2.5 Time Overcurrent Protection for Earth Current
187
7UT613/63x Manual
C53000-G1176-C160-2
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 pro-
duced in accordance with the dropout characteristic, as described under margin head-
ing„ Dropout Behaviour“ in subsection 2.5.
Dynamic Cold Load
Pickup
An alternative set of pickup values can be set for each stage. It may be selected au-
tomatically in a dynamic manner during operation. For more information on this func-
tion, see Section 2.6. For the stages the following alternative values are set here.
for definite time overcurrent protection I
E
:
• address 2511 for pickup value IE>>,
• address 2512 for delay time T IE>>,
• address 2513 for pickup value IE>,
• address 2514 for delay time T IE>,
for inverse time overcurrent protection I
E
acc. to IEC characteristics:
• address 2521 for pickup value IEp,
• address 2522 for time multiplier T IEp;
for inverse time overcurrent protection I
E
acc. to ANSI characteristics:
• address 2521 for pickup value IEp,
• address 2523 for time multiplier D IEp;
User-Defined
Curves
For inverse time overcurrent protection the user may define his own tripping and
dropout characteristic. For configuration in DIGSI a dialogue box appears. Enter up to
20 pairs of current value and tripping time value.
The procedure is the same as for phase current stages. See subsection 2.4.2 under
margin heading „User-Defined Curves“.
To create a user defined tripping characteristic for earth current, the following has to
be set for configuration of the functional scope: address 124 DMT/IDMT Earth,
option User Defined PU. If you also want to specify the dropout characteristic, set
option User def. Reset.
Inrush Restraint In address 2402 InRushRestEarth of the general settings, the inrush restraint can
be enabled (ON) or disabled (OFF). This inrush restraint is only sensible for transform-
ers and if overcurrent time protection is activated on the earthed feeding side. Func-
tion parameters of the inrush restraint are set in „Inrush“.
The inrush restraint is based on the evaluation of the 2nd harmonic present in the
inrush current. The ratio of 2nd harmonics to the fundamental component 2.HARM.
Earth (address 2441) is set to I2
fN
/I
fN
= 15 % as default setting. It can be used
without being changed. To provide more restraint in exceptional cases, where ener-
gising conditions are particularly unfavourable, a smaller value can be set in the afore-
mentioned address.
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