Motor Overload Protection - Mitsubishi Electric FR-A800 Installation Manuallines

APPENDIX
A.2.5 Motor overload protection
When using the electronic thermal relay function as motor overload protection, set the rated motor current to Pr. 9 "Elec-
tronic thermal O/L relay".
Electronic thermal relay function operation characteristic
Pr. 9 = 50 % setting of
*1, *2
inverter rating
70
30Hz
*3
or more
20Hz
60
10Hz
6Hz
0.5Hz
50
240
180
120
60
105%
52.5%
50
Inverter output current [%]
(% to the rated inverter current)
CAUTION
The internal accumulated heat value of the electronic thermal relay function is reset by inverter power reset and reset
signal input. Avoid unnecessary reset and power-OFF.
When using multiple motors with one inverter, or using a multi-pole motor or a specialized motor, provide an external
thermal relay (OCR) between the inverter and motor. And for the setting of the thermal relay, add the line-to line leakage
current to the current value on the motor rating plate (details in the Instruction Manual).
For low-speed operation where the cooling capability of the motor reduces, it is recommended to use a thermal
protector or thermistor-incorporated motor.
When the difference between the inverter and motor capacities is large and the setting is small, 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.
Set Pr. 9 = "0" for vector-control-dedicated motors (SF-V5RU) because they are equipped with thermal protectors.
Electronic thermal relay may not operate when 5% or less of rated inverter current is set to electronic thermal relay
setting.
Motor over temperature sensing is not provided by the drive.
60
Pr. 9 = 100 % setting of
*2
inverter rating
*3
30Hz
or more
Operation region
20Hz
Region on the right of
10Hz
characteristic curve
Non-operation region
6Hz
Region on the left of
characteristic curve
0.5Hz
Characteristic when electronic
thermal relay function for
motor protection is turned OFF
(Pr. 9 = 0 (A))
Region for
transistor
*4
protection
100
150 230
This function detects the overload (overheat) of the
motor, stops the operation of the inverter's output tran-
sistor, and stops the output. (The operation character-
istic is shown on the left.)
When using the Mitsubishi constant-torque motor set
one of "1", "13" to "16", "50", "53", "54" in Pr. 71. For
FR-A842 models set one of "1", "13" to "16" in Pr. 71.
This provides a 100 % continuous torque characteristic
in the low-speed range. Set the rated current of the
motor in Pr. 9.
*1
When 50% of the inverter rated output current (current
value) is set in Pr. 9.
*2
The % value denotes the percentage to the inverter rated
output current. It is not the percentage to the motor rated
current.
*3
When you set the electronic thermal relay function
dedicated to the Mitsubishi constant-torque motor, this
characteristic curve applies to operation at 6 Hz or higher.
*4
For FR-A842 models: Transistor protection is activated
depending on the temperature of the heatsink. The
protection may be activated even with less than 150%
depending on the operating conditions.