Problem 94-1    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 94-01.1, that is, a voltage step-up. Consider N₁ 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.

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.

Problem 94-3      Source:   Adapted Example 3-19 - page 234 -    BHATTACHARYA, S. K. -    Book:    Electrical Machines - 4th ed. - McGraw-Hill - 2014.

The primary and secondary voltages in an autotransformer are 440 V and 200 V, respectively.

a) Calculate the current in all windings when the load current is 240 A

b) Calculate the power transformed under the conditions of the previous item.

c) Calculate the power per conduction under the conditions of the previous item.

d) Calculate the copper savings compared to a conventional transformer.

Problema 94-4      Source:   Adapted Example 3-16 - page 96 -    SHADEV, S. K. -    Book:    Electrical Machines - 1st ed. - Cambridge University Press - 2018.

A conventional single-phase two-winding transformer of S_n = 20 kVA and nominal voltage of 2,000 / 200 volts is connected as a step-up autotransformer as shown in Figure 94-04.1. The a-b winding is 200 V and the b-c winding is 2,000 V. Calculate:

a) the voltages V_L and V_H of the autotransformer.

b) the apparent power of the autotransformer.

c) the power transformed and by conduction.

Problema 94-5    Source:   Problem prepared by the author of the site.

A single-phase autotransformer of 50 kVA, 60 Hz and voltage 13,200 / 9,000 V has a ratio of 6 V / turns. Consider that the maximum magnetic flux density is 1.2 T. Find:

a) the core area.

b) the number of turns of the autotransformer.

c) in which turn should the 9,000 V tap be removed.

d) Calculate the copper savings compared to a conventional transformer.