08-08-2012, 01:49 PM
Concepts of Synchronous Machine Stability as Affected by Excitation Control
Concepts of Synchronous Machine Stability.pdf (Size: 2.71 MB / Downloads: 362)
INTRODUCTION
THE PHENOMENON of stability of synchronous machine
operation has received a great deal of attention in the past
and will receive increasing attention in the future. As economies
in system design are achieved with larger unit sizes and higher
per unit reactance generating and transmission equipment designs,
more emphasis and reliance is being placed on controls to
provide the required compensating effects with which to offset
the reductions in stability margins inherent from these trends
in equipment design [1].
Concurrent with these trends are improvements in calculating
methods and computing capability which permit predicting
complex dynamic effects [2]-[5], providing the means for designing
control equipment with the proper characteristics.
STABILIZING SIGNALS FROM SPEED
Phase and Magnitude Relations
The stabilizing signal requirements to provide damping through
transient manipulation of the voltage reference in response to
speed can be derived as follows. Fig. 10 shows the elements of
the system in question relating the effect of speed through the
stabilizing function G(S) through the voltage regulator loops
affecting AEq', which produces a component of torque ATsig.
The question is: what should be the nature of G (S) to provide
adequate damping over a wide range of machine and system
parameters and operating conditions?
SEARCH FOR UNIVERSALLY APPLICABLE
STABILIZING FUNCTION
General Approach
The insights that have been developed into the problem of
providing damping from stabilizing signals may convince one
that there is no way of developing a universally applicable
stabilizing function that would be optimal for a wide range of
machine and system parameters, and operating conditions. However,
even if not optimal, it would be highly desirable to have
a signal transfer function which would provide damping in those
cases where it was badly needed without deteriorating damping
in those instances where there was no particular need for providing
supplementary damping.
CONCLUSION
The small perturbation stability characteristics of a single
machine supplying an infinite bus through external impedance
have been explored by means of frequency response analyses
giving insights into effects of machine and system parameters,
voltage regulator gain, and stabilizing functions derived from
speed and working through the voltage reference of the voltage
regulator.
The study has explored a variety of machine loadings, machine
inertias, and system external impedances with a determination
of the oscillation and damping characteristics of voltage or speed
following a small disturbance in mechanical torque. An attempt
has been made to develop some unifying concepts that explain
the stability phenomena of concern, and to predict desirable
phase and magnitude characteristics of stabilizing functions.