Siemens SIPROTEC 7SA522 Manual page 160

2 Functions
Direction Determi-
nation of Negative
Sequence System
Direction Determi-
nation with Com-
pensated Zero-Se-
quence System
Power
160
the direction can only be determined if it is polarized with the transformer starpoint
current and this exceeds a minimum value corresponding to the setting I
tion determination with 3U
ported via binary input.
Figure 2-69 Directional characteristic of the earth fault protection
It is advantageous to use negative sequence system values for the direction determi-
nation if the resulting zero sequence voltages during earth faults are too small for an
accurate measurement or when the zero sequence values are subject to interference
by for example mutual coupling from a parallel line. It can also be used if the zero se-
quence voltage is not available at the device.
Otherwise this function operates the same as the direction determination with zero se-
quence current and zero sequence voltage. Instead of 3 I
quence signals 3 I and 3 U
2
must also have a minimum magnitude of ,! or 8!.
It is also possible to determine the direction with a zero sequence system or a negative
sequence system. In this case the device determines whether the zero sequence
quantity (U according to Figure 2-69) is larger, or the negative sequence voltage. The
P
direction is determined by the larger of the two values.
The zero-sequence power may also be used for direction determination. In this case
the sign of the compensated zero-sequence power is decisive. This is the zero-se-
quence power component as mentioned in the above paragraph "Zero-Sequence
in direction of a configurable compensation angle ϕ
Power" S
r
·cos(ϕ – ϕ
S = 3I · 3U
r 0 0
The direction determination yields
is positive and 6 )25:$5' < S
• forward if S
r
is negative and – 6 )25:$5' > S
• reverse if S
r
For the determination of direction a minimum current I
voltage which can be set as 8!. The prerequisite is still that the compensated zero-
sequence power has a configurable minimum magnitude. The direction determination
is also inhibited when a "trip of the voltage transformer mcb" is reported via binary
input. Figure 2-70 gives an example for the directional characteristic.
is inhibited if a "trip of the voltage transformer mcb" is re-
0
are simply used for the measurement. These signals
2
).
comp
,
r
>. The direc-
Y
and 3 U the negative se-
0 0
, i.e.
comp
.
r
and a minimum displacement
0
7SA522 Manual
C53000-G1176-C155-3