Power Systems Flashcards
Explain the principles of operation of a combined cycle gas power station and explain why its electrical efficiency is higher than that of other thermal power stations.
Single fuel source, two power cycles, heat recovery from gas turbine, so reduced heat losses to environment and increased efficiency.
The electrical efficiency of a combined cycle gas power station is higher because the energy conversion takes place in a gas turbine rather than in a boiler.
Explain what the term “dispatchable” means when applied to electricity generating plant and explain why it is important in the operation of electrical power systems, particularly those with a significant amount of electricity derived from renewable sources.
Dispatchable generation that can be operated to a schedule and singly or collectively can provide flexibility in supply – reducing output at times of high wind or solar generation and increasing their output at times of low wind or solar generation.
This capability is critical to ensuring that there is a continuous supply demand match. Examples include hydro and gas power stations.
With reference to fundamental nature of renewable electricity supplies, the location of the bulk of the UK’s renewable resource and the current configuration of the electricity transmission and distribution system describe some of the problems associated with substantially increasing the UK’s renewable electricity generation capacity and explain how these problems could be alleviated.
Increasing renewable capacity causes increased variability in supply – as renewable output such as PV and wind are weather related. This makes demand-supply matching more difficult and could ultimately lead to power system stability problems.
Current transmission/distribution system infrastructure is weak where there is the greatest renewable resource (e.g. NW Scotland), so bringing power from remote areas to demand centres will require investment and some reconfiguration of the current network topology.
Possible solutions are:
Greater power system interconnectivity opening up options for power import and export and increasing the diversity of demand and renewable supply.
Increased deployment of storage to make up for peaks and troughs in RE output. Similarly, investing in dispatchable generation.
Developing flexible demand, manipulating demand to better match a less predictable supply.
Improving weather forecasting, enabling longer term scheduling of dispatchable generation and flexible demand, improving the overall controllability of the power system.
Explain some of the advantages and disadvantages of adding microgeneration onto the power system.
Advantages: Localised low carbon generation can help reduce carbon emissions. Can reduce peak demand ‘seen’ by the grid. Reduces reliance on grid power and could increase resilience.
Disadvatanges: However it is usually more expensive £/kWh. Without storage, uses the grid as a power ‘dump’ possibly leading to power quality problems associated with reverse power flows e.g. high voltage. Possible increase in harmonics due to power electronic conversion from DC to AC.
Describe the operation of a “smartgrid” and highlight the main differences between this and a more conventional electricity network
Co-ordinates the operation of generation, loads and storage; conventional power system usually only controls generation. Greater diversity of power sources compared to conventional power system. Can be small or large scale – conventional power systems tend to be large. Smartgrid can operate autonomously or co-operate with neighbouring grids. Sections of the network are not autonomous in conventional power systems.
How will electricity demand be effected in the future?
Increasing numbers of populations will lead to an increase in applications. As standards of living develops more and more appliances will be needed. The tighter emission and policy control will affect the supply and demand of the future. Through the use of electrical vehicles and other developing technologies the electricity demand will increase but use more effective techniques to produce the power required.
Why is electricity a commonly used utility?
It is a high grade of energy source which has a huge number of end uses. There is an ease of transmission straight to the source over a long distance and an unobstructive distribution, which is a mature and robust technology.
What is the environmental impact to Scotland as a result of renewable energy?
The UK grid carbon has been intensely decreasing as the production of electricity is accounting for less c02 emissions, especially in Scotland where is as low as around 34%.
How do we balance supply and demand and why is this important?
The electricity network is a displacement system: power consumed at one point must be supplied at another. For the network to remain stable, supply must balance demand otherwise the system would collapse.
As electricity cannot be directly stored, the means to match supply and demand are to modulate generation, modulate demand, modulate both or indirectly store energy. Typically modulating generation is used for current power systems.
How do we modulate generation and what is the term often used to describe this?
Dispatchable: A generator with output that can be increased or decreased according to the level of demand or which can be brought on or offline to a schedule is said to be dispatchable. In the UK supply and demand are matched by bringing different mixes of generation on and offline.
What is the common way to achieve base load and what is used to control fluctuations?
Typically high cost generators such as nuclear power stations are used to meet base load, as the source is non-dispatchable. Dispatchable lower cost generators such as gas turbines and pumped hydro are used to modulated to meet the fluctuations in demand.
What does the future of power supply look like?
Radical change in power supply mix - phase out of older power stations, new nuclear build, more stringent emission regulations, fossil fuel price rises.
Continued growth of renewable energy, using on and offshore wind, wave and tidal energy. Smart metering and increased demand management. New technologies for fuel uses, such as electric vehicles.
What is the ultimate penetration of renewable sources depedant on?
Grid capacity and grid upgrades
Increasing grid interconnectivity
Increased use of demand management
Better prediction of renewable output
Energy Storage (limited technologies)
