Danfoss FC 101 Design Manual page 41

Product Overview
the ETR cuts off and trips the frequency converter. The
curves are showing the characteristic nominal speed at
twice the nominal speed and at 0.2x the nominal speed.
It is clear that at lower speed the ETR cuts off at lower
heat due to less cooling of the motor. In that way the
motor are protected from being over heated even at low
speed. The ETR feature is calculating the motor
temperature based on actual current and speed.
The thermistor cut-out value is >3 kΩ.
Integrate a thermistor (PTC sensor) in the motor for
winding protection.
Motor protection can be implemented using a range of
techniques: PTC sensor in motor windings; mechanical
thermal switch (Klixon type); or Electronic Thermal Relay
(ETR).
R
(Ω)
4000
3000
1330
550
250
 nominel -5°C
-20°C
Illustration 2.28 Trip due to High Motor Temperature
®
VLT HVAC Basic Drive FC 101 Design Guide
 [°C]
 nominel +5°C
 nominel
MG18C502 - Rev. 2013-09-06
Using a digital input and 10 V as power supply:
Example: The frequency converter trips when the motor
temperature is too high.
Parameter set-up:
Set 1-90 Motor Thermal Protection to [2] Thermistor Trip
Set 1-93 Thermistor Source to [6] Digital Input 29
BUS TER.
OFF ON
61 68 69 18 19 27 29 42 45 50 53 54
0/4-20mA A OUT / DIG OUT
OFF
ON
<800 Ω
Illustration 2.29 Digital Input/10 V Power Supply
0/4-20mA A OUT / DIG OUT
12 20 55
COM A IN
COM DIG IN
R
>2.9 kΩ
39
2 2