ABB RELION 670 Series Technical Manual page 409

1MRK 502 066-UUS B
ANSI11000065 V1 EN-US
Figure 216: Equivalent diagram for Sensitive rotor earth fault protection principle
The impedance Z
ground (1/ωC
is eliminated. R
reference impedance and can be calculated as :
= -
Z
ref
EQUATION2510 V1 EN-US
alternative
1
=
Z
ref
EQUATION2511 V1 EN-US
Where
w p
=
2
EQUATION2512 V1 EN-US
The injected frequency f
frequency (50 or 60 Hz). The injected frequency can be set within the range 75 – 250 Hz with the
recommended value 113 Hz in 50 Hz systems and 137 Hz in 60 Hz systems.
If the machine (generator) is stationary running (a few seconds or more) on 1/3 of the injection
frequency, the injection function will start to send errors. Therefore, 1/3 of the injection frequency
will not be used for spinning reserve, either the machine frequency or the injection frequency has
to be changed. The error occurs because the 3
frequency and causes interference.
For example, if the injection frequency is 87Hz and the fundamental frequency of machine is on
87/3 = 29Hz, then the 3
errors.
The solution is to either change machine frequency or injection frequency.
R is a resistance in the REX061 unit used to protect against overvoltage to the injection unit.
series
Such overvoltages can occur if the unit is fed from static excitation system.
Technical manual
DC
C
rot
AC
R
f
is equal to the capacitive reactance between the rotor winding and
Measured
) and the ground fault resistance (R
rot
is very large in the non-faulted case and the measured impedance, called the rotor
f
1
j
w
C
rot
w
j C
rot
×
f
inj
of the square wave, is a set value, deviating from the fundamental
inj
rd
harmonic of machine is 87Hz, which can cause injection interference
R
f
REX 061
I
inj
+
V
inj
-
). The series resistance in the injection circuit
f
rd
harmonic of the machine is on top of the injection
Impedance protection
I
inj
+
C V
rot inj
-
Rotor Reference
Impedance
ANSI11000065_1_en.vsd
Section 7
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