Danfoss VLT DMS 300 Manual page 11

Principle of a adjustable frequency drive
using a DC link coil
The Danfoss option is to add coils to the DC link in
all drives as shown in the figure. This way a high
DC link voltage with a very low voltage ripple is
obtained and the electric strength of the drive with
regard to line transients is improved.
Further advantages are the prolonged lifetime of the
capacitors, reduced harmonic disturbance of the net
supply and presence of 150-160% start torque.
Numerous manufacturers of frequency inverters
use slim DC links leading to bad efficiency rates
- even if users due to the activity of for instance
the CEMEP now tend to use high efficiency
motors - meeting at least EFF2.
Danfoss' aim is to provide high efficiency drives that
also improve the efficiency of the motors. There
should be no need for expensive over-dimensioning
and inefficient operation.
Environmental considerations
Drives - both centrally-mounted and distributed in the
plant - are exposed to the environment. As motor
controls handle high voltages and currents at the
same time they must be protected from dust and
humidity so that they do not fail or break down. Both
manufacturers and installers must take account of this
and Danfoss Drives have designed the decentralized
products with a deep concern in both aspects.
Decentralized motor controls must also meet increasing
demands in respect of hygiene levels in pharmaceutical
industries and in food- and beverage production
in particular, where drives are exposed to cleaning
agents for extensive periods of time, high pressure
hosing and the like. The exterior of the decentralized
motor controls must be designed in such a way as
to achieve this. Complicated heat sinks as illustrated
in the figure must be avoided as it is difficult to clean
and not resistant to common cleaning agents.
MG.90.F2.22 - VLT is a registered Danfoss trademark
Decentral Solutions
Danfoss decentralized drives are designed to meet
the requirements as shown in Figure 9. There
are no hard-to-clean places, blind plugs have no
notches or indentations and two-layer robust surface
treatment - tested to withstand commonly used
cleaning agents - protects the housing.
Non-cleaning friendly pin fin heat sink versus
the easy to clean Danfoss solution
All corners are rounded to prevent dust sticking, and
the distance between ribs allows high-pressure air
cleaning, hosing and easy cleaning with a brush.
These concerns are more or less irrelevant if not applied
to all elements and standard AC motors are normally
designed without these concerns in mind - stressed by
integrated fans and cooling ribs both difficult to clean.
Danfoss has met the challenge by designing a range
of aseptic geared motors. These motors have no fans
and only smooth surfaces. An IP65 enclosure class is
standard as is the special CORO coating resistant to
acid, alkali and cleaning agents used in for instance
food and beverage industry. See the photo of an
example of the aseptic geared motor series.
Aseptic Danfoss geared motor
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