Siemens SIPROTEC 7UM62 - Page 206

Functions
2.28 90-%-Stator Earth Fault Protection (ANSI 59N, 64G, 67G)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
206
The protection then detects a machine earth fault if the following three criteria are fulfilled:
• Displacement voltage larger than set value U0>,
• Earth fault current across the measurement location larger than set value 3I0>,
• Earth fault current is flowing in the direction of the protected machine.
Figure 2-87 Characteristic of the Stator Earth Fault Protection for Busbar Connection
On the occurrence of an earth fault in the machine zone, the disconnection of the machine is initiated after a
set delay time.
If the earth fault current fails to provide an unambiguous criterion for detecting an earth fault when the circuit
breaker is open, the earth current detection can be switched off for a certain time via a binary input. By this
means it is possible to switch to sole evaluation of the displacement voltage e.g. during run-up of the generator.
Figure 2-89 shows the logic diagram of the stator earth fault protection.
If the stator earth fault protection is used as directional or non-directional busbar connection protection, the sen-
sitive current measuring input of the 7UM62 device is thus occupied. The user must be aware that the sensitive
earth fault detection can use the same measuring input (if I
ee2
configured) and thus the same measured value.
Thus two additional, independent pickup thresholds Iee> and Iee>> could be formed for this measured value
by means of the sensitive earth fault detection (see Section 2.29). If the user does not desire this, he should
remove the sensitive earth fault configuration at address 151, or use it with I
ee1
.
If the rotor earth fault protection (see Section 2.34) is used, it occupies the additional voltage input; the dis-
placement voltage U
0
for the stator earth fault protection is therefore calculated from the phase-earth voltages
in that case.