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Chapter 4
4.2.30 Overload restriction/overload notice
(1) Overload restriction function
- The overload restriction function allows you to make the inverter
monitor the motor current during acceleration or constant-speed
operation and automatically reduce the output frequency
according to the deceleration rate at overload restriction when
the motor current reaches the overload restriction level.
- This function prevents the moment of inertia from excessively
increasing during motor acceleration and prevents the inverter
from tripping because of overcurrent, even when the load
changes suddenly during the constant-speed operation of the
motor.
- You can specify two types of overload restriction operation by setting functional items "b021", "b022", and "b023"
and functional items "b024", "b025", and "b026" separately.
- To switch the overload restriction operation between the two settings (setting with b021, b022, and b023 and setting
with b024, b025, and b026), assign function "39" (OLR) to an intelligent input terminal. Turn the - OLR signal on and
off to switch between the two settings.
- The overload restriction level specifies the current at which to trigger the overload restriction function.
- The deceleration rate at overload restriction specifies the length of time to decelerate the motor from the maximum
frequency to 0 Hz.
- When this function operates during deceleration, the acceleration time is prolonged over the set time.
When you have selected the sensorless vector control, 0Hz-range sensorless vector control, or vector control with
sensor as the V/F characteristic curve selection (see Section 4.2.18) and "03" for "b021" or "b024", the inverter
output frequency increases if the current over the overload restriction level flows during the regenerative operation.
If the value set as the deceleration rate at overload restriction (b023/b026) is too small, the inverter automatically
decelerates the motor even during acceleration because of the overload restriction, and may trip because of the
overvoltage caused by the energy regenerated by the motor.
If this function operates during acceleration and the output frequency cannot reach the target frequency, try to make
the following adjustments:
-
Increase the acceleration time. (See Section 4.2.8.)
-
Increase the torque boost setting. (See Section 4.2.19.)
-
Increase the overload restriction setting (b022/b025).
Item
Function code
Overload
restriction
b021/b024
operation mode
Overload
b022/b025
restriction setting
Deceleration rate
at overload
b023/b026
restriction
Terminal function
C001 to C008
(NOTE)<>:applied for 75 to 150kW
Overload restriction level
b022/b025
Output current
Maximum frequency
A004/A204/A304
Inverter output
frequency
Data or range of data
00
01
02
03
CT mode
0.20 to 2.00 x rated current
<0.20 to 1.80 x rated current>
VT mode
0.20 to 1.50 x rated current
<0.20 to 1.50 x rated current>
0.1 to 30.0 (s)
39
b023/b026
4-39
Explanation of Functions
Related code
b021: Overload restriction operation mode
b022: Overload restriction setting
b023: Deceleration rate at overload restriction
b024: Overload restriction operation mode (2)
b025: Overload restriction setting (2)
b026: Deceleration rate at overload restriction (2)
C001 to C008: Terminal [1] to [8] functions
C021 to C025: Terminal [11] to [15] functions
C026: Alarm relay terminal function
C040: Overload signal output mode
C041: Overload level setting
C111: Overload setting (2)
Description
Disabling the overload restriction
Enabling the overload restriction during acceleration
and constant-speed operation
Enabling the overload restriction during constant-speed
operation
Enabling the overload restriction during acceleration
and constant-speed operation (increasing the frequency
during regenerative operation)
Current at which to trigger the overload restriction
Deceleration time to be applied when the overload
restriction operates
Terminal to switch the overload restriction setting
Deceleration according to the
deceleration rate at overload
restriction
Target frequency
F001
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