Operating instructions7SV512
V1
75C53000---G1176---C91
6.3.4 Settings for circuit breaker failure protection --- address block 12
Different possibilities exist for the initiation of the
breaker failure protection:
--- Initiation by the trip command of the feeder pro-
tection. The trip command may be single-pole or
three-pole. In each case, current flow through
each ofthe breaker poles is monitored individual-
ly. The current threshold I---BF (address 1202)
shall be selected such that the protection will op-
erate at the smallest expected short-circuit cur-
rent. To be sure of this, the value should be 10 %
less than the minimum anticipated fault current.
On the other hand, the value should not be set
lower than necessary.
--- Initiation by the trip command of a protection or
supervision device which does not necessarily
react to short-circuit current (e.g. Buchholz pro-
tection, overvoltage protection). The circuit
breaker auxiliary contacts are the criteria for the
breaker reaction in this case. Depending on the
connection of the auxiliary contacts, the breaker
can be supervised three-pole or on a pole-segre-
gated three-pole basis.
--- Initiation bythe trip command ofabus-bar protec-
tion. This corresponds to a three-pole trip com-
mand ofthe first possibility.In case of breaker fail-
ure, the trip command must be transmitted to the
remote end circuit breaker via a communication
link to ensure proper clearance of the fault.
The breaker failure protection 7SV512 can be oper-
ated single-stage or two-stage:
With two-stage operation, the trip command is re-
peated after a time delay T1 to the local feeder
breaker,normally toa different set oftripping coils of
this breaker.A choice can be made whether this trip
repetition shall be single-pole or three-pole if the ini-
tialfeeder protection tripwassingle-pole; thischoice
is made in address 1204. After a further delay time
T2 (address 1212 or 1213), the adjacent circuit
breakers (i.e. the breakers of the bus-bar zone and
--- if signal transmission is possible --- the breaker at
the remote end) are tripped provided the fault has
not yet been cleared. An example of the time se-
quence is illustrated in Figure 6.2.
With single-stage operation, the adjacent circuit
breakers (i.e. the breakers of the bus-bar zone and
--- if transmission of the signal is possible --- the
breaker at the remote end) are tripped after a delay
time T2 following initiation. The local trip command
is switched off under address 1203 in this case. An
example of the time sequence is illustrated in Figure
6.3.
Separate delay times can be set:
--- for single- or three-pole trip repetition to the local
feeder circuit breaker after single-pole trip of the
feeder protection under address 1205
T1---1POLE.
--- for three-pole trip repetition to the local feeder cir-
cuit breaker after three-pole trip ofthe feeder pro-
tection under address 1206 T1---3POLE.
--- for trip of the adjacent circuit breakers (bus-bar
zone and remote end if applicable) when using
current detection as breaker failure criterion, un-
der address 1212 T2---CURRENT,
--- for trip of the adjacent circuit breakers (bus-bar
zone and remote end if applicable) when using
the breaker auxiliary contacts as breaker failure
criterion, under address 1213 T2---CB---AUX.
The delay times are determined from the maximum
operating time of the feeder circuit breaker,the reset
time of the current detectors of the breaker failure
protection, plus a safety margin which allows forany
tolerance of the delay timers. The time sequence is
illustrated in Figure 6.2 for two-stage breaker failure
protection, andinFigure 6.3forsingle-stage breaker
failure protection.
For sinusoidal currents one can assume that the re-
set time of the current detectors is less than 10 ms
butifcurrent transformer saturation is expected then
20 ms should be calculated.
With two-stage breaker failure protection, a choice
can be made whether the timers T2 for trip of the ad-
jacent breakers will be started at the instant of trip
repetition, i.e. after expiry of T1 (the solid line in Fig-
ure 6.2), of whether it will be started already with the
trip command of the main protection (dotted line in
Figure 6.2 is also part of T2), i.e. T2 includes T1 (ad-
dress 1211).
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