Table 35: Time characteristics
Curve name
ANSI Extremely Inverse
ANSI Very Inverse
ANSI Normal Inverse
ANSI Moderately Inverse
ANSI/IEEE Definite time
ANSI Long Time Extremely Inverse
ANSI Long Time Very Inverse
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 (51N_67N) 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 pickup 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 MULTPUx 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 pickup 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 (51N_67N)
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.
1MRK 506 369-UUS - Section 9
Current protection
Line distance protection REL670 2.2 ANSI 509
Application manual
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