Schweitzer Engineering Laboratories SEL-421-4, Инструкция по эксплуатации

Страница: 488 / 1518

6.152
SEL-421 Relay Instruction Manual Date Code 20171021
Protection Applications Examples
Circuit Breaker Failure Application Examples
to the local terminal. Remote backup protection operates if a fault outside the
local protection zone persists. Circuit breaker failure relaying is local backup
protection.
The SEL-421 features four types of circuit breaker failure and retrip protection
capability:
1. Failure to interrupt fault current for phase currents
2. No current/residual current circuit breaker failure protection
3. Failure to interrupt load current
4. Flashover circuit breaker failure protection
Protection against failure to interrupt fault current for phase currents is the most
common implementation. This subsection describes failure to interrupt fault cur-
rent circuit breaker failure protection.
Failure to Interrupt Fault Current for Phase Currents
The SEL-421 provides two schemes for failure to interrupt fault current for phase
currents. Scheme 1 is protection for basic cases involving both multiphase faults
and single-phase faults with a common breaker failure time delay. Scheme 2 is
for more elaborate protection that discriminates between multiphase and single-
phase faults and features separate circuit breaker failure time delays. Use
Scheme 2 for separate circuit breaker failure timing for three-pole and single-
pole faults.
Basic Operation—Scheme 1 and Scheme 2
NOTE:
The following discussion
specifies three elements. There is one
element for each phase:

=A, B,
and C).
A trip output from the local primary or backup line protection typically initiates
the failure to interrupt fault current circuit breaker failure scheme (BFI3P1 and
BFI

1 for Scheme 1 or BFI

1 for Scheme 2). When initiated, the relay starts cir-
cuit breaker failure timing; the time delay is BFPU1 (Breaker Failure Time
Delay—BK1). The SEL-421 does not require an external BFI contact when
applied for local circuit breaker failure protection because the relay detects line
faults. In addition, you can add external BFI from an input in parallel with the cir-
cuit breaker trip coil to capture additional trip initiations to increase scheme
dependability.
Set the instantaneous overcurrent element pickup threshold 50FP1 to pick up for
all line faults. The relay asserts Relay Word bit 50F

1 when the phase current
exceeds the 50FP1 threshold. The 50F

1 element must reset quickly even during
the presence of subsidence current at the circuit breaker opening.
If 50F

1 is asserted when timer BFPU1 expires, the relay asserts circuit breaker
failure protection Relay Word bit FBF1 (Breaker 1 Breaker Failure). Assign
FBF1 to SEL
OGIC
control equation BFTR1 (Breaker Failure Trip—BK1) as one
of the circuit breaker failure elements that can cause a circuit breaker failure trip.
When SEL
OGIC
control equation BFTRI asserts, the relay asserts corresponding
Relay Word bit BFTRIP1 (Breaker 1 Failure Trip Output). Assign BFTRIP1 to a
high-current interrupting control output to perform circuit breaker failure tripping
or to a standard control output to operate an 86 lockout relay.