Mounting and Commissioning
3.3 Commissioning
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
409
Table 3-28 Operational measured values of the rotor earth fault protection
Measured Value Explanation
fgen = xx.x Hz Shows the frequency of the injected square-wave voltage. The frequency can be
set by a jumper in the 7XT71. The default setting is approx. 1.5 Hz (tolerance
approx. ± 10 %).
Ugen = xx.x V This measured value indicates the present amplitude of the injected square-
wave voltage. The measured value amounts to approx. 50 V (tolerance of the
7XT71 can be up to ± 4 V).
Igen = X.xx mA This measured value is nearly zero in fault-free conditions. If a fault resistor is in-
stalled between rotor and earth, the current to be expected can be estimated as
follows:
R
E
: Fault resistance
R
tot
: Coupling resisitance (20 kΩ + 720 Ω = 20.720 kΩ)
Qc = x.xxx mAs This measured value indicates the charge which is a function of the rotor earth
capacitance. Half of the measured value must be set at address 6106 as Qc <.
If the capacitance is very small, it may be necessary to deactivate the measuring
circuit monitoring (setting value 0).
Rearth = xxx.x kΩ This measured value indicates the rotor earth resistance. In fault-free condition,
the upper limit value 999.9 kΩ is displayed. If it is not, there must be some addi-
tional capacitances in the excitation system. The square-wave voltage frequency
in the 7XT71 must be reduced by a jumper. No polarity reversal may occur in the
measuring current Igen for at least 3 cycles. To visualise what is going on, a test
fault record (instantaneous values record) should be started and track TD2,
which traces Igen, should be checked (see following Figure).
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