The document provides an introduction to power system planning. It discusses the key elements of power systems including generation, transmission, and loads. It describes different types of power system studies conducted over various time horizons from long-term planning studies conducted years in advance to short-term operational studies conducted within hours or minutes. The document also discusses different types of power system planning issues including load forecasting, generation expansion planning, substation expansion planning, network expansion planning, and reactive power planning. It notes the challenges of planning in the presence of uncertainties in an deregulated electric power market.

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
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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
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 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
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Fig. : One line diagram of a typical power system

7. Power System Studies- A Time Horizon
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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
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• 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
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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
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• 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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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21. Thank You.
Questions? Confusions!
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