Power System Analysis

1. Dr. Sanjeev Kumar
Assistant Professor
Department of Electrical & Electronics Engineering
HCST, Mathura, India
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2. Course Outcome
CO1 Identify power system components on one line diagram of power system and its
representation including the behavior of the constituent components and sub
systems and Analyze a network under both balanced and unbalanced fault
conditions and design the rating of circuit breakers.
K4
CO2 Perform load flow analysis of an electrical power network and interpret the results
of the analysis.
K4
CO3 Describe the concept of travelling waves in transmission lines and use the
travelling wave theory to determine the over voltage caused by surge propagation
in transmission networks.
K4
CO4 Assess the steady state and transient stability of the power system under various
conditions.
K4
CO5 Describe Operating Principle of a relay and classify them according to
applications. Explain working principle of Circuit breaker and phenomenon of arc
production and quenching.
K3
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3. UNIT-I
Fault Analysis in Power System
One-line diagram, Impedance and reactance diagram, per unit system changing the base of
per unit quantities, advantages of per unit system.
Symmetrical Components: Significance of positive, negative and zero sequence
components, Average 3-phase power in terms of symmetrical components, sequence
impedances and sequence networks.
Fault Calculations: Fault calculations, sequence network equations, single line to ground
fault, line to line fault, double line to ground fault, three phase faults, faults on power
systems, and faults with fault impedance, reactors and their location, short circuit capacity of
a bus
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5. Definition: In power engineering, a one-line diagram or single-line diagram
(SLD) is a simplified notation for representing a three-phase power system. A
single line diagram is a representation of the essentials of a system in a most
simplified form.
 It is a form of block diagram graphically depicting the paths for power flow
between entities of the system.
 The theory of three-phase power systems tells us that as long as the loads on
each of the three phases are balanced, we can consider each phase separately.
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6.  In power engineering, this assumption is often useful, and to consider all
three phases requires more effort with very little potential advantage.
 The one-line diagram has its largest application in power flow studies.
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7.  The electrical elements such as circuit breakers, transformers, capacitors,
bus bars, and conductors are shown by standardized schematic symbols.
 An accurate diagram ensures optimum system performance and
coordination for all future testing and can highlight potential risks before
a problem occurs.
 The information supplied by a single line diagram varies according to the
requirement. For example the one line diagram for load flow studies may
not include circuit breakers. For stability studies circuit breakers and
relay positions are shown in one line diagram.
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8.  In many process facilities, loads are continually added or removed in
small increments. The net effect is not always seen until some part of the
system becomes overloaded or exhibits other problems.
 Therefore, single line diagram helps to analyze a building's electrical system,
provide the facility to outline any identification of possible problem places,
improved safety conformity, and enhanced staff safety.
 Inaccuracy in this documentation and failure to update one-line diagrams on
a regular basis as electrical systems invariably grow over time often results
in increased down time when system failures occur.
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9. Figure shows the symbols used to represent the typical components of a power
system.
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12. Draw one-line diagram of a power system described as follows: Two
generators, one grounded through a reactor and one through a resistor,
are connected to a bus and through a step up transformer to a
transmission line. An other generator grounded through a reactor is
connected to a bus and through a transformer to the opposite end of the
transmission line.Aload is connected to each bus.
Solution:
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13. Draw one-line diagram of a power system described as follows: three
generators solidly grounded are connected to a bus and through a step up
transformer to a transmission line. The other two generator solidly
grounded are connected to a bus and through a transformer to the
opposite end of the transmission line.Aload is connected to each bus.
Solution:
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14. Definition: A diagram in which all the equipment of the system are
represented by their impedances is known as Impedance Diagram. In the
impedance diagram, the different components of the power system are
replaced by their equivalent circuits.
 In impedance diagram, the synchronous generator is replaced by a constant
voltage source behind proper impedance.
 The transformer is replaced by its equivalent circuit.
 The transmission line is replaced by nominal pi-equivalent circuit.
 The diagram should take induction motor into account by a generated emf
in series with an inductive reactance if the diagram is to be used to
determine the current immediately after the occurrence of a fault.
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15.  However, Induction motors are ignored in computing the current a few
cycles after the fault occurs because the current contributed by an
induction motor dies out very quickly after the induction motor is short
circuited.
 Since the shunt current of a transformer is usually insignificant compared
with the full load current, the shunt admittance or capacitance is usually
omitted in the equivalent circuit of the transformer.
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16. A diagram in which all the equipment of the system are represented by their
reactance is known as Reactance Diagram”.
In many power system studies, the resistance of synchronous generator, transformer
windings, transmission lines, line charging and magnetizing circuits of transformers
are neglected. The impedance diagram then becomes the reactance diagram.
Resistance is often omitted when making fault calculations, even in computer
programs. Of course, omission of resistance introduces some error, but the results
may be satisfactory since the inductive reactance of a system is much larger than its
resistance.
The one line diagram may be converted to an impedance diagram and vice versa.
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17. Draw impedance diagram of the single line diagram given below. Also draw the
reactance diagram by omitting all static loads, all resistances, magnetizing current of
each transformer and the capacitance of Transmission line.
Example:
Figure: Single Line Diagram
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18. Solution
Impedance Diagram
Reactance Diagram
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19. Draw impedance diagram of the single line diagram given below. Also
draw the reactance diagram by omitting all static loads, all resistances,
magnetizing current of each transformer and the capacitance of
Transmission line. For transmission line use nominal T method.
However, nominal Pi method can also be used.
Example
Figure: Single Line Diagram 19

20. Solution
Reactance Diagram
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Impedance Diagram