Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Patent
1974-11-25
1976-08-31
Strecker, Gerard R.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
317 18D, 340255, G01R 3102, H02H 316
Patent
active
039784002
ABSTRACT:
A ground fault detector for an ungrounded electrical distribution system responds to a wide range of ground fault current levels by providing the ground fault sensing circuitry with a high impedance at low ground fault signal levels and a low impedance at higher ground fault signal levels. The varying or nonlinear impedance of the sensing circuitry occurs due to the presence of the series combination of a Zener diode and a resistor connected in parallel with a level sensing means. At ground fault signals below the Zener voltage of the Zener diode, the impedance of the sensing circuitry is that of the level sensing means. When the ground fault signal exceeds the Zener voltage, the impedance of the sensing means is significantly reduced since the Zener resistor is now in effective parallel combination with the impedance of the level sensing means.
Varying degrees of filtering of the ground fault signal are accomplished through provision of alternate connection terminals of increasing resistance for a filtering capacitor.
A ground fault test circuit for the detector provides the equivalent of one-half ampere ground fault. Higher ground faults may easily be simulated by winding additional turns of a test winding on a differential transformer of the detector; each additional turn simulates an additional one-half ampere ground fault.
REFERENCES:
patent: 3165671 (1965-01-01), Mintz et al.
patent: 3187225 (1965-06-01), Mayer
patent: 3259802 (1966-07-01), Steen
patent: 3268813 (1966-08-01), Pendleton
patent: 3356939 (1967-12-01), Stevenson
patent: 3419756 (1968-12-01), Philibert et al.
patent: 3506906 (1970-04-01), Nestor
patent: 3535590 (1970-10-01), Mayer
patent: 3555360 (1971-01-01), Lee et al.
patent: 3571660 (1971-03-01), Phillips
Pristelski James S.
Rathbun Harold J.
Schmeling William H.
Square D Company
Strecker Gerard R.
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