•
•
•
Mains drop-out
During a mains dropout, the drive keeps running until the DC-link voltage drops below the minimum stop level, which is typically
15% below the drive's lowest rated supply voltage. The mains voltage before the drop-out and the motor load determines how long
it takes for the drive to coast.
3.7.2 Motor Thermal Protection (ETR)
Danfoss uses ETR to protect the motor from being overheated. It is an electronic feature that simulates a bimetal relay based on
internal measurements. The characteristic is shown in the following illustration.
1.2
1.0
1.4
30
10
20
100
60
40
50
1.8
1.6
2.0
2000
500
200
400
300
1000
600
t [s]
e7
5z
a0
52
.1
3
I
M,N
(parameter 1-24)
I
M
f
OUT
= 2 x f
M,N
(parameter 1-23)
f
OUT
= 1 x f
M,N
f
OUT
= 0.2 x f
M,N
Illustration 31: Motor Thermal Protection Characteristic
The X-axis shows the ratio between I
motor
and I
motor
nominal. The Y-axis shows the time in seconds before the ETR cuts off and trips
the drive. The curves show 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 is protected from
being overheated even at low speed. The ETR feature calculates the motor temperature based on actual current and speed.
3.7.3 Thermistor Inputs
The thermistor cutout 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).
Electronic thermal relay (ETR).
AJ363928382091en-000101 / 130R0983
42 | Danfoss A/S © 2021.04
Product Overview
VLT® Flow Drive FC 111
Design Guide
