signal with a frequency different from the generator rated frequency is injected into
the rotor circuit.
To implement the above concept, a separate injection device is required. The injection
device generates a square wave voltage signal which is fed into the rotor winding of
the generator.
The magnitude of the injected voltage signal is measured at the injection point; the
magnitude of the injected current is measured through a resistive shunt located within
REX060. These two measurements are fed to the IED. Based on these two measured
quantities, the IED determines the rotor winding resistance to earth. The resistance
value is then compared to the preset fault resistance alarm and trip levels.
The protection function can detect earth faults in the entire rotor winding and
associated connections. The function can also detect excitation system earth faults on
the AC side of the excitation rectifier. The measuring principle used is not influenced
by the generator operating mode and is fully functional even with the generator at
standstill.
8.7.2.1
Rotor earth fault protection function
The injection to the rotor is schematically shown in figure
DC
AC
REX
061
C
rot
R
f
+
U
inj
-
I
inj
C
rot
Rotor Reference
Impedance
R
f
+
U
inj
-
I
inj
IEC11000065-1-en.vsd
IEC11000065 V1 EN
Figure 154:
Equivalent diagram for Sensitive rotor earth fault protection principle
The impedance Z
Measured
is equal to the capacitive reactance between the rotor
winding and earth (1/ωC
rot
) and the earth fault resistance (R
f
). The series resistance in
the injection circuit is eliminated. R
f
is very large in the non-faulted case and the
measured impedance, called the rotor reference impedance and can be calculated as :
1
ref
rot
Z
j
C
w
= -
EQUATION2510 V1 EN
alternative
1MRK 502 071-UEN -
Section 8
Impedance protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
291
Application manual
Содержание Relion REG670
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