Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Patent
1990-04-06
1991-05-28
DeBoer, Todd E.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
361 49, H02H 328
Patent
active
050199358
ABSTRACT:
A protection device for an electric appliance comprising a differential transformer comprising a magnetic core disposed around a pair of wires leading to the appliance from the source and a sensing wire thereon; a solenoid driven switch for cutting off the source in response to a leakage current in the wires; an SCR which is normally non-conducting for connecting the solenoid to the source in the conducting state so as to cause the switch to be in a cut-off state; a voltage regulator for supplying suitable regulated voltage to an amplifier and a latched-trigger circuit; an amplifier connected to the sensing wires for providing a signal to the latched-trigger circuit; and a latched-trigger circuit for taking the signal from the amplifier and in response thereto provide a trigger signal to cause the SCR to be in a conducting state so as to operate the solenoid and cut-off switch. Advantageously, a Zener diode is provided at one input terminal of the amplifier to provide a threshold level for the differential current detected by the sensing winding to operate the amplifier. By simply adjusting the value of the Zener diode, the threshold level can be simply adjusted. Advantageously, the invention is simple, inexpensive, and reliable.
REFERENCES:
patent: 3891895 (1975-06-01), Wittlinger
Deboer Todd E.
Kojima Moonray
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