The working principle of autotransformer power supply is based on electromagnetic induction principle. Voltage conversion is achieved by sharing part of the windings. The core is to adjust the output voltage by using different faucets in a single winding. The following is a description of the specific principles:
Shared winding structure: The autotransformer wraps the coil around the same core and is part of both the primary and secondary sides. The input-output voltage ratio can be adjusted by changing the position of the tap. For example, when used as a pressure-relief transformer, a portion of the elbow is pulled out of the winding as a secondary winding; when used as a booster transformer, the external voltage acts only on a portion of the winding bend. The part of winding that belongs to both primary and secondary winding is usually called ordinary winding and the rest is called series winding.
Electromagnetic induction energy transfer: When a winding is connected to an alternating current, the current produces alternating current, which passes through the core and generates an electromotive force in a secondary winding. The energy transfer efficiency is higher because the primary winding and the second winding share part of the coil.
Voltage regulation mechanism: by adjusting the tap position, change the number of turns of one winding and two winding, so as to achieve voltage rise rise and fall. For example, when the turns ratio is 2:1, the input voltage is 55kV and the output voltage is 25kV.
Characteristics of current distribution: In an autotransformer, the primary current and secondary current are inversely proportional to the number of turns. During the power supply process, one part of the current is transmitted directly through the winding, and the other part is transmitted through electromagnetic induction, making the energy transfer more efficient.
Application of Power supply: In the AT mode of electrified railway lines, for example, the autotransformer doubles the power supply voltage of the traction network, while the supply voltage for electric locomotives remains 25kV. After the electric locomotive is supplied by the catenary, the traction current usually flows back through the guide rail. Due to the action of the autotransformer, the current returns to the substation through the rail, through the winding of the autotransformer and the positive feed line. When an auto-transformer winding flows through a locomotive current, its other winding produces an electric current that supplies the locomotive. Therefore, when the locomotive load current is I, the contact wire and the positive feed line provide 0.5I, while the other load current is provided by the current generated by the autotransformer.
