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If you are using the zero-sequence power protection and the fault direction is determined on the basis of the
zero-sequence power, address 3169 S forward indicates the value of the compensated zero-sequence
power above which the direction is recognized as forward. This value should be smaller than the reference
power S ref (address 3156, see paragraph „Zero-Sequence Power Stage"). This ensures the availability of
direction determination even with smaller zero-sequence power conditions.
The position of the directional characteristic can be changed in dependence on the selected method of direction
determination (address 3160 POLARIZATION, see above). All methods based on angle measurement
between measured signal and reference signal (i.e. all methods except POLARIZATION = zero seq.
power), allow the angle range of the direction determination to be changed with the setting angles Dir.
ALPHA and Dir. BETA (addresses 3162 and 3163). This parameter can only be changed in DIGSI at Display
Additional Settings. As these set values are not critical, the presettings may be left unchanged. If you want
to change these values, refer to margin heading „Direction Determination with Zero-Sequence System" for the
angle determination.
The direction determination POLARIZATION with zero seq. power determines the directional characteristic
by means of the compensation angle PHI comp (address 3168) which indicates the symmetry axis of the di-
rectional characteristic. This value is also not critical for direction determination. For information on the angle
definition, refer to 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 heading „Zero-Sequence Power Stage").
The ancillary function for increased directional sensitivity for long lines is set with parameter 3186 3U0<
forward. With default setting 0, the ancillary function is disabled. This parameter can only be altered in DIGSI
at Display Additional Settings.
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
2.8 Earth Fault Protection in Earthed Systems (optional)
Functions
241
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