2 Functions
190
7SD610 Manual
C53000-G1176-C145-4
Figure 2-77 Time sequence example for normal clearance of a fault, and with circuit breaker
failure, using two-stage breaker failure protection
Single-stage
breaker failure
protection
With single-stage operation, the adjacent circuit breakers (i.e. the breakers of the
busbar zone and, if applicable, the breaker at the remote end) are tripped after a delay
time T2 (address 3906) following initiation, should the fault not have been cleared
within this time.
The timers T1-1pole (address 3904) and T1-3pole (address 3905) are then set to
∞ since they are not needed.
But you may use the T1 timers for single-stage protection if you wish to utilise the fa-
cility of setting different delay times after single-pole trip and three-pole trip of the
feeder protection. In this case set T1-1pole (address 3904) and T1-3pole (ad-
dress 3905) separately, but address 3903 1p-RETRIP (T1) to NO to avoid a single-
pole trip command to the busbar. Set T2 (address 3906) to ∞ or equal to T1-3pole
(address 3905). Be sure that the correct trip commands are assigned to the desired
trip relay(s).
The delay time is 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 for any tolerance of the delay timers. The time sequence
is illustrated in Figure 2-78. The dropout time for sinusoidal currents is ≤ 15 ms. If
current transformer saturation is anticipated, the time should be set to 25 ms.
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