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2.35 Sensitive Rotor Earth Fault Protection with 1 to 3 Hz Square Wave Voltage Injection (ANSI 64R - 1 to 3 Hz)
Monitoring Functions
On each polarity reversal, the charging current of the earth capacitance is determined. If this is undershot,
errors in the measuring circuit such as wire break, poor brush contacts etc. can be detected. This is possible
however only if the earth capacitances are sufficiently large (> 0.15 µF) and excitation disturbances minimal.
As an alternative, the protection function offers an external test option using a test resistor (included in the
7XR6004 and 7XR6003). The test mode is activated via a binary input, and the fault resistor then connected to
a slip ring with an external relay. The protection function must be informed of the relevant test resistance. The
protection function issues appropriate indications showing the test results. It is also able to detect one-sided
interruptions (such as wire breaks or loose terminals in a coupling).
The evaluation logic is shown in the following figure.
Figure 2-112
Logic Diagram of the Rotor Earth Fault Protection in Test Mode
In addition, the control voltage is monitored. If the control voltage is found to be missing or too low, a failure of
the control unit is assumed (see also logic diagram).
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
Functions
247
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