ABB Relion 670 Series Technical Reference Manual page 493

1MRK505222-UUS C
7.13.2
Technical reference manual
Principle of operation
Broken conductor check (BRCPTOC, 46) detects a broken conductor condition by
detecting the asymmetry between currents in the three phases. The current-measuring
elements continuously measure the three-phase currents.
The current asymmetry signal output PICKUP is set on if:
• 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 246
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.
Section 7
Current protection
487