Mitsubishi Electric 800 Series Installation Manualline page 77

A.2.6 Short circuit ratings
l 200V class
Suitable for use in a circuit capable of delivering not more than 100kA rms symmetrical amperes, 240V maximum.
l 400V class
Suitable for use in a circuit capable of delivering not more than 100kA rms symmetrical amperes, 480 Y / 277 V
maximum.
A.2.7 Motor overload protection
The following explains the details of the 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".
Pr. 9 = 50 % setting of
*1, *2
inverter rating
70
30Hz
*3
or more
20Hz
60
10Hz
6Hz
50 0.5Hz
240
180
120
60
105%
52.5%
50
Inverter output current [%]
(% to the inverter rated current)
l The internal accumulated heat value of the electronic thermal O/L relay is reset to the initial value by the inverter's power
reset or reset signal input. Avoid unnecessary reset and power-OFF.
l Install an external thermal relay (OCR) between the inverter and motors to operate several motors, a multi-pole motor or
a dedicated motor with one inverter.
When configuring an external thermal relay, note that the current indicated on the motor rating plate is affected by the
line-to-line leakage current. (Refer to the Instruction Manual (Function).) The cooling effect of the motor drops during
low-speed operation. Use a motor with built-in thermal protector. When the difference between the inverter and motor
capacities is large and the set value is small, the protective characteristics of the electronic thermal relay function will be
deteriorated. Use an external thermal relay in such cases.
l A dedicated motor cannot be protected by the electronic thermal relay. Use an external thermal relay.
l Motor over temperature sensing is not provided by the drive.
Pr. 9 = 100 % setting of
*1, *2
inverter rating
30Hz
*3
l Operation region
or more
Region on the right of
20Hz
characteristic curve
l Non-operation region
10Hz
Region on the left of
6Hz
characteristic curve
0.5Hz
Characteristic when electronic
thermal relay function for
motor protection is turned OFF
(Pr. 9 = 0 (A))
Region for
transistor
protection
100
150 230
This function detects the overload (overheat) of the
motor and shut off the inverter output by stopping the
operation of the transistor at the inverter output side.
(The operation characteristic is shown on the left.)
When using the Mitsubishi Electric constant-torque
motor set one of "10", "13" to "16", "50", "53", "70",
"73", "1800" or , "1803" in Pr. 71. (This enables a 100%
constant-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 the electronic thermal relay function dedicated to the
Mitsubishi Electric constant-torque motor is set, this
characteristic curve applies to operation at 6 Hz or higher.
APPENDIX
71