In 1963 Celem designed the first low voltage conduction cooledTM 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-cooledTM 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-cooledTM 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 coolingTM 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 δ < 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 :
