Voltage failure sensing circuit

Claim 1

A circuit for sensing voltage failure in a multiphase conductor power supply comprising: first circuit means connected to at least one of the phase conductors for deriving a first DC. voltage corresponding to the maximum phase conductor voltage; second circuit means connected to certain of the phase conductors for deriving second DC. voltages respectively corresponding to the phase conductor voltages thereof; sensing means in circuit with said first voltage; electronic switching means having a control element, said switching means being in series circuit with said sensing means and ground, said sensing means being energized upon application of said first voltage thereto when said switching means is conductive; first gating means in circuit with said control element, said first gating means being conductive upon application of a predetermined voltage thereto; biasing means in circuit with said first voltage and said first gating means for conductively biasing said switching means through said first gating means upon conduction of the latter when said first voltage exceeds said predetermined voltage; and second gating means connecting each said second circuit means to said first gating means, each said second gating means being conductive when the said second voltage derived thereto decreases to a value below said predetermined voltage, conduction of a said second gating means serving to decrease the voltage on said first gating means to sAid value for rendering the latter nonconductive, thereby interrupting the bias to said switching means; whereby voltage failure of any of the phase conductors to a value less than said predetermined voltage serves to interrupt bias to said switching means to de-energize said sensing means.