4-49
4-2 Function Mode
4
Functions
Overload Limit/Overload Warning
This function helps prevent an overcurrent trip due to rapid load fluctuation in acceleration or
constant speed operation.
Overload Limit
•The Inverter monitors the motor current during acceleration or constant speed operation in order
to lower output frequency automatically according to the overload limit parameter once the motor
current reaches the overload limit.
•This function prevents an overcurrent trip caused by excessive moment of inertia during
acceleration, or caused by rapid load fluctuations during constant speed operation.
•You can set two types of overload limit functions in b021/b022/b023 and b024/b025/b026.
•To switch between b021/b022/b023 and b024/b025/b026, allocate 39 (OLR) to a multi-function
input and then turn it on/off.
•The overload limit level sets a current value for this function to work.
•The overload limit parameter sets a time of deceleration from the maximum frequency to 0 Hz.
•When this function operates, the acceleration time becomes longer than the set time.
•If "sensorless vector control", "0-Hz sensorless vector control", or "sensor vector control" is selected
as the control method (V/f characteristics) (refer to "Control Method (V/f Characteristics)" (page 4-
21)), and "03" is selected for b021/b024, the frequency increases when a current exceeding the
overload limit level flows during regenerative operation.
•If overload limit parameter b023/b026 is set too short, an overvoltage trip may occur because of
regenerative energy from the motor caused by automatic deceleration of this function even during
acceleration.
•Make the following adjustments if this function operates before the frequency reaches the target
value during acceleration.
Increase the acceleration time. (Refer to "Acceleration/Deceleration Time" (page 4-8).)
Increase the torque boost. (Refer to "Torque Boost" (page 4-19).)
Parameter No. Function name Data Default setting Unit
b021 Overload limit selection 00: OFF (Disabled)
01: ON-Acc/Cnst (Enabled in acceleration/
constant speed operation)
02: ON-Cnst (Enabled in constant speed
operation)
03: ON-A/C(R) (Enabled in acceleration/
constant speed operation (accelerates
during regeneration))
01
b024 Overload limit selection 2 01
b022 Overload limit level
0.20 × Rated current to 2.00 × Rated
current (0.4 to 55 kW)
0.20 × Rated current to 1.80 × Rated
current (75 to 132 kW)
1.50 × Rated
current
A
b025 Overload limit level 2
1.50 × Rated
current
A
b023 Overload limit parameter
0.10 to 30.00
1.00 s
b026 Overload limit parameter 2 1.00 s
C040
Overload warning signal
output mode
00: ACC/DEC/CST (Enabled during
acceleration/deceleration/constant
speed)
01: Const (Enabled only during constant
speed)
01
C041 Overload warning level 0.0: Does not operate.
0.1 × Rated current to 2.00 × Rated current
(0.4 to 55 kW)
0.1 × Rated current to 1.80 × Rated current
(75 to 132 kW)
(Outputs OL and OL2 signals when
reaching the overload warning level.)
Rated current
A
C111 Overload warning level 2 Rated current
Related functions C001 to C008, C021 to C025, C026
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