An auto-transformer is a type of electrical transformer with a single winding that serves both as the primary and secondary winding. It differs from a conventional transformer, which has separate primary and secondary windings. In an auto-transformer, a portion of the winding acts as the common winding shared by both primary and secondary circuits.
The concept of an auto-transformer is based on the principle of electromagnetic induction, where a changing magnetic field induces a voltage across a coil. When an alternating current flows through the winding, it creates a varying magnetic field, which, in turn, induces a voltage in the same winding. This induced voltage is then added to or subtracted from the applied voltage, depending on the winding configuration.
The basic construction of an auto-transformer consists of a laminated core and a single winding that is tapped at different points. The tapping points determine the ratio of the input voltage to the output voltage, making it possible to step up or step down the voltage level. The portion of the winding before the tap serves as the primary winding, while the portion after the tap serves as the secondary winding.
Auto-transformers are commonly used in various electrical applications for voltage regulation, especially in systems where a small voltage adjustment is needed. They offer advantages such as reduced size, weight, and cost compared to traditional transformers for the same voltage conversion ratio. However, they also have certain limitations, including lower isolation between the input and output voltages and a higher risk of short-circuiting between windings. Therefore, their use is often carefully considered based on the specific requirements of the application.