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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
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 current (%)
(% to the rated output 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 (refer to
• 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.
• Set Pr.9 = "0" for vector-control-dedicated motors (SF-V5RU) because they are equipped with thermal protectors.
• Motor over temperature sensing is not provided by the drive.
• Electronic thermal memory retention function is not provided by the drive.
140
APPENDIX
Pr.9 = 100% setting
of inverter rating*
2
30 Hz or more*
3
20 Hz
Operation range
Range on the right of
10 Hz
characteristic curve
6 Hz
Non-operation range
Range 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
transistor
protection*
4
100
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 Electric 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.
page
76) when selecting the setting for an external thermal relay.
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 heat sink. The protection
may be activated even with less than 150%
depending on the operating conditions.
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