Siemens siprotec 7SA6 User Manual page 221

Angular
Dependence
7SA6 Manual
C53000-G1176-C133-1
The characteristic has to be set such that it is just below the minimum expected volt-
age at the maximum expected load current. If in doubt, check the pick-up conditions
in accordance with the U/I characteristic.
If a distinction between short circuit and load conditions is not always possible using
the U/I characteristic which is independent of the phase angle, the angular dependent
section d-e can additionally be used. This is required for long lines and section of lines
with intermediate infeed in combination with small source source impedances. Then
the local measured voltage will only drop to a small extent in the event of a short circuit
at the line end or in the back-up range of the distance protection so that the phase
angle between current and voltage is required as an additional criterion for fault
detection.
The parameters ,ϕ! (address ) and 8SKH ,ϕ! (address ) or
8SKSK ,ϕ! (address ) determine the characteristic in the range of large angles
ϕ
, i.e. in the short-circuit angle range. The threshold angles themselves, which define
K
the short-circuit angle range ϕ
short-circuit angle range ϕ
voltage settings according to the "Pickup Mode" (see above) are relevant.
The characteristic for the load angle range has to be set in a way that is just below the
minimum expected operating voltage at the maximum expected load current. In the
range of the short circuit angle ϕ
pick-up in this area. If reactive power has to be tranferred via this line it must be
ensured that the maximum reactive current at minimum operating voltage is not within
the pick-up range, i.e. the short-circuit angle range ϕ
should be checked in accordance with the U/I/ϕ characteristic. An arithmetic short-
circuit calculation is recommended for extensive networks.
The lower threshold angle should be between the load angle and the short-circuit
angle. Therefore, it must be set smaller than the line angle ϕ
(approx. 10° to 20°). Further, you should check that the angle is not exceeded during
load conditions. If this is the case, for instance because the reactive power has to be
transferred via this line, it must be ensured that the parameters of the voltage-
dependent segment d, that is ,SKL! and 8SKH ,SKL! or 8SKSK ,SKL! rule
out a pick-up as the result of reactive power (see above).
The upper threshold angle ϕ (address ) is not critical. 100° to 120° should be
sufficient.
Angular dependence, i.e. increasing the sensitivity for a large short-circuit angle with
section d and e in the characteristic, can be limited to the forward direction (line
direction) using address  ())(&7 ϕ. In this case ())(&7 ϕ is set to )RUZDUG
Otherwise it remains ())(&7 ϕ = IRUZDUG
®
made with DIGSI 4 "Additional Settings".
, are set in the addresses  ϕ! and  ϕ . The
K
is between these two angles. Here too, the required
K
it must be ensured that load current may not cause
K
UHYHUVH. This setting can only be
Functions
. If in doubt, pick-up conditions
K
= arctan (X /R
L L
)
L
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