Datasheet
7.10. Inrush currents
Inrush currents can be captured by the Analyzer. Inrush currents are surge currents that occur when a
large, or low-impedance load comes on line. Normally the current will stabilize after some time when the
load has reached normal working condition. For example the start-up current in induction motors can be
ten times the normal working current. Inrush is a ‘single shot’ mode that records current and voltage
Trends after a current event has occurred. An Inrush occurs when the current waveform exceeds
adjustable limits. The Trends builds up from the right of the screen. Pretrigger information allows you to
see what occurred in advance of the inrush.
Trend display
Use the arrow keys in the Start menu to adjust the trigger limits: expected inrush time, nominal current,
threshold and hysteresis. The maximum current determines the vertical height of the current display
windows. Threshold is the current level that triggers the trend capture. The inrush time is the time
between trigger and the time that the current falls to the value indicated by Hysteresis and is indicated on
the trend display between two vertical markers. The screen header displays the rms of all phases during
the inrush time. If the Cursor is on, the rms measuring values at the Cursor are displayed.
Available function keys:
F1
Switch parameters to be displayed.
F3
Access to Cursor.
F4
Selection of Zoom or Cursor.
F5
Switch between RUN and HOLD.
Tips and Hints
Check the inrush currents and their duration, use the Cursor for readout of momentary values. Check if
fuses, circuit breakers, and conductors in the power distribution system can withstand the inrush current
during this period. Check also if phase voltage stay stable enough.
High peak currents can cause circuit breakers to trip unexpectedly. Measuring Inrush current can help in
setting trip levels. Since the Analyzer simultaneously captures Inrush current and voltage Trends, you
can use this measurement to check voltage stability as large loads come on line.
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