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 frequency converter during periodic
maintenance. Remove dust off the heat sink and fans and
clean the filter mats.
5.1.7.3 Potentially Explosive Atmospheres
Systems operated in potentially explosive atmospheres
must fulfil special conditions. EU Directive 94/9/EC
describes the operation of electronic devices in potentially
explosive atmospheres.
Motors controlled by frequency converters 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.
•
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-
sation, 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 a frequency converter is usually
limited to the mains 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 frequency
converter output has proven to be an effective
means to attenuate the high peak voltage.
NOTICE
Do not install a frequency converter in a potentially
explosive atmosphere. Install the frequency converter in
a cabinet outside of this area. Using a sine-wave filter at
the output of the frequency converter 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 frequency
converters are operated with sine-wave output filters.
5.1.8 Maintenance
Danfoss frequency converter models up to 90 kW are
maintenance free. High power frequency converters (rated
at 110 kW or higher) have built-in filter mats which require
periodic cleaning by the operator, depending on the
exposure to dust and contaminants. Maintenance intervals
for the cooling fans (approximately 3 years) and capacitors
(approximately 5 years) are recommended in most
environments.
5.1.9 Storage
Like all electronic equipment, frequency converters must
be stored in a dry location. Periodic forming (capacitor
charging) is not necessary during storage.
It is recommended to keep the equipment sealed in its
packaging until installation.
System Integration
VLT
®
AutomationDrive FC 301/FC 302 Design Guide, 0.25-75 kW
48
MG33BF02 - Rev. 2013-12-20
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