Abstract:
Load Shedding plays a major role as the guard which protects the power system from a
disturbance-induced collapse. In Sri Lanka, Ceylon Electricity Board being the major
power network authorizer practice „under-frequency load shedding‟ with the support of
under-frequency load shedding relays.
There are some drawbacks of this under frequency load shedding scheme which
promotes power system authorizers to shift into a computerized power management
system to form an „automated load shedding scheme‟.
An intelligent load shedding system can provide faster and optimal load relief by
utilizing actual operating conditions and knowledge of past system disturbances [1]
As the first step in this study, a research survey was done about present load shedding
system practiced in Ceylon Electricity Board. Past failure analysis was done to identify
major drawbacks of the system.
During literature survey characteristics of an intelligent load shedding system were
observed and the way of forming an intelligent load shedding system in a power network
was studied.
Through selection of southern part of CEB network including seven grid substations,
two major hydro power plants, two thermal power plants and three mini hydro power
plants, model was designed using MATLAB software.
Initially a data bank was formed including load data, generation data for the selected
network. Load data at each grid substation for a week day, Saturday and for Sunday were
formed based on the load equations derived depending on the time of the day (off-peak,
day-peak, night-peak). Generation data was adjusted according to the total load
requirement. Feeders that can be shed were selected considering the category of load connected at each feeder and categorization by System Control center as high priority
feeders and low priority feeders.
Coding was built up in MATLAB software after importing excel sheets consisting all the
data collected and modeled to create a „Graphical User Interface‟(GUI). Further code
was extended for the load shedding process which activates once a power imbalance
occurs between generation and demand. Simulation was done for tripping of major hydro
power plants which contribute to load shedding process.
Further comparisons were done between existing load shedding mechanism which is
under frequency load shedding(UFLS)and Intelligent Load Shedding (ILS) mechanism
in Power System Simulator for Engineering(PSS/E) software which is the software used
by System Control Center branch in transmission division for analyzing and simulating
power system performance.
It is concluded that reasonable improvements can be achieved through application of
intelligent load shedding mechanism to CEB network which contributes to quality of
uninterrupted supply to consumers.
