Siemens SIPROTEC 4 7SD80 Manual page 156

Functions
2.14 Monitoring Functions
condition, dropout of the signal
sequence current or negative sequence current, but only by the voltages in the zero sequence and negative
sequence system falling below a threshold value. The signal
ently of the magnitude of the phase currents.
[lo-ffm-mcl-02-20101014, 1, en_US]
Figure 2-70
A 3-phase failure of the secondary measuring voltages can be distinguished from an actual system fault by
the fact that the currents have no significant change in the event of a failure in the secondary measured
voltage. For this reason, the current values are routed to a buffer so that the difference between present and
stored current values can be analyzed to recognize the magnitude of the current differential (current differen-
tial criterion), cf.
A 3-pole measuring voltage failure is detected if:
•
All 3 phase-to-ground voltages assume a value smaller than the threshold value FFM V<max (3ph)
(address 2913).
•
The current differential in all 3 phases is smaller than the threshold value FFM Idiff (3ph) (address
2914).
If such a voltage failure is recognized, the protection functions that operate on the basis of undervoltage are
blocked until the voltage failure is removed; afterwards the blocking is automatically removed. The definite
time overcurrent protection as emergency function is possible during voltage failure, provided that the time
overcurrent protection is parameterized accordingly (see
A 3-pole measuring voltage failure is also detected in the absence of these criteria if the signal
(no. 170) was previously generated due to an unbalanced measuring voltage failure. In this condition, meas-
uring voltage failure is still detected if the 3 phase-to-ground voltage subsequently falls below the threshold
value FFM V<max (3ph) (address 2913).
156
VT FuseFail can no longer be accomplished by the increase of the zero
Fuse Failure Monitor part 2: detection of the 3-phase measuring voltage failure
Figure 2-70.
VT FuseFail can also be generated independ-
2.4 Backup overcurrent).
E50417-G1100-C474-A2, Edition 02.2018
VT FuseFail
SIPROTEC 4, 7SD80, Manual