Siemens siprotec 7SA6 User Manual

Functions
6-38 7SA6 Manual
C53000-G1176-C133-1
If U/I pick-up is required because the minimum short-circuit current is below the
maximum load current (incl. a safety factor of 1.2), the condition for maximum load
current in respect to ,SK!! still has to be observed. Then, the minimum current limit
,SK! (address ) 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  SK)$8/76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 SK)$8/76 = SKDVHHDUWK is useful if no or only little
earth current can flow via the measuring point in the event of earth faults. With SK
)$8/76 = SKDVHWRSKDVHRQO\the leading phase–phase loop is measured in
the event of a single–phase pick-up in the earthed network.
Two further general settings refer to the final times, i.e. the tripping times in a worst
case scenario for faults outside all distance zones. They should be set above the delay
times for distance zones providing a final back-up option (also see “Independent
Zones Z1 up to Z5” in Section 6.2.4.2).
The directional final time '(/$<)25:38 (address ) only works with short
circuits in forward (line) direction if there is no impedance within a distance zone after
pick-up.
The non-directional final time '(/$<121',5 (address ) 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. ,SK! (section a, address
) is the minimum current as described in the previous section, ,SK!! (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  8SKH,! and  8SKH,!! the voltages for
phase–to–earth are inserted to determine the voltage-dependent branch b;
correspondingly when using
Uphph the voltages for phase–to–phase are set in the
addresses  8SKSK,! and  8SKSK,!!. The relevant settings are
determined according to the “Pickup Mode” (see above).
123
10
20
30
40
50
60
U
V
I
I
N
8,
ϕ
!
8,!!
8,!
,SK! ,
ϕ
! ,SK!!
Pick-up only
at ϕ>
Load Range
Pick-up Independent
from Angle
a
b
c
d
e

Siemens siprotec 7SA6 Specifications

General

Brand	Siemens
Model	siprotec 7SA6
Category	Relays
Language	English