Built-In Undercurrent Protection Steps - ABB RES670 Technical Manual

Section 11
Multipurpose protection
11.1.6.4
344
Current restraint feature
The overcurrent protection step operation can be made dependent of a restraining
current quantity (see table 191). 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 118: 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.

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 189) 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
1MRK 511 408-UUS A
Restraint
en05000255.vsd
Phasor measurement unit RES670 2.2 ANSI
Technical manual
M13751-338 v3
M13751-231 v2