Mitsubishi Electric A800-GF Instruction Manual page 120

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
70
30 Hz
∗3
or more
20 Hz
60
10 Hz
6 Hz
0.5 Hz
50
240
180
120
60
52.5%
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.
• 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. Note that the current indicated on the motor rating plate is affected by the line-to-line
leakage current (refer to 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 such case, use an external thermal relay.
• A dedicated motor cannot be protected by an electronic thermal O/L relay. Use an external thermal relay.
• Motor over temperature sensing is not provided by the drive.
Pr.9 = 100% setting
of inverter rating
∗1, 2 ∗2
30 Hz
Operation region
∗3
or more
Region on the right of
characteristic curve
20 Hz
Non-operation region
10 Hz
Region on the left of
6 Hz characteristic curve
Characteristic when
0.5 Hz
electronic thermal relay
function for motor
protection is turned off
(When Pr.9 setting is 0(A))
Range for
the transistor
protection
105%
100
50 150
Inverter output power (%)
(% to the inverter rated current)
This function detects the overload (overheat) of
the motor and trips the inverter 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
(1) Set one of "1", "13" to "16" in Pr.71. (This
setting will enable the 100% constant-torque
characteristic in the low-speed range.)
(2) Set the rated current of the motor in Pr.9.
∗4
230

When a value 50% of the inverter rated output
current (current value) is set in Pr.9

The % value denotes the percentage to the
rated inverter 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 150%
depending on the operating conditions.
APPENDIX
119