Table 39: 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.
Section 9 1MRK 504 163-UUS A
Current protection
536 Transformer protection RET670 2.2 ANSI
Application manual
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