Selection And Protection Of A Motor; Motor Protection From Overheat (Electronic Thermal Relay Function) (Pr. 9, Pr. 51) - Mitsubishi Electric FR-A720-0.4K Instruction Manual

Selection and protection of a motor

4.13 Selection and protection of a motor

Purpose
Motor protection from overheat
Use the constant torque motor
The motor performance can be
maximized for operation in magnetic
flux vector control system
High accuracy operation unaffected
by the motor temperature and stable
operation with high torque down to
ultra low speed are performed

4.13.1 Motor protection from overheat (Electronic thermal relay function) (Pr. 9, Pr. 51)

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
thermal O/L relay
*1 The initial value of the 0.4K and 0.75K is set to 85% of the rated inverter current.
*2 When parameter is read using the FR-PU04, a parameter name different from an actual parameter is displayed.
(1) Electronic thermal relay function operation characteristic (THM)
[Electronic thermal relay function operation characteristic (E.THM)]
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
52.5% 105%
50
Ration of the motor current to
Pr. 9 Electronic thermal relay function (%)
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.
176
Electronic thermal O/L relay
Applied motor
Offline auto tuning
Online auto tuning
Initial Value
Rated inverter
current
*1
9999
*2
Pr. 9 = 100% setting
of inverter rating*
2
30Hz or more*
3
20Hz Operation region
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))
Electronic thermal relay
function for transistor
protection
100
150
Parameter that must be Set
Pr. 82 to Pr. 84,
Pr. 90 to Pr. 94, Pr. 96
Pr. 95, Pr. 574
Setting Range
55K or less 0 to 500A
75K or more 0 to 3600A
55K or less 0 to 500A
75K or more 0 to 3600A
9999
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 200V/220V(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" or any of "13" to "18", "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.
*1 When a value 50% of the rated inverter current (current value) is
set in Pr. 9
*2 The % value denotes the percentage to the rated inverter 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
Pr. 9, Pr. 51
Pr. 71
Description
Set the rated motor current.
Made valid when the RT signal is on.
Set the rated motor current.
Second electronic thermal O/L relay
invalid
176
180
182
192