22
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
.
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.
• Electronic thermal memory retention function is not provided by the drive.
Operation characteristics of electronic thermal relay function
This function detects the overload 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 Electric 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 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.
Range for
transistor
protection*
4
230
52.5%
105%
50
100
150
60
120
180
240
50
60
70
6Hz
20Hz
10Hz
6Hz
0.5Hz
30Hz or more*
3
20Hz
10Hz
0.5Hz
Pr. 9
= 50% setting of
inverter rating*
1.2
Pr. 9
= 100% setting
of inverter rating*
1.2
Second display in this range
Minute display in
this range
Operation time (min)
Operation time (s)
Characteristic when electronic thermal
relay function for motor protection is
turned off (When
Pr. 9
setting is 0(A))
30Hz
or more*
3
Inverter output current (%)
(% to the rated output current)
Operation range
Range on the right of
characteristic curve
Non-operation range
Range on the left of
characteristic curve
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