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2 Functions
small, the direction can only be determined if it is polarized with the transformer star-
point current and this exceeds a minimum value corresponding to the setting IY>. The
direction determination with 3U
reported via binary input.
Figure 2-94
Direction Determi-
It is advantageous to use negative sequence system values for the direction measure-
nation with Nega-
ment if the resulting zero sequence voltages during earth faults are too small for an
tive Phase-Se-
accurate measurement or when the zero sequence values are subject to interference
quence System
by, for example, mutual coupling from a parallel line. It can also be used if the zero
sequence voltage is not available at the device.
Otherwise this function operates the same as the direction measurement with zero se-
quence current and zero sequence voltage. Instead of 3 I
quence signals 3 I
must also have a minimum magnitude of 3I2> or 3U2>.
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
direction is determined by the larger of the two values.
Determination of
The zero-sequence power may also be used for direction determination. In this case
Direction with Com-
the sign of the compensated zero-sequence power is decisive. This is the zero-se-
pensated Zero Se-
quence power component as mentioned in the above paragraph „Zero-Sequence
quence System
Power" S
Power
The direction determination yields
• forward if S
• reverse if S
For the determination of direction, a minimum current 3I
ment voltage which can be set as 3U0> is required. The prerequisite is still that the
compensated zero-sequence power has a configurable minimum magnitude. The di-
216
Directional characteristic of the earth fault protection
and 3 U
2
according to Figure 2-94) is larger, or the negative sequence voltage. The
P
in direction of a configurable compensation angle ϕ
r
·cos(ϕ – ϕ
S
= 3I
·3U
r
0
0
Comp
is positive and S
r
negative and |S
r
is inhibited if a „trip of the voltage transformer mcb" is
0
are simply used for the measurement. These signals
2
).
> S FORWARD,
r
| > S REVERSE,
r
and 3 U
the negative se-
0
0
, i.e.
comp
and a minimum displace-
0
7SD5 Manual
C53000-G1176-C169-1
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