Functions
6-377SA6 Manual
C53000-G1176-C133-1
With the U/I(/ϕ) pick-up mode you have the option to determine the voltage measuring
and, if applicable, the phase-angle measuring for phase–to–earth measuring units,
and for phase–to–phase measuring loops separately. Address 352*$08,
states which loop voltages shall apply to phase–to–earth (3K() and which ones to
phase–to–phase (3K3K).
In networks with earthed
star point, a selection using U
Ph–E
with earth faults and
U
Ph–Ph
with non-earthed faults is often preferred (address 352*$08, =
3K(8SKH3K3K8SKSK). This mode has a maximum sensitivity for all fault
types, however it requires the unambiguous detection of earth faults via the earth-fault
detection function (also see Section 6.2.1). Otherwise, a mode using U
Ph-E
for all fault
types may be useful (address 352*$08, = 3K(8SKH3K3K8SKH),
accepting lesser sensitivity for earth-free faults, as the overcurrent stage Iph>> usually
picks up here.
In networks with low–resistance earthed
neutral point, the U/I/ϕ pick-up should only
come into effect on earth faults as phase–to–phase faults are detected by the
overcurrent pick-up. Therefore, the address 352*$08, =
3K(8SKH3K3K,!!is useful in this case.
As far as there is a danger of the earth fault detection picking up when a applicable
earth fault occurs in isolated
or resonant-earthed networks owing to the starting
transient, this can be delayed using a parameter 7,3+$6. If the earth fault pick-
up can also be exceeded during steady-state conditions, 7,3+$6 (address
) should be set to ∞. As a result of this, pickup by one phase alone will not be
possible even with a large earth current. Double earth faults are however correctly
detected and measured according to the preference program (also see Section
6.2.3.1, “Double Earth-Faults in Non-earthed Systems”).
In isolated
or resonant-earthed networks it is possible to control the U/I/ϕ pick-up
using phase–to–phase voltages only (address 352*$08, =
3K(8SKSK3K3K8SKSK). Naturally, this excludes pick-up by single earth
faults, however, it also does not allow a correct double earth fault detection, therefore
it is suitable only for small isolated cable networks.
General
Settings
for Pick-Up
The maximum operational load current that can occur is crucial for the setting of
overcurrent pick-up
. Pick-up due to overload must be ruled out! Therefore the pick-
up value must be set above the maximum (over-)load current that is expected (approx.
1.2 times). Then, it must be ensured that the minimum short-circuit current is above
this value. If this is not the case, U/I pick-up is required.
Arithmetic example:
Maximum operational current (incl. overload) is 680 A, for current transformers 600 A/
5 A, minimum short circuit is 1200 A. the following has to be set:
,SK!! = I
L max
⋅ 1.2 = 680 A ⋅ 1.2 = 816 A
This value is sufficiently below the minimum short-circuit current of 1200 A. When
configuring via PC and DIGSI
®
4 this value can be entered directly. Conversion to
secondary quantities is
The condition for minimum short-circuit current also applies to earth faults (in the
earthed network) or for double earth faults as long as overcurrent pick-up is solely
used.
Iph>>
816 A
5A
600 A
----------------
⋅=
= 6.8 A
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