Siemens siprotec 7SD5, Руководство пользователя

Страница: 216 / 698

2 Functions
216
7SD5 Manual
C53000-G1176-C169-1
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
0
is inhibited if a „trip of the voltage transformer mcb“ is
reported via binary input.
Figure 2-94 Directional characteristic of the earth fault protection
Direction Determi-
nation with Nega-
tive Phase-Se-
quence System It is advantageous to use negative sequence system values for the direction measure-
ment 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
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
0
and 3 U
0
the negative se-
quence signals 3 I
2
and 3 U
2
are simply used for the measurement. These signals
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
P
according to Figure 2-94) is larger, or the negative sequence voltage. The
direction is determined by the larger of the two values.
Determination of
Direction with Com-
pensated Zero Se-
quence System
Power 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
Power“ S
r
in direction of a configurable compensation angle
ϕ
comp
, i.e.
S
r
= 3 I
0
·3U
0
·cos(
ϕ
–
ϕ
Comp
).
The direction determination yields
• forward if S
r
is positive and S
r
>
S FORWARD
,
• reverse if S
r
negative and |S
r
| >
S REVERSE
,
For the determination of direction, a minimum current 3 I
0
and a minimum displace-
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-
www
. ElectricalPartManuals
. com