Date Code 20010515
Applications
5-5
SEL-2BFR, -2/BFR Instruction Manual
in 8.5 cycles or less. All other trips must clear within 10 cycles. Because the protected breaker
has trip and close resistors and three-phase potentials are available on both sides of the breaker,
the example uses the SEL-2BFR Relay trip and close resistor thermal protection schemes.
Breaker closure and pole flashover failures are covered. The MOD Trip logic automatically
isolates the protected breaker in the event of breaker failure.
Setting Selection
Select Failure to Trip Fault Current Scheme
The SEL-2BFR Relay provides six different protection schemes for failure of the protected
breaker to interrupt fault current.
Logic Description
in
Section 2: Specifications
provides logic
diagrams and details regarding the operation of each scheme. Setting considerations for each of
the six schemes are provided below. All six schemes are applicable to single-pole trip
installations.
Table 5.2: Fault Current Scheme Setting Considerations
Scheme
Bus Configuration
Operating Considerations
1 Single,
Breaker-and-a-Half,
Ring-Bus
62TTpu setting is not used.
Set 62TTdo greater than worst case protected
breaker operating time.
Set 62FC greater than 62TTdo by at least two
cycles (relay logic requirement).
Trip input may be immediately deasserted.
2 Single
Breaker
62TT timer settings are not used.
Set 62FC timer greater than local breaker
operating time, plus 50FT reset time, plus a safety
margin.
Trip input may be deasserted after 50FT element
asserts.
3 Single
Breaker
62TT timer settings are not used.
62FC timer may be set without respect to 50FT
element reset time if the trip input drops out when
current no longer flows in the breaker.
Following initiation, trip input must remain
asserted while current flows in the breaker.
4 Single,
Breaker-and-a-Half,
Ring-Bus
62FC timer setting is not used.
62TT timer output asserts each time a trip input
asserts. Setting should be greater than local
breaker operating time, plus 50FT reset time, plus
a safety margin.
50FT setting must exceed maximum load current.
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