2 Functions
170
7SA522 Manual
C53000-G1176-C155-3
Only if you have set in the 36\VWHP'DWD (see Section 2.1.3.1) the connection
of the fourth current transformer ,WUDQVIRUPHU (address ) = ,<VWDUSRLQW,
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 asymmetry in the system does not lead to a
pickup.
If you are using the zero-sequence power protection and the fault direction is deter-
mined on the basis of the zero-sequence power, address 6IRUZDUG indicates
the value of the compensated zero-sequence power above which the direction is rec-
ognized as forward. This value should be smaller than the reference power 6UHI (ad-
dress , see above paragraph at “Zero-Sequence Power Stage”). This ensures
the availability of direction determination even with smaller zero-sequence power con-
ditions.
The position of the directional characteristic can be changed in dependance of the se-
lected method of direction determination (address 32/$5,=$7,21, see above).
All methods based on angle measurement between measured signal and reference
signal (i.e. all methods except 32/$5,=$7,21 = ]HURVHTSRZHU), allow the angle
range of the direction determination to be changed with the setting angles 'LU
$/3+$ and 'LU%(7$ (addresses and ). This setting is only possible via
DIGSI
®
at "Additional Settings". As these set values are not critical, the presettings
may be left unchanged. If you want to change these values, refer to Section 2.7,
margin heading “Direction Determination with Zero-Sequence System” for the angle
determination.
The direction determination 32/$5,=$7,21 with ]HURVHTSRZHU determines the
directional characteristic by means of the compensation angle 3+,FRPS (address
) which indicates the symmetry axis of the directional characteristic. This value
is also not critical for direction determination. For information on the angle definition,
refer to Section 2.7, margin heading “Direction Determination with Zero-Sequence
Power”. This angle determines at the same time the maximum sensitivity of the zero-
sequence power stage thus also affecting indirectly the trip time as described above
(margin title “Zero-Sequence Power Stage”).
Teleprotection with
Earth Fault Protec-
tion
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 2.8. 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 line direction. If for example the
3I
0
> stage should operate as directional comparison, set address 2SPRGH
,! = )RUZDUG (see above “Definite Time Stages”).
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 ,!7HOHS%, is set to
<(6. 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 12, therefore, in this example: Address
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