Basler BE1-CDS240, Instruction Manual

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BREAKER FAILURE PROTECTION
50BF - Breaker Failure Protection
BE1-CDS240 relays provide four independent breaker failure protection functions. Each current circuit
has an associated breaker failure function. For example, Current Circuit 1 is internally connected to 50BF;
Current Circuit 2 is internally connected to 150 BF and so on. This section discuses 50BF but applies to
all BF functions. Figure 4-49 shows the breaker failure function block which has two outputs,
BFRT (1, 2,
3, 4) (Breaker Failure Retrip) and BFT (1, 2, 3, 4) (Breaker Failure trip) which is true after the breaker
failure Delay Timer has timed out. The BFIALM (1, 2, 3, 4) (Breaker failure initiate alarm) occurs if the
Control Timer has expired (closing the window of breaker failure opportunity), and there is no BLK (Block
input) and the BFI50 (internal protection element) is still calling for a trip.
Figure 4-49. Breaker Failure Logic Block
A BESTlogic expression defines how the BLK (Block) input functions. When this expression is TRUE, the
element is disabled by forcing the outputs to logic 0 and resetting the timer to zero. For example, this may
be an input wired to a test switch such that breaker failure protection is disabled when the primary
protective elements are being tested to prevent inadvertent backup tripping during testing.
The breaker failure Delay Timer is stopped by the fast-dropout current detector function. See Section 3,
Input and Output Functions, Power System Inputs, Current Measurement, for more details on this
function. The fast-dropout current detector is designed to directly determine when the current in the poles
of the breaker has been interrupted without having to wait for the fault current samples to clear the one-
cycle filter time used by the normal current measurement function. This function has less than one cycle
dropout time. The
Delay Timer can also be stopped by the BLK (Block) logic input being asserted.
Upon sensing 50 INI transition from 0 to 1 state, a Control Timer seals in the 50 INI signal for the duration
of the Control Timer setting. If the Control Timer expires and the 50 INI signal is still present, a BFIALM
(Breaker Failure Initiate Alarm) signal will occur. The Control Timer serves the purpose to improve
security by presenting a window of opportunity for the breaker failure element to operate. It improves
dependability by sealing in the initiate to prevent stopping breaker failure timing if the tripping relay drops
out prematurely. A
Control Timer setting of zero shall disable the control timer seal in function allowing
the Control Timer to follow the 50 INI input.
Phase and neutral fault detectors are provided to monitor current. At least one of these four fault
detectors must be picked up to start the breaker failure
Delay Timer .
The current detector logic is TRUE if the current has been interrupted and is used to stop the BF timer.
The I = 0 algorithm looks at the sample data directly and does not rely upon the 1 cycle phasor estimation
calculation. It rejects dc tail-off by looking for the characteristic exponential decay. Current shall be
declared interrupted when the current in all three phases is below 10% nominal or if the current is
decaying exponentially. Only the three phase currents shall be monitored by this function.
Logic to start the breaker failure timing via the 52 INI input is provided with breaker status supervision.
Both the 52 STATUS and the 52 INI have to be TRUE for a 52 INI to cause a trip condition. A breaker
status logic input monitors the breaker state.
The breaker failure timer is initiated by the either the 52 INI or the 50 INI . When both signals are in the
zero state the breaker failure Delay Timer will be stopped. When the breaker failure Delay Timer is
actively timing, the BFRT (Breaker Failure Retrip) output shall be TRUE. When the breaker failure Delay
9365200990 Rev F BE1-CDS240 Protection and Control 4-55