Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G4/00—Fixed capacitors; Processes of their manufacture
  • H01G4/002—Details
  • H01G4/005—Electrodes
  • H01G4/008—Selection of materials
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01G—CAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES, LIGHT-SENSITIVE OR TEMPERATURE-SENSITIVE DEVICES OF THE ELECTROLYTIC TYPE
  • H01G4/00—Fixed capacitors; Processes of their manufacture
  • H01G4/002—Details
  • H01G4/005—Electrodes
  • H01G4/015—Special provisions for self-healing

Definitions

• the invention is based on a self-healing electrical capacitor, in particular an AC capacitor, according to the preamble of the main claim.
• a self-healing electrical capacitor in particular an AC capacitor, according to the preamble of the main claim.
• square resistances surface resistances per square unit
• a circular, progressive degradation of the aluminum layers sets in a, which leads to a corresponding progressive decrease in capacity due to the loss of contribution area.
• the layer degradation begins at a frequency of 50 Hz with an effective field strength of approx. 40 V! L1m.
• fluorescent lamp capacitors with metallized polypropylene foils as a dielectric for nominal voltages from 220 to 250 V / 50 Hz are made with known aluminum covering layers made of 8 ⁇ m thick foil, although the foil thickness of 6 ⁇ m for sufficiently thin aluminum layers with a square resistance greater than 3 , 5 ohms would be sufficient.
• the resulting field strength is too high, however, because at least the prescribed electrical test voltages, for example 1.25 x nominal voltage or higher, cause the layer degradation mentioned. This layer degradation therefore causes higher costs for the capacitor and larger volumes than are necessary per se.
• the aim is to prevent the above-mentioned layer degradation up to the highest field strengths permitted for the respective dielectric, or at least in the case of increased mean field strengths, or to reduce it to a practically insignificant level.
• reliable, single-layer capacitors made of metallized polypropylene or polycarbonate film are to be created for effective alternating nominal voltages up to 320 V with film thicknesses up to 6 ⁇ m, for 400 to 500 V with a film thickness of 8 ⁇ m and for voltages over 500 V with film thicknesses of 9 around or above.
• the self-healing electrical capacitor according to the invention with the characterizing features of the main claim has the advantage that the field strength-dependent layer degradation no longer occurs.
• the average proportion by weight of copper in an aluminum layer should preferably be between 2 and 5%. Copper fractions below about 0.5%, as can occur, for example, as impurities in the production of the layered metals, have no influence in the sense of the invention; with weight fractions above 10%, it can be expected that the same degradation phenomena can occur in areal precipitation of the added copper as in the aluminum layer.
• the covering layer of the capacitor is produced by the vapor deposition process, because here layers can be produced in the desired manner with high uniformity at relatively low costs.
• the healing properties of the electrical capacitor are particularly favorable if the aluminum covering layer has an average covering of less than 10 ⁇ m aluminum per cm 2 of the covering surface.
• the lower limit is recommended to be about 4 ⁇ g / cm 2 in order to limit the size of the coating resistance depending on the vapor deposition conditions.
• 6 .mu.m thick polypropylene film strip was vapor-coated on one side by thermal evaporation in vacuo with an aluminum layer which contained a weight fraction of approx. 4% copper and had a square resistance of 5 to 7 ohms.
• An alloy wire with a copper alloy content was used as the evaporation material, the total mean area coverage with the evaporation material being approximately 7 ⁇ g / cm 2 .
• Winding capacitors were produced from a pair of rolls of these tapes. Under otherwise identical conditions and dimensions, capacitors were produced for comparison with the same polypropylene film, but the coatings of which, in a known manner, consisted of aluminum layers with square resistances of 2.5 to 3 ohms. Evaporation material was high-purity aluminum wire, the average area coverage was approx. 9 ⁇ g / cm 2 .
• the covering layers according to the invention can be produced using known physical or chemical metallization processes, provided that a sufficiently homogeneous distribution of the copper admixtures to the required extent and the keeping away of harmful additives is ensured in the covering layer.
• the new capacitor covering layers can also be applied to a capacitor dielectric in the case of thin multiple layers;
• an aluminum alloy layer in combination with a metallized Zn coating layer can serve as a corrosion-inhibiting thin aluminum layer, which is more resistant to environmental influences than a Zn layer due to its oxide skin.
• the covering layer according to the invention has made it possible to provide higher nominal field strengths for the capacitors and thus to manufacture the capacitors smaller and less expensively.
• the application of the covering layer requires practically no additional effort, especially when vapor deposition, and brings considerable technical and economic advantages. Interlayers or multilayer systems, as have already been proposed, are not required. When combined with a zinc layer, for example, the higher conductivity of aluminum and the protective effect of the aluminum oxide skin could result in a reduction in the overall application for the coating layer.
• the structure of the covering layer according to the invention also has the advantage that electrical breakdowns in the dielectric, which can be triggered by operational surge peaks, burn out properly. Furthermore, higher test voltages are possible without the risk of bad burnouts, which means that the test voltage can be increased with a shorter test duration. Finally, it is also advantageous that, due to the smaller layer thickness, shorter evaporation times and a lower thermal load on the layer carrier are achieved.
• the covering layers according to the invention can be used advantageously both in impregnated and in non-impregnated capacitors, since layer degradation is also observed with impregnated capacitors from a certain average field strength.
• a layer degradation is observed with a pure aluminum layer at an average field strength of approximately 80 V / ⁇ m (50 Hz); for capacitors with a mixed dielectric of 8 microns thick metallized paper tape and 6 [tm polypropylene film with a sheet resistance of the aluminum layer of approximately 15 Q is a layer degradation 'detected in the voltage 475 V; 50 Hz.
• An aluminum covering layer has an average covering of 4 to 10 ⁇ g aluminum per cm 2 of the covering surface.

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Manufacturing & Machinery (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Fixed Capacitors And Capacitor Manufacturing Machines (AREA)

Applications Claiming Priority (2)

Publications (2)

Family

ID=6013059

Family Applications (1)

Country Status (5)

Families Citing this family (13)

Family Cites Families (6)

• 1977
  • 1977-07-02 DE DE2730038A patent/DE2730038C2/de not_active Expired
• 1978
  • 1978-06-01 EP EP78200006A patent/EP0000210B1/de not_active Expired
  • 1978-06-01 DE DE7878200006T patent/DE2861777D1/de not_active Expired
  • 1978-06-23 US US05/918,431 patent/US4190878A/en not_active Expired - Lifetime
  • 1978-06-30 IT IT25170/78A patent/IT1096867B/it active
  • 1978-06-30 JP JP7968778A patent/JPS5413958A/ja active Granted

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