Siemens siprotec 7SA6, Manual

Page: 229 / 876

Functions
6-39
7SA6 Manual
C53000-G1176-C156-2
(address
1611
) is set to below the minimum short-circuit current (approx. 10 %). This
also applies to the phase currents during earth faults or double earth faults.
In address
1630 1ph FAULTS
you can choose whether a phase–to–earth loop shall
be selected in an earthed network during single–phase pickup without earth current
(I
E
–release). The setting
1ph FAULTS
=
phase-earth
is useful if no or only little
earth current can flow via the measuring point in the event of earth faults. With
1ph
FAULTS
=
phase to phase only
the leading phase–phase loop is measured in
the event of a single–phase pick-up in the earthed network.
Two further general settings refer to the final times, i.e. the tripping times in a worst
case scenario for faults outside all distance zones. They should be set above the delay
times for distance zones providing a final back-up option (also see “Independent
Zones Z1 up to Z5” in Section 6.2.4.2).
The directional final time
DELAY FORW. PU
(address
1602
) only works with short cir-
cuits in forward (line) direction if there is no impedance within a distance zone after
pick-up.
The non-directional final time
DELAY NON-DIR.
(address
1603
) works for all short-
circuits if there is no impedance within a distance zone after pick-up.
U/I(/
ϕ
) Pickup The meaning of the settings can be seen from Figure 6-21.
Iph>
(section a, address
1611
) is the minimum current as described in the previous section,
Iph>>
(section c)
is the overcurrent pick-up.
Figure 6-21 Parameters of
U/I/
ϕ
pick-up
In most cases the angular dependence is not required. Then the voltage-dependent
section b is valid which results in the characteristic a-b-c. When controlling with Uphe
in the addresses
1612 Uph-e (I>>)
and
1613 Uph-e (I>)
the voltages for
phase–to–earth are inserted to determine the voltage-dependent branch b; corre-
spondingly when using Uphph the voltages for phase–to–phase are set in the ad-
dresses
1614 Uph-ph (I>>)
and
1615 Uph-ph (I>)
. The relevant settings are
determined according to the “Pickup Mode” (see above).
The characteristic has to be set such that it is just below the minimum expected volt-
age at the maximum expected load current. If in doubt, check the pick-up conditions
in accordance with the U/I characteristic.
1 2 3
10
20
30
40
50
60
U
V
I
I
N
U(I
ϕ
>)
U(I>>)
U(I>)
Iph> I ϕ > Iph>>
Pick-up only
at
ϕ
>
Load Range
Pick-up Independent
from Angle
a
b
c
d
e