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The series resistors R
sistance (address 6007) since the brush resistance and the series resistance are connected in series in the
measurement circuit. The resultant resistance applies for R SERIES, i.e. the parallel connection in each case
of the series resistors R
lated from the parallel connection of the two coupling capacitors C
In some cases, the inductor integrated in the 7XR6100 is included in the coupling circuit to reduce very high
harmonics content of the excitation voltage. This forms, together with the coupling capacitance, a band pass
for the system frequency. In these cases, it must be considered that the reactance must not become less than
–100 Ω (lower threshold of setting 6006 X COUPLING).
Angle Error Correction
Coupling reactance and series resistance can be measured by the protection itself during commissioning (see
Subsection 3.3 in the Section „Installation and Commissioning"). It may be advantageous to measure any angle
errors of the input CTs of the device and adjust them at address 6009 PHI I RE in order to increase accuracy.
Thus, if the warning stage in particular does not pick up during testing at the expected insulation resistance
level, you should check and correct the correction angle and the coupling reactance (see also Subsection 3.3
in the Section „Installation and Commissioning").
The values calculated and displayed by the device may become negative due to CT angle errors, wrong set-
tings of the coupling impedance or malfunctions of the excitation equipment. In that case, it is checked whether
the current I
RE
is marked as invalid, and the rotor earth resistance R
ensures that even if the setting of the correction angle or the coupling impedance is wrong, tripping in case of
low-resistance earth faults is ensured although the warning stage may not pick up correctly.
Measuring Circuit Monitoring
If a sufficiently high rotor capacitance (C
also be recognized. A measurement circuit interruption is assumed when the voltage drops below the threshold
set at address 6008 I RE<, and the voltage U
current is 0.5 mA or 20 % above the setting value, or when the voltage falls below 20 V. If I RE< is set to 0.0
mA, there is no current monitoring and no alarm.
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
for the protection of the coupling capacitors can be considered with the total series re-
S
and for the resistance of the two brushes. Similarly, the coupling reactance is calcu-
S
is higher than 7 mA. And if it is, tripping will be initiated. If the current is < 7 mA, the measurement
E
2.34 Rotor Earth Fault Protection R, fn (ANSI 64R)
coup
= ∞ is displayed. This additional consistency check
E
≥ 0.15 µF) is available, an interruption in the measurement circuit can
is at the same time above 25 V. The alarm is reset when the
RE
.
Functions
243
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