Mitsubishi Electric A800 Plus Instruction Manual page 122

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
or more ∗3
20 Hz
60
10 Hz
6 Hz
0.5 Hz
50
240
180
120
60
52.5%
(% 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.
• 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
• 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
or more ∗3
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 ∗4
105%
50 100 150 230
Inverter output power (%)
page 72) when selecting the setting for an external thermal relay.
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.)
• 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.
∗1
When a value 50% of the inverter rated output current
(current value) is set in Pr.9
∗2
The % value denotes the percentage to the inverter rated
current. It is not the percentage to the rated motor current.
∗3 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.
∗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.
121
APPENDIX