Gas type Unit
Class
3C1 3C2 3C3
Average
value
Max.
value
1)
Average
value
Max.
value
1)
Sea salt n/a None Salt mist Salt mist
Sulfur oxides
mg/m
3
0.1 0.3 1.0 5.0 10
Hydrogen sulde
mg/m
3
0.01 0.1 0.5 3.0 10
Chlorine
mg/m
3
0.01 0.1 0.03 0.3 1.0
Hydrogen
chloride
mg/m
3
0.01 0.1 0.5 1.0 5.0
Hydrogen
uoride
mg/m
3
0.003 0.01 0.03 0.1 3.0
Ammonia
mg/m
3
0.3 1.0 3.0 10 35
Ozone
mg/m
3
0.01 0.05 0.1 0.1 0.3
Nitrogen
mg/m
3
0.1 0.5 1.0 3.0 9.0
Table 3.2 Conformal-coating Class Ratings
1) Maximum values are transient peak values not to exceed 30
minutes per day.
3.1.7.2
Dust Exposure
Installation of adjustable frequency drives in environments
with high dust exposure is often unavoidable. Dust aects
wall- or frame-mounted units with IP55 or IP66 protection
ratings, and also cabinet-mounted devices with IP21 or
IP20 protection ratings. Consider the three aspects
described in this section when adjustable frequency drives
are installed in such environments.
Reduced cooling
Dust forms deposits on the surface of the device and
inside on circuit boards and the electronic components.
These deposits act as insulation layers and hamper heat
transfer to the ambient air, reducing the cooling capacity.
The components become warmer. This causes accelerated
aging of the electronic components, and the service life of
the unit decreases. Dust deposits on the heatsink in the
back of the unit also decrease the service life of the unit.
Cooling fans
The airow for cooling the unit is produced by cooling
fans, usually located on the back of the device. The fan
rotors have small bearings into which dust can penetrate
and act as an abrasive. This leads to bearing damage and
fan failure.
Filters
High-power adjustable frequency drives are equipped with
cooling fans that expel hot air from the interior of the
device. Above a certain size, these fans are tted with lter
mats. These lters can become quickly clogged when used
in dusty environments. Preventive measures are necessary
under these conditions.
Periodic maintenance
Under the conditions described above, it is advisable to
clean the adjustable frequency drive during periodic
maintenance. Remove dust o the heatsink and fans and
clean the lter mats.
3.1.7.3 Potentially Explosive Atmospheres
Systems operated in potentially explosive atmospheres
must fulll special conditions. EU Directive 94/9/EC
describes the operation of electronic devices in potentially
explosive atmospheres.
Motors controlled by adjustable frequency drives in
potentially explosive atmospheres must be monitored for
temperature using a PTC temperature sensor. Motors with
ignition protection class d or e are approved for this
environment.
•
d classication consists of ensuring that if a spark
occurs, it is contained in a protected area. While
not requiring approval, special wiring and
containment are required.
•
d/e combination is the most often used in
potentially explosive atmospheres. The motor
itself has an e ignition protection class, while the
motor cabling and connection environment is in
compliance with the e classication. The
restriction on the e connection space consists of
the maximum voltage allowed in this space. The
output voltage of an adjustable frequency drive is
usually limited to the AC line voltage. The
modulation of the output voltage may generate
unallowable high peak voltage for e classication.
In practice, using a sine-wave lter at the
adjustable frequency drive output has proven to
be an eective means to attenuate the high peak
voltage.
NOTICE!
Do not install an adjustable frequency drive in a
potentially explosive atmosphere. Install the adjustable
frequency drive in a cabinet outside of this area. Using a
sine-wave lter at the output of the adjustable frequency
drive is also recommended to attenuate the dU/dt
voltage rise and peak voltage. Keep the motor cables as
short as possible.
System Integration
Design Guide
MG20N622 Danfoss A/S © 09/2014 All rights reserved. 41
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