Method of operation
7SV512
V1
30
C53000---G1176---C91
4.2.4.2 Two-stage breaker failure protection
with common phase initiation
Two-stage protection means that two timers (or sets
of timers) with different delay times are started. After
expiry of the first stage T1, the trip command of the
feeder protection is normally repeated on the feeder
circuit breaker, often on a second trip coil (local trip
or cross trip), if the breaker has not responded to the
original trip command. A second time stage T2 mon-
itors the response to this repeated trip command
and trips the breakers of the relevant bus-bar sec-
tion, if the fault is not yet cleared after this time. A
choice can be made whether the two timers are
started at the same time or one after the other.
The functional scheme is shown in Figure 4.10. The
operation sequence of the first stage is, in principle,
the same as that of the single-stage example shown
in Figure 4.8 (refer Section 4.2.4.1). After expiry of
the time T1---3POLE, the trip commands ”
BFP Trip
L123
” and ”
BFP Cross Trip
” are generated
which normally repeat the command for the feeder
circuit breaker (local trip or cross trip). After expiry of
the second time stage, the bus-bar (section) is dis-
connected by the command ”
BFP Trip BB
”.
With the second stage, distinction can be made be-
tween start by means of the current criterion
T2---CURRENT or by means of the auxiliary contact
criterion T2---CB---AUX. Thus, e.g. a longer time can
be set for the auxiliary contact criterion if the auxiliary
contacts may react slower.
The parameter switch T---TRIP---BB determines
whether the timers T2 can be started only after T1
has expired (times operate in sequence) or whether
the timers T2 are started with T1 at the same time
(times operate in parallel). The first possibility means
that T2 starts with the trip command of the first stage,
in the second case both timers start with the initial
trip command of the feeder protection.
>1
&
&
&
T1---
3POLE
BFP
Trip L123
L1>
L2>
L3>
(acc.
Fig 4.4)
>Trip 3pole
>B/F
Block.
internal
blocking
>Start
Aux
(acc.
Fig 4.6)
>1
&
&
&
>1
”1”
”1”
T---TRIP---BB
T2
T1+T2
T2---CB---
AUX
T2---
CURR.
BFP
Trip BB
BFP
CrossTrip
Figure 4.10 Two-stage breaker failure protection with common phase initiation
4.2.4.3 Phase segregated initiation
Phase segregated initiation is necessary if the circuit
breaker poles can be switched individually, e.g. if
single-pole auto-reclosure is used.
For safety reasons, initiation can only be valid when
at least two binary inputs are energized. To achieve
this, the main protection must deliver, besides the
three single-pole trip commands at the inputs
”
>Trip L1
”, ”
>Trip L2
”, and ”
>Trip L3
”, at
least an additional fault detection signal at the input
”
>Start
”. In addition, earth fault detection can be
connected to ”
>Start N
”.
The initiation logic is shown, in principle, in Figure
4.11, if the feeder protection is able to give phase
segregated trip commands. Similar to the logic of
current flow monitoring (Section 4.2.2), a 2-out-of-4
logic is used. That means, that initiation of a phase is
valid only when at least a trip command of another
phase is present, or an earth fault is detected
(”
>Start N
”). Additional safety is achieved in that
the general fault detection signal of the feeder pro-
tection is required. In case the feeder protection
relay does not output the earth fault detection, it can
be omitted; the fault detection signal ”
>Start
” en-
sures, nevertheless, dual channel processing of the
trip criteria in any case.
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