Instruction manual
–
AQ G3x7 Generator protection IED
139 (211
)
e.m.f. collapses, the locus of the impedance on the impedance plane travels to this negative
reactive value. With an appropriate characteristic curve on the impedance plane, the loss of
excitation state can be detected. The applied characteristic line is a closed offset circle, the
radius and the centre of which is defined by parameter setting.
If the calculated impedance gets into the offset circle then the function generates a trip
command.
The loss of excitation protection function provides two stages, where the parameters of the
circles and additionally the delay times can be set independently.
The main features of the loss of excitation protection function are as follows:
•
A full-scheme system provides continuous measurement of impedances separately in three
independent phase-to-phase measuring loops.
•
Impedance calculation is conditional on the values of phase currents being sufficient.
•
The operate decision is based on offset circle characteristics.
o
Two independent stages.
•
Binary input signals and conditions can influence the operation:
o
Blocking/enabling.
o
VT failure signal.
3.2.23.1
Structure of loss of excitation protection function
Figure below shows the structure of the loss of excitation protection function with
compounded circular characteristic.
Figure 3-84: Structure of loss of excitation protection function.
