26-05-2012, 12:39 PM
Simple and efficient method for load flow solution of radial distribution networks
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Introduction
Load flow analysis of distribution systems has not
received much attention unlike load flow analysis of
transmission systems. However, some work has been
carried out on load flow analysis of a distribution network
but the choice of a solution method for a practical
system is often difficult. Generally distribution networks
are radial and the R/X ratio is very high.
Because of this, distribution networks are ill-conditioned,
and conventional Newton-Raphson (NR) and fast
decoupled load flow (FDLF) methods 1-4 are inefficient
at solving such networks.
Many researchers 5-7 have suggested modified versions
of the conventional load flow methods for solving
ill-conditioned power networks.
Recently researchers have paid much attention to
obtaining the solution of distribution networks.
Assumptions
We assume that the three-phase radial distribution networks
are balanced and can be represented by their
equivalent single line diagrams. This assumption is
quite valid for 11 kV rural distribution feeders in India
and elsewhere. Line shunt capacitance (different from
shunt capacitor banks that are considered as loads) is
negligible at the distribution voltage levels as is found in
most practical cases.
Solution methodology
Figure 1 shows a single-line diagram of an existing
rural distribution feeder. Branch number, sending-end
and receiving-end nodes of this feeder are given in
Table 1. Figure 2 shows the electrical equivalent of
Figure 1.
Conclusions
A simple and efficient load flow technique has been
proposed for solving radial distribution networks. It
completely exploits the radial feature of the distribution
network. The proposed method always guarantees
convergence of any type of practical radial distribution
network with a realistic R/X ratio. Computationally,
the proposed method is extremely efficient compared
with Baran and Wu's method as it solves a simple
algebraic expression of voltage magnitude only.
Another advantage of the proposed method is that it
requires less computer memory. The proposed method
can easily handle the composite loads if the break up of
the loads is known. The proposed method has been
implemented on an IBM PC-AT. Several Indian rural
distribution networks have been successfully solved by
using the proposed load flow technique.