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Explanation of functions (parameters)
2.3.6
Selection and protection of a motor (Pr. 9 , Pr. 71 )
• * 0.75K or less is set to 85% of the rated inverter current.
<Setting>
•Refer to the following list and set Pr. 71 according to the motor used.
•Set the rated current [A] of the motor in Pr. 9. (Normally set the rated current at 50Hz.)
•Setting "0" in Pr. 9 disables electronic thermal relay function (motor protective
function). (The protective function of the inverter is activated.)
Set the motor used and protect the motor from overheat.
This feature provides the optimum protective characteristics, including reduced
motor cooling capability, at low speed.
POINT
•When using the Mitsubishi constant-torque motor
Set "1" in Pr. 71 for V/F control or automatic torque boost control.
The electronic thermal relay function is set to the thermal characteristic of the
constant-torque motor.
•When you selected the Mitsubishi constant-torque motor, the values of the following
parameters are automatically changed. (only when the setting values of those
parameters are at factory setting)
Pr. 0 "torque boost", Pr. 12 "DC injection brake voltage"
Para
meter
Name
Factory
Setting
Setting
Range
Remarks
9
Electronic thermal
O/L relay
Rated
inverter
current(*)
0 to 100A
71 Applied motor 0 0, 1 Setting is enabled when Pr. 30 = "1"
Pr. 71 Setting Thermal Characteristic of the Electronic Thermal Relay Function
0 Thermal characteristics of a standard motor
1
Thermal characteristics of a Mitsubishi constant-torque motor
(This provides a 100% continuous torque characteristic in the low-speed range.)
CAUTION
•When two or more motors are connected to the inverter, they cannot be
protected by the electronic thermal relay function. Install an external thermal
relay to each motor.
•When a difference between the inverter and motor capacities is large and the
setting becomes less than half amount of the rated inverter current, the
protective characteristics of the electronic thermal relay function will be
deteriorated. In this case, use an external thermal relay.
•A special motor cannot be protected by the electronic thermal relay function.
Use an external thermal relay.
CAUTION
Set this parameter correctly according to the motor used.
Incorrect setting may cause the motor to overheat and burn.
♦Related parameters♦
•
Automatic torque boost
⇒
Pr. 98 "automatic torque boost selection (Motor capacity)" (refer to page 133)
• Pr. 0 "torque boost" ⇒ refer to page 73
• Pr. 12 "DC injection brake voltage" ⇒ refer to page 81