Siemens SIPROTEC 4 User Manual page 188

Functions
2.12 Monitoring Functions
[7sj62-64-ffm-messspag-ausfall-20120611, 2, en_US]
Figure 2-74
Single- and Two-phase Failures in Voltage Transformer Circuits
The measuring voltage failure detection is based on the fact that a significant negative sequence system is
formed in the voltage during single- or two-phase voltage failure, however without influencing the current.
This enables a clear distinction from asymmetries impressed by the power system. If the negative sequence
system is related to the current positive sequence system, the following rules apply to the Fault-free Case:
[u2-u1-fehlerfreier-fall-020828-ho, 1, en_US]
If a fault occurs in the voltage transformer secondary system, the following rules apply to the Single-phase
Failure:
188
Logic diagram of the Fuse Failure Monitor for isolated and grounded systems
SIPROTEC 4, 7SJ62/64, Manual
C53000-G1140-C207-8, Edition 08.2016