Functions
2.34 Rotor Earth Fault Protection R, fn (ANSI 64R)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
240
2.34 Rotor Earth Fault Protection R, fn (ANSI 64R)
Rotor earth fault protection is used to detect earth faults in the excitation circuit of synchronous machines. An
earth fault in the rotor winding does not cause immediate damage; however, if a second earth fault occurs it
constitutes a winding short-circuit of the excitation circuit. The resulting magnetic imbalances can cause
extreme mechanical forces which may destroy the machine.
2.34.1 Functional Description
Measurement Method
The rotor earth fault protection in the 7UM62 uses an external system frequency auxiliary voltage of approxi-
mately 36 to 45 V AC, which can be taken e.g. from the voltage transformers via a coupling unit 7XR6100-
0*A00. This voltage is symmetrically coupled to the excitation circuit and simultaneously connected to the mea-
surement input U
E
of the device provided for this purpose. The capacitors C
coup
of the 7XR6100 coupling unit
are protected by series resistors R
pre
and - in case high harmonics content is expected in the excitation circuit
(e.g. excitation by thyristor circuits) - by an additional filter choke (for a connection example with terminal as-
signment see Appendix A.3).
The coupled voltage drives a small charging current (normally a few mA) through the coupling unit, as the case
may be the brush resistance and the capacitance to earth of the excitation circuit. This current I
RE
is measured
by the device.
Figure 2-107 Determination of the rotor earth resistance R
E
Note 3PP13 is only necessary if more than 0.2 A
eff
are flowing permanently; (rule: Uerr load > 150 V).
In this case the internal resistors Rpre inside the 7XR61 must be shorted.
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