Areva MiCom P120, Техническое руководство

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Application Guide P12x/EN AP/A96
MiCOM P120/P121/P122/P123
Page 63/80
26. CIRCUIT BREAKER FAILURE PROTECTION: CBF (P122 & P123 ONLY)
When a fault is detected, one or more main protection elements will issue a trip order to the
associated circuit breaker(s). To isolate the fault, and prevent (heavier) damage on the
power system it is essential that the circuit breaker operates correctly.
On power systems, a fault that is not clear quickly enough threatens the stability of the
system. It is therefore common practice to install circuit breaker failure protection, which
monitors that the circuit breaker has opened within a reasonable period of time. If the fault
current has not been eliminated after the set time delay, the breaker failure protection (CBF)
will send a signal.
The CBF protection can be used to back-trip upstream circuit breakers to ensure that the
fault is correctly isolated. The CBF protection can also eliminate all blocking orders
associated to logic selectivity.
CB Fail Alarm
Any Trip
CBF Ia<
CBF Ib<
CBF Ic<
CB Fail Enabled
External CBF
Initiate
tBF
1
S
R
Q
P0428ENa
FIGURE 16: CB FAIL PRINCIPLE
26.1 Circuit Breaker Failure Protection mechanism
Hereafter is described how the CB failure protection available in MiCOM P122 & P123 relays
works.
The t BF timer is initiated when a trip order is given to the output relay RL1 . Note that the trip
order can be issued either by a protection element, or by a logic input. Then the relay
monitors the current signal of each phase and compares each phase current signal with the
bandzone made by the undercurrent I< threshold. This threshold value can be set under the
AUTOMAT. CTRL/CB FAIL menu.
Once the t BF timer has been initiated, the relay detects the first time that the current goes
out of the I< bandzone. When the relay detects this transition, it initiates an other timer. This
timer is of fixed duration and equivalent to 20 samples.
The relay sampling rate being 32 samples by cycle, this timer is of 12,5 ms duration for
system at 50 Hz and 10,4 ms for a system at 60 Hz. During this period of time, the relay is
checking if the current goes out the I< bandzone again. In case that the current is not
eliminated, the current signal should again go out the I< bandzone, and this after half a
cycle, i-e 16 samples (10ms at 50Hz).
Each time the relay detects that the current goes out the I< bandzone, the relay re-initiates
again the timer ( of a 20 samples). In this 20 samples time window, the relay checks that the
current signal going out the I< bandzone is in opposite way than the first one.
•
If there is no current signal going out in opposite way compared to the first one, the
relay considers that there is an opened CB pole condition. The « CB pole open »
internal signal is initiated.