2 Functions
126
7SD5 Manual
C53000-G1176-C169-1
The preset value 3I0>/ Iphmax = 0,10 (address 1507) usually is recommended for
the slope of the 3I0 characteristic. This setting can only be changed via DIGSI
®
at Ad-
ditional Settings.
Addresses 1504 and 1509 are only relevant for earthed power systems. In non-
earthed systems this setting is not relevant and therefore not accessible.
When setting 3U0> Threshold (address 1504), care must be taken that operational
asymmetries do not cause a pickup. 3U
0
is defined as the sum of the phase-earth volt-
ages |U
L1-E
+ U
L2-E
+ U
L3-E
|. If the U
0
criterion is not required, the address 1504 is set
to ∞.
In earthed power systems the earth fault detection can be complemented by a zero
sequence voltage detection function. You can determine whether an earth fault is de-
tected when a zero sequence current
or a zero sequence voltage threshold is exceed-
ed or when both criteria are met. 3I0> OR 3U0> (default setting) applies at address
1509 E/F recognition if only one of the two criteria is valid. Select 3I0> AND
3U0> to activate both criteria for earth-fault detection. This setting can only be
changed via DIGSI
®
at Additional Settings. If you want to detect only the earth cur-
rent, set 3I0> OR 3U0> and also 3U0> Threshold (address 1504) to ∞.
Note
Under no circumstances set address 1504 3U0> Threshold to ∞, if you have set
address 1509 E/F recognition = 3I0> AND 3U0>, or earth-fault detection will
no longer be possible.
If in isolated or resonant earthed systems the earth fault detection threatens to pick up
due to fault inception transients following the occurrence of a single earth fault, the de-
tection can be delayed with setting address 1218 T3I0 1PHAS. Set parameter T3I0
1PHAS to ∞ if the earth current threshold can also be exceeded during steady-state
conditions. Then, even with high earth current, no single-phase pickup is possible any-
more. Double earth faults are however correctly detected and measured according to
the preference program (also see Section 2.5.1 at margin heading „Double Earth
Faults in Non-earthed Systems“).
Please note that the parameter T3I0 1PHAS is also used by the differential protection
function. The setting that you make here affects the differential protection function as
well (see also Section 2.3.2 under margin heading „Delay Times“).
Application with
Series-Compensat-
ed Lines
With series-compensated lines (lines with series capacitors), set address 1508 SER-
COMP. to YES, to ensure that the direction determination works correctly in all cases.
The influence of the series capacitors on the direction determination is described in
Section 2.5.2 under margin heading „Direction Determination in Case of Series-com-
pensated Lines“.
Start of Delay Times As was mentioned in the description of the measuring technique, each distance zone
generates an output signal which is associated with the zone and the affected phase.
The zone logic combines these zone fault detections with possible further internal and
external signals. The delay times for the distance zones can be started either all to-
gether on general fault detection by the distance protection function, or individually at
the moment the fault enters the respective distance zone. Parameter Start Timers
(address 1510) is set by default to on Dis. Pickup. This setting ensures that all
delay times continue to run together even if the type of fault or the selected measuring
loop changes, e.g. because an intermediate infeed is switched off. This is also the pre-
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