With the increased loading and exploitation of the power
transmission system, the problem of voltage stability and
voltage collapse attracts more and more attention. A
voltage collapse can take place in systems or subsystems
and can appear quite abruptly. Continuous monitoring
of the system state is therefore required.
There are both static and dynamic aspects involved in
voltage stability [19]. Static considerations relate voltage
instability to the reaching of some maximal admissable
load, beyond which a load-flow solution no longer exists.
Investigations are still required into the dynamic
mechanism and modelling of real systems. In addition,
apart from simplified system modelling for which both
approaches coincide, there is still a need to relate both
static and dynamic counterparts. This paper is restricted
to the static aspects only.
The phenomenon of voltage collapse on a transmission
system, due to operation near the maximum transmissible
power, is characterised by a fall in voltage, which
is at first gradual and then rapid. The latter is aggravated
by certain control systems, in particular the transformer
tap-changers, becoming unstable.