Placement of Multiple Distributed Generators in Distribution Network for Loss Minimization

Placement of Multiple Distributed Generators in Distribution Network for Loss Minimization Page 19
International Journal for Modern Trends in Science and Technology
ISSN: 2455-3778 |Volume No: 02 | Issue No: 01 | January 2016
Placement of Multiple Distributed Generators
in Distribution Network for Loss
Minimization
M.R.B.N. Sitarama Gupta1, M.V. Durga Rao S 2
1,2 Ramachandra College of engineering, Eluru, AP, India.
Article History ABSTRACT
Received on: 22-01-2016
Accepted on: 28-01-2016 This paper presents a methodology for multiple distributed
generator (DG) placement in primary distribution network for loss
reduction. Optimal location for distributed generator (DG) is selected by
Analytical expressions and the optimal DG size calculated by IA method
and loss sensitivity factor (LSF). These two methods are tested on two
test systems 33-bus and 69-bus radial distribution systems. The final
results showed that LSF gives same loss reduction and minimum
voltage in the system with less DG size than obtained in IA method.
Published on: 30-01-2016
Keyword
IA Method
Loss Sensitivity Factor
Optimal Location
Optimal DG size
Multiple DG
Analytical Expression
Distributed Generation
Copyright © 2015 International Journal for Modern Trends in Science and Technology
All rights reserved.

I. INTRODUCTION
The central power plants are thermal, nuclear
or hydro powered and their rating lies in the range
of several hundred MW‟s to few GW‟s [2]. central
power plants are economically unviable in many
areas due to diminishing fossil fuels, increasing
fuel costs, and stricter environmental regulations
about acid deposition and green house gas
emission[3].smaller power plants with a few dozens
of MW‟s, instead of few GW‟s, became more
economical[2]. Also, generators with renewable
sources as wind or solar energy became more
economically and technically feasible. This has
resulted in the installation of small power plants
connected to the distribution side of the network,
close to the customers and hence referred to as
“embedded” or “distributed” generation (DG).
Sometimes it is also called “dispersed generation”
or “decentralized generation”. [4].
Distributed generation technologies are
renewable and nonrenewable. Renewable
technologies include solar, photovoltaic or thermal,
wind, geothermal, ocean. Nonrenewable
technologies include internal combustion engine,
ice, combined cycle, combustion turbine, micro
turbines and fuel cell. [5] Most of the DG energy
sources are designed using green energy which is
assumed pollution free [6].
Installing DGs at the load centers will prevent
the new transmission lines extension to energize
new substation, DG is capable of providing some or
all of the required power without the need for
increasing the existing traditional generation
capacity or T&D system expansion. DG capital cost
is not large due to its moderate electric size and
modular behavior as it can be installed
incrementally unlike installing new substations
and feeders, which require large capital cost to
activate the new expanded distribution system [12].
The technical benefits include improvement of
voltage, loss reduction, relieved transmission and
distribution congestion, improved utility system
reliability and power quality [6] and increasing the
durability of equipment, improving power quality,
total harmony distortion networks and voltage
stability by making changes in the path through
which power passes [9].These benefits get the
optimum DG size and location is selected.
Distributed system planning using distributed
generation [12]. If the DG units are improperly
sized and allocated leads to real power losses
increases than the real power loss without DG and
reverse power flow from larger DG units. So, the
size of distribution system in terms of load (MW)
will play important role is selecting the size of DG.
The reason for higher losses and high capacity of
DG can be explained by the fact that the
distribution system was initially designed such that
power flows from the sending end (source
substation) to the load and conductor sizes are
gradually decreased from the substation to
consumer point. Thus without reinforcement of the
system, the use of high capacity DG will lead to
excessive power flow through small sized
conductors and hence results in higher losses.[7]
Different techniques are proposed by authors
the techniques are, a technique for DG placement
using “2/3 rule” which is traditionally applied to
capacitor allocation in distribution systems with
uniformly distributed loads has been presented.
Although simple and easy to apply, this technique
cannot be applied directly to a feeder with other
types of load distribution or to a meshed
distribution system. The genetic algorithm (GA)
based method has been presented to determine the
size and location of DG. GA is suitable for multi-
objective problems and can lead to a near optimal
solution, but demand higher computational time.
An analytical approach based on an exact loss
formula has been presented to find the optimal size
and location of single DG. A probabilistic-based
planning technique has been proposed for
determining the optimal fuel mix of different types
of renewable DG units (i.e., wind, solar, and
biomass) in order to minimize the annual energy
losses in the distribution system [1].
II. PROBLEM FORMULATION
This section describes to find the optimum size and
location of distributed generator.
A. Selection of Location
Find the best bus for the placement of DG, The DG
sizes at each bus is calculated by using (2).The
DG‟s are placed at each bus and calculate the real
power loss by (1).The bus which has minimum real
power loss is selected as best location for
placement of DG.

The real power loss in a system can be
calculated by (1). This is also called as “Exact loss
formula” [13].
Where
;
;
ijth element of [Zbus] impedance
matrix;
N is number of buses
Where Pi and Qi are Real and Reactive power
injections at node „i‟ respectively.
Real power injection is the difference between Real
power generation and the real power demand at
that node.
Where, and is the real power injection and
reactive power injection from DG placed at node i
respectively. and are load demand at the
node i respectively [14].
(3)
Where
„+‟ sign for injecting Reactive power
„- „sign for consuming Reactive power
The exact loss formula is a function of loss
coefficients and .These coefficients depends on
magnitude of voltage and voltage angle at each bus.
So for every DG placement at each bus the and
changes so for that every time requires load flow
calculation. But the results show that with and
without updating the and the results are same
[1].
B. Optimal DG size selection
The Distributed generator is placed at the
optimum location. The optimum DG size is selected
by varying the DG in small steps up to the point
where real power loss is minimum. The real power
loss is calculated by “back ward forward sweep”
load flow algorithm.
III. IA METHOD
The computational procedure of IA method is as
follows:
Step 1: Enter the number of DG units to be
installed.
Step 2: Run load flow for the base case and find
losses using (1).
Step 3: Find these optimal location of DG using the
following steps.
a) Calculate the optimal size of DG at each
bus using (2) and (3).
b) Place the DG with the optimal size as
mentioned earlier at each bus, one at a
time. Calculate the approximate loss for
each case using (1).
c)Locate the optimal bus at which the loss is
at minimum.
Step 4: Find the optimal size of DG and calculate
losses using the following steps.
a) Place a DG at the optimal bus obtained in
step 4, change this DG size in small step,
and calculate the loss for each case using
“Back ward forward” load flow.
b) Select and store the optimal size of the DG
that gives the minimum loss.
Step 5: Update load data after placing the DG with
the optimal size obtained in step 5 to allocate
the next DG.

Step 6: Stop if either the following occurs
a)the voltage at a particular bus is over the
upper limit
b) The total size of DG units is over the total
plus loss
c)The maximum number of DG units is
unavailable
d) The new iteration loss is greater than the
previous iteration loss. The previous
iteration loss is retained otherwise, repeat
steps 2 to6.
IV. LSF METHOD
Loss Sensitivity Factor (LSF) method is
employed to find the optimal location to place DG
units which supplies active power only. The
sensitivity factor method is based on the principle
of linearization of original nonlinear equation
around the initial operating point, which helps in
reduction of the number of solutions. The LSF at ith
bus is derived from equation (4) is given as
αi 2 ijPj – ijQj ) (4)
The procedure to find the optimal locations and
sizes of multiple DG units using the loss sensitivity
factor is described in detail as follows.
Step 1: Enter the number of DG units to be
installed.
Step 2: Run load flow for the base case and find
losses using (1).
Step 3: Find the optimal location of DG using the
following steps
(a) Find LSF using (4). Rank buses in
descending order of the values of their
LSFs to form a priority list.
(b) Locate the highest priority bus.
Step 4: Find the optimal size of DG and calculate
losses using the following steps:
(a) Place a DG at the bus with the highest
priority obtained in step 3, change this DG
size in “small” step, update the values α
and β , and calculate the loss for each
case using (1) by running load flow.
(b) Select and store the optimal size of the DG
that gives the minimum loss.
Step 5: Update load data after placing the DG with
the optimal size obtained in step 4 to
allocate the next DG.
Step 6: Stop if either the following occurs:
(a) The voltage at a particular bus is over the
upper limit;
(b) The total size of DG units is over the total
load plus loss;
(c) The maximum number of DG units is
unavailable;
(d) the new iteration loss is greater than the
previous iteration loss.
The previous iteration loss is retained; otherwise,
repeat steps 2 to 5.
V. RESULTS AND ANALYSIS
In this paper IA method and Loss Sensitivity
Factor method are tested on 33-bus [10] and 69-
bus [11] radial distribution system. Here Type 3 [1]
DG is considered
A. Assumptions
The assumptions for this paper are as follows:
1. The maximum number of DG units is three,
with the size each from 250KW to the total
load plus loss.
2. The maximum voltage at each bus is 1.0
p.u.
B. 33-Bus system
The simulation results of the optimal
location and optimal sizing of DG is shown in
Table-I. The real power loss of 33-bus system is
211kW without DG. In single DG placement by LSF
method the DG size is 850 kW, the real power loss
is 145.7kW and in case of IA is 2600 kW, the real
power loss is 105.21 kW. In case of 2 DG‟s
placement the DG size by LSF method 710 kW,
1010 kW the real power loss is 100.20 kW and in
case of IA is2310kW,710kW the real power loss is
94.78kW. In case of 3 DG‟s placement by LSF
Method is 610 kW, 910 kW, 910 kW the real power
loss is 84.11 kW and by IA Method is 1710 kW,710
kW,610 kW the real power loss is 76.93kW.

TABLE-I
COMPARISON OF DIFFERENT TECHNIQUES ON 33-BUS
SYSTEM
C. 69-Bus system:
The simulation results of the optimal location
and optimal sizing of DG shown in Table-II .The
real power loss of 69-bus system is 224 kW without
DG. In single DG placement by LSF method the DG
size is 1440kW the real power loss is 112.11kW
and in case of IA Method the DG Size is 1900 kW
the real power loss is 81.26 kW. In case of 2 DG‟s
placement the DG size by LSF method 1410 kW,
410 kW the real power loss is 100.51 kW and in
case of IA method 1810 kW, 510 kW the real power
loss is 70.36 kW. In case of 3 DG‟s placement the
DG size by LSF method 210 kW, 410kW, 1610kW
the real power loss is 73.62kW and by IA method
1810kW, 510kW, 710kW the real power loss is
68.87kW.
TABLE-II
COMPARISON OF DIFFERENT TECHNIQUES ON 69-BUS
SYSTEM
CONCLUSION
In this paper Loss Sensitivity Factor method is
proposed for multiple DG placement. The DG
location is finding by IA expressions and the
optimum DG size is finding by IA method and LSF
method. The results are compared with IA method.
Results shows that LSF method gives nearly same
real power loss and voltage with less DG size
occurred in IA method.
REFERENCES
[1] Duong Quoc Hung, Nadarajah Mithulananthan
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[8] M. Damodar Reddy, N. V. Vijaya Kumar “Optimal
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[11]M. E. Baran and F. F. Wu, “Optimum sizing of
capacitor placed on radial distribution systems,”
Cases DG
schedule
With
out DG
With DG
1 DG 2
DG‟s
3
DG‟s
LSF
Method
optimum
bus
---- 18 18,33 18,33
,25
DG Size
(kW)
850 710
1010
610
910
910
Loss (kW) 211 145.7 100.2 84.11
IA
Method
Optimum
bus
--- 6 6,25 6,25,
15
DG Size
(kW)
2600 2310
710
1710
710
610
Loss
(kW)
211 105.20 94.78 76.93
Cases DG
schedule
With
out DG
With DG
1 DG 2 DG‟s 3
DG‟s
Optimum
Bus
----- 65 65,27 65,27,
61
LSF
Method
DG size
(kW)
----- 1440 1410
410
210
410
1610
Loss
(kW)
224 112.11 100.51 73.62
IA
Method
Optimum
Bus
----- 61 61,22 61,22,
49
DG size
(kW)
----- 1900 1810
510
1810
510
710
Loss
(kW)
224 81.26 70.36 68.87

IEEE Trans. Power Del., vol. 4, no. 1, pp. 735-743,
Jan. 1989.
[12]W.El-Khattam, M.M.A.Salama, “Distribution system
planning using distributed generation,” IEEE CCECE
2003, vol.1, pp. 579 – 582.
[13]D.P. Kothari and J.S. Dhillon, Power System
Optimization. New Delhi: Prentice-Hall of India Pvt.
Ltd., 2006.
[14]N. Acharya, P. Mahat, and N. Mithulananthan, “An
analytical approach for DG allocation in primary
distribution network,” Int. J. Elect. Power Energy
Syst., vol. 28, no. 10, pp. 669-678, Dec. 2006.
BIOGRAPHY
M.R.B.N.Sitarama Gupta is pursuing M.Tech in
Department of Electrical Engineering, Ramachandra
college of Engineering, Eluru, India. Email:
sitarama.gupta@gmail.com
M.V.Durga Rao S is Assistant Professor in Department of
Electrical Engineering, Ramachandra college of
Engineering, Eluru, India. His areas of interest include
electrical power systems and Renewable energy resources.
Email: muralihve@gmail.com

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