Siemens siprotec 7SA522 User Manual page 351

Common phase
initiation
7SA522 Manual
C53000-G1176-C119-2
L1>
Start only L1
FNo 351
1
)
>CB Aux. L1
FNo 380
2
)
>CB 3p Open
Figure 6-100 Interlock of the auxiliary contact criterion — example for phase L1
On the other hand, current flow is not a reliable criterion for proper operation of the
circuit breaker for faults which do not cause detectable current flow (e.g. Buchholz pro-
tection). Information regarding the position of the circuit breaker auxiliary contacts is
required in these cases to check the correct response of the circuit breaker. For this
purpose, the binary input "!%) 6WDUW ZR ," is provided (Figure 6-101 left). This
input initiates the breaker failure protection even if no current flow is detected.
Common phase initiation is used, for example, for lines without automatic reclosure,
for lines with only three-pole automatic reclosure, for transformer feeders, or if the bus-
bar protection trips. This is the only available initiation mode if the actual 7SA522 mod-
el is able to trip three-pole only.
If the breaker failure protection is intended to be initiated by further external protection
devices, it is recommended, for security reasons, to connect two starting criteria to the
7SA522 device: the trip command to the input ´!%)  SROH" and an additional re-
lease signal (e.g. fault detection) to the input ´!%) 5HOHDVH". For Buchholz protec-
tion it is recommended that the trip command is connected to the 7SA522 by two sep-
arate wire pairs in order to achieve dual-channel initiation of the breaker failure pro-
tection.
Nevertheless, it is possible to initiate the breaker failure protection in single-channel
mode should a separate release criterion not be available. The binary input ´!%) 5H
OHDVH" must then not be assigned to any physical input of the device during configu-
ration.
The scheme functionality is shown in Figure 6-97. When the trip signal appears from
any internal or external feeder protection and at least one current flow criterion (ac-
cording to Figure 6-99) is present, the breaker failure protection is initiated and the cor-
responding delay time(s) is (are) started.
If the current criterion is not fulfilled for any of the phases the position of the circuit
breaker auxiliary contact(s) is interrogated provided that this is available. If the circuit
breaker poles have individual auxiliary contacts, the series connection of the three
normally closed (NC) auxiliary contacts is used. The circuit breaker has operated cor-
rectly after a three-pole trip command only when none of the phases carries current or
when all three NC auxiliary contacts have closed.
If an internal protection function or an external protection device trips without current
flow, the internal input "6WDUW ZLWKRXW ," or the external input "!6WDUW ZR ,"
is used to initiate the breaker failure protection. In these cases the breaker auxiliary
contact position is the only criterion for the response of the circuit breaker.
Initiation can be blocked via the binary input "!%) EORFN" (e.g. during testing of the
feeder protection relay). Additionally, an internal blocking option is provided.
&
S Q
R
1
) if phase dedicated auxiliary contacts available
> 1
2
) if series connection of NC contacts available
Functions
&
CBaux L1 closed
(refer to Fig. 6-101)
6-203