The preceding review leads to a number of important
conclusions and observations concerning power system oscillations:
a. Oscillations are due to natural modes of the system and
therefore cannot be eliminated. However, their damping and frequency can be
modified.
b. As power systems evolve, the frequency and damping of
existing modes change and new modes may emerge.
c. The source of ‘‘negative’’ damping is power system
controls, primarily excitation system automatic voltage regulators.
d. Inter area oscillations are associated with weak
transmission links and heavy power transfers.
e. Inter area oscillations often involve more than one utility
and may require the cooperation of all to arrive at the most effective and
economical solution.
f. Power system stabilizers are the most commonly used means
of enhancing the damping of
inter area modes.
g. Continual study of the system is necessar y to minimize
the probabilit y of poorly damped oscillations. Such ‘‘beforehand’’ studies may
have avoided many of the problems experienced in power systems.
It must be clear that avoidance of oscillations is only one
of many aspects that should be considered in the design of a power system and
so must take its place in line along with economy, reliability, security,
operational robustness, environmental effects, public acceptance, voltage and
power quality, and certainly a few others that may need to be considered.
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