Selection And Protection Of A Motor; Motor Overheat Protection (Electronic Thermal O/L Relay) (Pr. 9, Pr. 51) - Mitsubishi Electric FR-E720-0.1K(SC) Instruction Manual

Selection and protection of a motor

4.9

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.
4.9.1

Motor overheat protection (Electronic thermal O/L relay) (Pr. 9, Pr. 51)

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∗2
O/L relay ∗3
∗1
The initial value of the 0.75K or less is set to 85% of the rated inverter current.
∗2
The above parameters can be set when Pr. 160 User group read selection = "0". (Refer to page 188)
∗3
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
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)
NOTE
Fault 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
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.
The operation time of the transistor protection thermal shortens when the Pr. 72 PWM frequency selection setting
increases.
Electronic thermal relay may not function when 5% or less of inverter rated current is set to electronic thermal relay setting.
116
Electronic thermal O/L relay
Applied motor
Offline auto tuning
Initial Value
Inverter
rated current ∗1
9999
Pr. 9 = 100% setting of inverter rating*2
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
150 230
Parameter that should be Set
Pr. 9, Pr. 51
Pr. 71, Pr. 80 to Pr. 84, Pr.
90 to Pr. 94, Pr. 96, Pr. 859
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
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 functions (E.THT).)
When using a Mitsubishi constant-torque motor
1) Set "1" or "13 to 16", "50", "53", "54" 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.
∗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.
Refer to Page
116
Pr. 71
118
120
Description