Fail-Safe Principle For Relay Protection - ABB RELION REX640 Technical Manual

Basic functions
State
Process related alarm has been ac-
tive earlier, but is not any more ac-
tive
Relay set to Test Mode
The physical SHMI Home button has two operation modes.
• On the SHMI's navigation page, the Home button indicates the combined status
of all connected relays. If multiple relays have different statuses, the Home
button shows the indication with the highest priority.
• On the HMI view, the Home button indicates the status of the respective relay as
described in
3.3.4

Fail-safe principle for relay protection

The relay behavior during an internal fault situation has to be considered when
engineering trip circuits under the fail-safe principle. The considerations discussed
and examples given are mainly based on the need of protection scheme reliability.
The reliability need can be divided into two subparts: dependability and security.
The dependability can be described as the protection scheme's ability to operate
when required. The security can be described as the protection scheme's ability to
refrain from operating when not required. The protection scheme fail-safe principle
is typically related to satisfying these two performance criteria. Depending on the
requirements set to the electricity distribution process, one of the criteria may get
more attention than the other. However, in some industrial electricity distribution
networks, the main (productization) process is so dependent on reliable electricity
supply that both criteria are addressed equally.
The examples presented focus on the relay's protection role in the fail-safe circuitry
using traditional hardwiring. If communication between the relays, or to an upper
level system, is a part of the fail-safe functionality, it must be also be a part of the
circuitry.
3.3.4.1 Motor feeder
The target is to prevent the motor from running uncontrollably and to secure the
emergency stop circuit functionality.
110
Power supply
module Ready
LED
Steady green
LF blinking green LF blinking green No
Table 45
.
1MRS759142 F
LHMI Home Alarm
button acknowledged
Steady green Yes
Technical Manual
REX640