1. Power System Planning
Dr. Muhammad Yousaf Ali,
Asstt Professor, Department of Electrical Engg,
Gomal University, D.I.Khan.
myousafak@gu.edu.pk
2. • Quiz (s) 3-4 15%
• Mid Term Exam 30%
• Assignments 3-4 10%
• End Term Exam 40%
• Presentations 5%
3. Text Book
• Electric Power Distribution Engineering, By Turan Gonen, 2nd Edition
• Reference Books and Material: Internet or any other related Book
4. Lecture Contents
• Introduction to Course
• Power system
• Distribution System Planning
• Factors Affecting the System Planning
• Basic Definitions
5.
6. Definition
• An electric power system is a network of electrical components
deployed to supply, transfer, and use electric power
• An example of an electric power system is the grid that provides
power to an extended area
• An electrical grid power system can be broadly divided into
the generators that supply the power, the transmission system that
carries the power from the generating centres to the load centres,
and the distribution system that feeds the power to nearby homes
and industries.
7. • Smaller power systems are also found in industry, hospitals,
commercial buildings and homes
• The majority of these systems rely upon three-phase AC power—the
standard for large-scale power transmission and distribution across
the modern world
• Specialized power systems that do not always rely upon three-phase
AC power are found in aircraft, electric rail systems, ocean liners and
automobiles
8. • Since an Electric power system includes Generation, Transmission and
Distribution of Energy
• The electric utility industry grew very rapidly and the generation
stations and transmission and distribution networks spread across the
entire country
• Considering energy needs and available fuels that are forecasted for
the next century, energy is expected to be increasingly converted to
electricity
• Operation and maintenance is major part of power system planning
10. Power system Planning
• 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
• Capacitor/Reactors
11. Static Versus Dynamic Planning
• If the peak loading conditions are to be investigated, the studies
involve six loading conditions
• One way is to, study each year separately irrespective of the other
years, this type of study is referred to as static planning which focuses
on planning for a single stage
• The other is to focus on all six stages, simultaneously, so that the
solution is found for all six stages at the same time, this type of study
is named as dynamic planning
12. • Although static planning for specific year provides some useful
information for that year, the process leads to impractical results for
the period as the solutions for a year cannot be independent from the
solutions from the preceding years
• One way to solve the problem is to include the results of each year in
the studies for the following year
• This may be referred to as semi static, semi-dynamic, quasi-static or
quasi-dynamic planning
13. • It is apparent that the dynamic planning solution can be more optimal
in comparison with the semi-static planning solution
• We should mention that the word dynamic here should not be
confused with power system dynamics
14. Transmission Versus Distribution Planning
• We may distinguish three main levels for a power system structure,
namely, transmission, sub-transmission and distribution.
• Distribution level is often planned; or at least operated, radially
• Figure 1.5 depicts a typical distribution network, starting from a 63
kV:20 kV substation, ending to some types of loads, via both 20 kV
and 400 V feeders.
• Note that switches A and B are normally open and may be closed if
required
• Switches C and D are normally closed and may be opened if required.
15.
16. • A small generation is also connected to the network, as some types of
local generations (named as Distributed Generations, or DGs)
connected to the distribution systems, are of current industrial
practices.
• Since both transmission and distribution networks comprise of
lines/cables, substations and generators
• However, due to specific characteristic of a distribution system (such
as its radial characteristics), its planning is normally separated from a
transmission system, although much of the ideas may be similar.
17. Short term and Long term Planning
• There is no golden rule in specifying short-term or long-term planning
issues.
• Normally, <1 year falls into the operational planning and operational
issues in which the aim is typically to manage and operate available
resources in an efficient manner
• More than that falls into the planning stages
18. • 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
• Moreover, installing a new element (such as a 765 kV UHV line or a
nuclear power plant) should be decided well in advance so that it
would be available in due course.
19. Generation Planning Example
• 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
• His or her decision is a typical long-term (9-year) transmission
planning decision.
20. Distribution System Planning
• System planning is essential to ensure the 100% safe and appropriate
power system operation
• In the past, the planning for the other portions of electric power
system and distribution system frequently had been authorized at the
company division level without review of or coordination with long
range plans
• As a result increasing cost of energy, equipment and labor etc is
encountered
• The distribution system is particularly important to an electrical utility
for two reasons; (i) its close proximity to ultimate customer and (ii) its
investment cost
21. • If distribution system of power supply system is the closest to
customer, its failures affect customer more directly than for example
failure on transmission and generating systems, which usually do not
cause customer service interruptions
• Therefore, distribution system planning starts at the customer level
• The demand, type, load factor and other customer load
characteristics dictate the type of distribution system required
22. Distribution planning
The distribution planning is one portion of the distribution system is
closely related to design of other parts of the system like distribution
voltage, arrangement of equipment etc.
• It is advantageous to perform step to step expansion planning
• Investment is the major point in distribution planning
• Check the existing distribution system data
• Analyzed the load pattern
• Distribution planning is given in next slide;
26. Load Forecasting
• The load growth of the geographical area served by a utility company
is the most important factor influencing the expansion of the
distribution system
• Therefore, forecasting of load increases and system reaction to these
increases is essential for planning process
• Here are two common time scales of importance to load forecasting;
long range with time horizon in order of 15-20 year away and short
range with time horizon in order of 5 years away
• Next slide gives factors affecting Load forecasting;
27.
28.
29. Substation Expansion
• Fig in next slide presents some of the factors affecting substation
expansion
• The planner makes a decision based on tangible or intangible
information.
• For example, the forecasted load, load density and load growth may
require a substation expansion or a new substation construction
• For expansion present system configuration, capacity, and the
forecasted loads can play major roles
30. Substation Site Selection
• Fig shows factors that affect substation site selection
• The distance from load centers and from existing sub transmission
lines as well as other limitations, such as availability of land, its cost,
and land use regulations are important
• Service region is the area under evaluation defined as the territory of
the utility
• An initial screening is applied by using a set of considerations like
safety, engineering system planning, institutional economics etc
34. Distribution system planning- Technical
aspects
• One of the essential elements in distribution system planning is the
location of the load centre where the primary substation is situated
• Establishment of load centre or primary substation, particularly in a
densely populated area, must be prepared in long-term plan, for
example, in a 10-year plan
• The outlets from the primary substation will then supply the required
electrical energy to the nearby customer loads
• Customer substations will then further transform the distribution high
voltage to the LV (LV refers to the voltage below 1000V).
35. Basic Design Criteria
• Distribution network refers to those 22kV or 11kV network supplying
electricity to customers through cable or Overhead Line (OHL)
• From primary substation to various customer substations, various
types of network configurations are possible, for example, single-end
fed, double-end fed and closed ring network arrangement
• In the customer substation, it normally consists of the step down
transformer to LV; it may also contain HV circuit breaker(s), ring main
units
36. • Additional consideration is the availability of remote control facilities
to enhance the security of supply
• In transmission network, the typical design concept is the ‘N-1’
reliability application
• ‘N-1’ is referred to as any single component failure in the supply
network will not affect the electricity supply
• Hence in the case of a failure of a transmission line, or a transformer
connected to the distribution primary substation from the
transmission source, the supply to the distribution network will not
be affected
37. • It is normally achieved with suitable protection and associated inter-
tripping or switching scheme to the distribution incoming from the
transmission network
• Hence, the primary substation is thus designed to supply a firm load
based on the calculation of ‘N-1’ criteria
• On the other hand, the distribution network connected from the
primary source substation will depend on the geographical locations
of the customer substations
38. Transmission substation
• A transmission substation connects two or more transmission lines
• In case where all transmission lines have the same voltage: the
substation contains high-voltage switches that allow lines to be
connected or isolated for fault clearance or maintenance
• A transmission station may have:
• 1. Transformers to convert between two transmission voltages,
• 2. Voltage control/power factor correction devices such as capacitors,
reactors or static VAR compensators
• 3. Phase shifting transformers to control power flow between two adjacent
power systems.
39. • Transmission substations can range from simple to complex
• The large transmission substations can cover a large area (several
acres/hectares) with multiple voltage levels, many circuit breakers
and a large amount of protection and control equipment
40. Distribution substation
• A distribution substation transfers power from the transmission
system to the distribution system of an area
• The input for a distribution substation is typically at least two
transmission or sub transmission lines
• Distribution voltages are typically medium voltage, between 2.4 and
33 kV depending on the size of the area served and the practices of
the local utility
• Besides changing the voltage, the job of the distribution substation is
to isolate faults in either the transmission or distribution systems.
41. Types of Distribution Networks
• Single-end radial fed
• Single-end radial fed refers to a number of customer substations or
pole-mounted substations are connected to the primary substation
• The supply security is the lowest as any single point failure will result
in the loss of supply to the customer substation
• Similarly, any single failure in the customer substation will result in
loss of supply to the customer
• In case of fault, the supply restoration will depend on the fault repair
time.
42. Double-end fed with an NO Point
• To provide a higher supply security, the customer substations can be
fed from two sources as shown in fig
• The customer substation is normally supplied from a single end and in
the case of loss of supply from the one source end, for example due
to a component failure, the NO (normally open) point can be closed
to restore supply after the faulty portion of the component is isolated
• The supply restoration will be quicker and is not directly depending
on the fault repair time
• The customer substation may consist of Ring Main Unit (RMU) and
equipped with earth fault indicator as shown below;
44. In an electrical power distribution system, a ring main unit (RMU) is a factory assembled, metal
enclosed set of switchgear used at the load connection points of a ring-type distribution network.
45. • This configuration results in loss of supply in case of fault in the RMU
circuit since the controlling circuit breaker at the controlling/customer
substation will trip to isolate the faulty circuit
46. Ringed Network Arrangement
• A typical customer substation in a ring-configured network contains
two feeders and one transformer feeder
• The former have circuit breakers and cable connecting to other
substations while the later has circuit breaker and cable connecting to
11kV/LV transformer
• A typical ringed network arrangement is shown in fig
47.
48. Basic Understanding
• To understand some of the problems that the power industry faces let us
briefly review some of the characteristic features of generation and
transmission
• The power system must, be capable of matching the output from
generators to the demand at anytime at a specified voltage and frequency
• The difficulty encountered in this task can be imagined from the fact that
load variations over a day comprises three components-a steady
component known as base load; a varying component whose daily pattern
depends upon the time of day; weather, season, popular festival, etc. and
a purely randomly varying component of relatively
small amplitude
49. • Figure shows a typical daily load curve.
• The characteristics of a daily load curve on a gross basis are indicated
by peak load and the time of its occurrence and load factor defined
as;
• Average load/ maximum (peak) load = less than unity
50. • The average load determines the energy consumption over the day,
while the peak load along with considerations of standby capacity
determines plant capacity for meeting the load
• A high load factor helps in drawing more energy from a given
installation
