Problem 94-2    Source:  Problem created by the site's author.

Consider a conventional single-phase two-winding transformer of 110 kVA and nominal voltage of 2,200/220 volts. It is connected as an autotransformer as shown in Figure 94-02.1, that is, a voltage booster. Now consider N₂ as the common winding of the autotransformer. Find:

a) the currents in the windings.

b) the power transformed by induction and conduction.

c) the total power that the autotransformer can deliver to the load.

Solution of the Problem 94-2

This problem is similar to the previous one, where the windings N₁ and N₂ have been swapped. The same reasoning applies to the solution.

Item a

We have already calculated the values ​​of I₁ and I₂ in the previous problem. Repeating:

The currents calculated above are the currents when the transformer operates conventionally, that is, with two independent windings. When the transformer operates as an autotransformer at full power, the terminal currents I_L and I_H are:

Item b

The transformed power can be calculated by the equation given below.

Thus, we have:

Item c

And the input power is given by:

Performing the calculation, we obtain:

Também seria possível calcular a potência de entrada somando a potência transformada e a potência por condução, ou seja: