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Current limiting device for an electric power system

  • US 4,184,186 A
  • Filed: 09/06/1977
  • Issued: 01/15/1980
  • Est. Priority Date: 09/06/1977
  • Status: Expired due to Term
First Claim
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1. A current limiting device comprising:

  • (a) two normally-closed circuit interrupters, each interrupter comprising a set of separable contact structures,(b) means for electrically connecting said interrupters in series comprising an electrical conductor connected between said two interrupters, with one interrupter at the source side and one at the load side of said conductor,(c) a normally-open switch,(d) means comprising said switch and effective when said switch is closed for electrically connecting said conductor to ground via a low-impedance conductive path located electrically between said interrupters,(e) switch-operating means responsive to a fault on the circuit extending through the series-combination of said two interrupters for rapidly closing said switch, thereby connecting said conductor to ground through said switch,(f) said switch-operating means operating at such high speed that effective closing of said switch occurs within 1/4 cycle of power frequency current after inception of said fault, thereby effecting current-limiting action with respect to current through said series-combination of interrupters on the load side of said conductive path to ground, said conductive path having a sufficiently low impedance upon closing of said switch to divert through said conductive path despite the presence of said fault sufficient current to effectively produce said current-limiting action,(g) means comprising a mechanical coupling between said switch-operating means and one of the contact structures of said source-side interrupter for opening said interrupters in response to said fault sufficiently rapidly that said source-side interrupter interrupts the current therethrough at one of the first three natural current zeros following fault-inception and said load-side interrupter interrupts the current therethrough shortly thereafter, and(h) an impedance connected in parallel with said series combination of interrupters, and with no effective connection between said impedance and said conductor except through said interrupters, for conducting current, limited in magnitude by said impedance, around said interrupters when said interrupters have interrupted the respective currents therethrough following their aforesaid opening.

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