SJ700-2 Instruction Manual NT204DX - Hitachi America, Ltd.

Chapter 4 Explanation of Functions
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 Data or range of data Description
00 Disabling the overload restriction
01
Enabling the overload restriction during
acceleration and constant-speed operation
Overload
Enabling the overload restriction during
restriction
b021/b024
02
constant-speed operation
operation mode
Enabling the overload restriction during
03
acceleration and constant-speed operation
(increasing the frequency during regenerative
operation)
Overload
restriction setting
Deceleration rate
at overload
restriction
b022/b025
b023/b026
"Rated current x 0.5" to
"rated current
x 2.0< x 1.8>" (A)
0.1 to 30.0 (s)
Current at which to trigger the overload restriction
Deceleration time to be applied when the overload
restriction operates
Terminal function C001 to C008 39 Terminal to switch the overload restriction setting
(NOTE):applied for 75 to 150kW
Overload restriction level
b022/b025
Output current
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)
Deceleration according to the
deceleration rate at overload
restriction
Maximum frequency
A004/A204/A304
Target frequency
F001
Inverter output
frequency
b023/b026
4 - 40