Hitachi SJ7002 Series Instruction Manual page 116

Sj7002 series
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3–32
"B" Group: Fine-Tuning Functions
Electronic
Thermal Overload
Alarm Setting
The thermal overload detection protects
the inverter and motor from overheating
due to an excessive load. It uses a current/
inverse time curve to determine the trip
point. The thermal overload alarm [THM]
is the resulting intelligent output.
First, use B013 to select the torque
characteristic that matches your load.
This allows the inverter to utilize the best
thermal overload characteristic for your
application.
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). There-
fore, 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 E05) 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)
Example 1, setting for SJ700-110LFE2 (0.4 to 55kW) - The rated motor current is 64A. The
setting range is (0.2 * 64) to rated current, or 12.8A to 64.0A. For a setting of B012 = 64A
(current at 100% rated current), the curve is shown below.
Example 2, setting for SJ700-750LFE2 (75 to 150 kW) - The rated motor current is 149A. The
setting range is (0.2 * 149) to rated current, or 29.8A to 149A. For a setting of B012 = 149A
(current at 100% rated current), the curve is shown below.
SJ700-110LFE2
Trip
time (s)
60
3.0
0
53.4
109% 150%
Trip current at 60 Hz
Trip current
reduction
factor
Constant torque
x 1.0
x 0.8
x 0.6
0
5
Trip
time (s)
60
5.0
0
A
69
92
200%
B013=01
Reduced
B013=00
torque
20
60
120
Output frequency
Data or Range
Range is 0.2 x rated current to
1.0 x rated current
SJ700-750LFE2
158
223.5
268
106% 150%
180%
Trip current at 60 Hz
Hz
A

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