current of phase currents is formed from the difference between the present current phasor and the current
phasor of the previous period. This allows to take into account a jump of the current phase.
NOTE
If a voltage-transformer circuit breaker is installed in the secondary circuit of the voltage transformers, its
position is communicated to the device via a binary input (see chapter 9.3.4.1 Overview of Functions).
Switching onto a 3-Phase Measuring-Voltage Failure, Low Load
Logic
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Figure 9-8
Logic Diagram Switching to 3-Phase Measuring-Voltage Failure
Switching onto a 3-phase measuring-voltage failure is detected if the following criteria are fulfilled simultane-
ously:
•
All 3 phase-to-ground voltages have dropped below the threshold value 3ph.fail. - VA,VB,VC <.
•
The circuit breaker is detected to be in closed position. The detection takes place either via the phase
currents or via the ≥1-pole closed signal, which is generated via the circuit-breaker auxiliary contacts.
You can find more detailed information in chapter 5.8.5 Circuit-Breaker Condition for the Protected
Object.
A voltage jump – such as in a 3-phase measuring-voltage failure with closed circuit breaker (see
chapter9.3.2.4 3-Phase Measuring-Voltage Failure ) – does not occur in the case of switching to a 3-phase
measuring-voltage failure. If the monitoring is not blocked, the time delay SO 3ph.fail. - time delay
is started. After the time has elapsed, the indication SO 3ph.failure-alarm is displayed. A dropout of the
monitoring is only possible by a recovery of the voltage.
9.3.2.5
Supervision Functions
9.3 Supervision of the Secondary System
1248 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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