Field ground fault detector and field ground fault relay for det

Details Field ground fault detector and field ground fault relay for det Field ground fault detector and field ground fault relay for det

1995-02-23

1997-10-07

Gaffin, Jeffrey A.

Electricity: electrical systems and devices

Safety and protection of systems and devices

Ground fault protection

361 20, 361 23, H02H 300

Patent

active

056754655

ABSTRACT:
According to a field ground fault detector, a predetermined resistor is connected in series to a predetermined DC voltage. A DC voltage is applied between an N electrode side field circuit of a generator and a ground through the resistor. A voltage applied between terminals of the resistor is input to a low-pass filter. A voltage applied between the N electrode side field circuit and the ground is input to another low-pass filter. Output voltages of the low-pass filters are input to a level ratio determining circuit. The level ratio determining circuit outputs the determined result of the ground fault to the outside of the field ground fault detector corresponding to these voltages. Thus, even if the DC voltage varies or a higher harmonic voltage takes place in a generator of a thyristor exciting type, it does not affect the detecting sensitivity of the ground fault.

REFERENCES:
patent: 4187525 (1980-02-01), Nagura
patent: 4410925 (1983-10-01), Tucker et al.
patent: 4679111 (1987-07-01), Koch et al.
patent: 4864242 (1989-09-01), Hurley
Patent Abstracts of Japan, vol. 8, No. 229 (E-273), Oct. 20, 1984, JP59110395.
Patent Abstracts of Japan, vol. 5, No. 42 (P-053), Mar. 20, 1981, JP55164378.
Patent Abstracts of Japan, vol. 15, No. 486 (E-1143), Dec. 10, 1991, JP03212117.
Elektrotechnik, "Erkennt Effektivwerte, Leistungsschalter Mit RMS-Messystem," vol. 71, No. 4, Jun. 1989, p. 40.

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