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Electric motor underload protection system

  • US 4,703,387 A
  • Filed: 05/22/1986
  • Issued: 10/27/1987
  • Est. Priority Date: 05/22/1986
  • Status: Expired
First Claim
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1. An underload protection system adapted to be connected to an electric motor and first and second power supply lines, the lines being connectable to an AC power supply supplying a line voltage and line current, said system comprising line voltage sensing means adapted to be connected to said lines and to have a line voltage signal impressed therein, an amplitude adjustment circuit connected to said voltage sensing means and adjusting the duration of the line voltage signal in proportion to the value of the line voltage to produce an amplitude adjusted voltage signal, line current sensing means adapted to be connected to the second line and to have a line current signal impressed thereon, a phase adjustment circuit connected to the current sensing means and adjusting the phase of the current signal to produce a phase adjusted current signal, phase responsive means connected to said amplitude adjustment circuit and to said phase adjustment circuit and producing an adjusted power factor signal, and disconnect means connected to said phase responsive means and adapted to disconnect the power lines when the power factor is below a preset value.

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