ABB RELION REX640 Technical Manual page 1074

Section 5
Protection related functions
1068
I_A
I_B
I3P
I_C
POSCLOSE
START
Io
IRES
CB_FAULT
BLOCK
GUID-BE7D2E36-6C74-4B27-A628-E47DC6D3E52E V1 EN
Figure 573: 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
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.
Level
detector 1
Timer 1
t
Start logic
Timer 2
Level
t
detector 2
Timer 3
t
Table 1008. In all cases in
1MRS759142 C
Retrip
TRRET
logic
Back-up
TRBU
trip
logic
CB_FAULT_AL
Table 1008, however, the
REX640
Technical Manual