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BRIEF GUIDE TO CELEM TECHNOLOGY
Conduction-cooled
Power Capacitors
In 1963 Celem designed the first low voltage conduction
cooled power capacitor. Until this time all power capacitors
were cooled by immersing the terminals and dielectric
in an oil bed and water-cooling the oil. In contrast,
the conduction-cooled capacitor uses the same bus bar
connection that provides its electrical connection to
transfer away the heat dissipated within it. This approach
yields an enormous reduction in volume per unit power
as well as being simpler and cheaper for manufacture.
Celem's conduction-cooled power capacitors remain to
this day the unchallenged market leader in the high-frequency
induction heating market.
Assembly Systems
When building a large induction heating installation,
a need often arises for the combination of multiple
capacitors in series or parallel to obtain the required
capacitance, power and voltage ratings needed for the
system. In order to help our customers avoid much head-scratching,
trying to re-invent the wheel, Celem designed several
modular assembly systems ourselves. These systems allow
the combination of capacitors in a variety of ways,
and even allow hot-swapping of capacitors during usage
to change operating frequency.
Water-cooled Power Capacitors
Conduction cooling capacitors requires water-cooling
of the bus bars to which the capacitor is connected.
While this is the logical solution in a capacitor bank
composed of many capacitors in series or parallel, when
a single capacitor is used it makes more sense to integrate
the cooling into the capacitor itself. This approach
became possible after Celem began producing capacitors
based on a polypropylene dielectric, and provides the
customer with a ready-to-go solution at a lower cost
than an assembly system.
High Operating Temperature / UHF Power Capacitors
While polypropylene technology surpasses mica for specific
power, mica has a much higher operating temperature
than polypropylene and no frequency limitation. For
an operating environment above 85°C or frequencies
beyond 1MHz, mica capacitors provide a solution which
is far cheaper than the ceramic technology that dominates
this market.
Mica
This dielectric is characterised by:
· a low loss angle (tan d < 5x10-4)
· a dielectric constant that is independent of
temperature
· flexible operating temperature range (works
at over 200°C)
· reasonable thermal conductivity
· good dielectric constant (k=8), allowing higher
capacitances per unit volume
Celem historically began its product range using mica.
Today, mica technology has been surpassed for the most
part by polypropylene, and many legacy Celem mica products
can be replaced by cheaper and superior polypropylene
equivalents (such as CPRI400P that replaces CPRI300).
Polypropylene
The dielectric used in most of Celem's products, polypropylene
provides a number of advantages :
· higher power rating per unit volume
· allows construction of self-healing capacitors
· simpler to manufacture
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