ABB Relion 650 Series Technical Manual page 356

Section 11
Scheme communication
IEC05000157 V1 EN-US
Figure 187: 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).
11.3.6.2 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
for more than setting
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 188. 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.
IEC05000158 V1 EN-US
Figure 188: Loss-of-load acceleration - simplified logic diagram
Breaker closing signals can if decided be connected to block the function during normal closing.
350
tLowCurr , an overreaching zone will be allowed to trip "instantaneously"
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MinCurr
Line distance protection REL650
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