Fuji Electric FRENIC-HVAC User Manual page 370

Restart mode after momentary power failure (Basic operation: Auto search disabled)
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The inverter recognizes a momentary power failure upon detecting the condition that DC link
bus voltage goes below the undervoltage 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
recovery of power or held with an off-delay timer or 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), the run
command is retained inside the inverter so that the restart will begin as soon as the inverter
enters the ready-to-run state.
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