GE DBF, Instructions Manual

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2. OPERATION LOGIC
GEK-106168E DBF Breaker Failure Protection 3
2. 2. 2. 2. OPERATION OPERATION OPERATION OPERATION LOGIC LOGIC LOGIC LOGIC
(See figure 1 at the end of the Instruction Manual)
2.1. PROTECTION FUNCTIONS
2.1.1. OVERCURRENT UNITS
The DBF system incorporates the following overcurrent detectors:
•
Three Single Phase Low-Level Overcurrent Detectors
(Used by the 50BF 1P function.)
•
Three Single Phase High-Level Overcurrent Detectors.
(Used by the 50BF 3P function.)
•
One Ground Overcurrent Detector.
(Used by the 3P No I function.)
•
Three Single-Phase current detectors for the internal arc function.
Low-Level Overcurrent Breaker Failure Unit – 50BF 1P
The breaker failure operation is started by detecting any single phase above a setpoint threshold (PH Lo-Set
Pickup setting), ANDed with a tripping signal (breaker failure initiate signal) issued by the main feeder protection.
These breaker failure initiation signals can be single-phase or three-phase type at OR1, OR2 and OR3. There are
four digital signals available (50BF Initiate A, 50BF Initiate B, 50BF Initiate C and 3P BF Initiate) assignable to
any digital input (contact converter). The factory digital input configuration is the following (as shown in figure 1):
Digital Signal Input # Terminals
50BF Initiate A Input #1 C9 – D10
50BF Initiate B Input #2 D9 – D10
50BF Initiate C Input #3 C10 – D10
3P BF Initiate Input #7 E7 – E8
The AND1, AND2 and AND3 gates thus fully armed may perform (depending on settings) one or two time delayed
tripping steps. Use 50BF_1P setting (permitted/Not permitted) and number of output stages (N. of Output
Stages) setting to enable this function and to set the number of steps. Timers T1 and T2nd control the timing of
the first and second step respectively (1_Phase Timer T1 and 2nd Stage Timer settings).
If the tripping signal is three-pole type (digital input E7-E8 for the default factory configuration), the signal will be
placed at the same time in OR1, OR2 and OR3 and then to AND1, AND2 and AND3.
High-Level Overcurrent Breaker Failure Unit – 50BF 3P
This function operates if high-Level overcurrent is detected on 2 phases (or 3 phases if setting BF Logic (3P/2P)
is set to 3P) and if 2 breaker failure initiation inputs are energized (or just the 3P BF Initiate input, if Severe Fault
3P setting is set to permitted).
The starting of this function is similar to the 50BF 1P, but in this case the current level setting range is higher (PH
Hi-Set Pickup setting) and the output is controlled by the energization of two single pole initiation signals. This
function can also operate energizing the 3P BF Initiate signal, if Severe Fault 3P setting is set to ‘permitted’.
Other difference with respect to the 50BF 1P function, is that the current in all the three phases must exceed the
setpoint, or at least one pair of phases. This is selected with BF Logic (3P/2P) setting. In the first case (BF Logic
(3P/2P) set to 3P) the signal should progress through AND11 and AND12. If BF Logic (3P/2P) is set to 2P, then
the signal will go through AND8, AND9 or AND10 and then AND13. The outputs of AND12 or AND13 are sent via