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.

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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. An Auto transformer works as a voltage regulator.

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.

While in auto transformer the primary and the secondary windings are connected magnetically as well as electrically. In fact, a part of the single continuous winding is common to both primary and secondary. There are two types of auto transformer based on the construction. In one type of transformer, there is continuous winding with the taps brought out at convenient points determined by the desired secondary voltage.

However, in another type of auto transformer, there are two or more distinct coils which are electrically connected to form a continuous winding. The construction of Auto transformer is shown in the figure below. The supply voltage is applied across AB, and the load is connected across CB. The tapping may be fixed or variable. A part of this induced emf is taken in the secondary circuit. Therefore, the transformation ratio:.

As the secondary ampere-turns are opposite to primary ampere-turns, so the current I 2 is in phase opposition to I 1. The secondary voltage is less than the primary. Therefore current I 2 is more than the current I 1. Therefore, the resulting current flowing through section BC is I 2 — I 1. The weight of the copper is proportional to the length and area of a cross-section of the conductor. The length of the conductor is proportional to the number of turns, and the cross-section is proportional to the product of current and number of turns.

Now, from the above figure B shown of the auto transformer, the weight of copper required in an auto transformer is. If the same duty is performed with an ordinary two winding transformer shown above in the figure A , the total weight of the copper required in the ordinary transformer,. Now, the ratio of the weight of the copper in an auto transformer to the weight of copper in an ordinary transformer is given as.

Hence, saving in copper increases as the transformation ratio approaches unity. Hence the auto transformer is used when the value of K is nearly equal to unity. There are various advantages of the auto transformer, but then also one major disadvantage, why auto transformer is not widely used, is that.

Yes, the autotransformer uses as a step-up transformer by connecting the input supply from half of the winding and the load across the full winding.

It will then supply an frequency drive. Will that be OK with the regulations? Would it be more OK if I use an overvoltage relay to trip the main breaker in case the higher voltage comes down to secondary side? Your email address will not be published.

Save my name, email, and website in this browser for the next time I comment. Circuit Globe All about Electrical and Electronics. Electronic Instrumentation. Circuit Globe Transformer Auto Transformer. Figure B: Auto — Transformer. Can autotransformer be used as a step-up transformer. Well explained and it was in a clear cut way superb. When to use autotransformer to wye delta starter?

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Advantages and disadvantages of autotransformer

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.


Autotransformer: Working, Advantages, Disadvantages

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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