The document discusses power flow analysis, which determines the voltage, current, real power, and reactive power at points in an electrical network under normal operating conditions. It provides three key points: 1. Power flow analysis is important for planning, operations, and future expansion of power systems by studying the effects of new loads, generators, or transmission lines. 2. The analysis involves classifying buses as slack, generator, or load buses and formulating the network equations based on the bus admittance matrix. 3. Solving the load flow problem involves determining the complex voltages across all buses given the network configuration and bus demands. This provides critical information for monitoring overloads and voltage deviations.

1. Contents:
 Introduction
 Significance
 Importance
 Classification of Buses
 Description of Load Flow problem
Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi 1

2. Introduction:
 Power flow analysis is one of the basic tools used in
the power system studies.
 It is connected with the steady state analysis of the
system when it is working under the normal balanced
operating condition.
 Load flow or power flow analysis is determination of
the voltage, current,real power and reactive power at
various points in electrical network.
 The information of load flow is essential for analyzing
the effective alternate plan for the system expansion to
meet increase load demand.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

3. Significance in Load flow or power flow analysis
 The load flow studies are very important for planning,
economic scheduling, control and operations of existing
systems as well as planning its future expansion depends up on
knowing the effect of interconnections, new loads, new
generating stations, or new transmission lines, etc., before they
are installed.
 With the help of load flow studies, we can determine the best
size as well as the most favourable location for the power
system capacitors both for the improvement of power factor
and raising the bus voltages of the electrical network.
 It helps us to determine the capacity of the proposed generating
stations, sub stations, or new lines.
 Problems such as the optimization of the system losses,
stability check and general security of the system can be
studied with the help of load flow studies.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

4. Contd…
 The information obtained from the load flow studies are the
magnitude and phase angle of voltages at each bus, active and
reactive power flow in each line, and power loss in the line.
 It also gives the initial conditions of the system when the transient
behaviour of the system is to be studied.
 The mathematical formulation of the load flow problem results in a
system of non-linear equations.
 These equations can be written in the terms of either the bus
admittance matrix or bus impedance matrix.
 Using the bus admittance matrix is amenable to digital computer
analysis, because it could be formed and modified for network
changes in subsequent cases, and requires less computation time and
memory.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

5. Contd….
 The load flow analysis can be carried out for small and
medium size power systems.
 It suits for radial distribution systems with high R/X ratio.
 The load flow analysis helps to identify the
overloaded/underloaded lines and transformers as well as
overvoltage/undervoltage buses in the system.
 It is used to study the optimum location of capacity is and
their size to improve unacceptable voltage profile.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

6. Need for load flow analysis or importance of power flow
analysis in planning and operation of power systems
 Load flow analysis is performed on a symmetrical steady-state
operating condition of a power system under normal mode of
operation. This information is essential for long term planning
and operational planning.
Long term planning
 Load flow analysis helps in investigating the effectiveness of
alternative plans and choosing the best plan for system
expansion to meet the projected operating state.
Operational Planning
 It helps in choosing the best unit commitment plan and
generation schedules to run the system efficiently for the next
day’s load condition without violating the bus voltages and line
flow operating limits.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

7. Steps for load flow study:
The following work has to be performed for a
load flow study:
 Representation of the system by single line diagram
 Determining the impedance diagram using the information
in single line diagram
 Formulation of network equations
 Solution of network equations
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

8. Classification of buses
 In the network power system, buses become nodes and voltage can
be specified for each bus.
The power flow equation is
Pi+jQi =Vi 𝑌
𝑁
𝑗=1
ij
*Vj
* i=1,2,3,…N --------------(1)
Complex bus voltage Vi=| Vi|< 𝛿i ------------------(2)
 From equation (1) and (2) ,we know that power system is associated
with four quantities and real power(P),reactive power(Q),Voltage
magnitude|V|,and phase angle of the voltage(δ).
 In load flow problem,two quantities are specified for each bus and
the remaining two quantities are obtained by solving the load flow
equations.
There are three types of buses.
 Slack bus or swing bus or reference bus
 Generator bus or voltage controlled bus or P-V bus or regulated bus
 Load bus or P-Q bus
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

9.  The following table gives the quantities specified and
the quantities to be specified for each bus
S.No Bus Quantities Specified
Quantities to be
specified
1 Slack bus |V|,δ P,Q
2 P-V bus
P, |V|
Q,δ
3 P-Q bus P,Q |V|,δ
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

10. Slack Bus
 In slack bus, voltage magnitude and phase angle of voltages are
specified pertaining to a generator bus usually large capacity
generation bus is chosen. We assume voltage(V) as reference phasor.
 This bus makes up the difference between he scheduled loads and the
generated power that are caused by the losses in the network.
 Obtain (N-1) complex bus voltages from the (N-1) load flow
equations.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

11. Contd…
 Incidentally the specification of |Vslack| helps us to fix the
voltage level of the system. In power flow study, at all buses
net complex flow in to the network is not known in advance.
 While specifying a generation schedule for a given system
demand, one can fix up the generation setting of all the
generation buses except one bus because of the limitation of
not knowing the transmission loss in advance. Therefore it is
necessary to have one bus called slack bus.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

12.  PL depends on I2R loss in the transmission line and
transformers of the network.
 The individual currents in the various lines of the network
cannot be calculated until after the voltage magnitude and
angle are known at every bus of the system.
 Therefore PL in initially unknown.
 Real and reactive powers are not specified for slack bus.
 After the power flow problem has been solved, the difference
between the total specified real power going in to the system at
all the other buses and the total power consumed by loads plus
I2R losses are assigned to the slack bus.
 Therefore a geneator bus must be selected as a slack bus.
 The slack bus is needed to account for transmission line losses.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

13. Generator bus or P-V bus or voltage controlled bus or
regulated bus
 At these buses,the real power and voltage magnitudes are specified.
The phase angles of the voltages and the reactive power are to be
determined. The limits on the value of the reactive power are also
specified.
 In order to maintain a good voltage profile over the system,
Automatic Voltage Regulator(AVR) is used.
 Static VAR compensator buses are also called as P-V buses because
real power and voltage magnitudes are specified at these buses.
Load bus or P-Q bus
 At these buses,the active and reactive powers are specified. The
magnitude and phase angle of the voltage are unknown.These are
also called as load bus.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

14. Description of load flow problem
 In load flow analysis, the system is considered to be operating
under steady state balanced condition and per phase analysis is
used.
 The network consists of a number of buses[Generator, load
buses]representing either generating station or bulk power sub
station, switching stations interconnected by means of
transmission lines or power transformers.
 Each transmission line is characterized by its π equivalent
circuit.
 The transformer with off-nominal tap ratio is characterized by
their π equivalent circuit.
 Shunt compensating capacitors or reactors are represented as
shunt susceptance.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
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15. Contd…
 Load flow analysis is essentially concerned with the
determination of complex bus voltages at all buses, given
the network configuration and bus demands.
 The bus generation and demand are characterized by
complex powers flowing into and out of the buses
respectively.
 A generation schedule is nothing but a combination of MW
generation of the various generators should match the given
system demand plus the transmission losses.
 It should be noted that there are many generation schedules
available to match the given system demand and one such
schedule is chosen for load flow analysis.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

16. Ideal Load Flow Problem (or)Statement of Ideal load flow
problem:
 Load Flow Problem is stated as follows:
 Given: The network configuration[line impedance and half line
charging admittance] and all the bus power injections.
Pi=PG-PD
Where Pi=Bus power injection
PG =Bus generation
PD =Bus demand
 To determine the complex voltage at all the buses:
The state vector X is defined as
X=[V1, V2,…… VN,δ1, δ2,……….. δN]T
 Once the voltages at all the buses are known,then we can
compute slack bus power,power flows in the transmission lines
and power loss in the transmission lines.
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

17. Practical Load Flow problem or Statement of practical
power flow problem:
 Practical load flow problem can be stated as follows:
 Given: The network configuration, complex power
demands for all buses, real power generation Schedules
and voltage magnitudes of all the P-V buses and voltage
magnitude of slack bus
 To determine:
Bus admittance matrix
Bus voltage phase angles of all buses except the slack bus
and bus voltage magnitudes of all the P-Q buses.
State vector X=[V1, V2,…… VN,δ1, δ2,……….. δN]T
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Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi

18. 1. Hadi Saadat, ‘Power System Analysis’, Tata McGraw Hill Education Pvt. Ltd., New
Delhi, 21st reprint, 2010.
2. Kundur P., ‘Power System Stability and Control, Tata McGraw Hill Education Pvt.
Ltd., New Delhi, 10th reprint, 2010.
3. Pai M A, ‘Computer Techniques in Power System Analysis’, Tata Mc Graw-Hill
Publishing
Company Ltd., New Delhi, Second Edition, 2007.
4. J. Duncan Glover, Mulukutla S. Sarma, Thomas J. Overbye, ‘ Power System
Analysis & Design’, Cengage Learning, Fifth Edition, 2012.
5. Olle. I. Elgerd, ‘Electric Energy Systems Theory – An Introduction’, Tata McGraw
Hill Publishing Company Limited, New Delhi, Second Edition, 2012.
6. C.A.Gross, “Power System Analysis,” Wiley India, 2011.
7. M.Jeraldin Ahila “Power System Analysis”, Lakshmi Publications, Chennai,
Eleventh Edition 2017.
8. Web sources
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REFERENCES:
Kongunadu College of Engineering and Technology Power Flow Analysis Prepared by,
Mrs.S.Revathi