22
3.
Reduce the load on the motor during acceleration. Total motor load during
this period is the sum of the accelerating torque plus load torque. Once
motor is up to speed the load can be reapplied.
Inverter-to-Bypass Delay
The AF 600 FP bypass panels come standard with manual bypass functionality
only. This requires an operator to manually transition power from the drive to
the AC line via the Drive/Off/Bypass selector switch in the event of a drive fault.
When transitioning power to the motor from “Drive” to “Bypass” the operator
must place the switch in the “Off” position for a minimal of 10 seconds. This
delay is to allow for the motor’s rotor flux to decay prior to applying direct AC
line power, which would be out of sync and phase with the flux, resulting in a
potentially damaging current and torque pulsation. Typically a delay of three
motor AC time constants will be adequate to ensure that the flux has decayed
to a low enough level to apply AC line power. An induction motor’s open circuit
AC time constant is dependent on a number of factors including horsepower
rating and number of poles. Generally speaking the time constant increases as
HP goes up and as the number of poles go down.
If your bypass panel was ordered with the optional automatic bypass
functionality, the time delay required when transitioning between drive and
bypass has been designed into the panels control logic. For panels rated 30Hp
and below at 208 VAC plus 75Hp and below at 460 VAC & 575 VAC a
C-2000™
electronic timer mounted on top of the bypass contactor (M3). This timer is
factory set for a 5-second delay and can be easily adjusted via a small flat
blade screwdriver. For panels greater than 30Hp at 208 VAC and greater than
75Hp at 460 VAC & 575 VAC a separately mounted time delay relay is provided
to insert the required delay. This timer is factory set for a 10-second delay and
can be easily adjusted via manually turning the dial on the face of the relay. If it
is desired to change the delay setting when transitioning from drive to bypass
mode then consult with the manufacturer of your motor and adjust the time
delay accordingly.
DEH40602
– Page 15
AN 11-2021 Rev 05, 12/15/2011
WARNING: The overload relay should not be turned to a higher setting
than allowed by the rules above to allow starting the motor across the
line without tripping. Doing so will compromise the overload protection
which could lead to component damage or fire which could threaten
personnel safety. Refer to NEC for further information.
CAUTION:
Failure to insert enough time delay between operation of the
motor from the inverter and operation across-the-line can result in a
devastating torque pulse which can damage your motor, driven load and/or
installation. The AF 600 FP drive does not have a line synchronizing function
to permit a smooth switchover to AC line power, therefore the time delay is
the only way to ensure a safe transition.
