Siemens siprotec 7SA522, Руководство пользователя

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Functions
6-122
7SA522 Manual
C53000-G1176-C119-2
6.6.2 Applying the Function Parameter Settings
General The teleprotection supplement for earth fault protection is only operational if it was set
to one of the available modes during the configuration of the device (address
).
Depending on this configuration, only those parameters which are applicable to the
selected mode appear here. If the teleprotection supplement is not required the ad-
dress
is set to
7HOHSURW()
=
'LVDEOHG
.
The following teleprotection schemes can be selected:
− 'LU&RPS3LFNXS
=Directional Comparison Scheme, as described in Sub-sec-
tion 6.6.1.1,
− 8QEORFNLQJ
= Directional Unblocking Scheme, as described in Sub-section
6.6.1.2,
− %ORFNLQJ
= Directional Blocking Scheme, as described in Sub-section
6.6.1.3.
In address
)&77HOHS()
the application of teleprotection can be switched
21
or
2))
.
If the teleprotection has to be applied to a three terminal line the setting in address
must be
/LQH&RQILJ
=
7KUHHWHUPLQDOV
, if not, the setting remains
7ZR
WHUPLQDOV
.
Earth Fault
Protection
Prerequisites In the application of the comparison schemes, absolute care must be taken that both
line ends recognize an external earth fault (earth fault through-current) in order to
avoid a faulty echo signal in the case of the permissive schemes, or in order to ensure
the blocking signal in the case of the blocking scheme. If, during an earth fault accord-
ing to Figure 6-73, the protection at B does not recognize the fault, this would be inter-
preted as a fault with single sided infeed from A (echo from B or no blocking signal
from B), which would lead to unwanted tripping by the protection at A. For this reason,
the earth fault protection has an earth current stage
,R0LQ7HOHSURW
(address
). This stage must be set more sensitive than the earth current stage used for the
teleprotection. The larger the capacitive earth current (
I
EC
in Figure 6-73) is the small-
er this stage must be set. On overhead lines a setting equal to 70 % to 80 % of the
earth current stage is usually adequate. On cables or very long lines where the capac-
itive currents in the event of an earth fault are of the same order of magnitude as the
earth fault currents the echo function should not be used or restricted to the case
where the circuit breaker is open; the blocking scheme should not be used under these
conditions at all. This setting can only be modified with DIGSI
®
4 under “Additional
Settings”.
Figure 6-73 Possible current distribution during external earth fault
On three terminal lines (teed feeders) it should further be noted that the earth fault cur-
rent is not equally distributed on the line ends during an external fault. The most unfa-
vourable case is shown in Figure 6-74. In this case, the earth current flowing in from
A B
I
EC
C
E
I
EB
=
I
EA
–
I
EC
I
EA