Siemens SIPROTEC 7UT613 series Manual page 185

High-set Stage I
>>
E
Definite Time Over-
current Stage I
>
E
Overcurrent Stage
I
with IEC curves
Ep
7UT613/63x Manual
C53000-G1176-C160-2
If time overcurrent protection is applied on the feeding side of a transformer, select the
higher stage IE>>, which does not pick up by the inrush current or set the manual
close feature to Inactive.
At address 2402 InRushRestEarth inrush restraint (inrush restraint with 2nd har-
monic) is enabled or disabled. Set ON if the protection is applied at the feeding side of
an earthed transformer. Otherwise, retain setting OFF.
The IE>> stage (address 2411), combined with the IE> stage or the IEp stage,
results in a two-stage characteristic. If this stage is not required, the pickup value shall
be set to ∞. The IE>> stage always operates with a defined delay time.
This current and time setting shall exclude pickup during switching operations. With a
certain degree, current grading can also be achieved similar to the corresponding
stages of the time overcurrent protection for phase and residual currents. However,
zero sequence system quantities must be taken into consideration.
In most cases this stage operates instantaneously. A time delay, however, can be
achieved by setting address 2412 T IE>>.
The set time is an additional delay time and does not include the operating time (mea-
suring 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 threshold is set to
∞, neither a pickup annunciation nor a trip is generated.
Using the time overcurrent stage IE> (address 2413), earth faults can also be detect-
ed 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
2414 T IE>) 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 set time is an additional delay time and does not include the operating time (mea-
suring 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 threshold is set to
∞, neither a pickup annunciation nor a trip is generated.
The inverse time stage, depending on the configuration, enables the user to select dif-
ferent characteristics. In case of IEC characteristics (address 124 DMT/IDMT Earth
= TOC IEC) the following options are available at address 2425 IEC CURVE:
• Normal Inverse (inverse, type A according to IEC 60255-3),
• Very Inverse (very inverse, type B according to IEC 60255-3),
• Extremely Inv. (extremely inverse, type C according to IEC 60255-3), and
• Long Inverse (longtime, type B according to IEC 60255-3).
The characteristics and the equations on which they are based, are listed in the „Tech-
nical Data".
2.5 Time Overcurrent Protection for Earth Current
185