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.
Summary of Contents for MiCom P120
Page 1: ...MiCOM P120 P121 P122 P123 Overcurrent Relays Version 11 Technical Guide P12X EN T A96...
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Page 4: ...P12x EN T A96 Technical Guide Contents Page 2 2 MiCOM P120 P121 P122 P123 BLANK PAGE...
Page 13: ...Introduction P12x EN IT A96 MiCOM P120 P121 P122 P123 INTRODUCTION...
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Page 16: ...P12x EN IT A96 Introduction Page 2 8 MiCOM P120 P121 P122 P123 BLANK PAGE...
Page 22: ...P12x EN IT A96 Introduction Page 8 8 MiCOM P120 P121 P122 P123 BLANK PAGE...
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Page 35: ...User Guide P12x EN FT A96 MiCOM P120 P121 P122 P123 USER GUIDE...
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Page 40: ...P12x EN FT A96 User Guide Page 4 72 MiCOM P120 P121 P122 P123 BLANK PAGE...
Page 108: ...P12x EN FT A96 User Guide Page 72 72 MiCOM P120 P121 P122 P123 BLANK PAGE...
Page 109: ...Menu Content Tables P12x EN HI A96 MiCOM P120 P121 P122 P123 MENU CONTENT TABLES...
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Page 112: ...P12x EN HI A96 Menu Content Tables Page 2 68 MiCOM P120 P121 P122 P123 BLANK PAGE...
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Page 221: ...Application Guide P12x EN AP A96 MiCOM P120 P121 P122 P123 APPLICATION GUIDE...
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Page 370: ...P12x EN CT A96 Communications COURIER DATABASE Page 2 248 MiCOM P120 P121 P122 P123 BLANK PAGE...
Page 514: ...P12x EN CT A96 Communications COURIER DATABASE Page 146 248 MiCOM P120 P121 P122 P123...
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Page 518: ...P12x EN CT A96 Communications IIEC 60870 5 103 Page 2 248 MiCOM P120 P121 P122 P123 BLANK PAGE...
Page 536: ...P12x EN CT A96 Communications IEC 60870 5 103 Page 20 248 MiCOM P120 P121 P122 P123...
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Page 540: ...P12x EN CT A96 Communications DNP 3 0 Database Page 2 248 MiCOM P120 P121 P122 P123 BLANK PAGE...
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Page 573: ...Connection Diagrams P12x EN CO A96 MiCOM P120 P121 P122 P123 CONNECTION DIAGRAMS...
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Page 582: ...P12x EN RS A96 Commissioning Test Record Sheets Page 2 60 MiCOM P120 P121 P122 P123 BLANK PAGE...
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