Siemens SIPROTEC 4 7UT6 Series Manual page 168

Functions
2.5 Time Overcurrent Protection for Earth Current
The time multiplication factor may also be set to ∞. If set to infinity, the pickup of this function will be indi-
cated but the stage will not trip after pickup. If the IEp stage is not required, select address 124 DMT/IDMT
Earth = Definite Time when configuring the protection functions.
If under address 2424 TOC DROP-OUT the Disk Emulation are set, dropout is produced in accordance
with the dropout characteristic, as set out in the functional description of the inverse time overcurrent protec-
tion under margin heading "Dropout Behaviour".
Overcurrent Stage Ι with ANSI Characteristics
Ep
The inverse time stage, depending on the configuration, enables the user to select different characteristics.
With the ANSI characteristics (address 124 DMT/IDMT Earth = TOC ANSI) the following is made available in
address 2426 ANSI CURVE:
•
Definite Inv.,
•
Moderately Inv.,
•
Inverse,
•
Long Inverse,
•
Moderately Inv.,
•
Short Inverse and
•
Very Inverse.
The characteristics and the equations on which they are based, are listed in the "Technical Data".
If the inverse time trip characteristic is selected, it must be noted that a safety factor of about 1.1 has already
been included between the pickup value and the setting value. This means that a pickup will only occur if a
current of about 1.1 times the setting value is present.
Using the time overcurrent stage IEp (address 2421) earth faults can also be detected with weak fault
currents. Since the starpoint current originates from one single current transformer, it is not affected by
summation effects evoked by different current transformer errors like, for example, the zero sequence current
derived from phase currents. Therefore, this address can be set to very sensitive. Consider that the inrush
restraint function cannot operate below 10 % nominal current (lower limit of harmonic filtering). An adequate
time delay could be reasonable for very sensitive setting if inrush restraint is used.
Since this stage also picks up with earth faults in the network, the time delay (address 2423 D IEp) has to be
coordinated with the grading coordination chart of the network for earth faults. In most cases, shorter tripping
times than for phase currents may be set since a galvanic separation of the zero sequence systems of the
connected power system sections is ensured by a transformer with separate windings.
The time multiplier 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 stage IEp is not required at all, select address 124 DMT/IDMT Earth =
Definite Time during configuration of the protection functions.
If at address 2424 TOC DROP-OUT the Disk Emulation is set, dropout is thus produced in accordance with
the dropout characteristic, as described under margin heading "Dropout Behaviour" in Section
current Protection for Earth
Dynamic Cold Load Pickup
An alternative set of pickup values can be set for each stage. It may be selected automatically in a dynamic
manner during operation. For more information on this function, see Section
for Time Overcurrent
for definite time overcurrent protection Ι
•
address 2411 for pickup value IE>>,
•
address 2412 for delay time T IE>>,
•
address 2413 for pickup value IE>,
•
address 2414 for delay time T IE>;
for inverse time overcurrent protection Ι
168
Current.
Protection. For the stages the following alternative values are set here.
:
E
acc. to IEC characteristics:
E
2.5 Time Over-
2.6 Dynamic Cold Load Pickup
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016