91
Selection and protection of a motor
4
PARAMETERS
4.8 Selection and protection of a motor
4.8.1 Motor overheat protection (Electronic thermal O/L relay, PTC thermistor protection)
(Pr. 9, Pr. 561)
∗1 These parameters can be set when Pr. 160 Extended function display selection = "0". (Refer to page 144)
∗2 Refer to page 272 for the rated motor current.
(1) Electronic thermal O/L relay (Pr. 9)
This function detects the overload (overheat) of the motor and trips. (The operation characteristic is shown below)
Set the rated current (A) of the motor in Pr. 9.
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 drive unit is activated (E.THT).)
Purpose Parameter that should be Set Refer to Page
Motor protection from overheat
Electronic thermal O/L relay
PTC thermistor protection
Pr. 9, Pr. 561 91
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
Number
Name Initial Value Setting Range Description
9
Electronic thermal O/L
relay
Rated motor
current
∗2
0 to 500A Set the rated motor current.
561∗1
PTC thermistor protection
level
9999
0.5 to 30kΩ
Set the level (resistance value) for PTC
thermistor protection activates.
9999 PTC thermistor protection is inactive.
NOTE
The internal accumulated heat value of the electronic thermal relay function is reset by the drive unit's power reset or
a reset signal input. Avoid unnecessary resets and power-OFFs.
200
105%
50
125100
150
100
200
300
600
50
60
70
25 75 175
400
500
(s) unit display in this region
(min) unit display in
this region
Operation time (min)Operation time (s)
300r/min or more
Operation region
Region on the right of
characteristic curve
Non-operation region
Region on the left of
characteristic curve
0
The ratio of motor current to Pr.9 Electronic thermal O/L relay
