Electricity: electrical systems and devices – Safety and protection of systems and devices – Transformer protection
Patent
1982-07-29
1984-08-14
Moose, Jr., Harry E.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Transformer protection
361 54, 361 91, H02H 704
Patent
active
044660391
ABSTRACT:
A three-phase power supply has a current transformer in each power line. The transformer secondary winding is connected to a load. Generally, the load is a control means responsive to the current being sensed. A triac in parallel with the secondary winding and load has its gate connected by a voltage sensitive circuit to sense the corresponding secondary winding voltage and to conduct and protect the transformer in the event of load loss. The gate circuit includes a metal oxide varistor and a linear resistor in series connected in parallel with the secondary winding. A second linear resistor is connected to the common node of the first linear resistor and metal oxide varistor. The second linear resistor is in series with a diac and connects the gate to the common node of the varistor and first resistor. A trigger capacitor is connected between the common node of the second resistor and diac and the opposite end of the first linear resistor. On load loss, the secondary voltage rises and the varistor conducts, rapidly charging the trigger capacitor. The diac then conducts and the trigger capacitor supplies a large but controlled gate current to drive the triac "on." During the opposite half cycle, this cycle repeats until a load draws enough current to keep the secondary voltage within a critical level.
REFERENCES:
patent: 3031600 (1962-04-01), Euterneck
patent: 3571660 (1971-03-01), Phillips
patent: 3573550 (1971-04-01), Baker, Jr.
patent: 3723812 (1973-03-01), Lynch
patent: 3727104 (1973-04-01), Neal et al.
patent: 3878434 (1975-04-01), Voorhoeve
patent: 3947751 (1976-03-01), Bray
patent: 4075510 (1978-02-01), Pascente
patent: 4339695 (1982-07-01), Siglock
Transient Voltage Suppression Manual-GE, Copyright 1976, p. 49.
Sketch in a Note to J. Moran Dated 8/31/81.
Beckwith Electric Co., Inc. CT Secondary Protector-2 pages.
Moran Richard J.
Reis Norbert J.
Gealow Jon Carl
Gilroy Hugh M.
McGraw-Edison Company
Moose Jr. Harry E.
Sawall Eugene R.
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