ABB Relion 620 Series - Page 82

Q0 Circuit breaker (CB)
A1 Protection relay #1
A2 Protection relay #2
TO Protection relay trip output
TC1 CB trip coil 1
TC2 CB trip coil 2
F1 Miniature circuit breaker
In example 3, the fail-safe approach aims at securing circuit breaker tripping even if
one of the redundant relays fails. The scheme is often referred to as the 1-outof- 2
approach. This approach allows service continuation while the failed relay is waiting
for spare parts or a complete replacement. The redundancy in this example covers
relays and circuit breaker tripping coils but it can be expanded to auxiliary power
supplies (two station batteries and isolated distribution), cabling, circuit breaker
failure protection, and so on. Another variant of this approach is to have a main
relay and a backup relay instead of two fully redundant relays. The backup relay
does not have all the features of the main relay, mainly containing a minimum
acceptable set of protection functions.
TC2
Same principle
as for TC1
Control +
Control -
-A1
-A1
-TO1
-A2
-TO1
-A2
-TO2
-A3
-TO1
-F1
-Q0
TC1
-A3
-TO2
-A1
-TO2
AUX. POWER
-A2
AUX. POWER
-A3
AUX. POWER
Figure 20: Redundant protection fail-safe principle, example 4
Q0 Circuit breaker (CB)
A1 Protection relay #1
A2 Protection relay #2
A3 Protection relay #3
TO# Protection relay trip output
TC1 CB trip coil 1
TC2 CB trip coil 2
F1 Miniature circuit breaker
In example 4, the fail-safe approach aims at securing circuit breaker tripping even
if one of the redundant relays fails and, in addition, no single relay alone can
cause the circuit breaker tripping. The scheme is often referred to as the 2-out-
of-3 approach. This approach allows service continuation while the failed relay is
waiting for spare parts or a complete replacement. The redundancy in this example
covers relays and circuit breaker tripping coils but it can be expanded to auxiliary
power supplies (two station batteries and isolated distribution), cabling, circuit
breaker failure protection, and so on. All three relays are similar with the same
Basic functions
1MRS757644 H
82 620 series
Technical Manual