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Short Circuit Analysis & Over current Relaying Coordination of IEEE 9-Bus
System
Conference Paper · April 2018
DOI: 10.1109/IMTIC.2018.8467260
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Short Circuit Analysis & Over current Relaying
Coordination of IEEE 9-Bus System
Shoaib A. Shaikh, Kundan Kumar
Asif R. Solangi, Shubash Kumar
Aizaz Ali Soomro,
Hamdard University
Karachi
shoaib.ahmed@hamdard.edu.pk
FEST Indus University, Karachi
solangiasif66@gmail.com
NED UET, Karachi
Abstract—It is an essential and compulsory to design an empty
interrupted electrical power system network having security,
stability and reliability in this electricity dependent era. In this
paper Short circuit analysis and Protection relying
coordination of IEEE 9-Bus system is analyzed and designing
of overcurrent relaying scheme to operate the relay quickly and
disconnect the faulty section from healthy section. Electrical
Power system built in the industry needs appropriate protection
strategy for reliable operation. Undetected and sudden faults
can become hazardous and disturb the entire system, power
devices and causes the overheating, unbalanced system
conditions, up and down of the system voltage and blackouts
etc. Proposed designing consists of nine buses (two generator
buses, one slack bus and six load buses), three transformers of
100MVA at three buses Bus- 1, 2 &3, placement of transmission
lines are used. The load flow and fault analysis study are carried
out before the protection design of the system. The power flow
analysis keeps vital role due to identification of network
capability to run with maximum load having no any effect on
the system stability. The load flow and fault analysis study are
carried out before the protection design of the system.
Keywords— IEEE 9- Bus system, Load flow analysis, Short
circuit (SC) analysis, Protection relaying coordination, OC
protection.
I. INTRODUCTION
Electrical Power system covers three principal parts as
Generation, transmission and distribution systems. The main
objective of the power system is to fulfill all the segments of the
system electrical energy with high possible efficiency to deliver
to users at satisfactory frequency, voltages and reliability. An
important segment is the distribution system which connects the
generators and equipment used on the consumer side by
carrying the electricity from transmission system comprises of
feeders, distributors and service mains with suitable protective
and controlling devices [1].
A report has been created which showed that 80%
interruptions are observed to the consumer side in due to
failure of distribution system. To make it an efficient system,
distribution automation is made applicable to the
978-1-5386-6594-7/18/$31.00 ©2018 IEEE
distribution feeders for the achievement of substantial and
quick enhancement in security, reliability and quality to the
customers. Several techniques as var planning, optimization
of network, stat estimation, feeder reconfiguration, analysis
of fault etc. has mandated to construct distribution
automation (DA) effectively [2-6].
Old-style objects engaged to secure acceptable protection
whereas controlling the system have been insufficient [7].
The essential requirement of Power Company and utility is
classified as efficient arrangement and exact forecast of
equipment age having strictness to avoid the under-usage
and over-usage of existing resources. Requirements to model
power system of main three categories electrical power
generation, transmission and distribution has become
necessary for making some actual-value verdicts for capital
investment and management. The factors for modeling and
designing the efficient systems with the usage of analytical
tools comprise: augmented productivity, reduction of capital
disbursement, decrease in inventory outdated segments,
decrease in repair cost, investment reduction after first year
execution and enhanced amenities etc. [8].
Analysis of faults had become sophisticated and difficult in
old era but in this scientifically and technological era it has
become complex and convenient as numerous fast and
reliable computing methods have been introduced as
MATLAB, ETAP etc. The fast and reliable techniques for
different faults also require an effective and efficient faultanalysis technique. The exact information of fault is not only
acceptable for fault recognition algorithms or prototypes but
proper protective relays operation and correct resolve of
different fault types [9]– [12]. The software tools for the
analysis of power system are not partial to their main
technical characteristics though it also contains separate
competences for modeling, design and analysis of the
system. Key features comprise; power flow analysis, Load
flow analysis, short circuit (SC) analysis, power system
stability, power system protection,
coordination of the system, optimal power flow and
reliability etc.
In this paper we have worked on the short circuit analysis of
IEEE 9-bus system with overcurrent (OC) relaying scheme
on ETAP software by examining the normal load-flow along
with fault analysis. A procedure to obtain the electrical
power systems steady-stat voltages at fundamental
frequency is named as load flow [13]. Out of nine buses, we
have considered here two voltage-controlled buses i.e. 1 and
2, one as swing bus i.e. 3 and six buses as load buses i.e. 49, three transformers with a transmission line in between
them. For the protection circuit breakers have also been
placed with an addition of overcurrent relays. Several three
phase faults as L-G, L-L and L-L-G have been placed
individually on Bus-7 and results have been recorded also.
Furthermore, short circuit analysis of system is also included
in this paper to determine the positive (+ve), negative (-ve)
and zero -sequence impedance of faults. Last and the main
task of our work is on the sequence of operation of relays
connected on bus-7 and controlling on the relay having
minimal effect should run first and so on.
II. OVERVIEW OF FAULTS AND FORMULAE
In this era the electrical power system is almost
interconnected in which faults may occur and currents
flowing with a high rate must be disrupted before the
establishment of normal conditions. Several types of fault
occur as symmetrical and unsymmetrical faults. The
classification is also depicted in fig.1. From the faults, the
dangerous fault due to which maximum interruption arises
in network accessories is three phase fault or symmetrical
fault [14].
and protective relays keep vital role in designing of the
protection system to separate and disconnect the faulty
section from the normal or Steady State section. CBs rated
in MVA are designed and selected based on the interrupting
capacity of current by taking momentary SC current until
relay cross the threshold limit. It will be better for the system
that circuit ought to be separated on interruption at the initial
stage otherwise CB could not be able to break it because of
internal CB’s arc conduction
[14]. The equation 1 relevant to CB is given as:
SSC=√3*VPRE*ISC
(1)
Where;
SSC= Short circuit power,
VPRE=System pre-fault voltage
ISC= short circuit current
In this paper the fault is placed on the bus-7. For the
estimation of fault, the methodologies as base MVA and per
unit are applied here, the formulae in equation form are
given in equation 2-5.
!"#$ = Zold
Z Base = (
3 :;<,
* :;<,
Z p. u = Z ∗ (
I sc =
*+,*./0
)
+
3./0
3+,-
²
… (2)
………………………………. (3)
B CDEF
G CDEF²
)
…………………………. (4)
B EJ KLM∗NO⁶
R
G QDEF∗NOᵌ …………….…………… (5)
The protective relay is used for sensing the fault current
which then send the trip signal to the circuit breaker. The
proper setting of the relay is necessary for the efficient power
system. Different types of protective relays exist are selected
based on several applications as distance relays, differential
relays, overcurrent relays etc. The relay has two setting; plug
setting and time setting. The time setting is for deciding the
time of relay operation whereas plug setting decision is done
based on current required to pick up for the relay. The relay
for time setting and pick up setting is shown in fig.2
Fig. 1 Types of Fault
Fault is an undesired and sudden condition that not only
make the network stressed but also effect on the cost due to
equipment failure. Before damaging any equipment, it is
mandatory to block the high flow of current. Fault in a
distribution network is undesired situation that puts the
network into more stressed condition. The result of fault is a
very high current flow and it is necessary to block it before
it damages any section of network. Circuit breakers
Fig. 2 Overcurrent relay
Several mathematical models exist for the OC relays as
Inverse definite time over current relay, very inverse definite
time overcurrent relay and extremely inverse time
overcurrent relay are shown in equation 6-8 respectively.
top =
top =
top =
O.NU(VWB) X
YBW Z.Z[ \N
N].^(VWB) X
YBW X \N
_O.O(VWB) X
YBW [ \N
…………………… (6)
relays and in the last the results taken in the form of curves
in the graph.
…………………………..... (7)
……………………………. (8)
Where;
PSM= I relay / PS and Plug setting= rated CT secondary x
some percentage
The primary current of CT is decided by considering the
maximum load current which CT primary must carry. Next
category is the setting of relay which involves the selection
of pick up value of the relay and operating time of the relay.
The arrangement of pick-up setting should be done such that
coordination time in between relays must guarantee fault
interruption safely and securely [15]. Pick up value of the
relay can be set by keeping in mind that relay should operate
in both conditions in normal load conditions and certain
extension of overload to be supplied. Hence the pickup value
should be greater than maximum allowable load. At the same
interval, the response of the relay should also be sensitive on
the lowest fault as well. Thus, pick up value should always
be kept lesser than the smallest value of fault current If. To
set the pickup value, a rule is depicted as below:
`a, cde < `g. h < `i, cjk
A study of protection coordination is used for governing the
trip setting of each device used in the system network so as
to get minimum interruption but maximum protection for the
faults occur in the system [16]. A relay must gain an adequate
fortuitous for protecting the system from abnormal
conditions under the primary protection. If failure occurs in
primary protection to sense and clear the fault, then the
backup protection for clearing the fault should start their
work to initiate the trip. Therefore, as soon as initiation of
the fault occur, it must be detected by the both protection
primary as well as back up. Overshoot of the relay which is
due to moment of inertia is should be allowable. It is also
important that if fault occurs on any location of feeder then
OC relays must coordinate for transformer and feeder for
assuring safer as well as efficient operation of protection
scheme design otherwise it may fail. The stand coordination
time interval is 0.2 to 0.4sec [17].
III. METHODOLOGY AND SIMULTAION
RESULTS
It is an essential for any work to make a pictorial view or
flow chart which in short show the whole work in
conclusion. In this research work we have designed the IEEE
9-Bus system in ETAP software. The input data which was
used in designing the system is given in the table.1-6. The
formulae also represented in the second part. The flow chart
in fig. 3 depicts several parts which have been done in
designing the system include: simulation of the IEEE 9-Bus
system, Load flow analysis, Short circuit analysis, selection
of protective OC relays, relay coordination of CT and PT and
circuit breakers, calculation of currents after the setting of
Fig 3: Flow chart of the system
A. Load flow analysis of IEEE 9 Bus system
Load flow analysis is an essential for the designing of
protective equipment as CBs, CTs, and Relays etc. The
designing through computational methods has become
advantageous and beneficial for the power utility companies
and protection engineers. In the old era the system used was
very complicated, cost-effective and time consuming. In this
paper the first IEEE 9-Bus system is designed with different
types of buses (Generating, Swing and Load Bus),
Transformers, placement of T/L between the buses, Circuit
breakers adjacent to buses with OC relays and Capacitor as
shown in fig.4 and Fig.5.
After designing the IEEE 9-Bus system, the load flow
analysis is completed which shows that system is normal and
their parameters (active, reactive powers etc.) are within
permissible limits and
no
any
fault exist. The
input
data
of Generators, Buses, Transformers,
Conductor length etc. are represented in the diagrams.
B. Placement of fault on Bus-7
After inserting the data in normal load conditions, the
unsymmetrical faults (i.e., Line-t-ground, Line-Line and
Line-Line-Ground faults) were placed on bus 7 one by one
as shown in fig.6. The results are recorded, and it is being
observed that the three-phase fault current is most severe
and greater than other faults.
Fig. 4 IEEE 9-Bus system
Fig. 5 Proposed system
C. SC Analysis
Furthermore, the S.C analysis of IEEE 9-Bus system is
included for determining the fault of positive, negative and
zero-sequence impedance. The figure .8 also represent the
IEEE 9-Bus system with placement of fault.
Fig.6 Faults
IV.
RELAY OPERATION
The Load flow analysis, SC analysis has been completed with the
results in the form of tables. Now the main task of our research
work is the placement of protective relays on bus-7, CBS and their
proper operation. For this, the sequence of relay operation is
mandatory which is given in table. 7. The protective relays which
were connected to the bus-7 are checked a on their operation and
occurrence of tripping of CBs is also observed with some time
delay. The relay-5 due to the least effect of power system, energize
first and tripped the consistent circuit breaker and major part of
power system protection is observed from the SC current followed
by relay 6 and 7. The graph of the relay setting is given in the fig.
8&9 which clearly shows the operating time and the effect of
overcurrent according the desired conditions. Also, the operational
curve of the branches Cleary shows the pictorial view of the
operation of the branches and the faulty bus.
Fig 8. Operational Branches Curve
Fig 7. sequence of operation of relay
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Fig 9. Combine curve of all operational relay
V.
CONCLUSION
A power flow study, which has been considered as an important
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benefits to both the utility companies and consumers.
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