GE Industrial Solutions AF-650 GP Drive Panel - Manual (Page 35)

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Because instantaneous trip circuit breakers are so fast acting, the NEC actually
allows trip level settings up to 1300% of motor FLA if it can be shown to be
required by engineering evaluation. When a motor is started across the AC line
it can draw a very large peak current for the first half-cycle which can cause
nuisance tripping in instantaneous trip breakers set at 700%. GE Motors &
Industrial Systems has conducted analyses which show that certain models can
require this 1300% trip level to avoid nuisance tripping on across-the-line starts.
Generally the trip level will need to be higher for premium efficiency motors than
for standard efficiency ones.
In panels not requiring bypass the AF-650 GP drive essentially “soft-starts” the
motor by increasing the output voltage and frequency. Therefore high motor
inrush currents will not occur and should not be an issue. However, the rating
plugs for the circuit breakers in the AF-650 GP panels have been chosen to
allow trip level settings up to 13 times the current ratings of the panel. If the trip
level is set at 13 times the panel rated current and the circuit breaker still trips it
is probably due line conditions affect how the DC capacitor bank charges upon
applying AC power. The drive inherently contains a charge limiting circuit but in
a very small number of circumstances, the inrush may cause the circuit breaker
to trip even at a setting of 13 time the panel rating. If this is the case, possible
corrective actions are:
1) Check the trip setting in the rating plug
2) Make sure there is not an actual short causing the trip.
3) Try closing the breaker several times. Actual inrush is dependant on line
conditions when the breaker is closed. Closing the breaker when line
conditions are acceptable should prevent tripping.
4) Since actual inrush is dependant on the line conditions, correct the line
condition is the causing excessive inrush.
5) Try another rating plug. Perhaps the tolerances on the one included with
your breaker are unfavorable.
6) Add an AC Line Reactor to the input of the drive, which increases input
impedance and decreases the input current.
DEH40658 – Page 9 AN 11-2021 Rev 06, 12/16/2011