Power systems in general contain a large number of generators, transformers and
loads having complex interconnection through transmission and distribution networking.
Therefore, these are treated as complex dynamic systems. Hence, such systems need
dynamic study for better results (Hogan, 1992). As the active power demand grows
in the system, there is the need for adequate generation and supply of reactive
power to maintain the voltage at specified limits. However, bulk transmission of
reactive power over long distance is limited due to several reasons. Therefore,
it is very important to analyze the underlying principle of voltage stability in
every power system. Another aspect of dynamic simulation is that it requires time
domain analysis for which a complete dynamic system modeling is essentially required.
This leads to a very complex form of solution procedure and consumes a lot of processing
time. However, such practical difficulties may be overcome by assuming slow and
gradual changes in the system parameters, thereby it becomes possible to analyze
the system behavior in steady state (Llic, 1992).
Congestion in a power system means overburdening of the existing resources and capacities
due to sudden, unprecedented load variations and contingencies as well. As a matter
of fact, congestion is not a healthy situation, and if not prevented, it may lead
to several chaotic situations and the ultimate threat may be instability and collapse
of the system. Therefore, this aspect is drawing a rising attention among researchers
in this field. The causes of congestion are many. However, scheduled bidding and
pricing for the competitive market play an important role indirectly in system congestion
(Descamps and Feltin, 1995).
In the absence of congestion, several bidders may have similar optimal equilibrium
status in an energy market. However, in the presence of congestion, the results
of optimal equilibrium may vary due to the preference of consumers to manage their
financial risks in a real-life setting (Leotand and Llic, 1999). This fact would
give rise to deviations from simple bidding strategy. Also, the profit in the energy
market is directly dependent on congestion management. Therefore, it is very important
to devise versatile congestion management tools that would be applicable to any
system condition. Among other approaches, there are schemes for optimal placement
of High Voltage Direct Current (HVDC) and Flexible AC Transmission System (FACTS)
equipments, which also coordinate congestion management.
However, in this study, the approach to tackle the congestion problem is slightly
different. The approach proposed here takes care of identifying the lines in the
distribution network which get overburdened in the face of congestion at a particular
operating condition and hence finds alternate provisions to get rid of the congestion
problem. In view of this, two schemes have been suggested in this study: (1) reconductoring
of existing distribution lines; and (2) installation of new express distribution
feeders to relieve the stress on the congested lines in the said network. Results
presented in this study indicate that the former scheme with reconductoring of existing
distribution lines is more economical than the latter scheme of installation of
a new express distribution feeder.
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