Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – With coupling means
Patent
1988-03-22
1989-06-20
Tokar, Michael J.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
With coupling means
324 55, 324117R, 330293, G01R 120
Patent
active
048412368
ABSTRACT:
A current ratio device for use in constructing a current transformer comprises a first magnetic core, a second magnetic core, a measuring winding electromagnetically coupled with the first core but not with the second core, and a compensating winding electromagnetically coupled with both cores. An externally powered amplifier has its input connected to receive the voltage waveform across the measuring winding. Its output provides a compensating current through the compensating winding equal to a magnetizing current required to magnetize the second core. The amplifier output also provides a measuring current through the measuring winding in the direction opposite that of the compensating current and equal to the compensating current multiplied by the ratio of turns in the compensating and measuring windings. This device is a self-contained article of commerce that, when electromagnetically coupled (without electrical connection) to conventional primary and secondary windings and a burden, provides a current transformer with improved qualities. In particular, the magnetizing current needed by the transformer is provided by the separate current ratio device, thus avoiding the error inherent in current transformers that arises from the need to supply the magnetizing current from the primary circuit. Another disclosed feature is the ability to examine the waveform of the magnetizing current and in particular to detect the presence of even harmonics and hence a probability of direct current in the primary circuit.
REFERENCES:
patent: 3153758 (1964-10-01), Kusters
patent: 3534247 (1970-10-01), Miljanic
patent: 4255704 (1981-03-01), Milkovic
patent: 4424480 (1984-01-01), Stefan
patent: 4554513 (1985-11-01), So
patent: 4616174 (1986-10-01), Jorgensen
"The Zero-Flux Current Transformer"-A. Hobson-AIEE Transactions-Aug. 1953-pp. 608-615.
"A Circuit For Reducing The Exciting Current Of Inductive Devices" by D. L. H. Gibbings-The Institution of Electrical Engineers May 1981-pp. 339-342.
Miljanic Petar N.
Moore William J. M.
Canadian Patents and Development Limited-Societe Canadienne Des
Tokar Michael J.
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