28-09-2013, 02:13 PM
Analysis of Distribution Systems with DSTATCOM
Distribution Systems.pdf (Size: 1.79 MB / Downloads: 135)
ABSTRACT
Distribution system, as the name suggest, is the medium through which power
is
distributed among the end consumers. Among the distribution systems, Radial Distribution
System is popular due to cost and operational issues. In such systems due to high R/X ratio of the
cables/lines, the voltage decreases as moved away from the source and results in high losses.
Such issues of poor voltage regulation, high loses are related to the reactive power deficiency.
This problem of poor voltage or reactive power compensation can be minimized or sometimes
overcome by using suitable FACTS devices such as DSTATCOM. The DSTATCOM is also
capable of solving various power quality issues such as voltage unbalance etc. DSTATCOMs are
voltage source inverter (VSI) based devices, which regulate distribution bus voltage using
reactive power compensation.
The work reported in this thesis is carried out with the objective of identifying the
optimal location of DSTATCOM, as well as to carry out load flow analysis with a given rating of
DSTATCOM. For these purpose two stage methodologies is used. In the first stage pre-
compensated load flow of the distribution system is performed. On the basis of load flow
solution the voltage drop in each bus is observed. DSTATCOM is applied individually, one by
one to those buses which are below the safe limit. After compensation the Rate of Under Voltage
Mitigated Nodes (RUVMN) of that compensation are computed. This process is carried out for
each bus and the optimal location of DSTATCOM is computed upon these two parameters.
INTRODUCTION
OVERVIEW
An electric distribution system is part of an electric system between the bulk
power source or sources and the consumers service switches. The bulk power sources are
located in or near the load area to be served by the distribution system and may be either
generating stations or power substations supplied over transmission lines. Distribution
systems can, in general, be divided into six parts, namely, sub transmission circuits,
distribution substations, distribution or primary feeders, distribution transformers,
secondary circuits or secondary’s, and consumer’s service connections and meters or
consumer’s services.
With an increase in load demand, burden on lines and the voltage level is
challenged. Now a day’s maintaining voltage magnitude at an acceptable range is one of
the major system constraints. One of the classical methods to solve this is to place shunt
capacitor in line. But the reactive power provided by the shunt capacitor is bus voltage.
This may reduce its effectiveness in high and low voltages. Another problem related to
shunt capacitor is that they resonate when got tuned with system reactance.
OBJECTIVE OF THE WORK
Objective of the present work is to study and implement the DSTATCOM model
in the load flow and identify the nodes for DSTATCOM placement. The compensation
resulted by operating the DSTATCOM in fixed rating mode and complete compensation
mode is also to be investigated.
ORGANISATION OF THE THESIS
The work carried out in this Thesis has been summarized in five Chapters. The
Chapter 1 highlights the brief introduction, summary of work carried out by various
researchers, and the outline of the Thesis. The Chapter 2 explains load flow technique
using backward and forward sweep, DSTATCOM model suited for load flow and
DSTATCOM allocation strategy. Chapter 3 deals with results and discussion pertaining
to two test cases, namely 33 bus RDS and 69 bus RDS. The conclusions and the scope of
further work are detailed in Chapter 4.
MATHEMATICAL MODELING OF DSTATCOM
DSTATCOM is a shunt device which hast the capability to inject or absorb both
active and reactive current. The reactive power output of a D-STATCOM is proportional
to the system voltage rather than the square of the system voltage, as in a capacitor. This
makes DSTATCOM more suitable rather than using capacitors. Though storing energy is
a problem for long term basis, considering real power compensation for voltage control is
not an ideal case. So most of the operations considered is steady stat only and the power
exchange in such a condition is reactive. To realize such a model, it can be said that a
DSTATCOM consists of a small DC capacitor and a voltage source converter
CONCLUSIONS
The work has been carried out with an aim to identify the best suitable node for
DSTATCOM placement in a distribution network. Study has been carried out with both
fixed rating and variable rating DSTATCOM and a comparison has been made between
them. To perform this act initially load flow is performed with backward and forward
sweep method and then after modeling the DSTATCOM, again load flow is done with
DSTATCOM attachment on the desired bus. Study has been carried out on 33-Bus and
69-Bus radial distribution system taking into account that the system is completely in
steady state.