Selection And Protection Of A Motor; Motor Protection From Overheat (Electronic Thermal Relay Function) (Pr. 9, Pr. 51) - Mitsubishi Electric FR-F740-00023 Instruction Manual

4.8 Selection and protection of a motor

Purpose
Motor protection from overheat
Use the constant-torque motor
4.8.1

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
*2
thermal O/L relay *3
*1 The parameters can be set when Pr. 160 User group read selection = "0" (Refer to page 173)
*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
105%
52.5%
50
Inverter output current(%)
(% to the rated inverter 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.
If electric thermal is set to 5% or lower of the inverter rated current, electronic thermal may not operate.
Parameter that must be Set
Electronic thermal O/L relay
Applied motor
Initial Value
01160 or less
Rated inverter
current
01800 or more
01160 or less
01800 or more
9999
Pr. 9 = 100% setting
of inverter rating* 1.2
30Hz or more*
3
20Hz
Operation range
Range on the right of
10Hz
characteristic curve
6Hz
Non-operation range
Range 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
120
100 150

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
Valid when the RT signal is on.
Set the rated motor current.
0 to 3600A
Second electronic thermal O/L relay
9999
invalid
This function detects the overload (overheat) of the
motor and the inverter
characteristic is shown on the left)
Set the rated current [A] of the motor in Pr. 9.
(If the motor has both 50Hz and 60Hz rating and
the Pr.3 Base frequency is set to 60 Hz, set the 1.1
times of the 60Hz 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 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 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
95
99
Description
trips. (The operation
95
4