Dust Exposure; Potentially Explosive Atmospheres - Danfoss VLT AutomationDrive FC 301 Series Design Manual

System Integration

5.1.7.2 Dust Exposure

Installation of adjustable frequency drives in environments
with high dust exposure is often unavoidable. Dust affects
wall or frame mounted units with IP55 or IP66 protection
rating, and also cabinet mounted devices with IP21 or IP20
protection rating. Take the three aspects described below
into account when adjustable frequency drives are
installed in such environments.
Reduced Cooling
5 5
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 airflow 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 fitted with filter
mats. These filters can become quickly clogged when used
in very dusty environments. Preventative 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 off the heatsink and fans and
clean the filter mats.

5.1.7.3 Potentially Explosive Atmospheres

Systems operated in potentially explosive atmospheres
must fulfill 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.
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Design Guide
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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 filter 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.
NOTICE!
®
VLT AutomationDrive units with the MCB 112 option
have PTB-certified motor thermistor sensor monitoring
capability for potentially explosive atmospheres.
Shielded motor cables are not necessary when
adjustable frequency drives are operated with sine-wave
output filters.
Rev. 2014-04-04 All rights reserved.
e classification consists of preventing any
occurrence of a spark. The FC 302 with firmware
version V6.3x or higher is equipped with an
"ATEX ETR thermal monitoring" function for
operation of specially approved Ex-e motors.
When combined with an ATEX approved PTC
monitoring device like the PTC Thermistor Card
MCB 112 the installation does not need an
individual approval from an approbated organi-
zation, i.e., no need for matched pairs.
d classification 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 a e ignition protection class, while the
motor cabling and connection environment is in
compliance with the e classification. 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 classification.
In practice, using a sine-wave filter at the
adjustable frequency drive output has proven to
be an effective means to attenuate the high peak
voltage.
MG33BF22