[loveranw-100311-01.tif, 1, en_US]
Figure 7-9
Processing the Starting Signals of the CBFP
Current-Flow Criterion
The current-flow criterion is the primary criterion for determining the circuit-breaker switch position. A circuit-
breaker pole is supposed to be closed, and the current-flow criterion fulfilled, as soon as one of the phase
currents exceeds the phase-current threshold value and a plausibility current exceeds the associated threshold
value at the same time. The plausibility current can be either a 2nd phase current (to compare with the phase-
current threshold value) or the zero-sequence or negative-sequence current (to compare with the sensitive
threshold value). The additional evaluation of the plausibility current increases the safety of the criterion.
In the case of ground faults, the sensitive threshold value can be dynamically applied to the phase currents as
well. The current-flow criterion is fulfilled when the currents exceed the sensitive threshold value. The phase-
current threshold value is then ineffective. The binary signal >Threshold sensitive is used for the switch-
over.
If you set the 3I0 criterion parameter to Direct release, you prevent the plausibility check of the
zero-sequence current. In this way, a pickup only by way of this current can be achieved. With the Threshold
3I0 dir. release parameter, you set the threshold value to be exceeded.
If you set the I2 criterion parameter to Direct release, you also switch off the plausibility check of
the negative-sequence current. With the Threshold I2 dir. release parameter, you set the threshold
value to be exceeded.
If you set the I2 criterion parameter to Direct release, plausibility is checked via the phase currents
with 1/3 * Threshold I2 dir. release.
The measuring algorithm is optimized for fast dropout when the value drops below the threshold value.
The following figure shows an example for the logic for the current-flow criterion with 3-pole circuit breaker.
With the 1/3-pole circuit breaker, the activation signal of the current-flow criterion is phase-selective.
Protection and Automation Functions
7.1 Circuit-Breaker Failure Protection
522 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017
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