REG 316*4 1MRB520049-Uen / Rev. B ABB Switzerland Ltd
4-13
4.2.3. Rotor ground fault protection
4.2.3.1. Application
Ground faults on the rotor windings of synchronous generators
and motors can be detected by the protection function “Voltage”
in combination with an ancillary unit Type YWX111-11 or
YWX111-21.
The scheme is connected by coupling capacitors (electrical in-
sulation) to positive and negative poles of the rotor winding and
to the shaft ground. The ancillary unit Type YWX111-11/-21, the
coupling capacitors and the natural capacitance of the rotor
winding form a balanced R/C bridge. In the event of a ground
fault, the fault resistance shunts the capacitance of the rotor
winding to the shaft and disturbs the balance of the bridge. The
voltage difference across the bridge is applied to an input v.t. on
the REG 316*4 and causes its voltage function to trip.
Mechanical design
The ancillary unit Type YWX111-11/-21 is accommodated in a
casing of dimensions 183
´ 113 ´ 81 mm for surface mounting
on a panel.
4.2.3.2. Determining the settings
Since it is not possible with this scheme to set the value of leak-
age resistance directly, a voltage corresponding to the leakage
resistance has to be determined for setting on the REG 316*4
(U-Setting). The time delay t [s] before tripping takes place must
also be set. The normal setting range for the leakage resistance
R is between 0 and 5000
W:
· U-Setting = 0.5...3 V
· t = 0.5...5 s
R: leakage resistance between
the rotor winding and ground (shaft)
U-Setting: voltage setting
t: operating time.
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