Variacs

Autotransformers, another name for various, are a specific kind of electrical transformer with just one winding. The transformer winding serves as both the primary and secondary sides. Instead, the standard transformer type has two coils that are not electrically coupled. The one winding resolution enables the production of transformers that are smaller, lighter, and less expensive than conventional ones with two winds. They also have a higher VA rating for a given size and mass in addition to reduced leakage reactance, smaller losses, and lower excitation current. On the other side, there is no electrical shielding between circuits, which is a drawback. It may cause the output to receive the entire input voltage.

Frequently Used Variacs/Autotransformers 

• Power transmission and distribution – Variacs make sure that the voltage at the beginning and the end of the power distribution line are equal.
• Power conversions – Various ensures to transform frequent domestic mains current bands that are in use around the world. For instance, 200 V to 250 V or 100 V to 130V.
• Audio systems – Autotransformers are automated to adjust speakers to a fixed- voltage distribution and for matching preventing levels.

Applications 

• Power transmission and distribution: In power applications, autotransformers are typically used to link systems that operate at several voltage classes, such as 132 kV to 66 kV for transmission. Making equipment designed (for instance) for 480 V supplies run on a 600 V supply is another use in industry. Additionally, they are frequently employed to provide conversions between the two home mains voltage bands that are most widely utilized worldwide (100 V-130 V and 200 V-250 V). The "Super Grid" connections in the UK between the 400 kV and 275 kV networks typically consist of three-phase autotransformers with taps at the common neutral end.
• Audio system: Tapped autotransformers/Variacs are employed in audio applications to impedance matches, such as between a low-impedance microphone and a high-impedance amplifier input, and to adapt speakers to constant-voltage audio distribution systems.
• Railways: It is typical for trains to be powered at 25 kV AC in railway applications. They can be set up to provide a split-phase 25-0-25 kV feed with the third wire (opposite phase) out of the reach of the train's overhead collection pantograph to extend the distance between energy Grid feeder stations. One 25 kV point of the supply is linked to the overhead contact wire, while the supply's 0 V point is attached to the rail. An autotransformer connects the contact wire to the rail and the second supply conductor (antiphase) at regular (10 km) intervals.
• Autotransformer starter: Induction motors may be softly started using autotransformers. The Korndörfer starter is one of these starters' well-known designs.

Functions 

A single winding of an autotransformer has two end terminals and one or more terminals at the intermediate tap points. It is a transformer with shared turns between the main and secondary coils. The common part of the winding is the area that both the primary and secondary share. The series part of the winding is the area that is not shared by the main and secondary. Two of the terminals get the principal voltage. Two terminals are used to supply the secondary voltage, one of which is often shared with a primary voltage terminal.

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