The research paper published by IJSER journal is about Optimal Location of FACTS Device on Enhancing System Security 1
ISSN 2229-5518
Optimal Location of FACTS Device on
Enhancing System Security
Prakash Burade, Jagdish Helonde
Abstract: In this paper a Unified Power Flow Controller (UPFC) is a FACTS device that can be control the power flow in transmission li ne by injecting active and reactive in voltage components in series with the lines.The proposed methodologies are based on the use of line loading security Performance Index (sensitivity factors have been suggested in this paper for optimal placement of UPFC.This methods are computationally efficient PI sensitivity factors have been obtained with respect to change in two of the UPFC parameters vi z., magnitude and phase angle of the injected voltage in the lines. The proposed methodologies are tested validated for locating U PFC in IEEE 30-bus system.ACO based Optimal Power Flow (OPF) formulation has been suggested to determine the optimal PI values, after placement of UPFC based on the proposed sensitivity factors. Both AC and DC power flow approximations have been used to define the sensitivity factors and their results have been compared on IEEE 30-bus system
Keywords: PI sensitivity, ACO-OPF, UPFC, Performance Index, optimal location, A.C& D.C power appox.
—————————— ——————————
In emerging electric power systems, increased transactions may often lead to the situations where the systems no longer remain in the secure operating region. The security [1, 2] of a power system can be defined as its ability to withstand a set of severe, but credible contingencies and remain in an acceptable new steady state condition. Various factors, such as environmental, right-of way and high installation cost, limit the expansion of the transmission network. Utilities try to maximize the utilization of the existing transmission asset that may, sometimes, lead to insecure operation of the system. Increased loading in power systems, combined with deregulation of the power industry, motivate the use of Flexible AC Transmission Systems (FACTS) controllers [13] such as Thristor Controlled Series Compensator (TCSC), Thyristor Controlled Phase angle Regulator (TCPAR) and Unified Power Flow Controller (UPFC), for power flow control as a cost–effective means of dispatching specified power transaction and maintain systems security.
Corresponding authors:-1Head of electrical electrical engg 2 Principal, ITM college of engg, Nagpur, India, Email:1prakash.burade@gmail.com, 2drjbhelonde@itm.edu
However, due to the high cost of these controllers, it is necessary to locate them optimally in the network.
Several papers, reported in the literature, deal with the optimal placement of FACTS controllers. However very few [5, 6] have discussed the method of their optimal location in view of enhancing the system security. In [6] deals with optimal location of TCSC and [7] have presented a method of optimal al location of UPFC in view of
enhancing the security. These works used DC power flow approximation model and did not suggest a method to determine optimal settings of controllers. In [5] suggested the use of phase shifter for security enhancement and obtained its parameter using Optimal Power Flow (OPF) formulation. In [8] have proposed a new formation for reactive power planning problem including the allocation of FACTS device, but the result have been demonstrated on a very a small system. In [10], two objective functions
Have been considered, viz. maximization of system security and minimization of investment cost of FACTS devices, for their optimal placement. The effectiveness of the method was tested only on IEEE14-bus system. Three heuristic methods, viz. Genetic Algorithm, Tabu-Search and Simulated Annealing, have been applied in [9] for optimal location of the facts devices.
In this paper, a new index representing sensitivity
of line real power flow Performance Index (PI) with respect
to ACO based optimum controlled UPFC parameters has
been suggested for its optimal location in view of
enhancing the system security under different operating
conditions. The sensitivity of real power with respect to
optimum tuning control parameters of the UPFC has been
obtained utilizing AC power flow approximation. The
effectiveness of the proposed method has demonstrated on
IEEE 30-bus system, utilizing an Object Oriented
Programming of Ant Colony Based model that minimizes
the line flow PI values. The results have been compared
with an existing real power flow performance index (PI)
sensitivity approach utilizing DC power flow
approximation [4].
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ISSN 2229-5518
Nb
S mn Pn
f or m k
The relative severity of the system loading under normal
n 1 (5)
P
Nb
and each of the contingency cases can be described by a line real power flow performance Index (PI) [4], as given below.
S mn Pn
n 1
n s
Pju
th
f or m k
Where Smn
is the
mn element of sensitivity matrix [S]
Ni w
PI m m 1 2a
2 a
Pm
P m a x
m
(1)
m a x
which relates line flow with power injections at the buses without placement of UPFC, Nb is the number of buses in the system and s is the slack bus. Assume that the line-k,
Where, Pm
is the real power flow and Pm
is rated
between bus-i and bus-j is the line containing the
capacity of line-m, a is an exponent and wm
is a real non
UPFC.Using equations (4) and (5), the following
negative weighting coefficient, which may be used to reflect
the relative importance of the lines. The lack of
discrimination, in which the performance index for a case
relationship can be derived,
with many small violations may be comparable in value to
the index for a case with a few large violations, is known as
masking effect. By most of the operational standards, the
system with few large violation is much more severe than
that with many small violations, Masking effect, to some
extent, can be avoided by using higher order performance
indices (i.e. a>1). In this study, the value of exponent ‘a’ has been taken as 2 and weighting coefficient ‘ wm ’ for all the lines as 1.0.
(S mi
Pm
X k
(S mi
Piu X k Piu X k
S mj
S mj
Pju
)
X k
Pju
)
X k
Pju
X k
f or m k
f or m
The terms
Piu
X k
k
and
0
Pju
X k
k
can be obtained by
0
The control parameters of the UPFC using ACO
considered in this work are the magnitude and angle of the
partially differentiating the equations, with respect to the
UPFCs series parameters.
series injected voltage,
Vs and s , respectively. The line
loading PI sensitivity factors with respect to the control
parameters of UPFC can be defined as
K PI
Vs Vs
=PI Sensitivity with respect toVs
0
(2)
The real power mismatch ( Pis ) and reactive power mismatch ( Qis ) at any bus-i can be expressed in terms of voltage magnitudes ( V ), voltage angles ( ), and element
K PI
Vs s
= PI Sensitivity with respect to s
s 0
of bus admittance matrix ( Y ) as
Nb
* (7)
(3)
Pis
PGi
Piu
PDi
Re Vi
(V j Yi , j )
j 1
Nb
*
(8)
For deriving the PI sensitivity terms using DC power flow
approximation, the value of ‘a’ in equation (1) has been
Qis
QGi
Qiu
QDi
Im Vi
(V j Yi , j )
j 1
taken as 2. Using equations (2) and (3), the sensitivity of PI
Where, PGi , QGi
are the real and reactive power
generations, respectively, at bus-i.
Piu and
Qiu are the injections, given by equations at bus-i due to
k s s
UPFC.
PDi
and
QDi
are the base case real and reactive
PI Ni
X k m 1
Wm Pm
1 PI
m ax
m k
(4)
power demands, respectively, at the bus-i. Equation (7)
and (8), with UPFC, are function of bus voltage magnitudes
V ), and angles ( ), magnitude ( Vs ) and angles ( s ) of
The real power flow (
Pm ), in a line-m, can be represented in
(
the injected voltage due to UPFC.
terms of bus real power injections using DC power flow
equations [4, 6] as
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The research paper published by IJSER journal is about Optimal Location of FACTS Device on Enhancing System Security 3
ISSN 2229-5518
Pis
Qis
f pi (V ,
f qi (V ,
, s ,Vs )
, s ,Vs )
Equation (12) represents the limits on the reactive power generations. The limits on the bus voltage magnitude and angle. Equation (13) represents the limits on the UPFC
(9)
parameters (Vs ,
s ) .
The sensitivities of real power flow Performance Index
(PI) with respect to UPFCs series parameter s (voltage
magnitude and phase injection) have been calculated by
both AC and DC power flow approximation. The following
criteria have been used for optimal placement of an UPFC
in the system.
The branches having transformer are not
considered for the UPFC placement.
The line having highest absolute PI sensitivity (
The above OPF problem involves a nonlinear
objective function and a set of non linear equality and
inequality constraints. This problem is solved by Ant
Colony Optimization procedure. In this work, ACA
optimization programming is developed in objected
oriented in java programming and UML software is used
for design of object oriented class diagram and ACA coding
as a sub package and separately run to obtain the optimal
solution
2 and
2 ) with respect to the change in injected voltage
phase angle ( s ) is considered as the best location for the
UPFC placement followed by other lines having next
highest sensitivities.
When the values of absolutes PI sensitivities
The proposed line flow PI sensitivity method, derived based on DC power flow as well as AC power flow
2 and
2 ) with respect to change in injected voltage
approximations, for optimal location of UPFC has been
phase angle ( s ) for line more than one are very close to
each other ,the line having highest absolute value of the PI
C k F k
tested on IEEE 30-bus system.
sensitivities ( 1 ,
1 ) with respect to the change in injected
Line Outage Contingency Ranking
voltage magnitude (
for the UPFC.
Vs ) is considered as the best location
To obtain the critical contingencies (line outages) in the
IEEE 30-bus system, the PI values as defined in equations
The effectiveness of proposed PI sensitivity factors based approach for UPFC placement has been arrived in terms of its impact on the reduction I line flow performance Index (PI) values. For this purpose, an Optimal Power Flow (OPF) formulation is described below has been used.
(3.35) in previous chapter, are computed for each of the single line outage (N-1 contingency) cases. Five most critical lines are listed in Table1. Contingencies, for which feasible Ac load flow solution have not been obtained, are not considered in this list. For the base case, the PI values obtained from AC power flow solution for the IEEE 30-bus system are found to be 0.4250.
Minimize PI
(10)
Subject to the following constraints:
a. Equality constraints: Power balance equations
must be satisfied. This can be expressed, in general forms as
IEEE30-bus system
Where G is the vector of real and the reactive power flow equations at all the buses.
(a) Inequality constraints: These include the operating limits on the various power system variables and the parameters of the UPFC as given below.
Rank
order
Line
outage
Intact case
End buses
i-j
-
PI
0.4250
(12)
m in
G G
Vi Vi
i 
i
m in
G
Vgi
i
m a x
1 12 1-27 1.9130 (4.23)
2 33 27-11 1.8110
(4.24)
0.6372
0 Vs Vs
s
(13)
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3 5 2-5
(4.25)
The research paper published by IJSER journal is about Optimal Location of FACTS Device on Enhancing System Security 4
ISSN 2229-5518
4 | 7 | 11-13 | 0.6001 |
5 | 9 | 13-12 | 0.4889 |
1
s
2 s
Table 2 shows the optimal PI value obtained after optimal placement of the UPFC in few lines having high
value of the PI sensitivity factors ( C1 ).Optimal values of the PIs, given in the 3rd column, are when only series injected voltage magnitude of the UPFC is varied and
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The research paper published by IJSER journal is about Optimal Location of FACTS Device on Enhancing System Security 5
ISSN 2229-5518
those given in the 5th column are when both the magnitude and phase angle of the injected voltage by UPFC are varied in the corresponding lines. From Table2, it can be seen that the line-12 is the best location for optimal placement of UPFC in the 30- bus system
Table 3 shows the optimal PI values after placing the UPFC in the respective lines, one at a time, selected based on the PI sensitivity factors C2 . The PI values given in the column 4 are obtained with the fixed values of series injected voltage magnitude (considered as 0.01pu) and varying the phase angle injection by the UPFC. The optimal values of series injected voltage angle are shown in the 4th column. The effect of variation of both the series voltage magnitude and phase angle injection by the UPFC on optimal values is shown in the 5th column. From Table
1, 2 and 3, the best location for the UPFC placement, in the IEEE30-bus system, is found to be line-12, as the optimal PI value is minimum in most of the cases with the UPFC placement in this line.
It can be seen that the best locations for the UPFC
placement based on the optimal PI values (Table 3, column
6) are lines-12, 33, 11, 14, 7 and 6 in the rank order.
However, the ranking order obtained from the sensitivity
factors ( C k ) are lines-12, 33, 11,7,14 and 6 which are almost similar, but not exactly the same. This order is
exactly same as verified through the optimal
value of PI obtained after placement of the UPFC in
these lines. This confirms the validity of the proposed PI
sensitivity factor for the UPFC placement (Table 3).
The impact of the optimal placement of UPFC on PI value is given in Table 4, with the 5% increase in loading. The PI value was found to be 0.5012, when there was no UPFC in the system. It is found that the rank order of lines for optimal location of UPFC is the same as obtained through optimal PI values after placement of UPFC in these lines as shown in Table 5 for both series voltage and phase angle variations.
To show the effectiveness of the proposed method under contingencies, the sensitivity factors and optimal PI values were also computed for r different line outage case4s, which are shown in Table 6 for the 30-bus system.
k k First column show the line considered for outage and the
(C1 & C2 )
second column show the PI value at outage of the corresponding line without placement of UPFC. In the
k k
column three present the sensitivity factors
(C2 & F2 )
along with corresponding optimal pi value for the few
1 2 lines in priority order after outage of critical lines, as listed in the first column. Only the sensitivity factor
C k F k
with respect to the change in series injected
( 2 & 2 )
voltage phase angle by UPFC have been considered, as it
provided better results in base case. Due to the outage of
lines, the most optimal location of the UPFC changed.
From, the lines-11 is found to be the most suitable location
for the optimal placement of the UPFC in view of security
enhancement during outage of the lines-12, 33 and 5 in
IEEE30-bus systems.
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2 2
Line loading security Performance Index (sensitivity factors have been suggested in this work for optimal placement of UPFC. The PI sensitivity factors have been obtained with respect to change in two of the UPFC parameters viz., magnitude and phase angle of the
injected voltage in the lines. An Optimal Power Flow
approximations have been used to define the sensitivity factors and their results have been compared on IEEE 30- bus system. Test results obtained on the system show that the new sensitivity factors could be effectively used for optimal placement of UPFC in order to enhance the static security of the power system. The following criteria can be effectively used for deciding the optimal locations of the UPFC.
The UPFC can be placed in a line-k having largest absolute value of the sensitivity factors ( C k or F k )
2 2
with respect to change in
.
If two lines can are having similar values of
k k
(OPF) formulation has been suggested to determine the optimal PI values, after placement of UPFC based on the proposed sensitivity factors, in order to validate accuracy of the method. Both AC and DC power flow
( C2 or F2 ), the UPFC should be placed in a having most absolute value sensitivity index with respect to change in Vs .
(C k
line-k
or F1 )
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The research paper published by IJSER journal is about Optimal Location of FACTS Device on Enhancing System Security 7
ISSN 2229-5518
The impact of the UPFC placement on the security enhancement of the power system has been established, in terms of optimal PI values along with the optimal control settings of the UPFC, for system intact and optimal location of the UPFC as compared to that
obtained from the DC power flow based PI sensitivity factors method. The placement of the UPFC in a line, obtained from the proposed factors, has resulted in maximum reduction in the line real power flow performance index. The optimal placement does not change for increase in system loading. However, the locations differ under critical contingency conditions.
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