06-09-2013, 03:58 PM
Product Brief – Capacitors for power electronics
Capacitors for power electronics.pdf (Size: 1.48 MB / Downloads: 240)
Internal construction
The MKP‐type capacitors consist of a low‐loss dielectric
formed by pure polypropylene film. A thin self‐healing
mixture of zinc and aluminium is metallized directly on one
side of the PP‐film under vacuum. In some cases, additional
unmetallized layers are added between the metallized ones.
The plastic film is wound into stable cylindrical windings on
the most modern automated equipment. The ends of the
capacitor windings are contacted by spraying with a metal
contact layer facilitating a high current load and ensuring a
low‐inductance connection between the terminals and
windings.
Our long‐term experience as well as on‐going research and
improvements in this technology ensure the excellent self‐
healing characteristics of the dielectric and a long operating
life of all our capacitors.
The link between PP‐film and zinc contact layer is highly
stressed during high surge or rms current and therefore
considered very critical for operating life and reliability of
the capacitor. By cutting the film for selected types in a
wave‐like manner, we increase the contact surface between
film and zinc layer which substantially reduces this strain.
Impregnants
The use of filling materials in capacitors is necessary in
order to insulate the capacitor electrodes from oxygen,
humidity and other environmental interference. Without
such insulation, the metal coating would corrode, an
increasing number of partial discharges would occur, the
capacitor would lose more and more of its capacitance
and suffer increased dielectric losses, and a reduced
operating life.
Therefore, an elaborate vacuum drying procedure is
initiated immediately after insertion of the capacitor
elements into the aluminium case and biologically
degradable plant oil or solidifying PUR resin is
introduced. Both protect the winding from
environmental influence and provide an extended life‐
expectancy and stable capacitance.