Functions
2.5 Distance Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
132
Figure 2-50
Switching onto a fault
Note
When switching onto a three-pole fault with the MHO characteristic, there will be no voltage in the memory or
unfaulted loop voltage available. To ensure fault clearance when switching onto three-pole close-up faults,
please make sure that in conjunction with the configured MHO characteristic the instantaneous tripping function
is always enabled.
2.5.1.4
Setting Notes
At address
1501
FCT Distance
the distance protection function can be switched
ON
or
OFF
.
Minimum current
The minimum current for fault detection
Minimum Iph>
(address
1502
) in case of impedance pickup is set
somewhat (approx. 10 %) below the minimum short-circuit current that may occur. For the other pickup modes
it is set at address
1911
.
Earth fault detection
In systems with earthed starpoint, the setting
3I0> Threshold
(address
1503
) is set somewhat below the
minimum expected earth fault current. 3
I
0
is defined as the sum of the phase currents |
I
L1
+
I
L2
+
I
L3
|, which
equals the starpoint current of the set of current transformers. In non-earthed systems the setting value is rec-
ommended to be below the earth current value for double earth faults.
The preset value
3I0>/ Iphmax
= 0.10 (address
1507
) is usually recommended for the slope of the 3
I
0 char-
acteristic. This setting can only be changed in DIGSI at
Display Additional Settings
.
Addresses
1504
and
1509
are only relevant for
earthed
power systems. In non-earthed systems, they are
hidden.
When setting
3U0> Threshold
(address
1504
), care must be taken that operational asymmetries do not
cause a pickup. 3U0 is defined as the sum of the phase-to-earth voltages |U
L1-E
+ U
L2-E
+ U
L3-E
|. If the U0 cri-
terion is not required, address
1504
is set to
∞
.
