Using Intelligent Output Terminals
Oper
ations
a
nd Moni
tor
ing
4–52
Thermal Warning
Signal
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.
• 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.
Opt. Code
10
Symbol
[THM]
Valid for
Outputs
[11 to [15],
[ALx]
Required
Settings
C061
Default
terminals
Requires
config.
Function
Code
Function/Description
Data or Range
B012 / B212
/ B312
Electronic thermal setting (calculated
within the inverter from current output)
Range is 0.2 * rated current to
1.2 * rated current
B013 / B213
/B313
Electronic thermal characteristic (use
the setting that matches your load)
00
Reduced torque
01
Constant torque
02
Free-setting
Trip
time (s)
Trip current at 60 Hz
60
0.5
0
53.4
69
92
A
116% 150%
200%
Trip
time (s)
Reduced trip current at 20 Hz
Trip current
reduction
factor
x 1.0
x 0.8
x 0.6
0
5
20
60
Hz
A
60
0.5
0
73.6
42.7 55.2
92.8% 120%
160%
