2.19 Monitoring function
323
7SA522 Manual
C53000-G1176-C155-3
at address Σ,)$&725. These settings can only be changed via DIGSI
®
at Ad-
ditional Settings.
Note
Current sum monitoring can operate properly only when the residual current of the
protected line is fed to the fourth current input (I
4
) of the relay.
Asymmetrical Mea-
suring Voltage
"Failure Fuse
Failure Monitor"
The settings of the “fuse failure monitor” for asymmetrical measured voltage failure
must be selected such that on the other hand reliable pickup of the monitoring is
ensured in the case of loss of a single-phase voltage (address ))08!PLQ),
while on the other hand a pickup due to earth faults in an earthed system is avoided.
In accordance with this requirement, address ))0,PD[ must be set suf-
ficiently sensitive (below the smallest fault current due to earth faults). These settings
can only be changed via DIGSI
®
at Additional Settings.
In address )86()$,/021, the “fuse failure monitor” can be switched 2))
e.g. during asymmetrical testing.
Three-Phase Mea-
suring Voltage
Failure "Fuse
Failure Monitor"
In address ))08PD[SK the minimum voltage threshold is set. If the mea-
sured voltage drops below this threshold and a simultaneous current jump which
exceeds the limits according to address ))0,GHOWDS is not detected
while all three phase currents are greater than the minimum current required for the
impedance measurement by the distance protection according to address
0LQLPXP,SK!, a three phase measured voltage failure is recognized. These set-
tings can only be changed via DIGSI
®
at Additional Settings.
In address )86()$,/021, the “fuse failure monitor” can be switched 2))
e.g. during asymmetrical testing.
Additional Mea-
sured Voltage
Failure Monitoring
At address 96XSHUYLVLRQ the measuring voltage failure monitor can be
switched to Z&855683, Z,!&%DX[ or 2)). Address 79
6XSHUYLVLRQ is used to set the waiting time of the voltage failure monitoring. This
setting can only be changed via DIGSI
®
at Additional Settings.
Circuit Breaker for
Voltage
Transformers
If a circuit breaker for voltage transformers (VT mcb) is installed in the secondary
circuit of the voltage transformers, the status is sent, via binary input, to the device in-
forming it about the position of the VT mcb. If a short-circuit in the secondary side ini-
tiates the tripping of the VT mcb, the distance protection function has to be blocked
immediately, since otherwise it would be spuriously tripped due to the lacking mea-
sured voltage during a load current.The blocking must be faster than the first stage of
the distance protection.This requires an extremely short reaction time for VT mcb
(≤ 4ms at 50Hz, ≤ 3 ms at 60 Hz nominal frequency). If this cannot be ensured, the
reaction time is to be set under address 7PFE.
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