GE DBF, Instructions Manual

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2. OPERATION LOGIC
4 DBF Breaker Failure Protection GEK-106168E
OR5 to the bottom input of AND4. Any pair of single BF initiation signals placed at AND5, AND6, or AND7 will
activate the top input of AND4. This input to AND4 can also be ON if there is a 3P BF Initiation and Severe Fault
3P setting is set to ‘permitted’.
Ground Overcurrent Breaker Failure Unit.
The breaker failure action based in this ground overcurrent function basically performs an additional breaker
failure function through AND19, when the 3P BF Initiate (or 2 Single Pole BF Initiate, if Low Load 2P setting is
set to ‘permitted’) is present at OR10 and a ground current higher than Neutral Pickup setting is detected.
Breaker Failure without current (or very low current).
DBF includes internal logic to cover also no-current, or very low fault current BF applications. This function will
issue an output if the 3P BF Initiate input is energized (or 2 Single Pole BF Initiate, if Low Load 2P setting is set
to ‘permitted’), and at least one pole of the circuit breaker is still closed.
Breaker Arc Detection Device.
This function may close one output of the relay when it detects that: the circuit breaker is open and some amount
of current is present in any phase. There are two settings available for this function: ‘Internal Arc Pickup’ to set
the current threshold and ‘Internal Arc Timer’ to coordinate the operation time of the unit with the time it takes for
the breaker and auxiliary elements to open.
If the circuit breaker is open, then the 52/b contacts will energize the digital inputs corresponding to the circuit
breaker status (terminals C11-D12, D11-D12 and C12-D12 for the factory default configuration), and then the
upper input of AND16, AND17 and AND18. The other input will be energized if the DBF detects a current higher
than Internal Arc Pickup setting. The outputs of these AND gates are sent to OR8 and then to timer T4 (Internal
Arc Timer setting) to complete the arc detection function, this will close the auxiliary relay D2-C2 (according to the
factory default output configuration).
Reset of Latching Relays
The DBF breaker failure protection may be ordered with an expansion board, which includes two latching relays
that are operated in different ways depending on the number of steps selected (for additional reference see Figure
1), and will fix the tripping output once the breaker failure function has operated. A digital input through F11-F12
(factory default inputs configuration) (pulse signal, not sustained) resets these latching relays to its steady-state
position.