MOTOR MONITORING EXAMPLE
An IMH is employed to monitor AC current of a single-phase 10 horsepower
115V AC motor. Also, the meter will be used to total current for preventative
maintenance purposes. Knowing the maximum full load current is 100 amps AC,
a current transformer
(CT)
of 100:5 ratio is selected.
The IMH is scaled to indicate 0.00 at an input of 0.000 amps AC and 100.00 at
5.000 amps AC. Alarm #1 is programmed to activate if the motor current exceeds
84.00 amps AC, which is a 40% increase in current draw from the nominal of 60
amps AC. Alarm #1 is disabled by external control pin during motor start-up due
to current surges. Peak and valley
(max/min)
reading for each day are to be
recorded.
The amount of current drawn by an electric motor gives a good indication of
the overall condition of the motor. Using the totalizer to total current and
knowing the nominal current draw is 60 amps AC, preventative maintenance can
be performed on total amp-hours. Assigned to the totalizer, Alarm #2 is
programmed to latch when the predetermined amount of total amp-hours is
reached
(ex. 4320 amp-hours)
. Totalization is disabled if the input is below 30
amps AC.
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