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If you enable the "Restart mode after momentary power failure" (Function code F14 = 3, 4, or 5), the inverter
automatically restarts the motor running when the power is recovered. Design the machinery or equipment so that
human safety is ensured after restarting.
Otherwise an accident could occur.
Restart mode after momentary power failure (Basic operation with auto search disabled)
The inverter recognizes a momentary power failure upon detecting the condition that DC link bus voltage goes below
the undervoltage detection level, while the inverter is running. If the load of the motor is light and the duration of the
momentary power failure is extremely short, the voltage drop may not be great enough for a momentary power failure
to be recognized, and the motor may continue to run uninterrupted.
Upon recognizing a momentary power failure, the inverter enters the restart mode (after a recovery from momentary
power failure) and prepares for restart. When power is restored, the inverter goes through an initial charging stage and
enters the ready-to-run state. When a momentary power failure occurs, the power supply voltage for external circuits
such as relay sequence circuits may also drop so as to turn the run command OFF. In consideration of such a situation,
the inverter waits 2 seconds for a run command input after the inverter enters a ready-to-run state. If a run command is
received within 2 seconds, the inverter begins the restart processing in accordance with the F14 data (Mode selection).
If no run command has been received within 2-second wait period, the inverter cancels the restart mode (after a
recovery from momentary power failure) and needs to be started again from the ordinary starting frequency. Therefore,
ensure that a run command is entered within 2 seconds after a recovery of power, or install a mechanical latch relay.
When run commands are entered via the keypad, the above operation is also necessary for the mode (F02 = 0) in which
the rotational direction is determined by the terminal command, FWD or REV. In the modes where the rotational
direction is fixed (F02 = 2 or 3), it is retained inside the inverter so that the restart will begin as soon as the inverter
enters the ready-to-run state.
• When the power is restored, the inverter will wait 2 seconds for input of a run command. However, if the
allowable momentary power failure time (H16) elapses after the power failure was recognized, even within
the 2 seconds, the restart time for a run command is canceled. The inverter will start operation in the normal
starting sequence.
• If the "Coast to a stop" terminal command BX is entered during the power failure, the inverter gets out o
the restart mode and enters the normal running mode. If a run command is entered with power supply
applied, the inverter will start from the normal starting frequency.
• The inverter recognizes a momentary power failure by detecting an undervoltage condition whereby the
voltage of the DC link bus goes below the lower limit. In a configuration where a magnetic contactor is
installed on the output side of the inverter, the inverter may fail to recognize a momentary power failure
ecause the momentary power failure shuts down the operating power of the magnetic contactor, causing the
contactor circuit to open. When the contactor circuit is open, the inverter is cut off from the motor and load,
and the voltage drop in the DC link bus is not great enough to be recognized as a power failure. In such an
event, restart after a recovery from momentary power failure does not work properly as designed. To solve
this, connect the interlock command IL line to the auxiliary contact of the magnetic contactor, so that
momentary power failure can sure be detected. For details, refer to the descriptions of E01 through E07.
Function code E01 to E07, data = 22
IL Description
OFF No momentary power failure has occurred.
ON A momentary power failure has occurred. (Restart after a momentary power failure enabled)
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).
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