ABB RER620 Technical Manual page 243

1MAC309294-MB F
RER620
Technical Manual
Figure 108: Functional module diagram, when operation mode is selected as three
phase with three phase breaker failure function
Current Value Res
Level detector
When operation mode is selected as three phase and when the input START is energized,
the comparator, comparing the measured ground current or residual current with the set
Current value Res is effective. When three phase mode is chosen, the input POSCLOSE
is internally derived as AND combination of POSCLOSE_A, POSCLOSE_B and
POSCLOSE_C inputs to the logic. When three pole tripping device is involved, the
breaker close position can be looped to all the three inputs.
In three phase operation mode, if the measured ground current value exceeds the set
Current value Res, the level detector reports the exceeding of the value to the back-up trip
logic. In high impedance grounded systems, the ground current at phase to ground faults
are normally much smaller than the short circuit currents. To detect a breaker failure at
single-phase ground faults in these systems, it is necessary to measure the ground current
separately. In effectively grounded systems, also the setting of the ground-fault current
protection can be chosen at a relatively low current level. The CB failure trip mode is set
"1 out of 4". The current setting should be chosen in accordance with the setting of the
sensitive ground-fault protection.
Retrip logic
The operation of the retrip logic can be described by using a module diagram, for three
phase operation:
Section 4
Protection functions
237