Danfoss VLT HVAC Drive FC 102 Design Manual page 50

Introduction
nominal speed at twice the nominal speed and at 0.2x the
nominal speed.
2 2
t [s]
2000
1000
600
500
400
300
200
100
60
50
40
30
20
10
1.0
Illustration 2.33 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 is protected from overheating even at low speed.
The ETR feature is calculating the motor temperature
based on actual current and speed. The calculated
temperature is visible as a readout parameter in
16-18 Motor Thermal in the frequency converter.
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 (ETR).
48
f OUT = 1 x f M,N (par. 1-23)
f OUT = 2 x f M,N
f OUT = 0. 2 x f M,N
I
1.2 1.4 1.6 1.8 2.0
Danfoss A/S © Rev. 05/2014 All rights reserved.
Design Guide
R
(Ω)
4000
3000
1330
550
250
I
M
(par. 1-24)
MN
-20°C
Illustration 2.34 Trip
Example: Using a digital input and 24 V as power supply:
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 33
12 13 18
PTC / Thermistor
Illustration 2.35 Digital Input and 24 V Power Supply
 nominel -5°C
 nominel
OFF
19 27 29 32 33 20 37
ON
<6.6 k Ω >10.8 k Ω
 [°C]
 nominel +5°C
R
MG16C202