A power outage may result from either of two failures: load increases
beyond the capability of the transmission lines or a component failure
which leads to an undesirable operating point.
If a system's load were to continue to increase, it is possible for the
system to enter an overload situation and "voltage
collapse". We will consider this point to be the nose of the PV curve.
A power outage may also begin from a loss of a single
component such as with a downed transmission line or transformer failure.
This may result in an immediate loss of load and a "blackout".
Another problem that arises with power systems are low voltages. Low
system voltages can be a consequence of both overloads and component failures.
With respect to overloads, low system voltages can be illustrated with fixed
PV curves and abnormally high loads. Regarding a component loss, the operating
PV curve changes when the failure occur to a curve which supports a reduced maximum power transfer and,
as a result, causes a reduction in
system voltage. The term for this low voltage situation is a "brownout"
and it occurs when |V2| falls outside the range of 0.95 to
1.05 p.u.
The SEEKS software runs a number of scenarios to analyze
power outages and isolate points of voltage instability in an
effort to return the post-outage power system to stability.
