Mitsubishi Electric A800 Instruction Manual page 67

 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
30Hz
or more*
3
20Hz
60
10Hz
6Hz
0.5Hz
50
240
180
120
60
52.5% 105%
50 100
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 (details in the 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.
• 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.
30
Pr. 9 = 100% setting
of inverter rating*
1.2
30Hz or more*
3
20Hz
Operation range
Range on the right of
10Hz
characteristic curve
6Hz
Non-operation range
Range on the left of
0.5Hz
characteristic curve
Characteristic when electronic thermal
relay function for motor protection is
turned off (When Pr. 9 setting is 0(A))
Range for
transistaor
protection*
4
150 230
This function detects the overload (overheat) 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
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 150% depending on the operating
conditions.