burned within a combustion chamber or furnace and the heat produced heats the water and turns this into steam. This steam is then used to drive a generator which in turn produces electricity. Some of the main types of prime movers are Steam turbines, Gas turbines and the combined cycle. Steam turbine plants use the pressure created by expanding steam to drive the turbine. Gas turbine plants use the heat from gases to operate the turbine. Combined cycle as the name suggests combines both technologies, thereby increasing the overall efficiency. However, all the above require the burning of fossil fuels resulting in harmful carbon emissions being released into the atmosphere. A list of power plants operating on fossil fuels is given in table 3.3 below.

Location Plant Fuel Generation Capacity(MW)
Cork Aghada Natural Gas and distillate 963
Clare Moneypoint
Coal or Oil 915
Dublin Poolbeg
Natural gas with distillate as an emergency back-up 470
Dublin
North Wall Natural gas or distillate
262
Offaly
West Offaly Power Peat
150
Longford
Lough Ree Power
Peat
100
Cork
Marina Natural gas and distillate
96
Table 2.3-Power plants operating on fossil fuels

Moneypoint is one example of a thermal unit. Located in Kilrush, County Clare is one of Ireland’s largest electricity generating stations and operates using either coal or oil. The primary fuel however is coal and with a total of three generating units can produce a total of 915MW. Moneypoint consumes up to 7000 tonnes of coal per day in order to run at full output. This produces a large amount of carbon emissions however these have been reduced following an investment in emissions abatement equipment.

Figure 2.1-Moneypoint Power Station

An alternative for generating stations is use of renewable energy whereby natural resources such as hydroelectricity, wind, tidal, ocean and sunlight are harnessed and converted into electricity. Some of the more common methods are described below.

Wind
Ireland has one of the greatest natural resources of wind in the world. There has been a rise in the number of wind farms across the country with approx 24% of the total grid capacity now accounted for by wind energy. Wind energy is a clean and sustainable solution to our energy demands. It can be used to replace fossil fuels with the benefit of zero emissions of greenhouse gases. Ireland has to generate 40% of total grid capacity by means of renewable energy and it is expected that wind energy will account for the majority of this. There are a number of wind farms across the country, the first established in 1992 at Bellacorrick in County Mayo. Today there is approx 1.8GW of wind energy connected to the grid, with a further 3.5-4GW required by 2020.

Hydroelectricity

Hydroelectricity works on the basis of falling water in a stream/river or storage dam between two points. Water flows from an upper reservoir to a lower level reservoir via a pipe which is known as a penstock. The water is directed down to a turbine water wheel at the lower level. The pressure increases as it flows down the penstock. The higher the upper reservoir level is above the lower level the greater the pressure. This pressure is used to drive the turbine wheel which is connected to the generator. Inside the generator is the rotor that is spun by the turbine. Large electro magnets are attached to the rotor located within coils of copper wire called the stator. As the generator motor spins the magnets, a flow of electrons is created in the coils of the stator. This produces electricity that can be stepped up in voltage in order to be transmitted across the transmissions lines. The most famous hydroelectric plant in Ireland is Ardnacrusha. At its time of completion Ardnacrusha was capable of generating 86MW, enough to supply the entire country at that time. However today this capacity accounts for only 2% of the countries demands. Ardnacrusha works on the method described above but uses four penstocks to feed four turbines, each taking 100 tons per second.
Another example of a hydroelectric site in Ireland is the famous Turlough Hill which is Irelands only pumped storage power station. The station is capable of generating 292MW by releasing water from an upper reservoir, allowing it to flow through four turbines into a lower level reservoir. This occurs during high demand, during periods of low demand the water is pumped back up to the upper reservoir ready for use again. SEAI report Ireland has approx 660MW of Hydroelectricity contributing to the grid. Hydroelectric systems have many advantages such as they provide a reliable energy supply and they are robust in design with life spans in excess of 50 years (e.g. Ardnacrusha). There are no greenhouse gases, air pollutants or any waste products.

CHP

Combined Heat and Power systems generate electricity and useful heat simultaneously from the same plant. CHP covers a range of technology but will always use a prime mover driving an electrical generator and also a heat recovery system. Heat is recovered and is used to supplement the heat from the sites boilers, while the electricity generated is used for the onsite demands and in the event of any surplus electricity, this can be sold back to the grid. This method can lead to a 35% reduction in emissions. The installed capacity at the end of 2010 was 307MW of which 284 were operational. However this type of system is more suitable for large applications such as leisure centres where there is a simultaneous demand for heat and electricity, for a minimum of 16 hours per day.
Wave
Wave energy harnessing technologies are very much at an infancy stage, however there is no denying the potential it holds. One major problem for developing suitable technology from this area is the harsh environments into which it must be placed. There are many projects in place across the world such as the Pelamis Wave energy converter but as stated earlier these are at an early stage. There also a number of different technologies such as the sea snake, wave bob and the wave power station. All of the mentioned are installed around the world, however to date there are none installed in Ireland. A recent study suggests the wave industry could hold many benefits for Ireland including a possible 29GW capacity without any environmental effects. This would lead to a significant reduction in carbon emissions.

Tidal

Tidal energy is energy which is contained within a tide which can be converted to electricity. It is a result of the gravitational pull of the moon, and to a lesser extent the sun. Tidal energy projects rely on the twice daily tides which produce the ebb and flow of large volumes of water in estuaries and at sea. Energy can be extracted from the tidal from by means of Tidal Barges and tidal Streams.
Tidal Barges- A tide pool is filled during high tide and is then emptied quickly at low tide. This occurs every 6 hours and therefore there is a change in potential on each occurrence.
Tidal Steam-Work on a similar principle to wind turbines. They also come in horizontal and vertical-axis machines. The blades are rotated with the motion of the water and the turbine is coupled directly to a standard generator via a gearbox.

There is no pollution involved with tidal energy and it also has the advantage of a predictable of energy when compared to both wind and solar. It is also more efficient than wind due to the density of water.

Chapter 3

Line Distribution/Protection

The smooth operation of the national grid system is hugely important. As mentioned earlier in this report it is the reliability and sustainability of the national grid that helps attract foreign companies to set up in Ireland which helps keep our economy going. It is therefore essential to provide a safe and predictable system, which can be achieved through generators, circuit breakers, switches and loads.
Load Balancing
The transmission system must be capable of providing for both base and peak loads, while also taking safety and fault tolerance into consideration. Peak load times depend on many factors but in Ireland peak time generally occurs in the evening time as this is when the majority of people return home from work. Shower, ovens and heating may all be in use at the one time for a short duration at this time however this demand is not constant and can vary by season etc. Distribution systems therefore need to consider base load and peak load when designing the system.
The transmission system cannot simply be run at full capacity, accommodating both peak loads and base loads. Instead it is important voltage and frequency be kept stable, with energy generated closely matching demand at all times. Failure to do this can result in overloading failures of generation equipment. The NCC use statistical information to forecast the load demand over several timescales. When forecasting 24 hours in advance, factors such as day of the week, weather, sporting events etc are all taken into consideration, and based on all the information gathered, it schedules the required power stations and any suitable reserves.
Multiple sources and loads are connected to the transmission system at any one time. There are also a number of generating plants on standby which are switched online and offline depending on demand. The correct switching online of generating plants help to prevent large transients and overload conditions occurring. The connecting of a generating plant to the grid is known as synchronisation. The following describes the procedure in synchronising a plant to the grid.
Connecting generating plants to the National Grid is a complex procedure and one which requires great expertise. Phase and frequency of a perspective synchronous machine must be matched to the grid prior to connection. Failure to do so will result in a potential difference across the breaker contacts, resulting in excessive arcing and possibly generator failure. A synchronous machine connected to the grid operates at grid frequency and voltage. When a synchronous machine receives insufficient mechanical power to generate load it operates as a synchronous motor and this cannot be tolerated, resulting in reverse power trip.

The following steps should be carried out for generator/grid synchronisation:
1. Run synchronous machine to synchronous speed and insure speed stability after heat soak.
2. Switch on excitation. This controls DC voltage to the rotor, which in turn controls generation of the voltage.
3. Make fine adjustments to generator speed and voltage for best match to grid.
4. Switch on synchroscope. Ensure filament lamps operate in unison with synchroscope. Adjust fuel to create a rotation of 0.1 Hz clockwise rotation.
5. Close generator breaker at ’11o’clock’ clockwise.
6. Immediately load the generator by increasing the fuel to 25% or as per instruction.
7. Switch off synchroscope.

As mentioned earlier, in a synchronous grid all the generators run at the same speed and in phase, each generator maintained by a local governor that regulates the driving torque. The generation and consumption of power must be balanced across the grid. Failure to one part of the grid requires immediate compensation; failure to achieve this may result in insufficient capacity to other areas of the grid resulting in further failures. This can lead to a cascading effect and lead to power failure across the country. This explains the necessity for 24 hours a day monitoring of the national grid by a central authority that would have protocols in place should a situation described above happen.
Generating plants can be switched online on receipt of voltage or frequency signals. These signals are used to balance the loads.
In frequency signalling, the generator frequencies match that of the transmission system. In speed droop control, if the frequency decreases, the power is increased. A synchronised machine will not run at 52 Hz on a 50 Hz system. However as the load percentage decreases the speed governor applies more fuel in an effort to increase the speed but the resulting effect is an increase in load. The increase in load percentage is a reduction in speed and a balance is found at a particular, percentage load to limit the governor’s efforts in reaching speeds above synchronous speed.
In voltage signalling, the variation of voltage is used to increase generation. The power added by any system increases as the line voltage decreases. This arrangement is stable in principle. Voltage Isoch maintains a fixed voltage, this machine being the chaser. The remaining machines in voltage droop will increase their voltage to increase their percentage load.

Failure Protection
Transmission lines are used to transfer AC power over long distances before reaching its destination. Voltage is stepped up to high values, usually 110kV, 220kV or 400kV in order to reduce energy losses. High voltage direct current (HVDC) technology can be used over distances in excess of 50km. HVDC links stabilize the system against control problems in larger distribution networks in order to prevent against synchronisation problems or cascading failures which could be caused due to new loads or blackouts to an area of the network.
As previously discussed, power generation must be matched to demand, as there are no methods of storing the surplus power. Should demand exceed the available supply, generation plants and transmission equipment could malfunction and this could result in blackouts. To reduce the risk of this, transmission networks are connected in mesh like formations, meaning in the event of a fault in one area of the system, an alternative route is available for power to flow.
Under excess load conditions, a system can be engineered to fail gracefully instead of all at once. Load shedding is intentionally engineered to deliver insufficient power when demand is greater than supply.
The following section outlines the various methods used to protect against problems such as short circuits, abnormal conditions and equipment failures in the system in order to prevent against overloads, improve system design and minimize damage to equipment. System equipment such as Generators, Transformers, Reactors, Lines, Buses, and Capacitors all need protecting in order to ensure the stability of the grid.
Protective relays are used to monitor currents and voltages in the power system to detect any problems which may arise in the system. These currents and voltages are supplied to these relays via Current Transformers (CT’s) and Voltage Transformer’s (VT’s).
Current Transformers are devices used to transform current on the power system from a large primary value to a safe secondary value. The secondary value will be proportional to the primary value.

Figure 3.1-400kV Current Transformer
Voltage transformers works on the same principal as the current transformer, transforming large primary voltage values to safe secondary values.

Figure 3.2- Voltage Transformer

Generators also need protecting against a number of possible faults such as stator winding problems, rotor problems and other abnormal conditions. Stator winding problems may arise in the form of winding-winding shorts or stator ground faults. Differential protection is used to detect shorts between any of the phases.Rotor problems can also occur, such as Loss of field, and field ground. Protection of the rotor is achieved by using imedance to prevent loss of field and a DC voltage relay to protect against field ground. The field ground is connected from the negative side of the field to DC ground.
Generator earthing is carried out in two ways: Low impedance and high impedance.
Low impedance(Direct Earthing)- The star point is tied directly to ground in the interest of human safety and results in an immediate/instantaneous trip on the first earth fault. It is also a referance point that assists in fault detection and protection .
High impedance(grounding via a high power resistor)- This resistor must be rated at full load current for a defined time, e.g 1 hour. Tis allows detection of the first earth fault without a generator trip . A second earth fault is an instantaneous trip since the resistor is rated for a full load current for one phase only.
Other abnormal conditions can also occur such as Over/ Under frequency, over excitation, reverse power, out of step and unbalance current .

Power transformers are expensive , and so protection is essential and must be effective. The types of problems that can arise with transformers are winding- winding faults, winding-ground faults and brushing faults. Protective methods used for power transformers include fuses, overcurrent protection and differential protection.
Transmission lines can vary in length from hundreds of feet to hundreds of miles, with voltage ranging from 46kV to 750kV. Construction can also vary from wooden poles with insulators on top of a crossarm with little spacing between the conductorsand from conductors to ground; to lattice structures with bundled conductors with large spacing between conductors and conductors and ground. The types of faults that can occur on transmission lines are short circuits which may be caused by Trees, lightning, animals such as birds, weather,natural disasters and finally faulty equipment(switches, insulators, clamps, etc). The resulting faults are in the form of single line-ground, line-line, three phase, and line-line-ground.
Transmission line protective devices protect against Overcurrent , Directional Overcurrent, Distance(Impedance), Pilot(Directional Comparison Blocking and Permissive Overreaching Transfer Trip),and Line Current Differential which are briefly explained below.
Overcurrent protection is non directional in which relays respond to an overcurrent condition.
With Directional Overcurrent Protection, relays respond to an overcurrnet condition in forward direction only . They will not respond to reverse faults. Directional Overcurrent Protection compares the current in the line versus a known reference.
Distance protection is provided by a relay which measures the impedance of a line using the voltage and current applied to the relay . Should a fault occur on a line, the current increases and voltage decreases. The distance relay determins the impedance using V/I. If impedance is within the reach value, the rela will operate.
Pilot Relaying Scheme- A protection scheme using communications to send signals from one station to another to either allow or prevent high speed tripping. Pilot protection allows over-reaching zones of protection to ensure full protection of the line as well as high speed tripping.
Bus protection methods use a bus differential system to ensure current into the bus equals current out. Some example are single bus with XFMR; double bus, breaker and a half; and double bs, double breaker.
Capacitor Protection is provided by monitoring the voltage across a capacitor back wich is determined by current flow and impedance of the bank. If a capacitor fuse blows or indeed a capacitor shorts, the voltage drop across the bank changes due to a change in capacitive reactance of the bank. A voltage relay detects the chancge in voltag and trips the breaker.

The distribution substation will also incorporate various types of protection including switches, circuit breakers (always paired with a relay which senses short-circuit condition using potential transformers (PTs) and current transformers (CTs)), reclosers similar to circuit breakers but include the ability to reclose after opening, open again, and reclose again, repeating this cycle a predetermined number of times until they lockout) and fuses.
Switches are often used on the high side of the transformer with protection devices used on the low side. However substations supplying large loads may employ protection on both sides of the transformer.

Chapter 4

Metering

Most substations do have some sort of metering device that records, at a minimum, existing current and current max and min that have occurred in the last time period (e.g., 1 hour). Digital recording is also heavily used and capable of recording a large amount of substation operational information.

Primary metering units are designed for three-phase primary metering applications. They consist of current transformers (CTs) and voltage transformers (VTs) mounted on an aluminium frame and wired to a terminal strip inside of a special junction box. The assembly is then equipped for pole mount installation. Medium voltage instrument transformer combinations are available in voltage classes from 5 to 34.5 kV.

There are two main metering configurations available. For three phase four wire systems there are the options of 3 CT’ and 3 VT’s and also 3 CT’s and 2 VT’s.
For three phase three wire systems, the arrangement is 2 CT’s and 2 VT’s.

Current transformers can be used to supply information for measuring power flows and the electrical inputs for the operation of protective relays associated with the transmission and distribution circuits or for power transformers. The primary winding of the current transformers is connected in series with the conductor carrying the current to be measured or controlled. The secondary winding being insulated from the high voltage and can therefore be connected to low-voltage metering circuits.

Care should be taken when installing meters, ensuring adequate space is provided. Meters and metering equipment should be ideally placed in a room designated for this purpose solely. The room must be illuminated and have a door opening to the outside of the building. The operation and maintenance of the metering system includes proper installation, regular maintenance of the metering system,, checking of errors of the CTs, VTs and meters, proper laying of cables and their protection, cleaning of connections/joints, checking of voltage drop in the CT/VT leads, condition of meter box and enclosure, condition of seals, regular/daily reading meters and regular data retrieved through CMRI and BCS, attending any breakdown/fault on the metering system etc.

Figure 4.1-Metering CT’s and VT’s

Chapter 5

Smart Grid

A smart grid is an intelligent digitised energy network delivering electricity in an optimum way from source to consumption. This is achieved by integrating information, telecommunication and power technologies with the modernisation of the existing electricity grid in Ireland. The existing electrical grid is generally used to transport power from generating plants over transmission lines to the customers. However, the new emerging smart grid will use two-way ‘ows of electricity and information to create an automated and distributed advanced energy delivery network. The Smart Grid will allow the generation, transmission and distribution of electricity around the system as efficiently as possible. This intelligent system has the capabilities to monitor consumer’s contribution to the grid, whether that is generating, consuming or both, and thereby act on this information in order to deliver a reliable, economic and secure supply. Advancements in areas mentioned above such as monitoring, control and communications through innovative products allows for better facilitation for connections of generators of different sizes; allows consumers to play an important role in the operation of the system; helps reduce the harmful emissions due to increased number of renewable energy systems connecting to the grid, and will improve the reliability and security of the supply.
The implementation of the Smart Grid will provide many benefits. The current infrastructure requires a large investment in order to upgrade this system to facilitate new connections such as wind farms to the existing grid. Approximately 1,150km of new transmission lines will be required, while 2,300km of the existing transmission network will need to be upgraded. The smart grid will therefore reduce the number of new fossil fuel generation plants needed in the future. This will lead to a reduction in carbon dioxide emissions. The Smart Grid will encourage new participants into the electricity generation and supply market which will increase competition with the end result being a cheaper rate for the consumer. Consumers will have greater control over their own electricity usage by having greater access to their usage information as well as implementing informative in-home devices.
The importance of the introduction of the Smart Grid is emphasised by the expected 60% increase in demand for electricity between now and 2025. The current infrastructure is in fact quite adequate for current demands. However with an expected upturn in the economy and the constant inventing of energy sapping devices, demand will increase. Furthermore, sales in electric cars has risen in the last year and a further increase in their popularity is expected which will inevitably see a large increase in demand on electricity as these cars will require regular charging. The current capacity will therefore be inadequate and more generation plants will be required resulting in an elevated price for electricity.
The two most important concepts that are crucial to the Smart Grid are advancements in metering and in the balancing of supply and demand. Advancements in metering will allow the consumer to effectively see their energy bill accumulate. In-home meters will illustrate the power consumption of various devices with the possibility in the future of devices having built in metering incorporated in the actual device. This will lead to consumers being more conscious and less wasteful with their energy needs, resulting in less demand on the grid.
The second area will be the implementation of an automated computer system which uses Phasor measurement units to keep a more accurate account of electrical usage and thereby providing instant responses to the ebbs and flows of energy production and demand across the entire grid ensuring less waste of energy generated.
Both approaches involve more information being available to both the consumer and the automated distributer, allowing for a more transparent and efficient system. It is these two concepts that will make the new grid ‘smart’.
Under the new laws to make the electricity market more competitive in Ireland, customers can now generate their own electricity and even sell any excess back to the national grid. It is hoped that these ‘micro’ generation plants will help to encourage the use of natural resources and help reduces reliance on oil and gas imports. There are in fact 52 micro (<1MW) hydro-electric generators connected to the distribution system with an installed capacity of 25.1MW. In order to encourage the construction of these micro generators a guaranteed price of 19cent per kW/hr for electricity produced is being offered to the first 4000 micro-generation installations over the next three years. This applies to installations such as wind, hydro, photovoltaic and combined heat and power.
This represents a huge change in transmission networks as traditionally the network was designed to transport electricity from large generating plants to the customer. However today the national grid can be looked upon as a two way system, with micro generators meaning the customer can buy electricity to make up a shortfall in their own requirements or indeed selling any surplus electricity produced back to the grid
EirGrid plans to invest 3.2 billion euro in a new grid system, doubling its current transmission capacity. Although the demand for the power is not there now, it’s being billed as a once in a generation investment. Between now and 2025, EirGrid plan to build 800km of new power lines and upgrade 2000km of existing lines. The project called grid25 plans for three new 400kV lines across the country; one is a new north’south interconnection, there’s a grid west connecting to mayo whose preferred route has been chosen; and there’s grid link which will connect cork via great island in Wexford with Kildare. Several possible 1km wide corridors have been identified but it will take a year to narrow down options. Its grid link which could be coming through the lush pasture land of west Waterford , like many part of rural Ireland its seen the emergence of wind farms . The new grid will build the infrastructure to harness this resource.
The Smart Grid represents an opportunity to transform the energy industry from one in danger of being incapable of supplying an ever increasing demand, into one which can offer reliability, availability, and efficiency and one which contributes to our economic and environmental health.
The Smart Grid will also go to eliminating and blackouts which can very costly to any business as well an inconvenience. These blackouts can disrupt banking, traffic, and more importantly security and communications such as wifi. It can also present a serious danger to the lives of the elderly who can be deprived of heating in the event of power loss to their homes. A smarter grid will add resiliency to our electric power system and make it better prepared to address emergencies such as severe storms, or any adverse weather conditions. Because of its two-way interactive capacity, the Smart Grid will be capably of rerouting power when equipment fails or outages occur. This will minimize outages and minimize the effects when they do happen.
In the event of a power outage, Smart Grid technologies will detect these outages and isolate them, containing them before they escalate. The new technologies will improve recovery times and will reroute power to emergency services first where needed. In addition, the Smart Grid will avail of customer generated electricity which in some case can help a community keep its health centre, garda station, hospital etc powered in times of emergencies.
The smart grid will allow consumers to manage their electricity bills is a similar manner to the way in which they manage their personal banking online. It will allow the consumer to view regular updates of their bill including up to date pricing and encourage the consumer to avail of electricity when it is at its cheapest.
The smart grid will be made up of millions of parts- controls, computer, power lines, new technologies etc. It will take a long time before these are all built and integrated together and all early problems corrected. However Ireland is in a great position as it has only one grid meaning thing can be achieved more quickly. When matured the smart grid is likely to impact our lives in a similar way as the internet.

Future Concepts

Ireland’s government have drawn up a plan called Grid25 which is hoped to be completed within the next decade. This plan will see a total transformation of the current grid system and will deliver the grid into the 21st century. This new grid will be known as the smart grid (see previous chapter). It will aim to take advantage of many novel ideas in order to meet the growing energy demand. As discussed in the previous chapter the two main concepts are an automated computer system which will be employed to match supply and demand thereby reducing wastage of energy, and smart metering which will ultimately lead to a more conscious consumer when it comes to energy consumption.
Small scale generation of energy such as domestic wind generators will be able to connect to the grid. Consumers will be able to construct their very own renewable energy source in order to provide electricity to meet their own needs, and can even apply to EirGrid or ESB networks for connection to the grid in order to sell electricity back to the grid which will lead to a far more competitive energy market. In fact the energy regulator has introduced a fund called REFIT to encourage wind generation. With this fund a generous fee is paid per unit of power generated by wind upon connection to the grid. There are also schemes available for other methods of renewable energy. Renewable energy is also given preference when extra load is required with wind given first preference. This means should the grid need extra energy, a wind generator will be connected before any other form, in particular one which produces harmful emissions.
Smart metering will also allow customers to gain a better knowledge and understanding of their energy bills. It is predicted devices will incorporate in built metering devices allowing the consumer to visually see what each device is costing each time it is powered on. This will no doubt make consumers more conscious of their usage of electricity again resulting in a decrease in demand on the grid.
Looking to the future and the possibility of a Super Grid could revolutionise the energy sector. The super grid would involve all grids in Europe joining to form one Super Grid. This would enable the renewable energy industry to sell electricity to distant markets, the removal of congestion, and an increase in the usage of intermittent energy sources by balancing them across vast geological regions. However, as always such a large scale idea is met with strong opposition with concerns regarding the level of investment needed and the siting of new lines. A study for the European Super Grid estimates an additional 750GW of transmission capacity will be required. These would be accommodated in increments of 5GW HVDC lines.
Research is underway to finance, build, operate, and regulate a super grid in order to enable the trading of renewable energy across great distances. The future of the electric grid will be built on renewable energy. It eliminates the use of finite resources such as coal, oil, gas and nuclear energy. It also eliminates harmful carbon dioxide emissions for the burning of the aforementioned fuels. Ireland is one of the leading countries when it comes to renewable energy. Europe in general also has an abundance of sources with off-shore wind farms in the North Sea and Baltic Sea, hydropower plants in Scandinavia and the Alps, and solar stations around the Mediterranean Sea. These renewable sites are quite a distance from the load centres and therefore existing AC grids will be inadequate. Therefore a HVDC grid will be used to link these renewable sources to the load centres.
There are problems which need to be addressed before the evolution of the super grid takes place as many grids around Europe operate at different voltage levels meaning connecting to a super grid is more complex. However synchronizing can be avoided by the choosing of DC current for the super grid. This leads to a more efficient and controllable transporting of electricity.
The East-West interconnector between Ireland and the UK is an example of a modern link utilising HVDC. A converter station in Woodland, Ireland can convert the DC voltage into an AC voltage for use across Ireland.
One future concept currently under research is the possibility of a viable electric based heating system. This would further reduce the use of fossil fuels as it would lead to the decline of oil burners and gas burners. Another concept that will make a substantial contribution to the super grid capacity is Ocean energy. Recent studies have indicated that the available European wave energy resource is capable of delivering 320,000MW of electrical power which will significantly reduce reliance on fossil fuels thus reducing carbon emissions. However technology in this area is at development stage. There are currently three forms of technology currently being trialled, The Sea Snake, The Wave Bob and also the Wave Power Station.

‘ The Pelamis is the first deep water, grid connected trial of a full size wave power generator to take place anywhere in the world. Currently installed and undergoing sea trials at the European Marine Energy Centre in Orkney. The Pelamis is 120 metres long, 3.5 metres wide and 700 tonnes in weight. When floating on the sea, hinged joints between its articulated cylindrical sections move with the waves powering hydraulic motors that generate electricity. Each ingle 750kW Pelamis could generate the same amount of power as a wind turbine.

‘ The Wave Power Station is simple in design. An enclosed chamber has an opening beneath sea level which allows water to flow from the sea to the chamber and back. The water level in the chamber rises and falls with the rhythm of the waves and the air is forced forwards and backwards through the turbine connected to an upper opening in the chamber. As it is compressed and decompressed the airflow has sufficient power to drive the wells turbine.

‘ The Wave bob uses the lift and fall of the ocean waves to drive generators. It can be deployed offshore. They are better able to cope with turbulent seas. The wave bob is best described as a point absorber device and generates power from each wave.

With the above forms of renewable technology, together with the current methods such as wind, tidal and solar, the future looks bright for a super grid powered solely on renewable energies making for a more sustainable, green future.