100
Selection and protection of a motor
4.8 Selection and protection of a motor
4.8.1 Motor protection from overheat (Electronic thermal relay function)
(Pr. 9, Pr. 51, Pr. 561, Pr. 986)
*1 The parameters can be set when Pr. 160 User group read selection = "0" (Refer to page 185)
*2 When parameter is read using the FR-PU04, a parameter name different from an actual parameter is displayed.
*3 The initial value may slightly differ for each inverters.
(1) Electronic thermal relay function operation characteristic (THM)
Purpose Parameter that must be Set Refer to page
Motor protection from overheat Electronic thermal O/L relay Pr. 9, Pr. 51, Pr. 561, Pr. 986 100
Use the constant-torque motor Applied motor Pr. 71 105
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
Number
Name Initial Value Setting Range Description
9
Electronic thermal
O/L relay
Rated
inverter
current
01160 or less 0 to 500A
Set the rated motor current.
01800 or more 0 to 3600A
51
*1
Second electronic
thermal O/L relay
*2
9999
01160 or less 0 to 500A
Valid when the RT signal is ON.
Set the rated motor current.
01800 or more 0 to 3600A
9999
Second electronic thermal O/L relay
invalid
561
PTC thermistor
protection level
9999
0.5 to 30k
Set the PTC thermistor protection
level (resistance value from terminal
2).
9999
PTC thermistor protection with
terminal 2 is invalid.
986
Terminal 10
calibration for PTC
thermistor
5.00V
*3
(9999)
4 to 6V
Set the voltage between terminal 10
and terminal 5.
(Setting increments: 0.01V)
8888
Set when a voltage measurement is
unavailable.
9999 (Read only)
Displayed when terminal 10
calibration has not been performed.
[Electronic thermal relay function operation characteristic (E.THM)]
This function detects the overload (overheat) of the
motor and the inverter trips. (The operation
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.
120
Electronic thermal relay
function for transistor
protection
52.5%
105%
50
100
150
60
120
180
240
50
60
70
6Hz
20Hz
10Hz
6Hz
0.5Hz
30Hz or more*
3
20Hz
10Hz
0.5Hz
Pr. 9 = 50% setting of
inverter rating*
1.2
Pr. 9 = 100% setting
of inverter rating*
1.2
(s) unit display in this range
(min) unit display in
this range
Operation time (min)Operation time (s)
Characteristic when
electronic thermal relay
function for motor
protection is turned OFF
(When Pr. 9 setting is 0(A))
30Hz
or more*
3
Inverter output current(%)
(% to the rated inverter current)
Operation range
Range on the right of
characteristic curve
Non-operation range
Range on the left of
characteristic curve
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