Siemens siprotec 7SA6 User Manual page 436

Functions
Measured Value
Acquisition —
Currents
Measured Value
Acquisition —
Voltages
6-254
Four measuring inputs are available in the current circuits. If the three phase currents
and the earth current from the current transformer star-point or from a separate earth
current transformer on the protected circuit are connected to the device, the sum of
the four digitized currents must equal 0. Faults in the current circuits are detected if
I = |I + I + I + k
F L1 L2 L3
(parameter ,,SK &7) takes the eventual ratio difference of a separate
whereby k
I
–current transformer into consideration (e.g. core balance CT). Σ, 7+5(6+2/' and
I
E
Σ, )$&725 are setting parameters. The amount Σ, )$&725 · I
permissible current proportional ratio errors of the input transducers into account
which are particularly prevalent during large fault currents (Figure 6-130). The reset
ratio is approx. 97 %.
This failure is alarmed by ")DLOXUH Σ ,".
Note:
The current sum monitoring is only effective if the fourth current measuring input (I
is connected to measure the earth current of the protected line.
I
F
I
N
DÃUCS@TCPG9
Σ
Figure 6-130 current sum monitoring
Four measuring inputs are available in the voltage circuits: three for phase–earth
voltages as well as one input for the displacement voltage (e-n voltage of an open
delta connection) or a busbar voltage. If the displacement voltage is connected to the
device, the sum of the three digitized phase voltages must equal three times the zero
sequence voltage. Errors in the voltage transformer circuits are detected when
U = |U + U + U
F L1 L2 L3
The factor k allows for a difference of the transformation ratio between the
U
displacement voltage input and the phase voltage inputs (parameter 8SK  8GHOWD).
The reset ratio is approx. 97 %.
This fault is alarmed by ")DLO Σ 8 3K(".
Note:
The voltage sum monitoring is only effective if the measuring input U
a displacement voltage which was generated externally.
| > Σ, 7+5(6+2/' · I
· I
I E
slope:
DÃA68UPS
Σ
+ k · U | > 25 V.
U EN
+ Σ, )$&725 · I
N
takes the
max
I
max
I
N
is connected to
4
C53000-G1176-C133-1
max
)
4
7SA6 Manual