5-30
During a momentary power failure, the motor slows down. After power is restored, the inverter
restarts at the frequency just before the momentary power failure. Then, the current limiting
function works and the output frequency of the inverter automatically decreases. When the
output frequency matches the motor speed, the motor accelerates up to the original output
frequency. See the figure below. In this case, the instantaneous overcurrent limiting must be
enabled (H12 = 1).
Restart mode after momentary power failure (Allowable momentary power failure time)
(H16)
H16 specifies the maximum allowable duration (0.0 to 30.0 seconds) from an occurrence of a
momentary power failure (undervoltage) until the inverter is to be restarted. Specify the
coast-to-stop time during which the machine system and facility can be tolerated.
If the power is restored within the specified duration, the inverter restarts in the restart mode
specified by F14. If the power is restored after the specified duration, the inverter recognizes
that the power has been shut down so that it does not restart but starts (normal starting).
If H16 (Allowable momentary power failure time) is set to "999," restart will take place until the
DC link bus voltage drops down to the allowable voltage for restart after a momentary power
failure (50 V for 230 V class series and 100 V for 460 V class series). If the DC link bus voltage
drops below the allowable voltage, the inverter recognizes that the power has been shut down
so that it does not restart but starts (normal starting).
The time required from when the DC link bus voltage drops from the threshold o
options, and other factors.
Auto-restart after momentary power failure (Restart time) (H13)
H13 specifies the time period from momentary power failure occurrence until the inverter
reacts for restarting process.
If the inverter starts the motor while motor’s residual voltage is still in a high level, a large
inrush current may flow or an overvoltage alarm may occur due to an occurrence of temporary
regeneration. For safety, therefore, it is advisable to set H13 to a certain level so that restart
will take place only after the residual voltage has dropped to a low level. Note that even when
power is restored, restart will not take place until the restart time (H13) has elapsed.
Factory default
By factory default, H13 is set at one of the values shown below according to the inverter
capacity. Basically, you do not need to change H13 data. However, if the long restart time
causes the flow rate of the pump to overly decrease or causes any other problem, you might
as well reduce the setting to about a half of the default value. In such a case, make sure that
no alarm occurs.
Inverter capacity (HP) Factory default of H13 (Restart time in seconds)
1/8 to 10 0.5
15 to 20 1.0
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