Selection And Protection Of A Motor; Motor Protection From Overheat (Electronic Thermal Relay Function) (Pr.9) - Mitsubishi Electric F700 Instruction Manual

Selection and protection of a motor

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 overcurrent protection to protect the motor from overheat. This feature
Pr.8
provides the optimum protective characteristics, including reduced motor cooling capability, at low speed.
page 74
Pr.10
page 81
Parameter
Pr.50
Number
page 95
Pr.52
page 100
9 Electronic thermal O/L relay
Second electronic thermal O/
51
*
L relay
* The parameters can be set when Pr. 160 User group read selection = "0" (Refer to page 140)
(1) Electronic thermal O/L relay (Pr.9)
Electronic thermal relay function operation characteristic
Pr. 9 = 50% setting of
inverter rating*
70
30Hz
or more*
20Hz
60
10Hz
6Hz
0.5Hz
50
240
180
120
60
52.5%
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 overcurrent protection 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.
78
Electronic thermal relay function
Applied motor
Name
Pr. 9 = 100% setting
of inverter rating*
1.2
30Hz or more*
3
20Hz Operation region
3
Region on the right 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))
105%
100 120
50 150
Inverter output power (%)
(% to the rated input current)
Parameter that must be set
Initial Value Setting Range
01160 or
less
Rated inverter
output current
01800 or
more
01160 or
less
01800 or
9999
more
9999
This function detects the overload (overheat) of the
motor, stops the operation of the inverter's output
1.2
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" to 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. (The output
transistor protection of the inverter functions (E.THT).)
⋅ When using the Mitsubishi constant-torque motor
1) Set "1" to Pr. 71. (This provides a 100% continuous
torque characteristic in the low-speed range.)
2) Set the rated current of the motor to Pr. 9.
*1 When a value 50% of the inverter rated output current (current
For transistor protection
value) is set to Pr. 9
Electronic thermal relay
*2 The % value denotes the percentage to the inverter rated output
function
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.
Pr.9, Pr.51
Pr. 71
Description
0 to
500A
Set the rated motor current.
0 to
3600A
0 to
Made valid when the RT signal is
500A
on.
0 to
Set the rated motor current.
3600A
Second electronic thermal O/L relay
invalid
Refer to page
78
80