Ch.589
—————— Wiring procedure ——————
5.10. AVy POWER DIP RIDE THROUGH DATA AND RESTART SETUP
The AVy has a 3-phase full-wave rectifier feeding the DC link.
If the DC link reaches the Undervoltage threshold for its voltage input (see tables 5.10.1, 5.10.2 and 5.10.3),
the AVy will disable the Drive, and generate an undervoltage alarm.
The undervoltage alarm can latch & trip the drive immediately, or be programmed to reset itself and restart.
The undervoltage alarm settings define how many restarts are permitted. There is a ‘restart time’ parameter
that sets how long the undervoltage condition can exist before the AVy gives up on the reset.
The DC link feeds the AVy power supply. If the DC link goes below 250 VDC the electronics reset as if just
powered up. The capacity of the DC link between the undervoltage shutdown of the Drivesection, the 250
VDC power supply threshold, and the power draw of the AVy electronics & cooling fan determine how long
the drive stays up under power dips or power loss.
The DC link can have extra capacitance added externally to the DC link to add time to keep the DC link
above 250 VDC as long as possible. The following tables calculate how long the Drive can keep the power
above 250 VDC for control power if the maximum amount of capacitance is added externally. Remember,
adding capacitance holds in the power supply longer, but also takes longer to recharge.
The survival of an input power dip without shutting down the Drive section depends on the relative load
(energy) that the DC bus has to output, and the magnitude and duration of the power dip. A power dip needs
to be below the DC undervoltage threshold before the drive would even see any trip condition from it.
Without external capacitors, as an estimate, a power dip of 1 cycle (16.6ms @ 60Hz) when the motor is at
full load will cause an undervoltage trip.
The undervoltage trip time can be calculated by means of the following formula:
fA027
t
(U - U )(C+C )
22
Buff Stdextdc
2P
am
=
10
6
where:
t: undervoltage trip time [ms]
U
dc: DC link voltage [V]
U
buff: trip threshold voltage [V]
C
Std
: DC link capacitance [mF]
C
ext: external capacitance [mF]
P
am: motor power consumption [W]
P
am depends on the motor load conditions:
- at full load, it can be calculated as follows:
fA028
P
am
P
m
h
m
=
where:
P
m: motor rated power
η
m: motor rated efficiency
- at no load, it depends on the iron losses, on mechanical losses, and stator joule losses. The sum of
these terms is about 50% of the full load losses.
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