28029 - Electrotechnics T

Course Unit Page

• Teacher Gabriele Neretti

• Credits 6

• SSD ING-IND/31

• Language Italian

• Campus of Bologna

• Degree Programme First cycle degree programme (L) in Energy Engineering (cod. 0924)

• Course Timetable from Feb 18, 2021 to Jun 03, 2021

Learning outcomes

Concepts and methodologies related to stationary and slowly variables electromagnetic phenomena. Basic instruments for the analysis of electrical and magnetic circuits. Principles of operation of the main electromagnetic and electromechanical devices.

Course contents

EN/Course Contents

EM phenomenology

Electric charges and their motion. Electric field, electric tension and potential difference. Electric current density. Electric current and conservation of electric charge. Total electric current density. Magnetic flux density. Induction law and Ampere law. Integral and local form of EM equations. Material relations. SI unit system.

DC circuits

Definition of a lumped parameters circuit. Voltage and current Kirchhoff laws. Direction convention. Tellegen theorem. Definition of passive and active, linear and non-linear, time dependent and time-independent components. Definition of the main two-terminal ideal components: resistor, capacitor, inductor. Series and parallel resistors. Delta-wye transformation. Current divider.

Methods for the circuit analysis

General Kirchhoff method. Superposition principle. Definition of transfer function. Thevenin and Norton theorems with independent and dependent sources. Theorem of the maximum power transfer. Nodal analysis and modified nodal analysis.

Transient reponse in electric circuits

Causes of a transient. Energy conservation principle. First order circuits: RC circuits (natural and step response), RL circuits (natural and step response). Second order circuirs; RLC circuit response. Definition of resonant frequency and damping factor. Analysis of the overdamped, critically damped and underdamped cases. General method for transient analysis in the time domain

AC circuits

Definition of amplitude, radian frequency and phase of sinusoidal quantities. Definition of phasors. Transformation from the time domain to the frequency domain: resistor, capacitor and inductor and RLC circuit. Series and parallel resonance. Power in AC circuits: definition of average, reactive, apparent and complex power. Power factor correction.

Frequency response

Definition of transfer function. Low pass, high pass, band pass and band stop filters. Definition of band width and quality factor.

Three phase systems.

Definition of a balanced line voltage system and a balanced line current system. Relations between line and phase voltages. Y-connected and D-connected load. Instantaneous power, active and reactive power in a three phase balanced system. Use of the neutral wire. Power factor correction. Comparison between different power transmission systems.

Magnetic fields and circuits

Magnetic properties of materials. Magnetic hysteresis cycle, soft and hard ferromagnetic materials. Definition of magnetic circuit. Hopkinson’s law. Definition and evaluations of self and mutual coefficients. Design of a permanent magnet.

Electric machines

Transformer and motional electro motive forces. The transformer: internal equations, turns ratio in the ideal case and iron losses (hysteresis and eddy currents). Rotating machines and rotating magnetic field. The induction machine. The synchronous machine. The DC machine

Electric Plants

Power stations classification based on the primary energy source. Daily load diagram. The electric power system: production, transformation, transmission and distribution. Overhead and cable lines. Overvoltages and overcurrents. Circuit breakers. Magnetic, thermal, magneto-thermal and differential relay. Fuse. Fundamental of electrical safety. The grounding system and its coordination with the differential relay.

Lessons are available on IOL. This material is exhaustive for the comprehension of the course. Recommended books are

-‘Circuiti elettrici’ di Charles K. Alexander, Matthew N. O. Sadiku

-‘Elettrotecnica: Principi e Applicazioni’ di G. Rizzoni

-'Elettrotecnica: elementi di teoria ed esercizi' di M. Repetto e S. Leva

- 'Elettrotecnica 1 e 2' di G. Chitarin, F. Gnesotto, M. Guarnieri, A. Machio, A. Stella

Teaching methods

The course includes lectures and exercises at the computer. The first provides theoretical and application basis of the course. The exercises performed with LTSpice software allow the student to learn more about topics discussed in the theoretical part.

Assessment methods

Achievements will be assessed by the means of a final exam. This is based on an analytical assessment of the "expected learning outcomes" described above.

In order to properly assess such achievement the examination is composed of different sections; a written session, which consist of a 2 hours test, composed of 2 exercises were the study of electrical and magnetic circuits are required. To be eligible to take the oral exam the student must score in the written test a minimum of 18/30.

The oral session consists of a technical conversation with two questions about theoretical aspects studied in the course. The oral exam is considered passed with a minimum score of 18/30. In the event that the oral is insufficient, the student can retake it, preserving the written vote only once. If also the second time the oral will be insufficient, the student will have to repeat even the written exam.

The final grade is the arithmetic mean of the grade obtained in the written test and the oral one.

Higher grades will be awarded to students who demonstrate an organic understanding of the subject, a high ability for critical application, and a clear and concise presentation of the contents. To obtain a passing grade, students are required to at least demonstrate a knowledge of the key concepts of the subject, some ability for critical application, and a comprehensible use of technical language. In particular the knowledge of fundamental concepts of electromagnetism and the ability to solve electric and magnetic circuits are required.

A failing grade will be awarded if the student shows knowledge gaps in key-concepts of the subject and the inability to solve electric and magnetic circuits.

Teaching tools

Use of LTSpice software

Office hours

See the website of Gabriele Neretti