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An isolation transformer is a transformer used to transfer electrical power from a source of alternating current (AC) power to some equipment or device while isolating the powered device from the power source, usually for safety reasons or to reduce transients and harmonics. [1]
Assuming the desired voltage is the same on the two and three phase sides, the Scott-T transformer connection (shown right) consists of a centre-tapped 1:1 ratio main transformer, T1, and a √ 3 /2(≈86.6%) ratio teaser transformer, T2. The centre-tapped side of T1 is connected between two of the phases on the three-phase side.
Charles Felton Scott (September 19, 1864 in Athens, Ohio – December 17, 1944) was an electrical engineer, professor at Yale University and known for his invention of the Scott-T transformer in the 1890s. [1] [2] He graduated from Ohio State University in 1885 and went on to graduate study at Johns Hopkins University.
The primary winding of the transformer is connected to the high voltage or high current circuit, and the meter or relay is connected to the secondary circuit. Instrument transformers may also be used as an isolation transformer so that secondary quantities may be used without affecting the primary circuitry. [14]
A transformer is the most widespread example of galvanic isolation. An opto-isolator is a very popular method of isolation in digital circuits. Cross-section of dual in-line package opto-isolators. Relative sizes of LED (red) and sensor (green) are exaggerated.
A line isolation transformer for telephone use is a special type of impedance matching transformer that is used to couple telephone land lines to subscriber equipment to prevent dangerous common mode voltages from appearing on the line.
The SWER line is a single conductor that may stretch for tens or even hundreds of kilometres, with a number of distribution transformers along its length. At each transformer, such as a customer's premises, current flows from the line, through the primary coil of a step-down isolation transformer, to earth through an earth stake
Any switched-mode power supply that gets its power from an AC power line (called an "off-line" converter [37]) requires a transformer for galvanic isolation. [citation needed] Some DC-to-DC converters may also include a transformer, although isolation may not be critical in these cases. SMPS transformers run at high frequencies.