Autotransformer is a transformer, common with a primary and secondary winding, which is common with a zero line, the transformation ratio have both fixed and adjustable. Advantages Step-down starter of auto-transformer transformation ratio is fixed, contact the transformation ratio of voltage regulator is variable. Autotransformer and General transformer of the same capacity in comparison, has a simple structure, the materials used, the advantages of small size. Especially in the occasion seem special economic of the transformation ratio is close to 1, so the voltages used by similar high-power transmission transformers more, in addition to the above kilowatt are widely used in the asynchronous motor starter.

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Electrical Academia. The autotransformer has a single winding on an iron core. One of the coil terminals is common to both input and output, and the other output terminal is movable so that it can make contact with any turn on the winding.

An autotransformer can be used as a step-up or a step-down transformer. As a step-up, it is often referred to as a boost, and as a step-down, it is called a buck connection.

Figure 1 shows the schematic representation of buck connection while figure 2 shows the boost connection. The autotransformer serves a function similar to that of the ordinary transformer to raise or lower voltage. It consists of a single continuous winding with a tap brought out at some intermediate point as shown in Fig. Because the primary and secondary windings of the autotransformer are physically connected, the supply and output voltage are not insulated from each other.

When a voltage V 1 is applied to the primary of the autotransformer, the induced voltages are related by. Neglecting voltage drops in the windings. When a load is connected to the secondary of the autotransformer, a current I 2 flows in the direction shown in Fig. As in the ordinary transformer, the primary and secondary ampere-turns balance each other, except for the small current required for core magnetization:. Equation 4 may also be written as.

Substituting Equation 5 into Equation 3 , the ratio of the winding current is found as. In an autotransformer, the total power transmitted from the primary to the secondary does not actually pass through the whole winding. This means that a greater amount of power can be transferred without exceeding the current rating of the windings of the transformer. Similarly, the output apparent power is given by.

However, the apparent power in the transformer windings is. This power is the component of the power transferred by transformer action or by electromagnetic induction. The difference S 2 —S w between the output apparent power and the apparent power in the windings is the component of the output transferred by electrical conduction.

This is equal to. Note that if the turns ratio of the transformer is large, the power rating as an autotransformer will be much larger than the rating as a conventional transformer. In a conventional transformer, all of the power is transformed, whereas in an autotransformer, most of the power is conducted at an elevated potential.

Asa result, an autotransformer is much smaller than a conventional transformer of the same rating. Other advantages of an autotransformer over a two winding transformer are:. Some of the disadvantages of an autotransformer are:. Applications of Autotransformer. Practical applications of autotransformers include:. Calculate the following. The single —phase, a two-winding transformer is reconnected as an autotransformer as shown in Fig.

The current ratings of the windings are given by. At full or rated load, the primary and secondary terminal currents are. Therefore, the kVA rating of the autotransformer is. Note that this transformer, whose rating as an ordinary two-winding transformer is only 10 kVA, is capable of handling 50 kVA as an autotransformer. However, not all of the 50 kVA is transformed by electromagnetic induction.

A large part is merely transferred electrically by conduction. The apparent power transformed by induction is. The apparent power transformed by conduction is. Want create site? Find Free WordPress Themes and plugins. Did you find apk for android? You can find new Free Android Games and apps.


Autotransformer: Working, Advantages, Disadvantages

An Auto Transformer is a transformer with only one winding wound on a laminated core. An auto transformer is similar to a two winding transformer but differ in the way the primary and secondary winding are interrelated. A part of the winding is common to both primary and secondary sides. On load condition, a part of the load current is obtained directly from the supply and the remaining part is obtained by transformer action.


Auto Transformer

The transfer of power between two circuits connected to an autotransformer occurs through two phenomena: the magnetic coupling as in a common transformer and the galvanic connection through the common socket between the two circuits. Likewise, a transformer increases its capacity to transfer power when connected as an autotransformer. 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. The operating principle is the same as that of the common transformer, so the transformation ratio between voltages and currents and the number returned is maintained. 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.


Autotransformer Advantages and Disadvantages

Electrical A2Z. An autotransformer is nothing more than a reactor coil single winding , but when tapped along a portion of the single winding, it will function as a single-phase single-winding AC transformer. The same winding, as shown in Figure 1 , or at least part of it, is used for both the primary and secondary windings. The other end of the winding marked N in the drawing is the common connection of both the secondary and primary circuits. Autotransformers are often used because of their lower installation costs lower manufacturing costs as compared to conventional isolation transformers. The tapped single-winding auto-transformer will obey all the laws of transformation voltage, current, and circuit impedance except isolation.

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