28029 - Electrotechnics T

Course Unit Page

Academic Year 2015/2016

Learning outcomes

Methods of circuit analysis in transient and regime conditions. Basic principles of magnetostatic and electric plants.

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. Mesh analysis

Transient response 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.

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).

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.

Computer lab

Electric circuits’ simulations by using LTSpice software. Use of Maxwell Ansoft (Student version) software for electrostatic and magnetostatic simulations.

Readings/Bibliography

"Electric Circuits", C.K. Alexander, M.N.O. Sadiku

"Electrotechniques- Principles and applications" G.Rizzoni

Teaching methods

Lectures, exercises and PC Lab

Assessment methods

• The exam will be divided into a first written test constituted by 2 exercises. The total time allowed will be 2 hours. During the writing you will be allowed to consult only an A4 form written by the student itself.
• The second part of the examination will be constituted by a mandatory oral examination. Only students who have achieved a mark greater or equal to 18/30 in the writing section will support the oral.
• The final grade will be the average of the written part related to the exercises and the oral.
•During oral a simulation of an electrical circuit through LTSpice could be required.
• Students who get a score of less than 14/30 in the script can not support the next  written session (jump of session). If the subsequent written session is after a month from the date of the previous examination, the rule of the jump of seccion will not be applied.
• The mark obtained in the written will remain valid for 6 months.
• If the oral mark is insufficient, the student will have another chance to retake the oral. In the case of new poor performance, the student must also repeat the script.

Teaching tools

Lesson notes, exercises with solutions and LTSpice Lab.

Office hours

See the website of Gabriele Neretti