Siemens SIPROTEC 7UM62, Manual

Page: 220 / 602

Functions
204
7UM62 Manual
C53000-G1176-C149-3
The series resistors R
pre
for the protection of the coupling capacitors can be
considered with the total series resistance (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
pre
and for the resistance of the two brushes. Similarly, the
coupling reactance is calculated from the parallel connection of the two coupling
capacitors C
K
.
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 Section 3.3.7). It may be advantageous to compensate for
the angle error of the input CTs of the relay in order to increase accuracy. This can be
done at address
6009 PHI I RE
. 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 Section 3.3.7).
The values calculated and displayed by the relay may become negative due to CT
angle errors, wrong settings of the coupling impedance or malfunctions of the
excitation equipment. In that case, a check is performed whether the current I
RE
> is
more than 7 mA, in which case a tripping decision is made. If the current is < 7 mA,
the measurement is marked as invalid, and the rotor earth resistance R
Rotor
∞
is
displayed. This additional consistency check 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
E
≥
0.15
µ
F) is available, an interruption in the
measurement circuit can 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
V
is at the same time above 25 V. The alarm is reset when the 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.
2.30.2.1 Settings of the Rotor Earth Fault Protection
Addr. Setting Title Setting Options Default Setting Comments
6001 ROTOR E/F OFF
ON
Block relay for trip com-
mands OFF Rotor Earth Fault Protection (R,
fn)
6002 RE< WARN 3.0..30.0 kOhm 10.0 kOhm Pickup Value of Warning Stage
Re<
6003 RE<< TRIP 1.0..5.0 kOhm 2.0 kOhm Pickup Value of Tripping Stage
Re<<
6004 T-WARN-RE< 0.00..60.00 sec;
∞
10.00 sec Time Delay of Warning Stage
Re<
6005 T-TRIP-RE<< 0.00..60.00 sec;
∞
0.50 sec Time Delay of Tripping Stage
Re<<