Table of Contents
Advertisement
2.28
90-%-Stator Earth Fault Protection (ANSI 59N, 64G, 67G)
The stator earth fault protection detects earth faults in the stator windings of three-phase machines. The
machine can be operated in busbar connection (directly connected to the network) or in unit connection (via
unit transformer). The criterion for the occurrence of an earth fault is mainly the emergence of a displacement
voltage, or additionally with busbar connection, of an earth current. This principle makes possible a protected
zone of 90 % to 95 % of the stator winding.
2.28.1
Functional Description
Displacement Voltage
The displacement voltage U
neutral earthing transformers (Figure 2-84) or via the e-n winding (broken delta winding) of a voltage transform-
er set or the measurement winding of a line connected earthing transformer (Figure 2-85). Since the neutral
earthing transformer or the line connected earthing transformer usually supply a displacement voltage of 500
V (with full displacement), a voltage divider 500 V/100 V is to be connected in series in such cases.
If the displacement voltage can not be directly applied to the device as a measured value, the device can cal-
culate the displacement voltage from the phase-to-earth voltages.
Address 223 UE CONNECTION serves for notifying the device of the way the displacement voltage is to be
measured or calculated.
In all kinds of displacement voltage formation, the components of the third harmonic in each phase are summed
since they are in phase in the three-phase system. In order to obtain reliable measured quantities, only the fun-
damental harmonic of the displacement voltage is evaluated in the stator earth fault protection. Higher harmon-
ics are filtered out by numerical filter algorithms.
For machines in unit connection the evaluation of the displacement voltage is sufficient. The possible sensitivity
of the protection is only limited by power frequency interference voltages during earth faults in the network.
These interference voltages are transferred to the machine side via the coupling capacitance of the unit trans-
former. If necessary, a loading resistance can be provided to reduce these interference voltages. The protection
initiates disconnection of the machine when an earth fault in the machine zone has been present for a set time.
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
2.28 90-%-Stator Earth Fault Protection (ANSI 59N, 64G, 67G)
can be measured either at the machine starpoint via voltage transformers or
E
Functions
203
Advertisement
Table of Contents
