Electronic thermal O/L relay (Pr. 9)
Set the rated current [A] of the motor in Pr. 9. (When the power supply specification is 400V/
440V 60Hz, set the 1.1 times the rated motor current.)
Set "0" to Pr. 9 when you do not want to activate the electronic thermal relay function, e.g. when
using an external thermal relay with the motor. (Note that the output transistor protection of the
inverter functions (E.THT).)
When using the Mitsubishi constant-torque motor set "1, 13 to 16, 50, 53 or 54" to Pr. 71. (This
provides a 100% continuous torque characteristic in the low-speed range.) After this set the rat-
ed current of the motor to Pr. 9.
The figure below shows the electronic thermal relay function operation characteristic. The re-
gion on the right of the characteristic curve is the operation region. The region on the left of the
characteristic curve is the non-operation region.
Fig. 6-36: Electronic thermal relay function operation characteristic
When a value 50% of the inverter rated output current (current value) is set to Pr. 9.
The % value denotes the percentage to the inverter rated output current. It is not the
percentage to the motor rated current.
When you set the electronic thermal relay function dedicated to the Mitsubishi constant-
torque motor, this characteristic curve applies to operation at 6Hz or higher.
Pr. 9 = 50 % setting of
the inverter rating %
Inverter output power (%)
(% to the rated input current)
Selection and protection of a motor
Pr. 9 = 100 % setting of
the inverter rating
– Range on the right of characteristic curve
Non operation range
– Range on the left of characteristic curve
Characteristic when electronic thermal
relay function for motor protection is
turned off (When Pr. 9 setting is 0(A)).
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