Mitsubishi Electric 800 Series Instruction Manual page 61

 Motor overload protection
When using the electronic thermal relay function as motor overload protection, set the rated motor current in Pr.9 Electronic thermal O/L relay.
Operation characteristics of electronic thermal relay function (LD rating)
Pr.9 = 50% setting
of inverter rating ∗1, 2
70
30 Hz
or more
∗3
20 Hz
60
10 Hz
6 Hz
0.5 Hz
50
240
180
120
60
105%
52.5%
50
Inverter output power (%)
(% to the inverter rated current)
NOTE
• 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 multiple motors are driven with a single inverter or when a multi-pole motor or a special motor is driven, install an external thermal relay (OCR) between the
inverter and motors. Note that the current indicated on the motor rating plate is affected by the line-to-line leakage current (details in the FR-F800 Instruction Manual
(Detailed)) when selecting the setting for an external thermal relay.
• The cooling effect of the motor drops during low-speed operation. Use a thermal protector or a motor with built-in thermistor.
• 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.
• Motor over temperature sensing is not provided by the drive.
• Electronic thermal memory retention function is not provided by the drive.
20
Appendix
Pr.9 = 100% setting
of inverter rating ∗2
30 Hz or more
∗3
20 Hz
Operation region
Region on the right of
10 Hz
characteristic curve
6 Hz
Non-operation region
Region on the left of
0.5 Hz
characteristic curve
Characteristic when electronic thermal relay
function for motor protection is turned off
(When Pr.9 setting is 0 (A))
Range for
the transistor
protection ∗4
100 120
150 230
This function detects the overload of the motor, stops the operation of the inverter's
output transistor, and stops the output. (The operation characteristic is shown on
the left.)
• When using the Mitsubishi constant-torque motor
(1) Set one of "1", "13" to "16", "50", "53", "54" in Pr.71. (This provides a 100%
continuous torque characteristic in the low-speed range.)
(2) Set the rated current of the motor in Pr.9.

When a value 50% of the inverter rated output current (current value) is set
in Pr.9

The % value denotes the percentage to the inverter rated current. It is not
the percentage to the rated motor current.

When you set the electronic thermal relay function dedicated to the
Mitsubishi Electric constant-torque motor, this characteristic curve applies to
operation at 6 Hz or higher.

Transistor protection is activated depending on the temperature of the
heatsink. The protection may be activated even with less than 120%
depending on the operating conditions.