Automatically resetting overvoltage protection means for an alternating current circuit

Claim 2

An overvoltage protective apparatus comprising: terminals that may be connected to an alternating current supply; a load; a switching means; a circuit for supplying current to said load through said switching means from said terminals; means for causing said switching means to become conductive after a delay period after the beginning of a half-cycle of one polarity of said alternating current supply, means to sample the voltage of said supply during half-cycles of the opposite polarity; and means responsive to said sampled voltage being greater than a predetermined voltage to disable said means for causing said switching means to become conductive during said delay period.

Claim 3

The invention as expressed in claim 1 in which said switching means comprises an SCR and said delay means cOmprises a capacitor and a resistor connected in series across said terminals, and means are provided for applying the voltage across said capacitor to the control electrode of said SCR by way of a threshold device.

Claim 4

The invention as expressed in claim 2 in which said means to sample comprises a first diode and a resistor connected across said terminals and a second capacitor and a second diode connected across at least a portion of said resistor, said first diode being poled to prevent charging of said capacitor during said half-cycle of said one polarity and means for applying the voltage across said second capacitor through a threshold device to inhibit the conduction of said switching means during the half-cycle of said supply of said one polarity when the voltage across said second capacitor is great enough to break down said threshold device.

Claim 5

The invention as expressed in claim 1 and including a second switching device connected in parallel with said first switching device, said switching devices each having rectifying properties and being oppositely poled with respect to each other and means to render said second switching device conductive responsive to current flow through said load.

Claim 6

An overvoltage device comprising: a pair of terminals to which a source of alternating potential may be connected; a load; a first, a second and a third silicon controlled rectifier each having an anode, a cathode and a control electrode; means for connecting one of said terminals through said load and through the anode to cathode path of said first silicon controlled rectifier to the second one of said pair of terminals; means connected across said terminals to build up a predetermined voltage after a delay; a connection from said voltage building up means to the control electrode of said first silicon rectifier for causing said first silicon controlled rectifier to become conductive upon said predetermined voltage being built up on said voltage building up means; means for connecting said anode of said second silicon controlled rectifier to the cathode of said first silicon controlled rectifier and for connecting the cathode of said second silicon controlled rectifier to the anode of said first silicon controlled rectifier; means controlled by the current flow in said load and connected to the control electrode of said second silicon controlled rectifier for turning it on when said first silicon controlled rectifier is off; means for connecting the anode of said third silicon controlled rectifier to the control electrode of said first silicon controlled rectifier and for connecting the cathodes of said first and third silicon controlled rectifiers together; means for sampling the voltage across said source during a half-cycle of said alternating current; means including a connection between said voltage sampling device and the control electrode of said third silicon controlled rectifier for causing conduction of said third silicon controlled rectifier during a next half-cycle after the voltage sampled by said voltage sampling device reaches a predetermined amplitude, whereby when said third silicon controlled rectifier is conductive, said first silicon controlled rectifier is prevented from becoming conductive.

Claim 7

An overvoltage device comprising: a pair of terminals to which a source of alternating potential may be connected; a load; a first, a second and a third silicon controlled rectifier each having an anode, a cathode and a control electrode; means for connecting one of said terminals through said load and through the anode to cathode path of said first silicon controlled rectifier to the second one of said pair of terminals; means connected across said terminals to build up a predetermined voltage after a delay; a connection from said voltage building up means to the control electrode of said first silicon rectifier for causing said first silicon controlled rectifier to become conductive upon said predetermined voltage being built up on said voltage building up means; means for connecting said anode of said second silicon controlled rectifier to the cathode of said first silicon controlled rectifier and for connecting the cathode of said second silicon controlled rectifier to the anode of said first silicon controlled rectifier; means controlled by the current flow in said load and connected to the control electrode of said second silicon controlled rectifier for turning it on when said first silicon controlled rectifier is off; means for connecting the anode of said third silicon controlled rectifier to the control electrode of said first silicon controlled rectifier and for connecting the cathodes of said first and third silicon controlled rectifiers together; means for sampling the voltage across said source during a half-cycle of said alternating current; means including a connection between said voltage sampling device and the control electrode of said third silicon controlled rectifier for causing conduction of said third silicon controlled rectifier during a next half-cycle after the voltage sampled by said voltage sampling device reaches a predetermined amplitude, whereby when said third silicon controlled rectifier is conductive, said first silicon controlled rectifier is prevented from becoming conductive.

Claim 8

The invention as expressed in claim 5 in which said voltage sampling means comprises a diode and a resistor connected across said terminals and a capacitor in series with a diode connected across at least a portion of said resistor, the junction of the capacitor and the second mentioned diode being connected to the control electrode of said third silicon controlled rectifier.

Claim 9

The invention as expressed in claim 6 in which the cathode of the first mentioned diode is connected to the first of said pair of terminals.