Machine Protection
6-35
îš‹ Motor Overheat Protection Using PTC Thermistor Inputs
This function provides a motor overheating protection using a thermistor (PTC characteristic – Positive Tem-
perature Coefficient) that is built into the windings of each motor phase.
îš„Related Parameters
îš„PTC Thermistor Characteristics
The following diagram shows the characteristics of the PTC thermistor temperature to the resistance value.
The shown resistance value is for one motor phase. Normally the 3 resistors (1 for each phase) are connected
in series
Fig 6.30 PTC Thermistor Temperature-Resistance Value Characteristics
Parameter
Number
Name
Setting
Range
Factory
Setting
Change
during
Operation
Access
Level
L1-03 Alarm operation selection during motor overheating 0 to 3 3 No A
L1-04 Motor overheating operation selection 0 to 2 1 No A
L1-05 Motor temperature input filter time constant
0.00 to
10.00
0.20 sec. No A
Resistance (Ohms)
Class F
Class H
Tr: Temperature threshold value
Temperature
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