LOSS MINIMIZATION, FEEDER LOAD BALANCING
AND VOLT-VAR CONTROL BY DYNAMIC
REFERENCE NETWORK
Er. Harpreet Singh
1, Ravi Kant Yadav
21
Assistant Professor,
2M.Tech Scholar, Department of Electrical Engineering,
IET Alwar, Rajsthan, (India)
ABSTRACT
Network pricing is a complex issue, considering the network size and other facets. For distribution networks, reference network aids in quick decision making, for network operation and pricing. There is a sustained interest for development of dynamic network pricing mechanisms to reflect the network cost on a real time basis. Recent developments in smart grid technologies have offered opportunities to utilize these innovative technologies for real time network pricing.
This Paper proposes integrated concept and formation of Dynamic reference networks for practical distribution networks. Proposed works introduced algorithm for Reconfiguration of distribution networks, along with the algorithm of reference networks. Both concepts coupled to form Dynamic reference networks, with dynamic nature of load, or system parameter, the Reconfiguration algorithm helps to change the networks structure by closing and opening the switches to obtained optimal networks structure. There after the Dynamic Reference Networks has formed, which reflects the latest state of real Network, and it is also validated with reconfigured networks.
Keywords: Reconfiguration, optimal Flow Pattern,
Smart Grid Technology
I INTRODUCTON
The concept of distribution automation system in electric refers to a systems designed to operate and coordinate
remotely. Distribution automation system provides timely control and data acquisition through communication with
remote device. Hence to ensure safe, reliable uninterruptible power supply distribution automation systems are being
used to continuously monitor and control the power distribution network. There are so many meter, sensors and
remote terminal units are present in distribution automation, system which continuously checks the networks by
measuring appropriate quantities such as voltage, current flow, power flow, frequency etc. and subsequently send
these measured data to control station over communication link. These data analysed by appropriate software
remedial or control decision are taken and that are decided by application software in the control computer station.
Subsequently these decisions are sent to the network for proper implementation over the same or other
communication link obviously the success of the distribution automation systems largely depends upon the decision
software package. For maximum benefits of the distribution network the software analysis must be able to decide
the necessary control decision quite fast and accurately so that abnormality can be removed as soon as possible.
The various control decision functions, which are employed most commonly in any modern distribution automation
system, are as follows:
Feeder reconfiguration
a) For loss minimization
b) For feeder load balancing
c) For service restoration
Volt-VAR control
Fault location
Demand- side management
Above these various control decision functions, one of the most routinely executed functions is the feeder
reconfiguration. Distribution feeder supplies power to various types of load like residential, commercial, industrial
and agriculture. Each feeder has a different composition of these loads and their daily load variations are not similar.
Furthermore the peak loads on substation/ transformer occur at different times. Thus due to diverse nature of loading
pattern on different substation/ transformer , a particular configuration of the distribution system which is set for
minimum loss at a certain instant of time will no longer be a minimum loss configuration at different instant of time.
Hence there is need to carryout feeder reconfiguration whenever loading pattern will change in the system.
Distribution reconfiguration involves the opening and closing of distribution system switches to arrange a circuit
such that specified operating constraints and objectives are met. Under normal operating conditions, the objectives
are to avoid transformer overload, feeder thermal overloads and abnormal voltage while simultaneously minimizing
the real power loss. In the emergency state, the system can be arranged so that a maximum number of customers
retain electrical service.
II CONCEPT OF FEEDER RECONFIGURATION
Feeder reconfiguration is an important tool for minimum cost operation of distribution systems, additionally
improving system reliability, security and power quality. Distribution system reconfiguration is a process to identify
optimal switching of sectionalizes (normally closed) and tie switches (normally open). In the present context, the
main objective of reconfiguration is to minimize system losses. This enhances efficiency and improves system
The present work considers feeder reconfiguration based on optimal flow pattern method [6]. In any distribution
system, one switch is closed at a time to obtain a mesh network and to create individual loops.
2 19
20
21
3
23 24 25
4 5 6 7 8 9 10 11 13 14 15 16 17 18 30 29 28 27 26 s1 s18 s19 s20 s21 s33 s35 s34 s37 s36 s2 s3 s4 s5 s6 s7 s8 s9 s10 s11 s12 s13 s14 s15 s16 s17 s22 s23 s24 s25 s26 s27 s28 s29 s30 s31 s32 22 12 1 31 32 33
Fig.1.1 IEEE 33 Bus Distribution System
III LOAD FLOW FOR RADIAL AND WEAKLY MESHED DISTRIBUTION SYSTEM
The feeder reconfiguration algorithm starts with a power flow solution based on Bus Injection Branch Current
(BIBC) method. This is equally applicable for obtaining load flow of radial and weakly meshed systems [8]. The
load flow and reconfiguration formulation is explained with the help of IEEE 33-bus distribution system, as shown
in Fig.1.1 [6, 7].As the network information is continuously updating in a real network, there is a need to develop
BIBC algorithm for real time applications. During reconfiguration, some lines close while other lines open. To
consider these facts, a typical data file format of base case, used for real time application, is shown in Table 1.1.
T
ABLE1.1
T
YPICALD
ATAF
ILEF
ORMATConnectivity (c ) Switch From bus To bus Line impedance
1 s1 1 2 z1
1 s2 2 3 z2
1 s3 3 4 z3
. . . . .
. . . . .
. . . . .
1 s32 32 33 z32
0 s33 8 21 z33
. . . . .
. . . . .
. . . . .
Connectivity vector element ‘1’ reflects a closed line, while ‘0’ reflects an open line. The load flow algorithm considers only those row data for which the connectivity vector is ‘1’. So the load flow is executed only for the
currently connected system. Branch currents for the base case of the network are written as:
1 2
2 3
3 4
31 32
32 33
1 1 1 1 1
0 1 1 1 1
0 0 1 1 1
0 0 0 1 1
0 0 0 0 1
I j I j I j I j I j
I BIBC
j (1.1)Here,
I is the branch current vector, j is the bus- injection current vector and
BIBC
is the bus injection to branchcurrent matrix.
IV BIBC FORMATION
For real time load flow, real time BIBC and BCBV are to be calculated. Any change in system configuration during
reconfiguration is faithfully reflected in real time BIBC formation, shown with the help of flow chart of Fig.4.2.
BIBC is calculated by
D
, while BCBV matrix is calculated by
D
and
z matrix. Here, b is the total number ofbranches and c is the connectivity vector, considered from input data file.
The line impedance column vector Z is obtained by removing of first row of z matrix. The diagonal matrix
ZD of the line impedance can be obtained from Z , where Z is a
n 1 1
matrix andZDis a
n 1 n 1
matrix. BIBC matrix correlates branch current and bus injection current. The size of
BIBC
isn1 n1, wheren
is the total number of the buses.
T
BCBV BIBC ZD (1.2)
BCBV
is the branch current to bus voltage matrix, and its size is n1 n1.The source to node voltage drop for the base case is:
2 1 1
1
3 1 2 2
1
1 2 3 3
4 1
32 1 2 3 31 31
1
1 33 1 2 3 31 32 32
0 0 0 0
0 0 0
0 0
0
E z I
E
E z z I
E
z z z I
E E
E z z z z I
E
E E z z z z z I
E BCBV
I (1.3)Ei
is the voltage drop from source node to node i, and
E is voltage drop vector with dimension
n 1 1
. Considering equation (4.1), the voltage drop vector is
E BCBV
BIBC
j (1.4)
E DLF
j(1.5)
For the load flow computation of a radial network, the following calculation is done. The bus injection current
vector is:
1
. /
ki
k
ji s Ei
(1.6)
Where,
si
is the specified power at nodei
,ji
is the current injection at nodei
and
. / is a MATLAB operator tosignify element by element division of variable.
k k
E DLF j
(1.7)The new voltage vector is:
0
k k
E E E
(1.8)And the tolerance is:
Tolerance=max
Ek Ek1
(1.9)
The load flow is repeated till the tolerance is under acceptable limits.
Load flow calculation shows the voltage difference between open switches. The switch with the maximum voltage
difference is closed, resulting in a weakly meshed system. Connection of two nodes results in a loop formation in the
network. The new load currents and out-going branch currents to the other nodes, not associated with the loop, is
Start
Put D (1, 1) = 1, G (1, 1) =1 & v=1
Is node 'h' connected
to other node 'j' ?
Find minimum nonzeros value of [G], 'h'=min. nonzero value of [G]
Initialize D = zero matrix (n, n) , z = zero matrix (n, 1) , G = zero matrix (n, 1)
Input data file
G(h,1)=0, & k=1
Put D (j, j) = 1 , j
throw [D] = j
throw [D]+h
throw [D]
G (j, 1) = j,& c (k) = 0
v<=n
r<=b
z(j, 1) = data (k, 5)
v=v+1
Obtain D, z
BIBC = transpose of [D], with
removing row 1 & column 1
Stop
Yes
No
k=k+1
No
Yes
Yes
No
Fig.1.2.Flow Chart for BIBC Matrix Formation
V LOAD FLOW FOR WEAKLY MESHED SYSTEM
For the load flow of a weakly meshed system, suppose lthline connects node
i
j
to form a loop, with loop currentl
I , and line impedance
z
l. For load flow analysis, BIBCweakandBVBCweak, along withZD weak , is calculated.
ZD radial wT ZD weakw zl
(1.10)
1
T T T BIBC radial w BIBC weak th th
i j row B
(1.11)In the above equation,
w
is the null row vector of dimension
1 n 1
,
and Bis the matrix obtained by eliminating1stcolumn of
D matrix. Dimension of
B is
n n 1
. BCBV is calculated as hence:
T
BCBV weak BIBC weak ZDweak (1.12)
SLF
BCBV
weak
BIBC
weak
(1.13)Where
SLF
is the simplified load flow matrix of sizen n
. Applying Kron’s reduction technique for thecalculation ofDLFweak,
DLF weak Kron’sreductionofSLF. (1.14)
E weak
DLF
weak
j weak (1.15)The remaining process is similar to radial load flow.
VI FEEDER RECONFIGURATION BASED ON OPTIMAL FLOW PATTERN
Feeder reconfiguration is based on optimal flow pattern method, determined by solving the KVL and KCL equations of
the network [24]. The optimum flow pattern of an individual loop is identified by closing a normally open switch. After
assessing the flow pattern, the switch with minimum current is opened. Hence, radial network is again established by
opening a closed switch. This process is repeated till the minimum loss configuration is obtained.
6.1 Switches to Be Closed
During feeder reconfiguration, load flow helps to identify the voltage drop across open switches. These switches are
arranged in the order of voltage magnitudes across them, and the switch with maximum voltage difference is identified
and closed. Thereafter, load flow for the weakly meshed system is run. If optimal flow pattern technique identifies that the
switch to be opened is the same that was closed, then the switch with the next higher voltage difference is closed.
6.2 Optimal Flow Pattern Technique
This technique is used to reach optimal configuration of the networks. To find the optimal flow pattern of any loop,
number and jnis the load current. The total outgoing current at noden, ILn jnimx, where imxis the current flowing from node mto nodex, wherexis the node not associated with the loop. In the base case, all tie lines are
open. Upon running the load flow, it is assumed that switchs37is closed. This results in a loop formation with 11
nodes(3, 4,5,6,..., 29,..., 23)and associated 11 switches( , , , ,..., ) 5
3 4 25 22
s s s s s .Node 3 behaves as the source node for
that particular loop. For optimal flow pattern, the equation can be solved as:
3
3 4 5 25 26 27 28 37 24 23 22
4 5 25 26 27 28 37 24
1 1 0 0 0 0 0 0 0 0 0
0 1 1 0 0 0 0 0 0 0 0
0 0 1 1 0 0 0 0 0 0 0
0 0 0 1 1 0 0 0 0 0 0
0 0 0 0 1 1 0 0 0 0 0
0 0 0 0 0 1 1 0 0 0 0
0 0 0 0 0 0 1 1 0 0 0
0 0 0 0 0 0 0 1 1 0 0
0 0 0 0 0 0 0 0 1 1 0
0 0 0 0 0 0 0 0 0 1 1
i
r r r r r r r r r r r
i i i i i i i i
4 5 6 26 27 28 29 25 23 24 22 23 0 IL IL IL IL IL IL IL IL i IL i IL
Wherei i3,4,i i5,25, i22are the optimal flow patterns of the particular loop. After determination of optimal flow pattern, radial configuration of the network is restored by opening the branch through which the current flow is
minimum.
P erform radial load flow St art
Find out volt age difference across open swit ches
Close swit ch across which volt age difference is maximum
P erform load flow for weakly meshed syst em
Open swit ch across which current flow is minimum Obt ained opt imal flow pat t ern
Is minimum loss configurat ion ?
St op No
Yes
The feeder reconfiguration algorithm is repeated till the network switching results in minimal resistive line losses.
The minimum loss configuration is identified by considering the results of the optimal flow pattern. As the final
solution is arrived, it is found that the tie line closed to form a loop is the line that is to be opened, in order to
establish the optimal flow pattern. This method is a fast and efficient, the execution time depending on number of
tie-lines. Advantageously, the radial behaviour of the network is maintained.
VII. TEST CASE I: 70 BUS SYSTEM
The second system that is tested is an 11-kV radial distribution system that has two substations, four feeders, 70
nodes, and 78 branches (including tie lines) as shown in Fig.4.8. Tie switches of this system are open in normal
condition, and used voltage and power base are 11 kV and 10 MVA, res
Fig. 1.4 Test Case-II: 70-Bus Distribution Network
TABLE 1.2
RECONFIGURATION RESULTS OF TEST CASE-II
Reconfiguration results Optimal Flow Pattern Based Fuzzy Based Reconfiguration
Opened Switches 28, 39, 45,51,67,70,73,76 28,46,51,67,70,73,75,76
Power Loss in KW (base case) 341.42708 341.4270845
Power Loss in KW (after
reconfiguration)
304.736329 304.9038732
% of Power Loss Saving 10.74629202 10.69722143
Fig 1.5 System Voltage Profile of Test Case –II: Before And After Reconfiguration.
VIII CONCLUSION
The main objective of this paper is to construct Dynamic Reference Networks, which reflect the dynamic nature of
the Real Networks. In Smart Grid environment the Real Networks structure is online monitoring by performing
reconfiguration operation. The real networks structure is continuously varying by with varying the loading and
system parameter ,so there is need to form dynamic nature of the reference networks which should reflects the latest
state of the distribution networks. There are several objectives for reconfiguration such as, service restoration, load
balancing, and real power loss minimization. But the present work considering real power loss minimization.
For reconfiguration of distribution networks we more dedicated to use Optimal Flow Pattern method
because this method is very fast, gives more accurate results, execution time doesn’t depends on networks
size ,it depends in number of tie line.
For the online reconfiguration, this report presents online load flow, which is based on online formation of
BIBC matrix. The BIBC matrix based load flow method is simple, and very fast conversance. This load
flow method is equally applicable for radial and weakly meshed system by modifying the BIBC-matrix.
The concept of Reference Networks formation along with reconfiguration gives the dynamic behaviour
RNs, which reflects the latest state of the Real Networks.
The Reference Network depends on the clustering of the Real Networks feeder and GSS. Reference
networks topology depends on Real Networks topology but its equivalents networks parameter depends on
classification and clustering of Real Networks feeder and GSS.
For the validation of Dynamic Reference networks we comparing the voltage profile of reconfigured
The comparative analysis done between dynamic reference networks and static reference networks
(conventional reference networks).
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