Curve name
ANSI Long Time Inverse
IEC Normal Inverse
IEC Very Inverse
IEC Inverse
IEC Extremely Inverse
IEC Short Time Inverse
IEC Long Time Inverse
IEC Definite Time
User Programmable
ASEA RI
RXIDG or RD (logarithmic)
It is also possible to tailor make the inverse time characteristic.
Normally it is required that EF4PTOC shall reset as fast as possible when the
current level gets lower than the operation level. In some cases some sort of
delayed reset is required. Therefore different kinds of reset characteristics can be
used.
For some protection applications, there can be a need to change the current
operating level for some time. Therefore, there is a possibility to give a setting of a
multiplication factor INxMult to the residual current pick-up level. This
multiplication factor is activated from a binary input signal ENMULTx to the
function.
Power transformers can have a large inrush current, when being energized. This
inrush current can produce residual current component. The phenomenon is due to
saturation of the transformer magnetic core during parts of the cycle. There is a risk
that inrush current will give a residual current that reaches level above the
operating current of the residual overcurrent protection. The inrush current has a
large second harmonic content. This can be used to avoid unwanted operation of
the protection. Therefore, EF4PTOC has a possibility of second harmonic restrain
if the level of 2
nd
harmonic current reaches a value above a set percent of the
fundamental current.
8.4.3 Setting guidelines
IP14988-1 v1
M15282-3 v12
When inverse time overcurrent characteristic is selected, the
operate time of the stage will be the sum of the inverse time delay
and the set definite time delay. Thus, if only the inverse time delay
is required, it is important to set the definite time delay for that
stage to zero.
Section 8 1MRK 505 393-UEN B
Current protection
168 Line differential protection RED650 2.2 IEC
Application manual
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