Siemens 7SR224 Technical Manual page 344

Second Stage (Back Trip)
First CBF Time Delay
Trip Relay operate time
7SR224 Reset Time
CB Tripping time
Margin
Overall Second Stage CBF Time Delay
The safety margin is extended by 1 cycle for the second CBF stage as this will usually involve a back-trip of a
Busbar tripping scheme.
The timing sequence for each stage of the circuit breaker fail function is as below.
Relay
Operation
and CBF
Timer
Started
System
Fault
Main
does not occur
Trip
Failure of
Relay
CB to trip
Operation
20 40 60 80
CB Operate Time
Stage 1 CBF Timer (Backtrip) = 120ms
Figure 5.1-2 - Single Stage Circuit Breaker Fail Timing
Relay
Operation
and CBF
Timer
Started
System
Fault
Main
CBF elements
CB's
Trip
Fails to
Relay
Trip
Operation
40 60 80
CB Operate Time
Stage 1 CBF Timer (Retrip) = 120ms
Figure 5.1-3 - Two Stage Circuit Breaker Fail Timing
©2010 Siemens Protection Devices Limited
80ms
290ms
Backtrip
Trip Relay
Reset of
CBF elements Backtrip
Operation
100 120 140 160 180
CBF Retrip
Trip Relay
No Reset of
CBF Retrip
Operation
Failed CB Retrip
Operation
100 120 140 160 180
Stage 2 CBF Timer (Backtrip) = 250ms
120ms
10ms
20ms
60ms
CB Backtrip
Sucessful
200 220 240 260 280
Backtrip
Trip Relay
Operation
No Reset of
CBF elements
CBF Back trip
Operation
200 220 240 260 280
7SR224 Argus Applications
ms from fault
occuring
300 320 340
Operation of all
BB CB's
Reset of
CBF elements
ms from
occuri
300 320 340 360
Chapter 7 Page 45 of 50