Built-In Undercurrent Protection Steps - ABB Relion 650 Series Technical Manual

1MRK 511 424-UEN B
6.1.7.4
Bay control REC650 2.2 IEC
Technical manual
curves (overcurrent with IDMT curve will operate faster during low voltage
conditions).
Current restraint feature
The overcurrent protection step operation can be made dependent of a restraining
current quantity (see table 41). 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.
I
Measured
IsetHigh
IsetLow
atan(RestrCoeff)
IEC05000255 V1 EN-US
Figure 38: Current pickup variation with restraint current magnitude
This feature will simply prevent overcurrent step to start 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 operate times for IDMT curves. This means that the IDMT curve
operate time will not be influenced by the restrain current magnitude.
When set, the start signal will start definite time delay or inverse (IDMT) time
delay in accordance with the end user setting. If the start 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 start and trip signal can be instantaneous or time delay in
accordance with the end user setting.

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 39) with the set pickup level.
The undercurrent step will pickup and set its start signal to one if the magnitude of
the measured current quantity is smaller than this set level. The start signal will
start definite time delay with set time delay. If the start signal has value one for
longer time than the set time delay the undercurrent step will set its trip signal to
Section 6
Multipurpose protection
Restraint
en05000255.vsd
M13751-338 v3
M13751-231 v2
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