Problem 91-1    Source:  Problem developed by the site author.

Be an ideal transformer powered by a 220 V source and having 1000 turns in the primary. What must be the number of turns in the secondary so that we have a voltage of 110 V in it?

Problem 91-2    Source:  Problem developed by the site author.

If in the previous problem a 100 ohm load was connected to the secondary, what would be the currents in the primary and secondary? What would be the power dissipated in the load? Compare this result with the power supplied by the network to the transformer.

Problem 91-3    Source:   Problem developed by the site author.

Be an ideal single-phase transformer powered by voltage ratings 13200/660 volts . On the secondary a load is connected whose value is Z_L = 10 + j6 ohms.

a) Calculate the current at the secondary and primary of the transformer.

b) Calculate the real and reactive power the load consumes.

c) Calculate the module of the impedance that is seen by the network.

Problem 91-4    Source:   Adapted from example 2-1 - page 73 - CHAPMAN, Stephen J. -    Book: Fundamentals of Electric Machines - 5th Edition - Ed. McGrawHill - 2013.

A single-phase power system consists of a generator with voltage V_G = 480∠0° V that supplies a value load Z_L = 4 + j3 Ω through a transmission line that has an impedance Z_line = 0.18 + j0.24 Ω, as shown in Figure 91-04.1. It is asked:

a) Determine the voltage V_L on the load.

b) Calculate the real and reactive power that the load consumes.

c) Calculate the losses in the transmission line.

Problem 91-5    Source:   Adapted from example 2-1 - page 73 - CHAPMAN, Stephen J. -    Book: Fundamentals of Electric Machines - 5th Edition - Ed. McGrawHill - 2013.

A single-phase power system consists of a generator with voltage V_G = 480∠0° V that supplies an ideal transformer whose transformation ratio is 1:10. This transformer is connected to another transformer ideal with a transform ratio of 10:1 across a transmission line that has an impedance Z_line = 0.18 + j0.24 Ω. The secondary of the second transformer is connected to a load of value Z_L = 4 + j3 Ω, as shown in Figure 91-05.1. It is asked:

a) Calculate the currents in the circuit as shown in Figure 91-05.1.

b) Calculate the real and reactive power that the load consumes.

c) Calculate the losses in the transmission line.

Problem 91-6    Source:  Problem developed by the site author.

Consider a transformer that has a laminated core with dimensions of 5 cm x 6 cm and a flux density of 1.2 T. The nominal voltage of the primary is 220 V and of the secondary 44 V. The frequency of the network is 60 Hz. Find the number of turns of the windings.

Problem 91-7    Source:  Adapted example 10.6 - page 430 - SUDHAKAR, A. & PALLI, Shyammohan -    Book: Electrical Circuits Analysis - 1ª edition - Ed. McGrawHill - 2009.

An amplifier with an output impedance of 1,936 Ω must drive a speaker with an impedance of 4 Ω.

a) Calculate the transformation ratio of the transformer to interconnect the two systems.

b) A current of 20 mA and 500 Hz flows in the primary. Calculate the current in the secondary of the transformer at a frequency of 500 Hz.

c) What is the power supplied to the speaker?

Problem 91-8    Source:  Adapted example 2.4 - page 98 - SAHDEV, S. K. -    Book: Electrical Machines - 1ª edição - Cambridge University Press - 2018.

A 13.2 kV/220 V, 60 Hz transformer has a rating of 11 Volts/turn. The maximum magnetic flux density of the core is 1 T. Find:

a) The number of turns of the primary and secondary windings.

b) The cross-sectional area of ​​the core.

Problem 91-9    Source:  Problem developed by the site author.

A coil with 400 turns is completely traversed by a magnetic flux given by Φ = 4 sen 377 t + 0.05 sen 1,131 t (mWb). Find:

a) the instantaneous voltage induced in the coil.

b) the effective (or RMS) voltage induced in the coil.

Problem 91-10    Source:  Problem developed by the site author.

An ideal single-phase 10 kVA transformer has a transformation ratio a = 4. It is connected as a voltage reducer to a power grid 880 V, 60 Hz. Find:

a) the voltage in the secondary.

b) the current in the primary.

c) the current in the secondary.

Problem 91-11    Source:  Problem developed by the site author.

a)the number of turns in the secondary.

b) the number of turns in the primary.

Problem 91-12    Source:  Problem developed by the site author.

An ideal single-phase transformer has 600 turns in the primary winding. Assume that it supports a maximum flux of 99 mWb in its core when connected to a 13,200 V source. In this case, what is the mains frequency to which this transformer must be connected in order for these conditions to be satisfied?