Basler Electric BE1-700 - Manual (Page 96)

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 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 timer can also be stopped by the block logic input being asserted.
The current detector sensitivity is fixed at 10 percent of nominal. A traditional breaker failure relay
includes a fault detector function that serves two independent purposes: current detection and fault
detection. A current detector is generally included to stop breaker failure timing when it is determined that
current flow in all poles of the breaker has stopped. The secondary function of a traditional fault detector
is to provide an independent confirmation that a fault exists on the system and to increase security from
mis-operation caused by an inadvertent initiate signal. To do this, a fault detector by definition must be set
above load current which reduces its sensitivity as a current detector. Since this breaker failure timer is
included in a multifunction protection system, fault detector supervision is not required.
If external relays are used to initiate the breaker failure timer, it may be desirable to include fault detector
supervision of the initiate signal using an instantaneous overcurrent function in BESTlogic. For example, if
it is desired that certain initiate signals be supervised by a fault detector, it is possible to AND them with
one of the 50T protective functions using a virtual output expression. In other applications, it may be
desirable to have breaker failure timing with no current detector supervision. In this case, one of the
general-purpose logic timers (device 62) can be used as a breaker failure timer. See Section 8,
Application, Application Tips, for more details on this application.
When the breaker failure timer is picked up, the BFPU logic output is TRUE. This output would typically
be used as a re-trip signal to the protected breaker. This can provide an independent tripping signal to the
breaker that may also open the breaker to prevent backup tripping.
If the current detector remains picked up for the duration of the breaker failure delay time, the BFT output
is asserted. This output would normally be used to trip an 86F lockout relay, which will trip and prevent
closing of adjacent breakers and/or key transfer trip transmitters.
If the target is enabled for the function block, the target reporting function will record a target when the
protective function trip output is TRUE and the fault recording function trip logic expression is TRUE. See
Section 6, Reporting and Alarm Functions, Fault Reporting, for more details on the target reporting
function.
An alarm variable is also provided in the programmable alarms function that can be used to indicate an
alarm condition when the breaker failure protection trips. See Section 6, Reporting and Alarm Functions,
Alarms Function, for more details on the alarm reporting function.
BESTlogic Settings for Breaker Failure Protection
BESTlogic settings are made from the BESTlogic Function Element screen in BESTCOMS. Figure 4-35
illustrates the BESTCOMS screen used to select BESTlogic settings for the breaker failure element. To
open BESTlogic Function Element screen for the breaker failure element, select Breaker Failure from the
Screens pull-down menu. Then select the button labeled BESTlogic. Alternately, settings may be made
using the SL-50BF ASCII command.
4-40 BE1-700 Protection and Control 9376700990 Rev M