Setting Notes - Siemens 7SC80 Manual

Functions
2.12 Monitoring Functions
[anschl-spg-wdl-3phl12-131106, 1, en_US]
Figure 2-73
Current-Transformer Monitoring
A current-transformer fault results in an unbalance of the phase currents detected by the protection device. As
a consequence, the currents of the negative sequence system I2 increase. In case of 1- and 2-phase faults,
values around 0.3 x In are reached. In contrast to a real failure, however, the voltage levels of the negative
sequence system V2 do not increase. Thus, the algorithm can differentiate between a current-transformer
fault and a failure.
Table 2-14
Voltage V2 negative sequence
system
> setting value
< setting value
A current transformer fault will cause no or only low negative sequence voltages V2. A maximum of 0.1 x Vn
will be reached. To prevent that temporary effects lead to wrong decisions, the current transformer moni-
toring function works time-delayed.
Current transformers are independent components. The simultaneous failure of all three current transformers
is so unlikely that there is no need to consider this case.
2.12.1.8

Setting Notes

Measured Value Monitoring
The sensitivity of measured value monitoring can be modified. Default values based on experience are preset
and are sufficient in most cases. If especially high operating unbalance in the currents and/or voltages are to
be expected during operation, or if it becomes apparent during operation that certain monitoring functions
are activated sporadically, the setting should be less sensitive.
236
Wiring for 3-phase voltage transformer connection: VAB, VBC, VN
Erkennung Stromwandlerfehler (1- od. 2-phasig)
Current I2 negative sequence
system
> setting value
> setting value
Decision
Failure
Current transformer fault
SIPROTEC Compact, 7SC80, Manual
E50417-G1140-C486-A8, Edition 07.2017