Siemens SIPROTEC 4 7XT7100-0 A00/EE Series Product Information page 25

9.2 Changing the Polarity Reversal Frequency
9.2.1 Operating Conditions
Factory Setting for the Polarity Reversal Frequency
A polarity reversal frequency (frequency of the square-wave generator) of 1.5 Hz is
preset from the factory for normal operating conditions. This setting is documented
on the sticker affixed to the device.
Operating Conditions that Require the Polarity Reversal Frequency to be Increased
• Rotor ground capacitance too low
The reduction of the measuring time is achieved by increasing the polarity reversal
frequency.
Operating Conditions that Require the Polarity Reversal Frequency to be Reduced
• Rotor ground capacitance too large
• Capacitors are switched against ground in the excitation machine
To obtain an accurate measurement, make sure that the rotor ground capacitance
is charged before the charge reversal. This requires the output voltage at the mea-
suring output to be constant (ideally zero) for at least 100 ms when there is no fault.
For large ground capacitances, this can be achieved by reducing the polarity rever-
sal frequency.
NOTE
7UM62:
The SIPROTEC manual 7UM62, ordering code C53000-G1176-C149 provides a
detailed description of how to determine the current operating conditions using the
7UM62.
7UM85:
The SIPROTEC manual 7UM85, order no. C53000-G5040-C027 provides a de-
tailed description of how to determine the current operating conditions using the
7UM85.
SIPROTEC 4/5, Injection Unit 7XT71, Product Information
C53000-B1174-C128-7, Edition 09.2016
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