ABB RELION 670 SERIES REG670 - Page 319

DC
AC
REX 061
R
f
+
V
inj
-
I
inj
C
rot
Rotor Reference
Impedance
R
f
+
V
inj
-
I
inj
C
rot
ANSI11000065_1_en.vsd
ANSI11000065 V1 EN-US
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 ground (1/ωC
rot
) and the ground 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-US
alternative
1
rot
ref
j C
Z
w =
EQUATION2511 V1 EN-US
Where:
2
inj
f
w p = ×
EQUATION2512 V1 EN-US
The injected frequency f
inj
of the square wave, is a set value, different from the
fundamental frequency (50 or 60 Hz). The injected frequency can be set within the
range 75 – 250 Hz with the recommended value 1
13 Hz in 50 Hz systems and 137 Hz
in 60 Hz systems.
R
series
is a resistance in the REX061 unit used to protect against overvoltage to the
injection unit. Such overvoltages can occur if the unit is fed from static excitation
system.
1MRK 502 071-UUS A Section 8
Impedance protection
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062 313
Application manual