Hitachi SJ7002 Series Instruction Manual page 214

4–52
Using Intelligent Output Terminals
Thermal Warning
Signal
10
Opt. Code
[THM]
Symbol
[11 to [15],
Valid for
Outputs [ALx]
Required
C061
Settings
Default Requires
config.
terminals
The purpose of the electronic thermal setting is to protect the motor from overloading,
overheating and being damaged. The setting is based on the rated motor current. The inverter
calculates the thermal rise (heating) of the motor using the current output to the motor squared,
integrated over the time spent at those levels. This feature allows the motor to draw excessive
current for relatively short periods of time, allowing time for cooling.
The Thermal Warning output [THM] turns ON to provide a warning before the inverter trips for
electronic thermal protection. You can set a unique thermal protection level for each of the
three motor profiles, as shown in the table below.
Function
Function/Description
Code
B012 / B212 Electronic thermal setting (calculated
/ B312 within the inverter from current output)
B013 / B213 Electronic thermal characteristic (use
/B313 the setting that matches your load)
• The electronic thermal overload function uses the output current and time to calculate
thermal heating of the motor. Use parameter C061 to set the threshold from 0 to 100% of trip
level for turning ON the intelligent output [THM] at that level.
• The thermistor input of the inverter is a separate function from the electronic thermal
function. It has its own threshold to cause a trip alarm at a particular thermistor resistance.
For example, suppose you have inverter model
SJ700-110LFE2. 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 torque control the inverter
uses.
CAUTION: When the motor runs at lower
speeds, the cooling effect of the motor's internal
fan decreases.
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
Data or Range
Range is 0.2 * rated current to
1.2 * rated current
00
01
02
Trip
time (s)
60
0.5
0
Trip current at 60 Hz
Trip
time (s)
60
0.5
0
Hz
60 42.7 55.2
92.8% 120%
Reduced trip current at 20 Hz
Reduced torque
Constant torque
Free-setting
A
53.4 69 92
116% 150% 200%
A
73.6
160%