LITERATURE REVIEW

Historical background

According to Lee De Forest, Automatic Voltage Regulator (AVR) came into existence in 1959 when he invented an autotransformer (sometimes called auto-former). And it has an electrical connection points called taps. The voltage source and the load are each connected to two taps. One tap at the end of the winding is a common connection to both circuits (source and load). Each tap corresponds to a different source or voltage. In an auto-transformer a portion of the same winding acts as part of both the primary and secondary winding. Single-phase tapped auto-transformer with output voltage range of 40% - 115% of input. The ratio of secondary to primary voltages is equal to the ratio of the number of turns of the winding they are connected to. For example connecting at the middle and bottom of the auto-transformer will half the voltage. Depending on the application, that portion of the winding used solely in the higher voltage (lower current) portion may be wound with wire of a smaller gauge, through the entire winding is directly connected. A failure of the insulation or the windings of an auto-transformer can result in full input voltage applied to the output. This is an important safety consideration when deciding to use an auto-transformer in a given application. Because it requires both fewer windings and a smaller core, an auto-transformer for power applications is typically lighter and less costly than a two-winding transformer, up to a voltage ratio of about 3:1. beyond that range a two-winding transformer is usually more economical.

According to Fatirleitungan eletricher Bahen BG Teebner Verlag, Stuttgart. Page 672. An English edition Contact lines for electric Railways appears to be out of print. This industry standard text describes the various European electrification principles. Stated that a device used to change the voltage of an alternating current in one circuit to another in different voltage is called automatic voltage regulator. And a Transformers consist of two or more coils of conducting material such as wire, wrapped around a core (often made of iron). The magnetic field produced by an alternating current in one coil induces a similar current in the other coils. If there are fewer turns on the coil that carries the source of the power than the second coil, the second coil will provide the same power but at a higher voltage. This is called a step-up transformer. If there are fewer turns on the second coil than on the source coil, the outgoing power will have a lower voltage. This is called a step-down transformer.