Hitachi WJ200-001L, Instruction Manual

Page: 136 / 680

3

51
Current limitation Related Functions
Overload Restriction:

If the inverter’s
output current exceeds a preset current level
you specify during acceleration or constant
speed, the overload restriction feature
automatically reduces the output frequency
during powering drive (and can increase the
speed during regeneration) to restrict the
overload. This feature does not generate an
alarm or trip event. You can instruct the
inverter to apply overload restriction only
during constant speed, thus allowing higher
currents for acceleration. Or, you may use the
same threshold for both acceleration and
constant speed.
You can specify two types of overload restriction operation by setting functional items

,

,

, and

,

,

separately. To switch between these two is done
by assigning “

(OLR)” to an intelligent input terminal and make it ON/OFF.
When the inverter detects an overload, it must decelerate the motor to reduce the
current until it is less than the threshold. You can choose the rate of deceleration that
the inverter uses to lower the output current.
Over-current Trip Suppression:
 –
The
Over-current Trip Suppression function
monitors the motor current and actively
changes the output frequency profile to
maintain the motor current within the limits.
Although “LAD” refers to “linear acceleration /
deceleration”, the inverter only “STOPs” the
acceleration and deceleration ramp so that it
will not cause an over-current trip event.
The graph at right shows an inverter output
profile that starts acceleration to a constant
speed. At two different points during the
acceleration, motor current increases and
exceeds the fixed level of Over-current Trip
Suppression level.
When the Over-current Trip Suppression feature is enabled by

=

, the inverter
stops the acceleration ramp in each case until the motor current level is again less than
the threshold value, which is approximately 180% of the rated current of the inverter.
When using the Over-current Trip Suppression feature, please note the following:

When the feature is enabled (

=

), the actual acceleration may be longer
than the value set by parameters

/

in some cases.
 The Over-current Trip Suppression feature does not operate by maintaining a
constant motor current. So it is still possible to have an over-current trip event
during extreme acceleration.
Motor
current
Restriction area

0
t
Output
frequency
0
t

Regenerating
Powering

Motor
current
0
t
Output
frequency
0
t
Stops accel
Resumes accel

=

OC LAD STOP = Enabled
Set acc time (

)
Actual acc time
Approx. 150% of the inverter
rated current