• The difference in currents between the phase with the lowest current and the phase with the
highest current is greater than set percentage
Pickup_ub
of the highest phase current
• The lowest phase current is below 50% of the minimum setting value
Pickup_PH
The third condition is included to avoid problems in systems involving parallel lines. If a conductor
breaks in one phase on one line, the parallel line will experience an increase in current in the same
phase. This might result in the first two conditions being satisfied. If the unsymmetrical detection
lasts for a period longer than the set time
tOper
the TRIP output is activated.
The simplified logic diagram of the broken conductor check function is shown in figure
297
BRCPTOC (46) is disabled (blocked) if:
• The IED is in TEST status and the function has been blocked from the local HMI test menu
(BlockBRC=Yes).
• The input signal BLOCK is high.
The BLOCK input can be connected to a binary input of the IED in order to receive a block
command from external devices, or can be software connected to other internal functions of the
IED itself to receive a block command from internal functions.
The output trip signal TRIP is a three-phase trip. It can be used to command a trip to the circuit
breaker or for alarm purpose only.
BRC--BLOCK
BRC--TRIP
Function Enable
TEST-ACTIVE
AND
TEST
BlockBRC = Yes
PU_ub
Unsymmetrical
Current Detection
AND
OR
BRC--PICKUP
en07000123.vsd
IA<50%Pickup_PN
0-t
0
IB<50%Pickup_PN
IC<50%Pickup_PN
OR
IEC07000123 V2 EN-US
Figure 297: Simplified logic diagram for Broken conductor check BRCPTOC (46)
Section 8 1MRK 502 066-UUS B
Current protection
560
Technical manual
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