Transformer core having charge dissipation facility

{
  "publication_number": "US4327349A",
  "country": "US",
  "kind": "A",
  "title": "Transformer core having charge dissipation facility",
  "abstract": "Transformer cores are made electrically conductive during impulse voltage condition when a certain voltage is attained by a coating of semiconductor material applied to the edges or surface of the core laminations. Under ordinary operating conditions the semiconductor material provides a high resistance path to charges in the core. Upon the occurrence of a high voltage impulse, the semiconductor material rapidly equalizes the charges in the laminations and so avoids the danger of breakdown of the insulating coatings between individual laminations.",
  "claims": [
    "1. A transformer core comprising: at least two legs; upper and lower yokes joining said legs in a closed magnetic circuit, said legs and yokes each consisting of a plurality of steel laminations arranged in a stack and electrically insulated from each other; coatings of semiconductor material applied to the exposed edge surfaces of said leg and yoke laminations to accommodate current flow between said laminations; and an electrical ground lead connected with at least one of said core laminations and cooperating with said semiconductor material coatings to provide a current leakage path to ground for excessive electrical charges created on said core laminations as a result of a transformer impulse voltage condition.",
    "2. The core of claim 1 wherein said semiconductor coating is selected from the group consisting of silicon carbide and zinc oxide.",
    "3. The core of claim 1 wherein said laminations comprise a plurality of steel plates containing an inorganic insulating coating thereon.",
    "4. The core of claim 1 wherein said laminations comprise a plurality of steel plates having an enamel coating thereon.",
    "5. The core of claim 1 wherein said coating comprises an insulating enamel containing at least one to ten percent by weight of said semiconducting powder.",
    "6. The core of claim 5 wherein said semiconductor powder comprises three percent.",
    "7. The core of claim 4 wherein said enamel coating includes phenolic resin."
  ],
  "cpc": [
    "H01F 27/343",
    "H01F 27/245"
  ],
  "assignees": [
    "GEN ELECTRIC"
  ],
  "filing_date": "1980-03-19",
  "publication_date": "1982-04-27",
  "grant_date": "1982-04-27",
  "priority_date": "1980-03-19",
  "application_number": "US-13165280-A",
  "family_id": "22450415",
  "citations": [
    "US1322573A",
    "US1418856A",
    "US1822742A",
    "US1891716A",
    "US2042208A",
    "US3210461A",
    "US3214718A",
    "US3642664A",
    "US3663458A",
    "US3687871A",
    "US3705826A",
    "US3824683A",
    "US4008409A",
    "US4042532A",
    "US4095627A"
  ]
}