Electricity: electrical systems and devices – Safety and protection of systems and devices – Transformer protection
Patent
1985-08-19
1990-09-18
Jennings, D.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Transformer protection
361 56, 361 91, H02H 710
Patent
active
049582500
ABSTRACT:
A switching apparatus (30) provides a normally high impedance connection which is capable of switching currents with high magnitudes and high rates of rise between the primary (12) and secondary (15) neutrals of a service transformer (13), such as that used to supply power to a farmstead, such that undesirable voltages appearing on the primary neutral line are not transmitted to the secondary neutral. Upon the occurrence of a fault at the distribution transformer, or a surge on the power line, the switching apparatus (30) rapidly switches to provide a low resistance connection between the primary and secondary neutrals so that any fault current passing from the primary to the secondary of the transformer will be shunted back to the primary neutral. The apparatus preferably includes a pair of high speed electronic switches (34, 35), such as SCR thyristors, connected in parallel with opposite polarity, the combined SCR's connected in series with an inductor, and the resulting series-parallel combination connected in parallel with a varistor between the primary and secondary neutrals.
REFERENCES:
patent: 2087340 (1937-07-01), Davis
patent: 3213349 (1985-10-01), Gulzwiller
patent: 4186418 (1980-01-01), Seiler
patent: 4217618 (1980-08-01), Kellenbenz et al.
patent: 4237509 (1980-12-01), Asplund
patent: 4475139 (1984-10-01), Chadwick
patent: 4509089 (1985-04-01), Suedberg
"Stray Voltage Problems with Dairy Cows" by Cloud et al., Publication 125, Agricultured Extension Service Univ. of Minnesota, 1980.
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