Motor Thermal Protection - Danfoss VLT 380-500 V Design Manual

Motor
•
Lower the IGBT switching frequency.
•
Modify the inverter waveform, 60° AVM vs.
SFAVM.
•
Install a shaft grounding system or use an
isolating coupling.
•
Apply conductive lubrication.
•
Use minimum speed settings if possible.
•
Try to ensure that the mains voltage is balanced
to ground. This procedure can be difficult for IT,
TT, TN-CS, or grounded leg systems.
•
Use a dU/dt or sine-wave filter.
10 10

10.4 Motor Thermal Protection

The electronic thermal relay in the frequency converter has
received UL-approval for single motor protection, when
parameter 1-90 Motor Thermal Protection is set for ETR Trip
and parameter 1-24 Motor Current is set to the rated motor
current (see the motor nameplate).
For motor thermal protection, it is also possible to use the
®
VLT PTC Thermistor Card MCB 112 option. This card
provides ATEX certificate to protect motors in explosion
hazardous areas, Zone 1/21 and Zone 2/22. When
parameter 1-90 Motor Thermal Protection, set to [20] ATEX
ETR, is combined with the use of MCB 112, it is possible to
control an Ex-e motor in explosion hazardous areas.
Consult the programming guide for details on how to set
up the frequency converter for safe operation of Ex-e
motors.
106
- Provide a good high-frequency
connection between the motor and the
frequency converter. Use a shielded
cable that has a 360° connection in the
motor and the frequency converter.
- Ensure that the impedance from the
frequency converter to building ground
is lower that the grounding impedance
of the machine. This procedure can be
difficult for pumps.
- Make a direct ground connection
between the motor and load motor.
Danfoss A/S © 6/2016 All rights reserved.
®
VLT Parallel Drive Modules
10.4.1 Types of Thermal Protection
10.4.1.1 PTC Thermistor
Using a digital input and 10 V supply
39 42 50
12 13 18
PTC / Thermistor
Illustration 10.2 PTC Thermistor Connection - Digital Input
with 10 V Supply
Using an analog input and 10 V supply
39 42 50
PTC / Thermistor
Illustration 10.3 PTC Thermistor Connection - Analog Input
with 10 V Supply
Using a digital input and 24 V as supply
12 13 18
PTC / Thermistor
Illustration 10.4 PTC Thermistor Connection - Digital Input
with 24 V Supply
Check that the selected supply voltage follows the specifi-
cation of the used thermistor element.
Input digital/
analog
Digital
Analog
Digital
Table 10.2 PTC Thermistor Resistance Parameters
53 54 55
OFF
19 27 29 32 33 20 37
ON
<800 Ω
53 54 55
OFF
ON
<3.0 k
OFF
19 27 29 32 33 20 37
ON
<6.6 k Ω >10.8 k Ω
Supply Trip resistance
voltage [V] kΩ
10 >2.7
10 >3.0
24 >10.8
R
>2.7 kΩ
Ω R
>3.0 k Ω
R
Reset
resistance
<800 Ω
<3.0 kΩ
<6.6 kΩ
MG37N102