Siemens siprotec 7SA522 User Manual

2 Functions
160
7SA522 Manual
C53000-G1176-C155-3
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
Y
>. The direc-
tion determination with 3U
0
is inhibited if a “trip of the voltage transformer mcb” is re-
ported via binary input.
Figure 2-69 Directional characteristic of the earth fault protection
Direction Determi-
nation of Negative
Sequence System
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
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 ,! 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
P
according to Figure 2-69) is larger, or the negative sequence voltage. The
direction is determined by the larger of the two values.
Direction Determi-
nation 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
=3I
0
· 3U
0
·cos(ϕ – ϕ
comp
).
The direction determination yields
•forward if S
r
is positive and 6)25:$5' <S
r
,
• reverse if S
r
is negative and – 6)25:$5' >S
r
.
For the determination of direction a minimum current I
0
and a minimum displacement
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.

Siemens siprotec 7SA522 Specifications

General

Brand	Siemens
Model	siprotec 7SA522
Category	Protection Device
Language	English