13-08-2012, 03:22 PM
Optimal DG Allocation by Extending an Analytical Method to Minimize Losses in Radial Distribution Systems
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Abstract:.
This paper presents an analytical algorithm for
proper single Distributed Generation allocation in distribution
systems with regard to DG1 power factor effect, in order to
minimize the exact losses. this method is extended of the
sensitivity method by considering DG power factor and
achieving and driving a new analytical approach. The
algorithm is based on exact loss formula, and by extending
these formula and considering DG power factor, assess active
and also reactive power generation. Therefore DG power factor
must be defined. The proposed algorithm is tested on a 33 bus
test feeder to demonstrate the accuracy and verification of the
method. Simulation Results obtained from the proposed
methodology are compared with the common method that
calculates only active power generated by DG with unity Power
Factor, and proposed method. The power loss in proposed
method is lower and the DG size is smaller.
Keywords: Distributed generation, optimal placement,
power losses, DG power factor, sensitivity factors,
voltage profile improvement .
1. Introduction
The share of distributed generators (DGs) in power
systems has been slowly increasing in recent years. At
present, there is increasing number of the DGs connected
to the distribution system. Distributed Generation can be
defined as a small-scale electrical power source
connected to the distribution network or the consumer
side to supply the load directly .There are some DG
technologies that are available in the market today and
few of them are still in the research and development
stage. Some currently available DG technologies are:
reciprocating engines, micro turbines, combustion gas
turbines, fuel cells, photovoltaic and wind turbines. Each
of these technologies has its own characteristics so,
depending on situation the appropriate type must be used.
Among all the DGs, diesel or gas reciprocating engines
and gas turbines make up most of the capacity installed
so far[1] . The location and amount of power supplied
from the DG into the distribution system have influences
on the operation of the system. They can either increase
or decrease the efficiency and the stability of the system.
Large power supplied by the DG can make reverse power
flow from load side to substation , causing malfunction of
protection circuits . In addition flowing large amount of
1 Distributed Generation
power in the distribution line may cause a further increase
in power loss, Therefore, the suitable allocation of the
DG is preferred. The optimum DG allocation can be
treated as the optimum active and reactive power
compensation. There are different methods and
algorithms in DG allocation in studies. Ref. [2] supposed
a power flow method to find the optimum DG size at
each load bus, such methods need a huge amount of
computations of load flow for each step. Heuristic
algorithms such as genetic algorithm (GA) and PSO are
preferred for the multiobjective optimization. Although
the heuristic methods are intuitive, easy to understand and
simple to implement as compared to the analytical and
numerical programming methods, the results produced by
the heuristic algorithms are not guaranteed to be
optimal[3][4]. Ref. [5] presents an analytically method
based on phasor current, to define location of the DG. In
this method the DG size is fixed and algorithm calculates
only the DG place. In Acharya’s method [6] the optimal
size and location of the DG is calculated based on the
exact loss formula and compared with successive load
flows and loss sensitivity methods. The allocation
problem, is solved subjected to the system power losses.
This method considers only active power supplied by DG
to the system while DGs can generate active and reactive
power. Supplying active power to the system improves
power quality and hence results in voltage profile
improvement. In this study, an analytical approach which
is based on exact loss formula is presented. The DG is
considered to supply active and reactive power so the DG
power factor is not unity. Therefore by considering the
DG power factor and extending old algorithm (loss
sensitivity and Acharya’s method) and driving new
formulas, this new method defines the DG active and
reactive power injecting while DG operates under
constant power factor.
2. Optimum size and location of DG
In radial distribution network, the power flows from
the grid supply point to loads in one direction. Installing
high capacity DG with the purpose of exporting the
power beyond the substation (reverse flow of the power
through distribution substation), lead to very high losses.
Reza Karbalaei Hosseini*, Rasool Kazemzadeh*
* Sahand University of Technology, re_hosseini[at]sut.ac.ir
* Sahand University of Technology, r.kazemzadeh[at]sut.ac.ir
Pow er lo sses. (MW )
DG injected Power (MW)
The relation of the higher losses and DG higher
capacity can be explained by the fact that the distribution
system was initially designed such that the power flows
from the sending end (source substation) to the load and
conductor sizes were gradually decreased from the
substation to the consumer side. So, the size of the
distribution system in term of load (MW) plays an
important role in selecting the size of DG [5]. Thus
selecting high capacity of DGs without considering the
system restrictions will increase the system losses.