Method of operation7SV512
V1
29C53000---G1176---C91
4.2.4 Initiation conditions and delay times
Because of the high safety demand for the breaker
failure protection, initiation from the main protection
must always be performed by energization of at
least two binary inputs (dual channel initiation). In
addition, special supervisory measures are pro-
vided (refer Section 4.2.7).
4.2.4.1 Common phase initiation
Common phase initiation is used, for example, for
lines without automatic reclosure (e.g. cables), for
lines with only three-pole auto-reclosure (e.g. in
overhead line systems without earthed neutral), for
transformer feeders, or if the bus-bar protection
trips.
For safety reasons, initiation can only be valid when
at least two binary inputs are energized. To achieve
this, the main protection must deliver at least the
three-pole trip command at the input ”>Trip 3
pole” and an additional fault detection signal at the
input ”>Start”.ForBuchholz protectionitisrecom-
mended that the trip command is connected to
7SV512 by two separate wire pairs in order to
achieve dual channel initiation of the breaker failure
protection.
The function scheme is shown in Figure 4.8. When
the initiation conditions are fulfilled and at least one
current flow criterion (according Figure 4.4) is pres-
ent, the delay time T1---3POLE isstarted. After expiry
of this time, the trip command ”BFP Trip L123” is
issued.
>
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)
Figure 4.8 Breaker failure protection with com-
mon phase initiation
7SV512 provides facility to interrogate the circuit
breaker auxiliary contact(s) (according Figure 4.6)in
casethecurrent flowcriterion isnotfulfilled foranyof
the phases. If the circuit breaker poles can be
tripped individually, the parallel connection of the
three auxiliary contacts is used (signal ”any pole
closed” in Figure 4.7), or the OR combined signals
”L* closed”. The circuit breaker has operated cor-
rectly after three-pole trip command only whennone
of the phases carries current or when all three auxil-
iary contacts have opened.
Possibility exists to set different delay times depen-
dent onwhether thecurrent flow criterion or the aux-
iliary contact criterion is fulfilled. Thus, e.g. a longer
timecanbe set forthe auxiliary contact criterionifthe
auxiliary contacts could react slower. To achieve
this, the delay times T2areused, i.e. the breaker fail-
ure protection operates single-stage with T2; T1 is
ineffective. Initiation and current flowcriterion cause
the time T2---CURRENT to be started, initiation and
auxiliary contact criterion cause the time T2---CB---
AUX to be started (refer Figure 4.9).
>
1
&
&
&
T2---CB---
AUX
BFP
Trip BB
L1>
L2>
L3>
(acc.
Fig 4.4)
>Trip 3pole
>B/F
block
internal
blocking
>Start
Aux
(acc.
Fig 4.6)
&
T2---
CURR.
>
1
Figure 4.9 Breaker failure protection with com-
mon phase initiation
Initiation can be blocked via the binary input ”>B/F
block” (e.g. during test of the feeder protection
relay). Additionally,an internal blocking possibility is
provided (refer also Section 4.2.7).
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