Hitachi SJ Series User Manual page 308

Chapter 12
12.13 Using Trip Avoidance Function
12.13.1 Restraining to avoid overloading
Q
• I want to lower frequency to avoid overloading.
• I want to prevent stall.
• I want to accelerate while suppressing the motor
current.
• I want to prevent overcurrent tripping caused by
sudden fluctuation of load.
A
• Set [bA122] overload limit function to any value
other than 00, and the output frequency
automatically lowers according to overload limit
time once the output current reaches [bA123]
overload limit level.
• When [bA122] = 01, the output current is monitored
during acceleration or at constant speed. It limits
the excess inertial moment during acceleration and
overload state caused by sudden acceleration.
• When [bA122] = 02, the output current is monitored
only at constant speed. It prevents overloading
caused by sudden load fluctuation at constant
speed without decelerating during acceleration.
• When [bA122] = 03, the output current is monitored
during acceleration or at constant speed. In
addition to the operation with [bA122] = 01, it
accelerates to prevent overloading when
regenerative load is applied at constant speed.
Operation example
Overload Limit Level
[bA123]
Output Current
Max. Frequency
IM:[Hb105]
SM(PMM):[Hd105]
Inverter
Output
Frequency
!
• Setting the overload limit operation time to be too
short will cause this function to perform automatic
deceleration even during acceleration, which may
lead to overvoltage tripping caused by regenerative
energy from the motor.
• If this function is activated during acceleration and
the frequency does not reach the target frequency,
the situation can be improved with the adjustments
shown below.
- Make the acceleration time longer
- Adjust the torque boost
- Increase the overload limit level
• [bA124] overload limit time is the time to decelerate
from the maximum frequency to 0 Hz or to
accelerate from 0 Hz to the maximum frequency.
• If this function is activated while the inverter is
accelerating, the acceleration time will be longer
than the set time.
Deceleration set with
overload limit constant
[bA124]
12-13-1
Inverter Function
Command
Frequency