Application of active power sensitivity to frequency and voltage variationson 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 IEEE 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