Lecturer: Lucia Frosini  

Course name: Costruzioni elettromeccaniche
Course code: 064010
Degree course: Ingegneria Elettrica
Disciplinary field of science: ING-IND/32
The course relates to:
University credits: CFU 5
Course website: http://www.unipv.it/dmae/

Specific course objectives

The aim of this course is to study in depth the features of the electrical machines related to their design and sizing in order to obtain the operational performances required. These features include the conducting, insulating and magnetic materials, the geometrical dimensions, the magnetic circuit, the electric and magnetic loading, the windings and the magneto-motive forces.

Course programme

1. Magnetic, conducting and insulating materials. Hard and soft magnetic materials, hysteresis and eddy currents losses, laminations of grain-oriented silicon-iron. Skin effect in the conductors. Characteristics of the insulating materials (gaseous, liquid and solid), dielectric rigidity, partial discharges, thermal classes.

2. The transformer
Construction aspects: core, windings, cooling systems. Sizing formula and design criteria. Angular groups. Go-backs on the parallel of two transformers. Short circuit transient in a transformer. Outline of the Lorentz forces in the transformers. Calculation of the leakage inductance of a cylindrical winding in a transformer. Calculation of the Lorentz forces in case of short circuit in a transformer.

3. Commutator machine
Construction aspects. Wave and lap windings. Magnetic fluxes produced by the main field and by the armature reaction. Operation of the commutator machine as a motor: induced electromotive force. Separately excited motor, series motor, universal motor. The ideal commutation and the commutation with inductive phenomena: commutation poles. Saturation due to the armature reaction: compensation windings. Losses in the commutator motor.

4. AC machines
The rotating magnetic field. Types of AC stator windings: concentric and lap, single and double layer, full pitch and short pitch, fractional slot winding. Examples of realization of stator windings. Magneto-motive forces produced by the windings.

5. Induction machine
Go-backs on: equivalent circuit of the induction motor, power balance, electromagnetic torque, electromechanical characteristics. Double cage and deep bar rotor. Leakage reactance of a coil within a stator slot. Carter coefficient. Construction characteristics and types of rotor. Parasitic torques. Efficiency. Sizing of a three-phase induction motor. The single-phase induction motor. Outline of the asynchronous generator.

6. Synchronous machine
Operation of the synchronous machine as a generator: at no-load and in parallel with the grid. Armature reaction. Expression of the electromagnetic torque. Regulation of the active and reactive power. Construction aspects: rotor (smooth and with salient poles), damper windings, stator core. Construction problems and solutions for the high power electrical generators (in particular, turbo-generators). Design criteria for the synchronous machines: sizing, procedures for the electromagnetic and thermal calculation. Behn-Eschemburg method: determination of the synchronous impedance, capability curves, external characteristics. Potier method: determination of the Potier triangle. Outline of the Blondel method. The synchronous motor. V-curves.

7. Brushless motor
Construction characteristics: internal, external or axial-flux rotor; surface permanent magnets (SPM) and interior permanent magnets (IPM); materials for permanent magnets. Oscillating torques: cogging and ripple. Control techniques: square wave (DC brushless) and sinusoidal wave (AC brushless). Outline of sensorless control.

Course entry requirements

Principle of electrical engineering and three-phase electric systems; operation principles of the electrical machines and drives; materials for the electrical engineering.

Course structure and teaching

Lectures (hours/year in lecture theatre): 36
Practical class (hours/year in lecture theatre): 14
Practicals / Workshops (hours/year in lecture theatre): 0
Project work (hours/year in lecture theatre): 0

Suggested reading materials

Notes prepared by the lecture. To study in depth, the following books can be consulted:

Nicola Bianchi, Silverio Bolognani. Metodologie di progettazione delle macchine elettriche. CLEUP, 2001.

J.R. Hendershot Jr., TJE Miller. Design of brushless permanent-magnet motors. Magna Physics Publishing and Oxford Clarendon Press, 1994.

Testing and exams

The exam consists of an oral test on the contents of the course.