Selection And Protection Of A Motor; Motor Protection From Overheat (Electronic Thermal Relay Function) (Pr. 9) - Mitsubishi Electric FR-F740-00023-EC Instruction Manual

3.7 Selection and protection of a motor

Purpose
Motor protection from overheat
Use the constant torque motor
3.7.1

Motor protection from overheat (Electronic thermal relay function) (Pr. 9)

Set the current of the electronic thermal O/L relay to protect the motor from overheat. This feature provides the
optimum protective characteristics, including reduced motor cooling capability, at low speed.
Parameter
Name
Number
Electronic thermal
9
O/L relay
Second electronic
51
*2
thermal O/L relay
*1 The parameters can be set when Pr. 160 User group read selection = "0" (Refer to page 146)
*2 When parameter is read using the FR-PU04, a parameter name different from an actual parameter is displayed.
(1) Electronic thermal O/L relay (Pr. 9)
Electronic thermal relay function operation characteristic
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
105%
52.5%
50
Inverter output power (%)
(% to the rated input current)
CAUTION
⋅ Protective function by electronic thermal relay function is reset by inverter power reset and reset signal input. Avoid
unnecessary reset and power-off.
⋅ When multiple motors are operated by a single inverter, protection cannot be provided by the electronic thermal relay function.
Install an external thermal relay to each motor.
⋅ 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 the external thermal relay.
⋅ The operation time of the transistor protection thermal relay shortens when the Pr. 72 PWM frequency selection setting increases.
Parameter that must be Set
Electronic thermal O/L relay
Applied motor
Initial Value
01160 or less
Rated inverter
output current
01800 or more
01160 or less
01800 or more
9999
*3
Pr. 9 = 100% setting
of inverter rating*
1.2
30Hz or more*
3
20Hz
Operation region
Region on the left 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))
Electronic thermal relay
function for transistor
protection
100 120
150

Selection and protection of a motor

Pr. 9, Pr. 51
Pr. 71
Setting Range
0 to 500A
Set the rated motor current.
0 to 3600A
0 to 500A Made valid when the RT signal is
on.
0 to 3600A
Set the rated motor current.
Second electronic thermal O/L relay
9999
invalid
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)
⋅ Set the rated current [A] of the motor in Pr. 9. (When
the power supply specification is (400V/440V) 60Hz,
set the 1.1 times the rated motor current.)
⋅ Set "0" in Pr. 9 when you do not want to activate the
electronic thermal relay function, e.g. when using an
external thermal relay with the motor. (Note that the output
transistor protection of the inverter functions (E.THT).)
⋅ When using the Mitsubishi constant-torque motor
1) Set "1"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.
*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 output current.
It is not the percentage to the motor rated current.
*3 When you set the electronic thermal relay function dedicated to the
Mitsubishi constant-torque motor, this characteristic curve applies
to operation at 6Hz or higher.
Refer to page
83
85
Pr.10
Description
Pr.50
Pr.52
83
Pr.8
page 79
page 86
page 100
page 105
3