ABB Relion 670 Series RES670, Technical Manual

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Current restraint feature
The overcurrent protection step operation can be made dependent of a restraining current
quantity (see table
193 ). Practically then the pickup level of the overcurrent step is not
constant but instead increases with the increase in the magnitude of the restraining current.
IsetHigh
IsetLow
I
Measured
Restraint
atan(RestrCoeff)
en05000255.vsd
Op
er
ate
ar
ea
I>R
es
trC
oe
ff*I
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tra
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IEC05000255 V1 EN
Figure 115: Current pickup variation with restraint current magnitude
This feature will simply prevent overcurrent step to pickup if the magnitude of the
measured current quantity is smaller than the set percentage of the restrain current
magnitude. However this feature will not affect the pickup current value for calculation of
trip times for IDMT curves. This means that the IDMT curve trip time will not be
influenced by the restrain current magnitude.
When set, the pickup signal will start definite time delay or inverse (IDMT) time delay in
accordance with the end user setting. If the pickup signal has value one for longer time
than the set time delay, the overcurrent step will set its trip signal to one. Reset of the
pickup and trip signal can be instantaneous or time delay in accordance with the end user
setting.
11.1.6.4 Built-in undercurrent protection steps
Two undercurrent protection steps are available. They are absolutely identical and
therefore only one will be explained here. Undercurrent step simply compares the
magnitude of the measured current quantity (see table
191 ) with the set pickup level. The
undercurrent step will pickup and set its pickup signal to one if the magnitude of the
measured current quantity is smaller than this set level. The pickup signal will start
definite time delay with set time delay. If the pickup signal has value one for longer time
Section 11
1MRK 511 365-UUS A
Multipurpose protection
340 Phasor measurement unit RES670 2.1 ANSI
Technical manual