Measured impedance
will enter the asynchronous boundary after
running the asynchronous impedance. Therefore,
we can take asynchronous boundary as a
criterion for a differential low excitation or
loss-of-excitition faults. Due to the
asynchronous boundary in the static stability
boundary inside, so after loss-of-excitation,
terminal locus of measured impedance first
enters the static stability boundary, and then
enter the asynchronous boundary. That is to say
the asynchronous boundary as the criterion for
loss of excitation protection detect the loss of
excitation faults will be much later. Especially
the reactance is large, the difference is clear.
Usually, hydraulic motor are not allowed to run
asynchronous operation, and large turbine
motor are generally in short-term
asynchronous operation, in order to reduce the
harm. when the end of measured impedance
into the static-stable impendance, let out-of-step
protect.