Siemens SIPROTEC 7SJ61 Manual page 186

Functions
2.12 Breaker Failure Protection 50BF
The criteria used to determine if the circuit breaker has operated is selectable and should depend on the pro-
tective function that initiated the breaker failure function. On tripping without fault current, the current below the
threshold 50BF PICKUP is not a reliable indication of the proper functioning of the circuit breaker. In such
cases, pickup exclusively depends on the auxiliary contact criterion. In protection functions based on the mea-
surement of currents (including all short-circuit protection functions), the current flow is a preferential criterion,
i.e. it is given priority, as opposed to the auxiliary contacts. If current flows above the set threshold or thresholds
(enabled w/ 3I0>) are detected, the breaker failure protection trips even if the auxiliary criterion indicates
„Breaker Open".
Monitoring of the Current Flow
Address 170 50BF can be set in such a way that either the current criterion can already be met by a single
phase current (setting Enabled) or that another current is taken into consideration in order to check the plau-
sibility (setting enabled w/ 3I0>), see Figure 2-63.
The currents are filtered through numerical filters to evaluate the fundamental harmonic. They are monitored
and compared to the set limit value. Besides the three phase currents, two further current thresholds are pro-
vided in order to allow a plausibility check. For purposes of the plausibility check, a configuration of a separate
threshold value can be applied accordingly. (see Figure 2-63).
The ground current I
whether the measured (Ignd (measured)) or the calculated (3I0 (calcul.)) values are to be used. In
case of system faults not involving ground currents, no increased ground currents/residual currents are flowing,
and therefore the calculated triple negative sequence current 3·I
sibility current.
Figure 2-63 Monitoring of the current flow
186
) is preferably used as plausibility current. Via the parameters 613 you decide
(3·I
N 0
or a second phase current is used as plau-
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SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008