Siemens SIPROTEC 7SJ62 Manual page 205

Mode of Operation - Isolated System
The FFM can also function in isolated and compensated (grounded) systems where only low ground currents
are expected. This is indicated to the device via address 5301 FUSE FAIL MON..
The logic diagram on the mode of operation in an isolated system is illustrated in Figure 2-69. The following is
a description of the principles for single-, two- and three-pole faults in a voltage transformer secondary system.
If this part of the FFM logic picks up, the internal signal "Alarm FFM isol.N." is initiated, which further processing
is indicated in Figure 2-68.
Figure 2-69
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
Logic diagram of the Fuse Failure Monitor for ungrounded networks
Functions
2.11 Monitoring Functions
205