Led Indication Control Ledptrc - ABB RELION REX640 Technical Manual

Protection and control

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Basic functions

have all the features of the main relay, mainly containing a minimum acceptable set

of protection functions.

Figure 38: Redundant protection fail-safe principle, example 4

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

protection functions. This principle is used in cases where the primary process

requires absolute dependability and security from the supplying feeder protection.

LED indication control LEDPTRC

Circuit breaker (CB)

Protection relay #1

Protection relay #2

Protection relay #3

Protection relay trip output

CB trip coil 1

CB trip coil 2

Miniature circuit breaker

1MRS759142 F

Same principle

Technical Manual