11-12-2012, 12:44 PM
POWER GRID RESTORATION OPTIMIZATION CONSIDERING GENERATING PLANT ISLANDING SCHEME
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ABSTRACT
The restoration process of the bulk-power
transmission system following a partial or a total
blackout, have two main issues during a restoration,
those are voltage control and frequency control.
Special attention is therefore given to the behaviour of
network parameters, control equipments as they affect
the voltage and frequency regulation during the
restoration process. During restoration due to wide
fluctuations in the frequency and voltage it becomes
very difficult to maintain the integrity in the system.
Inability to control the frequency may lead to
unsuccessful restoration. Repeated collapse of the
system islands due to tripping of generators either due
to over frequency or under frequency causes delay in
getting normalcy. The paper considers aspects of
computer application in restoration and Islanding in
context of Maharashtra State power system. During
conditions of blackout, the process of Islanding can
satisfy the power requirements for a particular area,
thus assisting the grid operator as well as helping in
reducing the time required for the complex restoration
processes. The main obstacle in the process of
restoration or islanding is number of switchgears
located at various locations with different
configurations.
INTRODUCTION
Large interconnected power systems may be seriously
affected by severe occurrences that could lead to a
cascade of automatic actions. These types of events may
be the source of an uncontrolled network splitting with
harmful effects on power quality to end-users. In highly
stressed operating conditions, a cascade outage may
eventually conduct to a partial or complete blackout. The
power systems operated by the utilities in developing
countries suffer from a large gap between demand and
generation, inadequate transmission capacity, and
nonuniform location of the load centers and generating
stations. In most of the cases, occurrences of faults in such
systems end up with the worst consequence, which is
complete blackout. Uninterrupted power supply is
essential for the national productivity and social structure
and hence system must be made flawless at any cost.
After occurrence of severe system disturbances, the
system may split into parts, which may or may not survive
depending on the load generation balance. The part
system containing the generation sources and certain
loads, which are planned to be separated from the main
grid during system disturbance at preconceived points
either through under frequency and / or directional power
relays are called ‘Islands’.
MAHARASHTRA STATE POWER SYSTEM
The western region of Indian Power Grid consists of
Maharashtra State power system, with highest installed
generating capacity of around 15,000 MW (as on
31/03/2005), along with Gujrat, Madhya Pradesh,
Chattisgad, and Goa. Some private players also play a
power game in hands with state electricity Generation
Company. The wide electrical power grid also supports
the system. The figure below indicates the 400 kV power
system network in Maharashtra State with major
transmission lines. The major hydroelectric power station,
Koyna situated in Western Maharashtra has total installed
capacity of 1960 MW. Power generation of Dabhol Power
Corporation (DPC) of 728 MW is not available since 29th
May 2001. The major generating stations are located in
Eastern Maharashtra i.e. at Koradi (1080 MW),
Chandrapur (2340 MW), Khaparkheda (840 MW) and
Bhusawal (478 MW).
ISLANDING SCENARIO
The Islanding scheme is presently in operation in the state
for Mumbai region with Reliance (REL) and Tata (TEC),
the private players. For rest of the Maharashtra State,
generating station wise (or generator wise) islanding may
be a hopeful solution to avoid complete blackout for the
consumers. In this paper the stress is given to the
Islanding which will be helpful not only for the
interruption free power supply to the consumers but also
for the system restoration. This Islanding system is
designed for six different sectors in the Maharashtra State
which are consisting of generation, one sector without
generation, so in this way seven sectors are considered.
The figure below (figure: 3) illustrates the seven sectors
along with existing Islanding i.e. Mumbai with existing
transmission lines.
CONCLUSION AND FUTURE WORK
The main aim of the paper is to put more light on the
understanding of the new concept. This scheme is very
helpful for a big power system as in Maharashtra state. In
normal hierarchy, at the time of grid failure, the power
required to start restoration (generally power for thermal
power plants to run auxiliaries) is demanded from the
states where power is available. This of course includes
money and time matters. This can be avoided by using the
proposed scheme. As mentioned earlier the present
restoration methodologies have time constrains to
implement. So this new scheme will definitely help to
reduce restoration time and save the state from total
blackout.