Technical description
3 Supporting functions
3.3 Cold load pick-up and inrush
current detection
VM59.EN001
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NOTE! Inrush detection is based on FFT - calculation which requires full cycle of
data for analyzing the harmonic content. Therefore when using inrush
blocking function the cold load pick up starting conditions are used for
activating the inrush blocking when the current rise is noticed. If in the
signal is found second harmonic component after 1.st cycle the blocking
is continued, otherwise 2.nd harmonic based blocking signal is released.
Inrush blocking is recommended to be used in time delayed overcurrent
stages while non-blocked instant overcurrent stage is set to 20 % higher
than expected inrush current. By this scheme fast reaction time in short
circuit faults during the energization can be achieved while time
delayed stages are blocked by inrush function.
No activation because the current has not been under the
set I
dle
current.
Current dropped under the I
dle
current level but now it
stays between the I
dle
current and the pick-up current for
over 80ms.
No activation because the phase two lasted longer than
80ms.
Now we have a cold load activation which lasts as long as
the operation time was set or as long as the current stays
above the pick-up setting.
Figure 3-1 Functionality of cold load / inrush current feature.
