10-04-2017, 09:00 PM
Application of active power sensitivity to frequency and voltage variations on load shedding
Presented by
Ejas Kunhalan P.E.
S7 E1
College Of Engineering, Trivandrum
2007-11 batch
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Overview:
Objectives
Continued
Introduction
Frequency and voltage measurement techniques
Active power sensitivity to frequency and voltage variations
Testing
Conclusions
Future works
OBJECTIVES
A unique load shedding scheme that combines frequency, voltage, rate of change of frequency and rate of change of voltage to shed an optimal amount of load at suitable locations whenever there occurs a power system blackout.
Ways used to achieve this Goals
To use the rate of change of frequency to find the amount of
load to shed
To use the voltage variation to identify the appropriate buses
for load shedding
Introduction
Present day power system
Chances for power system failures
Emergency method to avoid the power system failure
Continuation
Traditional method.
Limitations of the above
It focus just on one parameter, either frequency or
voltage
It relied on just the level of frequency or voltage and ignored
the rate of change of these parameters
Frequency and voltage measurement techniques
Measured by devices like relays,PMU s etc
Phasor measurements units are the new technique
which synchronizes with new GPS technology
Synchrophasors devices are used which is already
present in the system
Different other methods
In absence of above sophisticated devices the
following methods are used:
From the voltage waveforms by different Mathematical
methods like Fourier analysis etc.
A two stage Kalman Filter
KALMAN FILTER
The first stage of this technique is an extended
Kalman Filter
Next stage is a linear Kalman filter
Active power sensitivity to frequency and voltage variations
The most basic equation of motion for a
Machine is given by
Inertia Constant is defined as
Continuation
Equivalent inertia constant is as follows
Substituting H in place of J in the basic equation of motion , we get
But we know that
Next task is to identify the appropriate buses for load shedding
Buses are Ranked
The buses with the steepest rate of voltage decline
can be selected as the first appropriate Bus
Continuation
Division of load shedding in critical buses is based on the
sensitivity of change in injected power with voltage
Now the Real power injected to the buses are given by
Along with losing Real Power, proportional amount of
Reactive power is lost
And it is given by the following equation
Main time consuming parts of this power system disturbance restore are as follows
Delays in measurement
Time taken for online computation of the
load shedding amount
The delay in sending control signals to breakers on
feeders to open and shed load
Now a days it is Practically possible to allow 0.1sec
between subsequent load sheds
Testing the proposed application
Testing is done on an IEE 30 bus system
It consists of 6 generators,41 lines and
about 190MW
Now the variations of frequency and voltages while
testing the proposed applications are shown below:
VARIATION OF FREQUENCY BEFORE IMPLEMENTING SCHEME
Conclusion
Preliminary results of load shedding based on the described principles show that:
The rate of change of frequency can estimate the
magnitude of disturbance accurately
The rate of change of voltage can identify the location for
load shedding