ABB Relion 670 Series Technical Reference Manual page 815

1MRK505222-UUS C
13.4.2.2
Technical reference manual
IEC05000157 V1 EN
Figure 399: Simplified logic diagram for local acceleration logic
After the autorecloser initiates the close command and remains in the reclaim state,
there will be no ARREADY signal, and the protection will trip normally with step
distance time functions.
In case of a fault on the adjacent line within the overreaching zone range, an unwanted
autoreclosing cycle will occur. The step distance function at the reclosing attempt will
prevent an unwanted retrip when the breaker is reclosed.
On the other hand, at a persistent line fault on line section not covered by instantaneous
zone (normally zone 1) only the first trip will be "instantaneous".
The function will be blocked if the input BLOCK is activated (common with loss-of-
load acceleration).
Loss-of-Load acceleration
When the "acceleration" is controlled by a loss-of-load, the overreaching zone used for
"acceleration" connected to input LLACC is not allowed to trip "instantaneously"
during normal non-fault system conditions. When all three-phase currents have been
above the set value MinCurr for more than setting tLowCurr, an overreaching zone
will be allowed to trip "instantaneously" during a fault condition when one or two of
the phase currents will become low due to a three-phase trip at the opposite IED, see
figure 400. The current measurement is performed internally and the internal STILL
signal becomes logical one under the described conditions. The load current in a
healthy phase is in this way used to indicate the tripping at the opposite IED. Note that
this function will not operate in case of three-phase faults, because none of the phase
currents will be low when the opposite IED is tripped.
Section 13
Scheme communication
809