Hitachi SJ300 Series Instruction Manual page 99

The torque developed in a motor is directly proportional to the current in the windings, which is
also proportional to the heat generated (and temperature, over time). Therefore, you must set
the thermal overload threshold in terms of current (amperes) with parameter B012. The range is
50% to 120% of the rated current for each inverter model. If the current exceeds the level you
specify, the inverter will trip and log an event (error E5) in the history table. The inverter turns
the motor output OFF when tripped. Separate settings are available for the second and third
motors (if applicable), as shown in the table below.
Function
Function/Description
Code
B012 / B212 Electronic thermal setting (calculated
/ B312 within the inverter from current output)
For example, suppose you have inverter model
SJ300-110LFE. The rated motor current is 46A.
The setting range is (0.2 * 46) to (1.2 *46), or
9.2A to 55.2A. For a setting of B012 = 46A
(current at 100%), the figure to the right shows
the curve.
The electronic thermal characteristic adjusts the
way the inverter calculates thermal heating,
based on the type of load connected to the motor,
as set by parameter B013.
CAUTION: When the motor runs at lower
speeds, the cooling effect of the motor's internal
fan decreases.
The table below shows the torque profile settings. Use the one that matches your load.
Function Code
B013 / B213 / B313
Reduced Torque Characteristic – The example below shows the effect of the reduced torque
characteristic curve (for example motor and current rating). At 20Hz, the output current is
reduced by a factor of 0.8 for given trip times.
Trip current
reduction
factor
x 1.0
x 0.8
x 0.6
0
5 20
Trip
time (s)
60
0.5
0
Data Function/Description
00 Reduced torque
01 Constant torque
02 Free-setting
Trip
time (s)
60
0.5
0
Hz
60
SJ300 Inverter
Data or Range
Range is 0.2 * rated current to
1.2 * rated current
53.4 69 92
116% 150% 200%
Trip current at 60 Hz
42.7 55.2 73.6
92.8% 120% 160%
Reduced trip current at 20 Hz
3–31
A
A