In an autotransformer, the common portion of the single winding acts as part of both the “primary” and “secondary” windings. The remaining. Electrical Tutorial about the Autotransformer and the Variable Auto The main advantage of this type of transformer design is that it can be made a lot cheaper for the same VA rating, but the biggest disadvantage of an autotransformer is that it. An autotransformer is an electrical transformer with only one winding. The “auto” ( Greek for and cheaper than typical dual-winding transformers, but the disadvantage of not providing electrical isolation between primary and secondary circuits. Other advantages of autotransformers include lower leakage reactance, lower.

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The supply voltage is applied across AB, and the load is connected across CB.

In short, we say advantwges there is a wide range of advantages of autotransformers. Now, from the above figure B shown of the auto transformer, the weight of copper required in an auto transformer is.

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There are also advsntages in which the secondary intake is achieved through a sliding brush, allowing a continuous range of secondary voltages ranging from zero to the voltage of the source. Hence, saving in copper increases as the transformation ratio approaches to unity.

Electrical Transformers and Power Equipment.

Autotransformer – Wikipedia

As in the ordinary transformer, the primary and secondary ampere-turns balance each other, except for the small current required for core magnetization: In audio applications, tapped autotransformers are used to adapt speakers to constant-voltage audio distribution systems, and for impedance matching such as between a low-impedance microphone and a high-impedance amplifier input.

This power is the component of the power transferred by transformer action or by electromagnetic induction. The primary and secondary currents are in opposition and the total current flowing through the coils in common is equal to the difference of the current of the low voltage winding and the high voltage winding.


This system increases usable transmission distance, reduces induced interference into external equipment and reduces cost. Archived from the original on In an ordinary transformer, the primary and the secondary windings are electrically insulated from each other but connected magnetically as shown in the figure below and in auto transformer the primary and the secondary windings are connected magnetically as well as electrically.

Autotransformer: Working, Advantages, Disadvantages | Electrical Academia

This industry standard text describes the various European electrification principles. Leave a Reply Cancel reply. 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, though the entire winding is directly connected.

A failure of the isolation of the windings advantagez an autotransformer can result in full input voltage applied to the output. In an autotransformer, the total power transmitted from the primary to the secondary does not actually pass through the whole winding.

Autotransformer Advantages and Disadvantages

As in a two-winding transformer, the ratio of secondary to primary voltages is equal to the ratio of the number of turns of the winding they connect to. Auto-transformers in comparison with the double winding transformers are generally advantageous of the voltage ratio is favorable from the point of view of the equivalent size. If an alternating voltage is applied between points C and D, and the output voltage is measured between points A and B, the autotransformer is said to be a voltage booster.

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On load condition, a part of the load current is obtained directly from the supply and the remaining part is obtained by transformer action. Another application is a lighting dimmer that doesn’t produce the EMI typical of most thyristor dimmers. By using this site, you agree to the Terms of Use and Privacy Policy. There are two types of auto transformer based on the construction.


Electrical Machines – I. If the same duty is performed with an ordinary two winding transformer shown above in the figure A. Some of the disadvantages of an autotransformer are: The output voltage adjustment can be manual or automatic. An example of an application of an autotransformer is one style of traveller’s voltage converter, that allows volt devices to be used on volt supply circuits, or the reverse.

The autotransformer serves a function similar to that of the ordinary transformer to raise or lower voltage. The single —phase, a two-winding transformer is reconnected as an autotransformer as shown in Fig. You can find new Free Android Games and apps. In other projects Wikimedia Commons.

Similarly, the output apparent power is arvantages by. By exposing part of the winding coils and making the secondary connection through a sliding brushdiaadvantages continuously variable turns ratio can be obtained, allowing for very smooth control of output voltage. At full or rated load, the primary and secondary terminal currents are. Substituting Equation 5 into Equation 3the ratio of the winding current is found as. The ” auto ” Greek for “self” prefix refers to the single coil acting alone, not to any kind of automatic mechanism.

In fact, a part of the single continuous winding is common to both primary and secondary. Can autotransformer be used as a step-up transformer. The content is copyrighted to ElectricalAcademia. Neglecting voltage drops in autotransfirmer windings. Surge Arrester protection is required As the short circuit impendace values of the auto-transformer are low, short circuit currents can reach higher critical values.

Disadvantagds construction of Auto transformer is shown in the figure below. Ordinary Two Winding Transformer. As the secondary ampere-turns are opposite to primary ampere turns, so the current I 2 is in phase opposition to I 1.