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
63
BRCPTOC is disabled (blocked) if:
• The IED is in test mode and BRCPTOC has been blocked from the HMI test menu
(Blocked=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.
BLOCK
Function Enable
TEST-ACTIVE
and
TEST
Block BRCPTOC=Yes
STI
Unsymmetrical
Current Detection
t
tOper
START
IL1<50%IP>
IL2<50%IP>
IL3<50%IP>
IEC09000158-3-en.vsd
or
or
TRIP
and
IEC09000158 V3 EN
Figure 63: Simplified logic diagram for Broken conductor check BRCPTOC
1MRK 511 287-UEN A Section 6
Current protection
143
Technical manual
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