Mitsubishi Electric FR-A802-P Instruction Manual page 115

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
50 0.5 Hz
240
180
120
60
105%
52.5%
100
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 the inverter is used to drive a multi-pole motor or a dedicated motor, install an external thermal relay (OCR) between
the inverter and the motor. 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 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.
• Electronic thermal memory retention function is not provided by the drive.
114
APPENDIX
This function detects the overload 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.)
Pr.9 = 100% setting
• Mitsubishi Electric constant-torque motor
of inverter rating ∗2
30 Hz
Operation region
or more ∗3
Region on the right of (1) Set one of "1" or "13 to 16" in Pr.71. (This setting will enable the 100%
characteristic curve
20 Hz
Non-operation region
10 Hz
Region on the left of constant-torque characteristic in the low-speed range.)
6 Hz characteristic curve
Characteristic when
0.5 Hz
(2) Set the rated current of the motor in Pr.9.
electronic thermal relay
function for motor
protection is turned off
(When Pr.9 setting is 0(A))
Range for
the transistor
protection ∗4
150 230
page 68) 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 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 heat sink.
The protection may be activated even with less than 150% depending on the
operating conditions.