Instruction manual

4-67
F43, F44
Current Limiter (Mode selection, Level) H12 (Instantaneous Overcurrent Limiting (Mode selection))
When the output current of the inverter exceeds the level specified by the current limiter (F44), the inverter
automatically manages its output frequency to prevent a stall and limits the output current. The default setting of
the current limiter is 130% and 160% for VT and CT mode inverters, respectively. (Once the VT or CT mode is
selected by F80, the current limit for each mode is automatically specified.)
Note that for VT and CT mode inverters of 7.5 HP or below, the current limiter is initialized to 160% with F80.
If overload current, 160% (or 130%) or more of the current limit level, flows instantaneously so that an output
frequency decrease problem arises due to the current limiter, consider increasing the current limit level.
The current limiter mode should be also selected with F43. If F43 = 1, the current limiter is enabled only during
constant speed operation. If F43 = 2, it is enabled during both of acceleration and constant speed operation.
Choose F43 = 1 if you need to run the inverter at full capability during acceleration and to limit the output current
during constant speed operation.
 Mode selection (F43)
F43 selects the motor running state in which the current limiter becomes active.
Data for F43
Running states that enable the current limiter
During acceleration
During constant speed
During deceleration
0
Disable
Disable
Disable
1
Disable
Enable
Disable
2
Enable
Enable
Disable
 Level (F44) Data setting range: 20 to 200 (%) (in ratio to the inverter rating)
F44 specifies the operation level at which the output current limiter becomes activated, in ratio to the inverter
rating.
The inverter's rated current differs depending upon the VT or CT mode selected.
 Instantaneous Overcurrent Limiting (Mode selection) (H12)
H12 specifies whether the inverter invokes the current limit processing or enters the overcurrent trip when its
output current exceeds the instantaneous overcurrent limiting level. Under the current limit processing, the inverter
immediately turns OFF its output gates to suppress the further current increase and continues to control the output
frequency.
Data for H12
Function
0
Disable
An overcurrent trip occurs at the instantaneous overcurrent limiting level.
1
Enable
If any equipment or machine malfunctions when the motor torque temporarily drops during current limiting
processing, it is necessary to cause an overcurrent trip (H12 = 0) and actuate a mechanical brake at the same
time.
• Since the current limit operation with F43 and F44 is performed by software, it may cause a delay in
control. For quick response current limiting, also enable the instantaneous overcurrent limiting with
H12.
• If an excessive load is applied when the current limiter operation level is set extremely low, the inverter
will rapidly lower its output frequency. This may cause an overvoltage trip or dangerous turnover of the
motor rotation due to undershooting. Depending on the load, extremely short acceleration time may
activate the current limiting to suppress the increase of the inverter output frequency, causing the
system oscillation (hunting) or activating the inverter overvoltage trip (alarm 0u ). When specifying the
acceleration time, therefore, take into account machinery characteristics and moment of inertia of the
load.
• The torque limiter and current limiter are very similar functions. If both are activated concurrently, they
may conflict and cause hunting in the system. Avoid concurrent activation of these limiters.
• The vector control itself contains the current control system, so it disables the current limiter specified
by F43 and F44, as well as automatically disabling the instantaneous overcurrent limiting (specified by
H12). Accordingly, the inverter causes an overcurrent trip when its output current exceeds the
instantaneous overcurrent limiting level.