Functions
2.16 Breaker Failure Protection 50BF
SIPROTEC, 7SJ62/64, Manual
C53000-G1140-C207-2, Release date 01.2008
279
The criteria used to determine if the circuit breaker has operated are selectable and also depend on the pro-
tection function that initiated the breaker failure function. On tripping without fault current, e.g. via voltage pro-
tection, 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 measurement 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 2-102.
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 2-102).
The ground current I
N
(3·I
0
) is preferably used as plausibility current. Via the parameters 613 you decide
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
2
or a second phase current is used as plau-
sibility current.
Figure 2-102 Monitoring of the current flow
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