Alternately low and high input-impedance detector for use in a GFI
AssigneeSprague Electric Company
InventorEdward C. Hudson, Jr.
Life of this patent
Estimating the term…
Abstract
A ground fault interrupter employs a single differential transformer that is made of a ferrite toroid with an eleven turn secondary winding. The transistorized fault detector circuit is for the most part formed on a silicon integrated chip. The hot-wire-to-ground-fault detector portion is an impedance-transforming circuit that when energized presents a low impedance, i.e. virtually a short circuit, to the secondary winding. A multiplexing circuit periodically de-energizes the hot-wire-to-ground-fault detector causing it to present a high input impedance during periods when neutral-wire-to-ground faults are sensed via the transformer.
Claims24
An alternately low and high input impedance detector, for use in a ground fault interrupter of the type comprising a circuit breaker in an AC voltage power line and a differential transformer having a secondary winding and two equal turn primary windings that are adapted to connect a "hot" wire and a "neutral" wire of said power line from a power source to an electrical load, comprising an impedance-transforming signal-transmitting means having an input for being directly connected across said secondary winding,
- for presenting, when energized, a low input impedance to said secondary winding to cause said differential transformer to behave as a current transformer,
- for tripping said breaker when a hot-wire-to-ground-fault causes a fault current exceeding a predetermined value, and
- for presenting, when not energized, a high input impedance to said secondary winding,
- said impedance transforming means including a first bipolar transistor having an emitter that is coincident with the input of said impedance transforming means, an inverting voltage amplifier having an input connected to said emitter and an output connected to the base of said first transistor to reduce the input impedance thereof and to produce an output current at the collector of said first transistor that is directly related to said fault current and effects said tripping of said breaker.
A ground fault interrupter comprising:
- (a) a differential transformer having a secondary winding, and having two equal turn primary windings that are adapted to connect a "hot" wire and the neutral wire, respectively, of an AC power line between an AC energy source and an electrical load;
- (b) an impedance-transforming signal transmitting means having an input connected across said secondary winding for presenting, when energized, a low input impedance to cause said differential transformer to perform as a hot-wire-to-ground-fault current transformer and for producing from a high output impedance an output current that is proportional to the current at said input, and for presenting, when not energized, a high input impedance to said secondary winding, said impedance transforming means being comprised of a first bipolar transistor having an emitter and a collector corresponding respectively to said input and output of said impedance transforming means, and an inverting feedback amplifier connected from said emitter to the base of said first transistor;
- (c) a neutral-wire-to-ground-fault detector means being connected to said secondary winding for, when energized, providing an output signal of a magnitude that is directly related to the value of a ground-to-neutral-fault resistance that may exist between the neutral line at said load and ground;
- (d) a switching means for periodically energizing said impedance-transforming means during some periods A and during other periods B de-energizing said impedance-transforming means, and simultaneously de-energizing and energizing, respectively, said neutral-wire-to-ground-fault detector means;
- and
- (e) a breaker means for breaking said power line when during said periods A said output current from said impedance-transforming means exceeds a predetermined value and when during said periods B said output signal from said neutral-wire-to-ground-fault detecting means falls below a predetermined value.
A power cord with ground fault interrupter comprising:
- I. A power cord, for making connection by one and the other ends of said cord, respectively, to an AC power outlet and an electrical load, said cord having two wires that are electrically insulated from each other;
- an electrically insulating sheath containing said wires, and a male plug at said one end of said cord being adapted to be plugged into said outlet and being electrically connected to said two wires;
- and
- II. A ground fault interrupter being attached at an intermediate point in said cord between said one and said other ends and comprising:
- (a) a differential transformer having a toroidal magnetic core and a secondary winding of a plurality of fine turns wound on said core, each of said two wires of said cord being threaded once through said toroid to serve as primary windings of said transformer;
- and
- (b) an impedance-transforming signal transmitting means having an input connected across said secondary winding for presenting, when energized, a low input impedance to cause said differential transformer to perform as a hot-wire-to-ground-fault current transformer and for producing from a high output impedance an output current that is proportional to the current at said input, and for presenting, when not energized, a high input impedance to said secondary winding, said impedance transforming means being comprised of a first bipolar transistor having an emitter and a collector corresponding respectively to said input and output of said impedance-transforming means, and an inverting a feedback amplifier connected from said emitter to the base of said first transistor.
Dependencies are inferred from the claim text.