Selection And Protection Of A Motor; Motor Overheat Protection (Electronic Thermal O/L Relay, Ptc Thermistor Protection) (Pr. 9, Pr. 51, Pr. 561) - Mitsubishi Electric FR-D720-0.4K Instruction Manual

4.8

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 method.
4.8.1 Motor overheat protection (Electronic thermal O/L relay, PTC thermistor protection)
(Pr. 9, Pr. 51, Pr. 561)
Set the current of the electronic thermal relay function 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 O/L
9
relay
Second electronic thermal
51∗1
O/L relay ∗2
PTC thermistor protection
561∗1
level
∗1
These parameters can be set when Pr. 160 Extended function display selection = "0". (Refer to page 163)
∗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 O/L relay operation characteristic
Pr. 9 = 50% setting of inverter rating*1, 2
Pr. 9 = 100% setting of inverter rating*2
70
30Hz
or more
*3
20Hz
60
10Hz
6Hz
0.5Hz
50
240
180
120
60
105%
52.5%
100
50
Inverter output current(%) (% to the rated inverter current)
∗1
When 50% of the inverter rated output current (current value) is set to 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 O/L relay dedicated to the Mitsubishi constant-torque motor, this characteristic curve applies to operation at 6Hz or higher.
NOTE
The internal thermal integrated value of the electronic thermal relay function is reset by inverter power reset and
reset signal input. Avoid unnecessary reset and power-OFF.
Install an external thermal relay (OCR) between the inverter and a motor when operating several motors by one
inverter, or when using a multi-pole motor or specialized motor. In this case, set 0A to the electronic thermal O/L relay
setting of the inverter. For the external thermal relay, determine the setting value in consideration of the current
indicated on the motor's rating plate and the line-to-line leakage current. Self-cooling ability of a motor is reduced at
low speed operation. Use a motor with a built-in thermal protector.
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.
The operation time of the transistor protection thermal shortens when the Pr. 72 PWM frequency selection setting value
increases.
Electronic thermal O/L relay
PTC thermistor protection
Applied motor
Offline auto tuning
Initial Value
Inverter
rated current
9999
9999
30Hz or more
*3
20Hz
Operation range
10Hz
Range on the right of characteristic curve
6Hz Non-operation range
Range on the left of characteristic curve
0.5Hz
Characteristic when electronic thermal
relay function for motor protection is turned OFF
(when Pr. 9 setting is 0(A))
Range for
transistor
protection
150 200

Selection and protection of a motor

Parameter that should be Set
Pr. 9, Pr. 51, Pr. 561
Pr. 71
Pr. 71, Pr. 80,
Pr. 82 to Pr. 84,
Pr. 90, Pr. 96
Setting Range
0 to 500A Set the rated motor current.
Valid when the RT signal is ON.
0 to 500A
Set the rated motor current.
9999 Second electronic thermal O/L relay invalid
Set the level (resistance value) for PTC
0.5 to 30kΩ
thermistor protection activates.
9999 PTC thermistor protection is inactive.
This function detects the overload (overheat) of the
motor and 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 60Hz, set the 1.1 times of
the 60Hz rated motor current.)
Set "0" in Pr. 9 when you do not want to operate the
electronic thermal O/L relay, e.g. when using an external
thermal relay with the motor. (Note that the output
transistor protection of the inverter is activated (E.THT).)
When using a Mitsubishi constant-torque motor
1) Set "1" or "13", "50", "53" in any of 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.
Refer to Page
101
104
106
Description
101
4