Mitsubishi Electric 800 Series Instruction Manual page 200

• Set the rated current (A) of the motor in Pr.9 Electronic thermal O/L relay. (If the motor has both 50 Hz and 60 Hz ratings
and the Pr.3 Base frequency is set to 60 Hz, set to 1.1 times the 60 Hz rated motor current.)
• Set "0" in Pr.9 to avoid activating the electronic thermal relay function; for example, when using an external thermal relay
for the motor.
(Note that the output transistor protection of the inverter is activated. (E.THT))
• When using the Mitsubishi Electric constant-torque motor, set the constant-torque motor in Pr.71 Applied motor referring
to page 294. (This setting enables the 100% constant-torque characteristic in the low-speed range.)
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
Inverter output power (%)
(% to the inverter rated current)
*1 When setting Pr.9 to a value (current value) of 50% of the inverter rated current
*2 The % value denotes the percentage to the rated inverter current. It is not the percentage to the rated motor current.
*3 When the electronic thermal relay function dedicated to the Mitsubishi Electric constant-torque motor is set, this characteristic curve applies to
operation at 6 Hz or higher. (For selection of the operation characteristic, refer to
*4 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.
NOTE
• The internal accumulated heat value of the electronic thermal relay function is reset to the initial value by the inverter's power
reset or 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. When setting an external thermal relay, note that the current indicated on the motor rating
plate is affected by the line-to-line leakage current. The cooling effect of the motor drops during low-speed operation. Use a
motor with built-in thermal protector. (For details of the line-to-line leakage current, refer to the Instruction Manual
(Connection).)
• When the difference between the inverter and motor capacities is large and the set value is small, the protective characteristics
of the electronic thermal relay function will be deteriorated. Use an external thermal relay in such cases.
• A dedicated motor cannot be protected by an electronic thermal O/L relay. Use an external thermal relay.
• The transistor protection thermal O/L relay is activated early when the Pr.72 PWM frequency selection setting is increased.
 Electronic thermal O/L relay when using PM motor (Pr.9)
• This function detects the overload (overheat) of the motor and shut off the inverter output by stopping the operation of the
transistor at the inverter output side.
• Set the rated current (A) of the motor in Pr.9 Electronic thermal O/L relay.
• Set "0" in Pr.9 to avoid activating the electronic thermal relay function; for example, when using an external thermal relay
for the motor.
(Note that the output transistor protection of the inverter is activated. (E.THT))
Pr. 9 = 100% setting
of inverter rating* 1.2
30Hz or more*
3
20Hz
Operation region
Region on the right of
10Hz
characteristic curve
6Hz
Non-operation region
Region 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
the transistor
protection
*4
100
150 230
page 294.)
10. (H) Protective Function Parameters
10.1 Motor overheat protection (electronic thermal O/L relay)
1
2
3
4
5
6
7
8
9
10
199