Theoretical Electrotechnics


Students should become able to apply the laws of electromagnetism to derive from them the properties of phenomena relevant to Electrotechnics, and the grounds of real equipment’s technical behaviour. They must learn the functioning, properties, and general behavior of electrical circuits operating in AC regime (including power factor issues and 3-phase circuits) and of transformers (including some dimensioning aspects related to efficiency).  3-phase transformers principle of operation and use will also be presented including parallel of transformers and load distribution between them.

General characterization





Responsible teacher

Anabela Monteiro Gonçalves Pronto


Weekly - 4

Total - 65

Teaching language



Students should have solid knowledge about eletcromagnetism nd mathematics in order to facilitate the comprehension of Electrotechnics topics.


  1. C. Alexander and M. Sadiku, Fundamentals of Electric Circuits, Mc-Graw Hill, 2nd Ed., 2002 
  2. Bessonov, L., Electricidade Aplicada para Engenheiros, Livraria Lopes da Silva, 1977
  3. Joseph A. Edminister, Circuitos Elétricos, Schaum MCGraw-Hill d0 Brasil, 2nd ed., 1985
  4. A.E. Fitzgerald, Charles Kingsley, Jr., Stephen D. Umans, Electric Machinery, 6th ed., McGraw-Hill, 2003. ISBN 0-07-366009-4
  5. Anabela Pronto, Slides of theoreticl classes, NOVA S&T, 2021.
  6. Ventim Neves, Apontamentos de Eletrotecnia Teórica (teóricas e práticas), FCT/UNL, 2000

Teaching method

Scientific principles are explained by professor at theoretical classes, supported by slides presentation. Students oral communication are stimulated through debate around technical and scientific questions. In practical classes two situations occur: in some classes, a group of technical problems are presented to be solved by students based on theoretical classes, in other students make laboratory work about specific parts of the subject in order to get some contact and experience with electrical installations and transformers, for example. In both cases, the debate between students is promoted and a qualitative evaluation is taken into consideration.


Written tests will be made structured in a way that students show if they are able to apply the knowledge acquire during theoretical and practical classes.

The students must present written reports describing laboratory work and, specially, analyzing and discussing the obtained results. In this component of evaluation process, teachers also want to promote team work skills and oral and written communication skills.

Both evaluation components will be taken into consideration to the final mark, and in both components the student should have a positive evluation (>= 10, in a 0 to 20 scale).

Evaluation method

The evaluation method could be one of the following:

 a) 2 Minitestes (MT) + 2 Labortory Work (TL) 

Mark (MT) = (0,40*MT1+0,60*MT2) >= 9,5 val.  

Mark(TL) = (0,50*TL1+0,50*TL2) >= 9,5 val. where TL1 >= 8,0 val.  and  TL2 >= 10,0 val.

Final Mark = 0,75*Mark(MT) + 0,25*Mark(TL) >= 9,5 val.

b) Final Exam (Ex) +  2 Labortory Work (TL) 

 Final Ex. Mark  >= 9,5 val. 

 Mark (TL) = (0,50*TL1+0,50*TL2) >= 9,5 val. where TL1 >= 8,0 val.  and  TL2 >= 10,0 val.

Final Mark = 0,75*Mark(MT) + 0,25*Mark(TL) >= 9,5 val.

In either case, the student will be approved if, and only if, his/her grade is equal to or higher than 9.5 (scale 0 to 20).

If teachers considered so, any of the evaluation elements could be subjected to oral discussion.

Students with practical component already concluded and approved in 2020/2021 will be dismissed of doing it again, if they wish. In any case, students must inform the teacher about their decision: if they want to keep the previous mark or to repeat the laboratory component.

Subject matter

  1. Complex notation of sinusoidal quantities. Circuits in sinusoidal regimen. Vector diagrams. Power.
  2. Power factor correction in industrial installations.
  3. Balanced and unbalanced three-phase systems.
  4. Magnetostatics: Ampère’s law. Magnetic circuits. Induction Flux. Coils. Linked flux, induction coefficients, magnetic linkage coefficient. Leakage and leakage induction coefficients.
  5. Ferromagnetism. Saturation and Hysteresis. Iron yoke coil.
  6. Induction law in stationary circuits.
  7. Transformer. Constitution, principle of operation and general equations. Real, perfect and ideal transformers. Magnetizing current and iron losses.  Steinmetz’ equivalent circuit. Short circuit and open circuit tests. Vector diagrams. Voltage drop and voltage regulation. Transformer efficiency. Parallel connection of transformers and load distribution.
  8. 3-phase transformers.


Programs where the course is taught: