Siemens 6MD85 Manual page 524

Protection and Automation Functions
7.1 Circuit-Breaker Failure Protection
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Figure 7-11
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Figure 7-12
Pickup/Dropout
After the start, a check is performed whether the circuit breaker is closed. The current-flow criterion and the
circuit-breaker auxiliary contact criterion are available for this purpose.
Even if the circuit-breaker auxiliary contact criterion is permitted, preference is given to the fulfilled current-
flow criterion because the current-flow criterion is the most reliable criterion for detecting whether the circuit
breaker is closed. This means that the circuit breaker is deemed to be closed if it is closed according to the
current-flow criterion but at the same time open according to the circuit-breaker auxiliary contact criterion.
If no current is flowing at the start time, the function can only pick up on the basis of the circuit-breaker auxil-
iary contact criterion. For this purpose, the circuit-breaker auxiliary contacts must be permitted as criterion.
When the current begins to flow after the start, the function switches over to the current-flow criterion.
If the circuit breaker (or a circuit-breaker pole with the 1/3-pole circuit breaker) is detected as closed and the
starting condition is present, the function picks up.
The pickup starts a time delay (see Delay/Tripping). While the delay is running, the system checks continuously
whether the circuit breaker (or the CB pole with the 1/3-pole circuit breaker) has opened. In the default
setting, the opening of the circuit breaker is checked on the basis of the currently valid criterion, which is
normally the current-flow criterion because it is preferred. If until expiration of the time delay, no current flow
524
Circuit-Breaker Auxiliary Contact Criterion for the 3-Pole Circuit Breaker
Circuit-Breaker Auxiliary Contact Criterion for the 1/3-Pole Circuit Breaker
SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017