Using Trip Prevention Functions; Restriction To Avoid Overload - Hitachi WJ Series User Manual

Chapter 9

9.9 Using Trip Prevention Functions

9.9.1

Restriction to Avoid Overload

 How to automatically reduce the output frequency to avoid overload when the load becomes
Q
too large?
 How to prevent stalling?
 How to accelerate the motor while reducing the current flowing to the motor?
 How to avoid overcurrent errors caused by sudden load fluctuations?
 The overload restriction function monitors the motor current during acceleration or operation at
A
a constant speed and automatically reduces the output frequency according to the overload
restriction action time when the overload restriction active level is reached. Depending on the
overload restriction mode selection setting, the operation is as follows.
 Two independent overload restriction action levels can be set. "Overload restriction selection
[OLR](39)" can be assigned to an input terminal, and the overload restriction 1/2 can be
switched by turning that terminal on or off.
Overload restriction selection
Enabled during accel. and
constant speed
([b021]=01)
Constant speed only
([b021]=02)
Enabled during accel. and
constant speed
(Accel. during regeneration)
([b021]=03)
 When this function is activated during acceleration, the acceleration time to reach the
!
frequency command will be longer than the setting.
 When the overload restriction action time is set too short, the automatic deceleration of this
function may result in an overvoltage trip due to regenerative energy from the motor.
 If the motor speed does not reach the target frequency due to the automatic deceleration
caused by this function during acceleration, the following adjustments may improve the
situation.
- Increase the acceleration time
- Adjust the torque boost
- Increase the overload restriction active level
Operation description
Monitors output current during acceleration or operation at a constant
speed. The current is suppressed by decelerating the motor against any
excessive load during acceleration or for sudden load fluctuations at a
constant speed.
Monitors output current only at a constant speed. The current is
suppressed by decelerating the motor only for sudden load fluctuations
at a constant speed.
Monitors output current during acceleration or operation at a constant
speed. In addition to the operation of "Enabled during accel. and
constant speed (01)", when a regenerative load is applied to the motor
at a constant speed, this function accelerates the motor to prevent
overload.
9-9-1
Inverter Functions