Siemens 7XT71 Series Manual page 10

English
Front view of switch S1 and S2:
Position „230 V"
Factory set:
Position „115 V"
Figure 3 Switch positions (example)
Matching the frequency of polarity reversal:
The preset value of 1.5 Hz is an experimental value and usually the user does not have to
change it.
The value must be lowered in case of larger rotor earth capacitances or if the excitation
system is equipped with capacitors towards earth. Read out the operational measured value
R of the protective device. If the value of the rotor earth capacitance is too low supposed
earth
there is no fault, the frequency of polarity reversal is to be reduced. As an alternative, the
fault recording function of the device can be applied. When executing fault recording select
its instantaneous value acquisition mode. Furthermore, a test record must be initiated via the
operating program with the generator not being excited. To ensure proper functioning the
protection system needs a signal, which is charge exchange free for approx. 100 ms, each
time polarity reversal is carried out (see Figure 4).
U (t)
Mess
Figure 4 Charge exchange process with the generator not being excited
For smaller rotor-earth-capacities the user may raise the frequency of polarity. In a next step
please check the measured results with the machine being excited.
10
approx. 100 ms
approx. 100 ms
7XT7100-0*A00/DD
Position „0,5 Hz"
Position „1,5 Hz"
C53000-B119U-C128-1