Electrical transmission or interconnection systems – Capacitor
Patent
1993-10-08
1995-12-12
Shoop, Jr., William M.
Electrical transmission or interconnection systems
Capacitor
3612753, 361329, 361 16, H01G 438
Patent
active
054752728
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a power capacitor with energy limiting properties without fuses and wherein the design and function combine technical advantages of capacitors with internal fuses with the simplicity of capacitors with external fuses.
BACKGROUND ART
Modern power capacitors are characterized by very great energy density, which makes it important to limit the consequences of a fault. As primary protection against capacitor explosions, fuses are used in conventional power capacitors. There are two accepted methods of providing power capacitors with fuses:
Protection of power capacitors by means of internal fuses is space-demanding and renders production expensive since each capacitor element is series-connected with a fuse. However, in relation to the constructionally simpler protection using external fuses, protection by means of internal fuses entails technical advantages since a fault leads to disconnection of the faulty element, which results in very small capacitance changes and increased availability of a power capacitor with internal fuses.
Currently used power capacitors have inherent limitations which can be derived from the respective fuse technique:
Power capacitor units with internal fuses require a certain number of parallel-connected capacitor elements in each group, which limits the maximum unit voltage to approximately 9 kV. High-voltage capacitor banks must therefore be composed of a large number of series-connected groups.
Power capacitors with external fuses have poor protective function at currents higher than 30 A, which limits the maximum unit current. In addition, a certain number of parallel-connected capacitor units in each group are required. Power capacitors protected by means of external fuses must therefore be connected in few series-connected groups with a relatively large number of parallel-connected capacitor units in each group.
Fuse-free power capacitor designed according to the invention eliminate the above-mentioned limitations, and thus, while utilizing the invention, power capacitors can be designed in the most economical way in all applications.
SUMMARY OF THE INVENTION
A power capacitor, which by its design and function combines the technical advantages of power capacitors with an internal fuse with the simplicity and compactness of power capacitors with an external fuse, are achieved by arranging, according to the present invention, a power capacitor comprising a plurality of series-parallel connected capacitor elements, wherein strings of capacitor elements, elements, wherein dielectrics and electrodes included in the capacitor element are arranged such that the electrodes are welded together in case of breakdown and a solid short circuit without the risk of partial discharge or restriking occurs.
Capacitor elements are preferably used in the form of so-called wound foil capacitors of full-film type, the would foil being composed of several wound turns of metal foils serving as electrodes and a solid dielectric arranged between the turns, in the form of one or more polymer films. In case of a controlled breakdown, the metal foils are welded together and thus achieve a solid short circuit. Such an element may remain in operation without the risk of restriking or partial discharge at the fault. A similar fault in a capacitor element with mixed or paper dielectric causes partial discharge and development of gas which in the long run, if the fault point is not disconnected by means of fuses, may blast away the casing surrounding the power capacitor, However, also a breakdown in a wound foil capacitor of full-film type included in a conventionally designed power capacitor would lead to partial discharge as a result of damage caused by the heavy energy development at the fault point of a conventionally designed power capacitor. This is avoided by designing the power capacitor according to the invention such that the energy development upon a breakdown is limited.
In case of breakdown of a capacitor element, this is short-circuited and the unit
REFERENCES:
patent: 1991707 (1931-10-01), Silbermann
patent: 2294099 (1938-10-01), Trapp
patent: 4459637 (1984-07-01), Shedigian
patent: 4771362 (1988-09-01), Behn
patent: 4891733 (1990-01-01), Mammone
patent: 5305178 (1994-04-01), Binder et al.
Asea Brown Boveri AB
Elms Richard T.
Shoop Jr. William M.
LandOfFree
Power capacitor does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power capacitor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power capacitor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1362088