TRANSIENT STABILITY ANALYSIS FOR IEEE-6 BUS SYSTEM
USING ETAP SOFTWARE
Name: Ms Medhanit Mulatu
School of Electrical and Computer Eng.
Haramaya Institute of Technology
Haramaya, Ethiopia
Name: Ms Delila Yalew
School of Electrical and Computer Eng.
Haramaya Institute of Technology
Haramaya, Ethiopia
Email:medhanitmulatu6796@gmail.com
Email:delila4y@gmail.com
Name: Ayele Nigussie (PHD)
School of Electrical and Computer Eng.
Name: Ayele Nigussie (PHD)
School of Electrical and Computer Eng.
Haramaya Institute of Technology
Haramaya, Ethiopia
Haramaya Institute of Technology
Haramaya, Ethiopia
ayelenigussie@yahoo.com
ayelenigussie@yahoo.com
Abstract
Name: Mr Menaleshewa Getahun
School of Electrical and Computer Eng.
Haramaya Institute of Technology
Haramaya, Ethiopia
Email:minaleshewa24@gmail.com
Name: Ayele Nigussie (PHD)
School of Electrical and Computer Eng.
Haramaya Institute of Technology
Haramaya, Ethiopia
ayelenigussie@yahoo.com
Fault; Transient stability
The purpose of this paper is to examine the
transient stability of the power system when a
I.
Introduction
Power system stability involves the study of the
symmetrical three phase fault is created at bus
dynamics of the power system under disturbances.
by using ETAP software. Transient stability is
Power system stability implies that its ability
the
to return to normal or stable operation after
ability
synchronous
of
speed
a
machine
even
to
focused
run
to
at
large
having
been
subjected
to
some
form
of
disturbances. At this juncture the transient
disturbances From the classical point of view
stability analysis is carried out for 6 bus system.
power system instability can be seen as loss of
The enrichment in stability and the power
synchronism (i.e., some synchronous machines
oscillation is damped out when the fault is cleared
going out of step) when the system is subjected
within time. The fault is created at bus 5 for 0.3
to a particular disturbance.Threetype of stability
second and the clear fault time is 0.5 second. If
are
the fault is not cleared within the time, the
dynamic stability Steady-state stability relates to
generator losses its synchronism that is the
the response of synchronous machine to a
generator goes out of step and produces power
gradually increasing load. It is concerned with the
oscillations in the output. In order to diminish the
determination of the upper limit of machine
power oscillations and bring the system again to
loading without losing synchronism, provided the
stable critical clearing time is used. After the fault
loading is increased gradually.
is cleared,
the system oscillations are damped
Dynamic stability involves the response to small
simultaneously the generator runs in synchronism.
disturbances that occur on the system, producing
Keywords:-Critical
oscillations. The system is said to be dynamically
clearing
time;
ETAP
software; Steady state stability; Three phase
of
concern: Steady state, transient and
stable if theses oscillations do not acquire more
When synchronous machine losses synchronisms
than certain amplitude and die out quickly.
with respect to the other machines, the rotor starts
If
continuously grow in
to rotate at higher or lower speed. The system is
amplitude, the system is dynamically unstable.
designed to operate with set of conditions. The
The source of this type of instability is
conditions considered are short circuits faults,
usually
phase to ground fault, phase to phase to ground
these oscillations
an
interconnection between control
systems. Transient stability involves the response
to large disturbances, which may cause rather
faults or three phase fault [6] – [9].
II.
Power System Modelling
large changes in rotor speeds, power angles and
power transfers. Transient stability is a fast
phenomenon usually evident within a few second.
The transients are Caused due to sudden addition
or rejection of loads, short circuit, and switching
operations [3] [5]. Instability of a system means
synchronous
machine
unable
to
maintain
synchronism and it comes to out of step condition.
That is the rotor oscillation goes beyond 180
degree, the machine losses
its
synchronism
therefore 180 degree is the standard transient
stability
limit.
If
the generator
oscillates
outside the limit the system will not be
operated in stable operating condition. In order
to make the system to be stable critical
clearing time is used. The critical clearing
time is the maximum allowable time for
clearing the fault. However, critical clearing
time is not adequate decisive factor to assess the
transient stability when severe fault occurred in
the power system. The oscillation of generator
is measured with infinite bus or grid which is
Figure 1:-Three Machine and six Bus IEEE
System
Represented as slack bus. As rotor oscillates the
synchronous machine, power output varies. Under
normal
operating
condition
speed
synchronous machine does not change.
of
III.
Software Used
The software used for simulation is ETAP
(Electrical Transient Analysis Program). The
designer
and
developer
of
ETAP
is
the
“Operation Technology, Inc” (OTI). ETAP is a
Swing bus is considered as the reference bus
graphical enterprise package.
while doing load flow study and also this
ETAP widely used as analysis software for the
also known as slack bus. Normally, this bus is
design,
used to account for the transmission line losses.
operation,
control,
simulation,
optimization, monitoring, and automation of
For load flow, analysis fast decouple gauss seidel
power systems [10] – [14].
this
and Newton Raphson methods are used. In this
software we can perform different analysis on
paper Newton Raphson method is used because it
a bus system, it includes load flow analysis,
is more efficient, take less time and less
arc flash analysis, harmonic analysis, short
Iteration count. The first generator connected to
circuit analysis, and transient stability analysis
the bus is kept as slack bus. Initially load flow
etc. Transient stability studies includes identifying
Analysis had to be performed to determine the
critical clearing time, preparing and testing load
power consumed by each loads [20] [21].
By using
shedding schedule, checking generator rotor angle
stability, evaluating relay setting.
IV.
Simulation Diagram
Load
flow
study
deals
with
the
various
methods used to obtain the solutions for the
power system network. As a result, we will
get the magnitude and phase of bus voltages,
real and reactive power flow values in all the
lines and the line loss data. The buses of power
system can be classified as
Load bus
Generator bus
Slack bus
Load bus
Real and reactive power of bus is precise.
The voltage is to vary within the limit.
Figure 2:- Test System
Generator bus
In generator bus, we know the P and V values.
Load flow analysis is used to find out reactive
Power and the phase angle.
Swing bus
V.
Simulation Result And Discussion
The transient stability is analyzed for 6-bus
system, which is shown in Figure 2. For initial
load flow, solution Newton Raphson method is
used. The maximum number of iteration is 3, the
solution precision for initial load flow is 0.001,
the time increment for integration steps is 0.001,
the total simulation time will be 10 seconds and
the plot time step will be of 20. The three-phase
fault is created at bus 5 for 0.3 second and is
cleared after 0.5 second with the help of transient
stability study case editor. At starting there will
not be any power oscillations in the output, the
machine runs at synchronous speed. When time is
at 0.3 second there will be oscillations in the
output, the generator losses its synchronism that is
the electrical power output is less than the
mechanical power input. When time is at 0.5
second the fault at bus is cleared so the
electromechanical oscillations are reduced and
the
system
remains
to
stable
operating
condition. In transient stability study case editor in
Figure:-3 Generator Relative power angle
Figure 3 shows generator power angle Vs time.
When the mechanical power is greater than the
electrical power, it produces oscillations in the
output. The electro mechanical oscillations are
reduced after clearing the fault at 0.5 second.
plot section, we have to mention the device id that
is generator 2 and 3, plot, and tabulate then only
the different output plots are generated. Using
ETAP the transient stability analysis can generate
report by using report manager.
VI.
Use ETAP program transient Stability
shown in Figure 2.
A three Phase Fault Occurs on line 5 near bus 6,
and cleared Simultaneous opening of Circuit
breaker both ends of the line. Determine System
Stability analysis when Fault cleared at 0.5 sec
The different plots for Generator 2 and Generator
3 are shown in figure below.
Figure:-4. Generator Electrical Power
Figure 5 shows generator electrical power Vs
time. The electro mechanical oscillations are
reduced and the power swing is damped out and
the system attains stable condition.
Figure:-8 Generator speed
Figure:-6 Generator Electrical Power
Figure 5 shows generator electrical power Vs
time. The electro mechanical oscillations are
reduced and the power swing is damped out and
the system attains stable condition.
Figure 9:- Generator Exciter voltage
Figure 7:- Generator Terminal Current
Figure 6 shows terminal current Vs. time. The
oscillations in the terminal current output is
reduced and when the system reaches stable
operating condition.
operate in stable operating condition. As the result
shows that at the beginning the generator is
operated at stable operation and when the fault is
created then there is a oscillation in the output
which represents that the generator loss its
synchronism and falling out of step. When the
fault is cleared then the oscillation are reduced
and produces stable output, which shows that the
generator has return to normal condition and
remains synchronism that is in step. During fault,
the oscillation is created in the output of
Figure 10:- Generator Characteristics
generator, after abnormal condition the power
oscillations and power swing are damped out and
get better response in the output.
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