How does an auto transformer work?

The common transformer transmits energy through the electromagnetic coupling of the far side coil, the far side has no direct electrical connection, the far side of the autotransformer has a direct electrical connection, and the low voltage coil is part of the high voltage coil. The protection of communication lines also uses electrical equipment such as automatic transformers.
The autotransformer is made according to the self-inductance phenomenon in the electromagnetic induction phenomenon, which mainly regulates the voltage level. Principle of autotransformer: In fact, the principle is the same as that of ordinary transformers, but the automatic transformer affects itself. Bypassing two or more coils on the closed core, when one coil enters the AC power supply, there will be an AC current flow in the coil, this AC current creates an AC magnetic field in the core, the AC main magnetic flux generates a self-induced electromotive force in the primary coil, and induces a mutual induced electromotive force in the other coil.
An autotransformer is a special transformer in which the output and input share a set of coils. Boost and buck are done with different pumps. Part of the tap voltage below the common coil is reduced. More partial tap voltage increases compared to shared coils.
An autotransformer has only one winding, and when it is used as a step-down transformer, part of the line in the winding is rotated as a secondary winding. When used as a boost transformer, the external application voltage is added to only part of the line rotation of the winding. In general, part of the second and second winding is called the general winding, the rest of the automatic transformer is called the serial winding, the same capacity of the automatic transformer compared with the ordinary transformer, small volume, high efficiency, the larger the capacity, the higher the voltage.
By changing the relationship between the primary and secondary coil turns ratio, the primary and secondary coil end voltage is changed to achieve the voltage transformation, and the general turn ratio is 1.5:1 ~ 2:1. Because the primary and secondary coils are directly connected, there is a risk of cross-stage leakage. So it can not be used as a lamp transformer.
The autotransformer is suitable for situations where the first and second isolation is not required, and has the advantages of small size, less consumables and high efficiency. Typical AC voltage regulator, transformer in household small AC voltage regulator, transformer in three-phase motor automatic decompression starting box, etc., are all application examples of automatic transformer.
The autotransformer has simple structure and low cost. And autobuck compensators are widely used. However, because the primary and secondary of the autotransformer are not isolated on the circuit, the safety performance is not high. Therefore, in places that require the use of safe voltage, the use of autotransformers is prohibited.
With the rapid development of China’s electrified railway industry, the autotransformer power mode has made great progress, which is very suitable for large-load power supply and has little interference to communication lines, so it is widely used in passenger dedicated lines and heavy-duty freight railways.