Trip time
Fault resistance
R
Trip
R
Alarm
IEC11000002-1-en.vsd
IEC11000002 V1 EN
Figure 142: Trip time characteristic as function of fault resistance
During run-up and shut down of the generator, i.e. when the rotational speed of the
generator changes, there will occur harmonic voltages with varying frequency at the
injection equipment connection point (for example see voltage generator U
n
in Figure
136). If such frequencies interfere with the injected frequency this might create an
error in the fault resistance estimation. Such situations are identified in the function
and the function is automatically stabilized to prevent unwanted operation of the
protection.
In connection with this calibration the reference impedance is also derived.
It is possible to have up to five different reference impedances. The need to change
reference impedance is due to different operating conditions for the generator, for
instance:
1. Generator stand still
2. Generator running, not synchronized to the power network
3. Generator in normal operation, synchronized to the power network
The following automatic choice for the actual reference impedance can for example
be made:
1MRK502052-UEN B Section 7
Impedance protection
315
Technical manual
To Next Page
Loading...
