Instruction manual
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AQ G3x7 Generator protection IED
102 (211
)
3.2.21
I
MPEDANCE PROTECTION
Z<
(21)
3.2.21.1
General
This impedance protection function can be applied as impedance protection with an offset
circular characteristic or as a loss-of-field protection function for synchronous machines. Its
main features are:
•
A full-scheme system provides continuous measurement of impedances separately in three
independent phase-to-phase measuring loops as well as in three independent phase-to-
earth measuring loops.
•
Impedance calculation is conditional on the values of phase currents being sufficient.
•
Full-scheme faulty phase identification is provided.
•
The operate decision is based on offset circle characteristics.
•
The impedance calculation is dynamically based on:
o
Measured loop voltages if they are sufficient for decision,
o
Voltages stored in the memory if they are available,
o
Optionally, the decision can be non-direction; in that case, the center of the circle is
not shifted away from the origin.
•
Binary input signals and conditions can influence the operation:
o
Blocking/enabling.
o
VT failure signal.
The distance protection function provides main protection for overhead lines and cables of
solidly grounded networks. Its main features are as follows:
•
A full-scheme system provides continuous measurement of impedance separately in
three independent phase-to-phase measuring loops as well as in three independent
phase-to-earth measuring loops.