ABB RELION REX640, Technical Manual, Page: 1164 / 1960

TRRET
BLOCK
CB_FAULT
TRBU
Back-up
trip
logic
POSCLOSE
START
Retrip
logic
Level
detector 2
Level
detector 1
t
Timer 2
t
Timer 3
CB_FAULT_AL
Start logic
t
Timer 1
I_A
I_B
I_C
Io
I3P
IRES
Figure 660: Functional module diagram
Level detector 1
The measured phase currents are compared phasewise to the set
Current value. If
the measured value exceeds the set
Current value, the level detector reports the
exceeding of the value to the start, retrip and backup trip logics. The parameter
should be set low enough so that breaker failure situations with small fault current
or high load current can be detected. The setting can be chosen in accordance with
the most sensitive protection function to start the breaker failure protection.
Level detector 2
The measured residual current is compared to the set
Current value Res. If the
measured value exceeds the set
Current value Res, the level detector reports the
exceeding of the value to the start and backup trip logics. In high-impedance
earthed systems, the residual current at phase-to-earth faults is normally much
smaller than the short circuit currents. To detect a breaker failure at single-phase
earth faults in these systems, it is necessary to measure the residual current
separately. In effectively earthed systems, also the setting of the earth-fault current
protection can be chosen at a relatively low current level. The current setting should
be chosen in accordance with the setting of the sensitive earth-fault protection.
Start logic
Start logic is used to manage the starting of Timer 1 and Timer 2. It also resets the
function after the circuit breaker failure is handled. On the rising edge of the
START
input, the enabling signal is sent to Timer 1 and Timer 2. Typically, the
START
input is
activated when any protection function operates and trips the circuit breaker.
The Start logic module is reset depending on the settings
CB failure mode and CB
failure trip mode as shown in Table 1113 . In all cases in Table 1113 , however, the
resetting is possible only after 150 ms from the activation of Start logic. This time is
for ensuring correct operation in case of oscillation in the starting signal.
Protection related functions 1MRS759142 F
1164 REX640
Technical Manual