132
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 (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 this case, use an external thermal relay.
• A special motor cannot be protected by the electronic thermal relay function. 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, 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 120%
depending on the operating conditions.
230
Inverter output power (%)
(% to the inverter rated current)
52.5
％
105
％
50
100 120
150
60
120
180
240
50
60
70
6Hz
20Hz
10Hz
6Hz
0.5Hz
30Hz or more
∗3
30Hz
or more
∗3
20Hz
10Hz
0.5Hz
(min) unit display in
this region
Operation time (min)
(s) unit display in this region
Operation time (s)
Pr.9
= 50% setting
of inverter rating
∗1, 2
Pr.9
= 100% setting
of inverter rating
∗2
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
Operation region
Region on the right of
characteristic curve
Non-operation region
Region on the left of
characteristic curve
