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What is autotransformer? , What is Autotransformer?

Hello friends, in this article we will know what is Autotransformer? How many windings are there in autotransformer? And learn about many facts related to it.

Autotransformer | Autotransformer

An autotransformer consists of a single winding on an iron core and a part of the winding primary and secondary. Circuit It is normal for both. Figure 19.24 shows the connections of (i) a step-down autotransformer while Figure 19.24 (ii) shows the connection of a step-up autotransformer. In either case, the N₁ turn winding is the primary winding and the N₂ turn winding is the secondary winding.


Note that the primary and secondary windings are connected electrically as well as magnetically. Therefore, electricity from the primary is transferred conductively as well as inductively (transformer action) to the secondary. of an ideal autotransformer voltage Transformation Ratio K is

Note that in an autotransformer, the secondary and primary voltages are related in the same way as the 2-winding Transformer In. However, the efficiency of an autotransformer is higher than that of an equivalent 2-winding transformer.


Figure 19.25 (i) shows a conventional two-winding step-down transformer with a voltage rating of 240/120 V, with a load of 5 connected to the secondary. Similarly, Figure 19.25 (ii) shows a step-down autotransformer having the same voltage rating (i.e. 240/120 V) with the same load of 5V connected to the secondary.

In any case, load current = 120/5 = 24 A.

  • In the case of a conventional two winding transformer, the primary volt – ampere (= 240 x 12 = 2880 VA) is equal to the secondary volt – ampere (= 120 x 24 = 2880 VA). An examination will show that this is also true for autotransformers. [देखें चित्र 19.25 (ii)](ii)
  • Note that in the autotransformer in Fig. 19.25 (ii) the portion of the winding cb is the same for both primary and secondary so that there is no electrical isolation between the two windings. Power from the primary is transferred to the load in two ways as conductive (i.e. by winding AC driven directly to the load) and remaining inductive (by transformer action) by winding CB.
  • Again, referring to the autotransformer in Fig. 19.25 (ii) the load volt – ampere = 120 × 24 = 2880 VA out of this 120 x 12 = 1440 VA is driven by the winding AC directly to the load and the remaining 120 x 12 = 1440 VA (or 2880 – 1440 = 1440 VA) is transferred inductively (by transformer action) to the load. curved cb if K (= V₂ / V₁ = N₂ / N₁) is the voltage transformation ratio of the autotransformer, then it can be shown that:

Power Inductively Transfer = Input ( 1 – K )

Power Conductively Transfer = K x Input

From the above comparison, it is clear that the number of turns (and hence the weight of Cu) required for an autotransformer is less than that of a two-winding transformer of the same rating. Also, in the above case the secondary of the autotransformer carries only 12 A.

Whereas the secondary of a two winding transformer is 24 A. Therefore, the X-sectional area of ​​the conductor is small. In addition to these advantages of autotransformer over two winding transformer, there are many advantages including cheap to manufacture, smaller in size, better voltage regulation and higher efficiency.


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