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Chapter 4
4.2.29 Electronic thermal protection
The electronic thermal protection function allows you to protect the
motor against overheating. Make settings of this function based on
the rated current of the motor. The inverter will trip for overheat
protection according to the settings.
This function provides optimum overheat protection that is also
designed with the lowering of the motor's cooling performance at
low speeds in mind.
You can configure this function so that the inverter outputs a
warning signal before it trips for electronic thermal protection.
(1) Electronic thermal level
Item
Electronic thermal setting (calculated
within the inverter from current output)
(Example) Setting on the SJ700-150LFF(0.4-55kW)
CT mode rated current: 64 A
Range of setting: 12.8 A (20%) to 64.0 A (100%)
When 64 A is set as the electronic thermal setting (b012),
the time-limit characteristic is as shown on the right.
Trip time (s)
60
3.0
0
69.8
96
(109%)
(150%)
(2) Electronic thermal characteristic
The frequency characteristic set as the electronic thermal characteristic is integrated with the value of "b012", "b212",
or "b312".
The cooling-fan performance of a general-purpose motor lowers when the motor speed is low. So load (current) is
decreased. The reduced-torque characteristic is designed to match the heat generation by Hitachi's general-purpose
motors.
Item
Electronic thermal
characteristic
(a) Reduced-torque characteristic
The time-limit characteristic determined by the value of "b012", "b212", or "b312" is integrated with each frequency
multiplied by reduction scales.
Reduction
scale
X1.0
X0.8
X0.6
0
5
16
0
6
20
Base frequency
Function code
b012/b212/b312
Motor current (A)
(Ratio to the rated
128
current of inverter)
(200%)
Function code
b013/b213/b313
Example) Setting on the SJ700D-150LFF3 (CT mode rated current: 64 A)
Inverter output
50
frequency (Hz)
60
Explanation of Functions
b012/b212/b312: Electronic thermal setting (calculated
within the inverter from current output), 1st/2nd/3rd
motors
b013/b213/b313: Electronic thermal characteristic,
1st/2nd/3rd motors
b015/b017/b019: Free setting, electronic thermal
frequency (1) (2) (3)
b016/b018/b020: Free setting, electronic thermal
current (1) (2) (3)
C021 to C025: Terminal [11] to [15] functions
C026: Alarm relay terminal function
C061: Electronic thermal warning level setting
Range of data
0.2 to 1.0 x rated current
(Example) Setting on the SJ700-750LFF3(75-150kW)
CT mode rated current: 149 A
Range of setting: 29.8 A (20%) to 149 A (100%)
When 149 A is set as the electronic thermal setting (b012),
the time-limit characteristic is as shown on the right.
Trip time (s)
60
0.50
.5
0
158
223.5
(106%)
(150%)
Data
00
Reduced-torque characteristic
01
Constant-torque characteristic
02
Free setting of electronic thermal characteristic
When "b012" is 64 A, the base frequency is 60 Hz,
and output frequency is 20 Hz:
Trip time (s)
60
3.0
0
55.8
(87.2%)
4-37
Related code
Description
See the Example below.
Motor current (A)
(Ratio to the rated
268
current of inverter)
(180%)
Description
Motor current (A)
(Ratio to the rated
76.8
102.4
current of inverter)
(120%)
(160%)
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