2.4 Time Overcurrent Protection for Phase and Residual Currents
173
7UT613/63x Manual
C53000-G1176-C160-2
In address 2202 InRushRest. 3I0 inrush restraint (inrush restraint with 2nd har-
monic) is enabled or disabled. Set ON if the residual current stage of the time overcur-
rent protection is applied at the supply side of a transformer whose starpoint is
earthed. Otherwise, retain setting OFF. If you set a very small pickup value, consider
that the inrush restraint function cannot operate below 10 % nominal current (lower
limit of harmonic filtering).
High Set Current
Stage 3I0>>
If stage 3I0>> (address 2211 or 2212) is combined with the 3I0> stage or the 3I0p
stage, a two-stage characteristic will be the result. If one stage is not required, the
pickup value has to be set to ∞. Stage 3I0>> always operates with a defined delay.
If the protected winding is not earthed, zero sequence current only emerges due to an
inner earth fault or double earth fault with one inner base point. Here, the 3I0>> stage
is usually not required.
The 3I0>> stage can, for example, be applied for current grading. Please note that the
zero sequence system of currents is of importance. For transformers with separate
windings, zero sequence systems are usually kept separate (exception: bilateral star-
point earthing or earthed auto-transformer).
Inrush currents can only be created in zero sequence systems if the starpoint of the
respective winding is earthed. If the fundamental exceeds the setting value, the inrush
currents are rendered harmless by delay times (address 2213 T 3I0>>).
„Reverse Interlocking“ is only sensible if the respective winding is earthed. In that
case, the multi-stage function of the time overcurrent protection is beneficial: For ex-
ample, stage 3I0>> is used as fast busbar protection with a short safety delay T
3I0>> (e.g. 50 ms). Stage 3I0>> is blocked for faults at the outgoing feeders. Stages
3I0> or 3I0p serve as backup protection. The pickup values of both elements (3I0>
or 3I0p and 3I0>>) are set equal. Delay time T 3I0> or T 3I0p (IEC characteristic)
or D 3I0p (ANSI characteristic) is set in such manner that it overgrades the delay for
the outgoing feeders. Here, the grading coordination chart for earth faults, which
mostly allows shorter setting times, is of primary importance.
The set time T 3I0>>is an additional delay time and does not include the operating
time (measuring time, etc.). The delay can be set to ∞. If set to infinity, the pickup of
this function will be indicated but the stage will not trip after pickup. If the pickup thresh-
old is set to ∞, neither a pickup annunciation nor a trip is generated.
Definite Time Over-
current Stage3I0>
The minimum appearing earth fault current is relevant for the setting of the time over-
current stage 3I0> (address 2214 or 2215). Please note that, in case of various mea-
suring locations, higher measuring tolerance may occur due to summation errors.
The time delay to be set (parameter 2216 T 3I0>) is derived from the grading coor-
dination chart created for the network. For earth currents with earthed network, a sep-
arate grading coordination chart with shorter delay times can be set up. If you set a
very small pickup value, it must be taken into consideration that the inrush restraint
function cannot operate below 10 % nominal current (lower limit of harmonic filtering).
An adequate time delay could be reasonable if inrush restraint is used.
The set time is an additional delay time and does not include the operating time (mea-
suring time, etc.). The delay can also be set to ∞. If set to infinity, the pickup of this
function will be indicated but the stage will not trip after pickup. If the pickup threshold
is set to ∞, neither a pickup annunciation nor a trip is generated.
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