Fuji Electric frenic mini series, User Manual

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9-18
Thermal time constant (F12)
F12 sets the thermal time constant of the motor. The inverter interprets the time constant as
an operation period of the electronic thermal facility. During the specified operation period,
the inverter will activate the electronic thermal facility if 150% current of the operation
level specified by F11 flows continuously.
The time constant of FUJI Electric's general-purpose motors and other induction motors is
set to 5 minutes by factory default.
- Data setting range: 0.5 to 75.0 (minutes, in 0.1-minute increment)
(Example) When 5 minutes has been
set to F12
As shown in the figure at right, if
150% current of the operation level
flows continuously for 5 minutes, the
motor overload alarm will be activated
(alarm code "
0L1 "). If 120% current
flows, the alarm will be activated after
approx. 13 minutes.
The thermal time constant includes the
time interval from the time when actual
current flowing into the motor exceeds
the allowable continuous current
(100% of the rated current) to the time
when the current reaches 150% of the
rated current. Therefore, the actual
time when the alarm is issued will be
earlier than the time specified by F12.
Typical operational characteristics of electronic
thermal facility
When an inverter drives the motor with a very frequent running/stopping
operation, the loaded current to the motor may fluctuate largely and enters the
short-time rated current range (100% or more) of the motor repeatedly. This may
cause an abnormal operation of the electronic thermal facility (e.g., for an
externally-powered forced ventilation fan).
To prevent such a problem, calculate the "equivalent RMS current" and keep the
loaded current within the motor rated current. Refer to Chapter 7, Section 7.1.3.4
"Calculating the RMS rating of the motor."
F14 Restart Mode after Instantaneous Power Failure
Set F14 to: The inverter will:
0 Trip immediately
1 Trip after recovery of power
4
Restart at the frequency at
which the power failure
occurred
Selects the action of the inverter to be
followed when an instantaneous power
failure occurs.
5
Restart at the starting
frequency
If the inverter detects that the DC link circuit voltage drops less than the specified
undervoltage limit, it interprets the state as an occurrence of an instantaneous power failure.
However, if the inverter runs with a light load and the period of the power failure is short,
then it does not detect the power failure and continues to run.