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Functions
2.7 Monitoring Function
Offset of the Analogue-to-Digital Converter
The offset of the ADC is measured cyclically for each channel and corrected. When the offset reaches an in-
admissibly high value, the indication „Error Offset" (No. 191) is displayed. The protective functions remain
active.
Sampling Frequency
The sampling frequency and the synchronism of the analog-digital converters is continuously monitored. If any
deviations cannot be removed by remedied synchronization, then the processor system is restarted.
Measured Value Capturing Currents
There are four measurement inputs in the current paths. If the three phase currents and the earth current from
the current transformer starpoint or a separated earth current transformer of the line to be protected are con-
nected to the device, their digitised sum must be zero. A fault in the current circuit is detected when
= |I
+ I
I
F
L1
L2
(address 221 I4/Iph CT) takes into account a possible different ratio of a separate I
Factor k
I
(e.g. cable core balance current transformer). ΣI THRESHOLD and ΣI FACTOR. are setting parameters.
The component ΣI FACTOR Σ | I | takes into account permissible current proportional ratio errors of the input
transformers which are particularly prevalent during large fault currents (Figure 2-45). Σ | I | is the sum of all
currents:
Σ | I | = |I
| + |I
L1
This malfunction is signalled as „Failure Σ I" (No. 162).
Note
Current sum monitoring can operate properly only when the ground current of the protected line is fed to the
fourth current measuring input (I
Figure 2-45
132
| > ΣI THRESHOLD·I
+ I
+ k
·I
L3
I
E
| + |I
| + |k
·I
|
L2
L3
E
I
) of the relay.
4
Current sum monitoring
+ ΣI FACTOR·Σ | I |
N
C53000-G1176-C159-3, Release date 05.2009
transformer
E
SIPROTEC, 7VK61, Manual
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