Lecture 1_Introduction to power system planning.pdf
- 1. Introduction to Power System Planning EEE 6561 taziz.eee@aust.edu POWER SYSTEM PLANNING
- 2. Contents Introduction to Power System Planning Power System Elements and Structures Power System Studies- A Time-horizon Perspective Planning Issues 2
- 3. 3 Failing to plan is planning to fail. Introduction How to Get Control of Your Time and Your Life (1973) Alan Lakein
- 4. Introduction 4 The electric power industry has evolved over many decades, from a low power generator, serving a limited area, to highly interconnected networks, serving a large number of countries, or even continents. Nowadays, an electric power system is the largest man-made system, comprising of huge number of components. Running this very large system is a real difficult task. It has caused numerous problems to be solved by both the educational and the industrial bodies. Lessons have to be learnt from the past. At the same time, the current situation should be run in an efficient manner with proper insights to the future. The word operation is the normal electric power term used for running the current situation. Referring to the future, the power system experts use the term planning to denote the actions required for the future. The past experiences are always used for efficient operation and planning of the system.
- 5. Power System Elements & Structure 5 A typical power system is comprised of enormous number of elements. The elements may vary from a small lamp switch to a giant generator. However, the main elements of interest are • Generation facilities • Transmission facilities – Substations – Network (lines, cables) • Loads In power system planning, the details of each element design are not of main interest. For instance, for a generation facility, the type (steam turbine, gas turbine, etc.), the capacity and its location are only determined.
- 6. Power System Elements & Structure 6 Fig. : One line diagram of a typical power system
- 7. Power System Studies- A Time Horizon 7 First, suppose it is foreseen that the predicted load in 10 years from now, may be served provided that a new power plant is built. The expert has to decide on its required capacity, type and where the plant has to be connected to the network. Once decided properly, its construction has to be started ahead of time, so that the plant is available in 10 years time. This is a typical long-term study of power systems. Two typical studies that power system experts perform in real life - Second, suppose we are going to build a transmission line, passing through a mountainous area. Once built, the line may be subject to severe lightning. Lightning is such a very fast phenomena that it affects the system within nanoseconds. The designer should think of appropriate provisions on the line, by proper modeling the system in these very fast situations and performing enough studies, to make sure that the line does not fail, if such lightning happens in practice. This is a typical very short- term study of power systems.
- 8. Power System Studies- A Time Horizon 8 • Hours to 1 week - example - unit commitment • Several minutes to 1 h- example - economic dispatch, Optimal Power Flow (OPF) • Minutes – Example - Automatic Generation Control (AGC). Fig: A time-horizon perspective of power system studies
- 9. Power System Studies- A Time Horizon 9 To discuss, briefly, the points mentioned above, suppose from ten power plants of a system, in the coming week, three are not available due to scheduled maintenances. The decision maker should decide on using the available plants for serving the predicted load for each hour of the coming week. Moreover, he or she should decide on the generation level of each plant, as the generation capacities of all plants may be noticeably higher than the predicted load. This type of study is commonly referred to as unit commitment. His or her decision may be based on some technical and/or economical considerations.
- 10. Power System Studies- A Time Horizon 10 • Commit unit 1 (generation level: 100 MW), unit 3 (generation level: 150 MW) and unit 6 (generation level: 125 MW), to serve the predicted load of 375 MW at hour 27 of the week (1 week = 168 h). • Commit unit 1 (generation level: 75 MW) and unit 3 (generation level: 120 MW), to serve the predicted load of 195 MW at hour 35 of the week. A complete list for all hours of the week should be generated. As mentioned earlier, this is known as unit commitment. Once we come to the exact hour, the actual load may not be equal to the predicted load. Suppose, for instance, that the actual load at hour 27 to be 390 MW, instead of 375 MW. A further study has to be performed in that hour to allocate the actual load of 390 MW among the available plants at that hour (units 1, 3 and 6). This type of study may be based on some technical and/or economical considerations and is commonly referred to as economic dispatch or Optimal Power Flow (OPF). Coming to the faster time periods, the next step is to automatically control the generation of the plants (for instance units 1, 3 and 6) via telemetry signals to required levels, to satisfy the load of 390 MW at hour 27. This task is normally referred to as Automatic Generation Control (AGC) and should be performed, periodically (say in minutes); as otherwise, the system frequency may undesirably change. Further going towards the faster time periods, we come to power system dynamics studies, in milliseconds to seconds. In this time period, the effects of some components such as the power plants excitation systems and governors may be significant. Two typical examples are stability studies and Sub-Synchronous Resonance (SSR) phenomenon. The last stage of study is called power system transients studies, involving studies on lightning, switching transients and similar. The time period of interest is from milliseconds to nanoseconds or even picoseconds.
- 11. Power System Planning Issues 11 Power system planning is a process in which the aim is to decide on new as well as upgrading existing system elements, to adequately satisfy the loads for a foreseen future. The elements may be • Generation facilities • Substations • Transmission lines and/or cables • Capacitors/Reactors • Etc. The decisions should be • Where to allocate the element (for instance, the sending and receiving end of a line), • When to install the element (for instance, 2019,2020), • What to select, in terms of the element specifications (for instance, number of bundles and conductor type).
- 12. Power System Planning Issues 12 There is no golden rule in specifying short-term or long-term planning issues. Normally, ‘less than 1 year’ falls into the operational planning, where the aim is to manage and operate available resources in an efficient manner. More than that falls into the planning stages. If installing new equipment and predicting system behavior are possible in a shorter time (for instance, for distribution systems, 1–3 years), the term of short-term planning may be used. More than that (3–10 years and even higher) is called long-term planning (typically transmission planning) in which predicting the system behavior is possible for these longer periods. Short-term planning for the peak loading condition of the coming year, a power system utility expert notices that from the two lines, feeding a substation, one would be overloaded by 10% of its rating, while, the other would be loaded by 60% of its rating. After careful studies, he or she finds out that if a control device is installed on one line, the load distribution may be balanced on both lines. Once decided, the installation process of this device can be performed in such a way that no problem arises for the coming year. Long-term Versus Short-term Planning Long term planning Suppose that the load forecasting for the coming years shows that with all already available and planned generations, there would be a shortfall of generation in 9 years from now, onward. After a careful study, the planner decides on adding a new 2 x 500 MW steam power plant at a specific bus in that year. Its construction should start well in advance so that it would be available at the required time.
- 13. Power System Planning Issues 13 Example of Short-term planning The equation of power flow in transmission line is shown as Where, VS and VR are sending and receiving end voltages, X is the impedance and δ is the power angle. Thyristor Controlled Series Capacitor (TCSC) is a FACTS device connected in series on the transmission lines to control the dynamic power flow.
- 14. Power System Planning Issues 14 Example of Short-term planning Power Grid Corporation of India Ltd (PGCIL) has purchased two Thyristor Controlled Series Capacitors (TCSC) from ABB. The banks were installed on the Rourkela-Raipur double circuit 400 kV power transmission interconnector between the Eastern and Western regions of the grid to enable export of surplus energy from the Eastern to the Western regions of India.
- 15. Power System Planning Issues 15 Load Forecasting The first crucial step for any planning study is to predict the consumption for the study period (say 2019–2024), as all subsequent studies will be based on that. This is referred to as load forecasting. The same term is used for operational purposes, too. However, it is understood that a short-term load forecasting, used for operational studies, is significantly different from the long-term one used in planning studies. In a short-term load forecasting, for predicting the load for instance, of the next week, we come across predicting the load for each hour of the coming week. It is obvious that the determining factors may be weather conditions, special TV programs and similar. In a long-term load forecasting which is of the main interest of this course, we normally wish to predict the peak loading conditions of the coming years. Obviously, the determining factors are different here. Population rate increase, GDP (Gross Domestic Product) and similar terms have dominant effects. Load Forecasting GEP SEP NEP RPP
- 16. Power System Planning Issues 16 Generation Expansion Planning (GEP) After predicting the load, the next step is to determine the generation requirements to satisfy the load. An obvious simple solution is to assume a generation increase equal to load increase. If, for instance, in year 2020, the peak load would be 40,000 MW and at that time, the available generation is 35,000 MW, an extra generation of 5,000 MW would be required. Unfortunately, the solution is not so simple at all. Some obvious reasons are • What types of power plants do we have to install (thermal, gas turbine, nuclear, etc.)? • Where do we have to install the power plants (distributed among 5 specific buses, 10 specific buses, etc.)? • What capacities do we have to install (5 x 1000 MW, or 2 x 1000 MW and 6 x 500 MW, or …)? • As there may be an outage of a power plant (either existing or new), should we install extra generations to account for these situations? If yes, what, where and how? Load Forecasting GEP SEP NEP RPP
- 17. Power System Planning Issues 17 Substation Expansion Planning (SEP) Once the load is predicted and the generation requirements are known, the next step is to determine the substation requirements, both, in terms of • Expanding the existing ones, • Installing some new ones. This is referred to as Substation Expansion Planning (SEP). SEP is a difficult task as many factors are involved such as •constraints due to the upward grid, feeding the substations, •constraints due to the downward grid, through which the substation supplies the loads, •constraints due to the factors to be observed for the substation itself. Load Forecasting GEP SEP NEP RPP
- 18. Power System Planning Issues 18 Network Expansion Planning (NEP) Through NEP, specifications of transmission lines, cables, etc. are determined. In fact, the network is a media for transmitting the power, efficiently and in a reliable manner from generation resources to the load centers. As inputs to the NEP problem, GEP and SEP results are assumed to be known. Reactive Power Planning (RPP) In running NEP, the voltages are assumed to be flat (i.e. 1 p.u.) and it is normally based on using Direct Current Load Flow (DCLF). Upon running GEP, SEP and NEP, the network topology is determined. However, it may perform unsatisfactorily. To solve such a difficulty, static reactive power compensators, such as capacitors and reactors may be used. Moreover, some more flexible reactive power resources such as SVCs may also be required. The problems include: • Where to install these devices? • What capacities do we have to employ? • What types do we have to use? Load Forecasting GEP SEP NEP RPP
- 19. Power System Planning Issues 19 Planning in Presence of Uncertainties The electric power industry has drastically changed over the last two decades. It has moved towards a market oriented environment in which the electric power is transacted in the form of a commodity. Now the generation, transmission and distribution are unbundled and may belong to separate entities. The planner can not, for instance, dictate where the generation resources have to be allocated. In this way, NEP problem is confronted by an uncertain GEP input. So, how NEP can be solved, once the input data is uncertain? Load Forecasting GEP SEP NEP RPP
- 20. Power System Planning Issues 20