5-33
Restart mode after momentary power failure (Basic operation)
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.
If the "Coast to a stop" terminal command
BX
is entered during the power failure,
the inverter gets out of 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 (F23).
