121
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.
• 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
) 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.
Operation characteristics of electronic thermal relay function
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.
230
52.5%
105%
50
100
150
60
120
180
240
50
60
70
Pr.9
= 50% setting
of inverter rating
∗1, 2
Pr.9
= 100% setting
of inverter rating
∗2
6 Hz
20 Hz
10 Hz
6 Hz
0.5 Hz
30 Hz
or more
∗3
30 Hz
or more
∗3
20 Hz
10 Hz
0.5 Hz
Range for
the transistor
protection
∗4
Second display in this region
Minute display in
this region
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))
Inverter output power (%)
(% to the inverter rated current)
Operation region
Region on the right of
characteristic curve
Non-operation region
Region on the left of
characteristic curve
Summary of Contents for FR-A842-07700
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