Functions
6-1077SA522 Manual
C53000-G1176-C119-2
no critical, the pre-settings may be left unchanged. This setting can only be modified
with DIGSI
®
4 under “Additional Settings”.
Finally, the threshold values of the polarizing signals must be set. 8! (address
) determines the minimum operating voltage for direction determination with U
E
.
If U
E
is not used for the direction determination, this setting is of no consequence. The
set threshold should not be exceeded by unsymmetries in the operational measured
voltage. U
E
is the sum of the phase voltages, i.o.w.
U
E
= U
L1
+ U
L2
+ U
L3
= 3·U
0
Only if the connection of the fourth current transformer ,WUDQVIRUPHU
(address ) = starpoint is registered in the 3RZHU6\VWHP'DWD36\VWHP
'DWD (see 6.1.1), the address ,<! will appear. It is the lower threshold for
the current measured in the starpoint of a source transformer. A relatively sensitive
setting can be applied for this value, as the measurement of the starpoint current is
quite accurate by nature.
If the direction determination must be done with the negative sequence system sig-
nals, the setting values 8! (address ) and ,! (address ) are decisive
for the lower limit of the direction determination. The setting values must in this case
also be selected such that operational unsymmetry in the system does not lead to a
pick-up.
Teleprotection with
Earth Fault
Protection
The earth fault protection in the 7SA522 may be expanded to a directional comparison
protection using the integrated teleprotection logic. Additional information regarding
the available teleprotection schemes and their mode of operation may be obtained
from Section 6.6. If this is to be used, certain preconditions must already be observed
when setting the earth current stage.
Initially it must be determined which stage must operate in conjunction with the tele-
protection. This stage must be set directional in the forward direction. If for example
the 3I
0
>–stage should operate as directional comparison, the address
2SPRGH,! is set to )RUZDUG (refer to “Definite Time Stages” above,
page 6-101).
Furthermore, the device must be informed that the applicable stage has to function to-
gether with the teleprotection to allow undelayed release of the tripping during internal
faults. For the 3I
0
>–stage this means that address ,S7HOHS%, is set to
<HV. The time delay set for this stage 7,! (address ) then functions as a
back-up stage, e.g. during failure of the signal transmission. For the remaining stages
the corresponding setting parameter is set to 1R, therefore, in this example: address
,!!7HOHS%, for the 3I
0
>>–stage, address ,!!!7HOHS%, for
the 3I
0
>>>–stage, address ,S7HOHS%, for the 3I
0P
–stage (if this is used).
If the echo function is used in conjunction with the teleprotection scheme, or if the
weak-infeed tripping function should be used, the additional teleprotection stage
,R0LQ7HOHSURW (address ) must be set to avoid non-selective tripping during
through-fault earth current measurement. This setting can only be modified with
DIGSI
®
4 under “Additional Settings”. Further comments are given in Sub-section
6.6.2 under the margin heading “Earth Fault Protection Prerequisites”.
Switching on to a
Dead Earth Fault
It is possible to determine with a setting which stage trips without delay following clo-
sure onto a dead fault. The stages have the setting parameters ,!!!627)7ULS
(address ), ,!!627)7ULS (address ), ,!627)7ULS (address
) and if required ,S627)7ULS (address ), which must accordingly be
set for each stage to either <HV or 1R. Selection of the most sensitive stage is usually
not reasonable as a solid short-circuit may be assumed following switching onto a
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