MACHINERY AND ELECTRICAL INSTALLATIONS

The course aims to provide fundamental knowledge of electrical machines and electrical installations. It also illustrates their appropriate use in practical applications, such as distributed electricity generation in smart grids and the use of electrical energy in industrial applications, home automation and electric traction, with particular emphasis on energy savings. The study of electrical machines provides the conceptual tools needed to understand their main construction features and steady-state behaviour through analytical and equivalent-circuit models, and to assess their performance. The study of electrical installations enables students to understand the preliminary design criteria for low-voltage electrical installations and the protective measures required to ensure their proper operation and the safety of people.

The overall aim of the course is to provide students with fundamental electrical engineering concepts that will facilitate professional communication with highly specialised engineers.

By the end of the course, students will have achieved the following learning outcomes, which express the competencies addressed by the course in the field of electrical machines and electrical installations.

1 Knowledge and understanding

Understand the theoretical and practical aspects and the main methods used to analyse the electrical machines and installations covered in the course. Describe the principles of electromechanical energy conversion, the properties of the materials used in electrical machines and the main loss mechanisms. Explain the construction features, operating principles and steady-state analytical and equivalent-circuit models of transformers and induction, synchronous and DC machines, identifying their operating conditions and limitations.

Explain the operating principles of rectifiers and inverters and the role of static power conversion in electrical applications. Describe the structure of electrical energy generation, transmission, distribution and utilisation systems, the preliminary design criteria for low-voltage lines, power factor correction, and the principles of protection against overcurrents and direct and indirect contact.

Understand the methods used to measure electrical quantities and the mechanical and thermal quantities relevant to electrical machines, together with the principles of processing signals acquired during testing. Understand the design methods used for low-voltage electrical installations.

2 Applying knowledge and understanding

Use equivalent models of electrical machines to determine steady-state operating quantities, losses, efficiency and torque–speed characteristics. Interpret nameplate data and the results of transformer no-load and short-circuit tests and induction-machine no-load and locked-rotor tests to determine the relevant machine parameters.

Describe and analyse the static and dynamic behaviour of electrical devices and systems using the models covered in the course, with reference to steady-state operation, machine starting and switching in power converters. Analyse the basic operation of the static power converters covered in the course. Formulate and solve problems involving the sizing and verification of low-voltage lines, the determination of design loads and power factor correction. Apply criteria for selecting and coordinating overcurrent protection devices and for protection against indirect contact in TT systems.

Use MATLAB/Simulink during practical exercises to analyse models and interpret numerical results, comparing them with theoretical predictions. Relate the characteristics of electrical machines and installations to industrial applications, distributed generation and electric traction, with attention to energy efficiency.

3 Making judgements

Independently assess design solutions in electrical engineering. Evaluate the suitability of the assumptions and simplifications adopted in models and check the physical plausibility and dimensional consistency of the results. Propose, evaluate and compare alternative technical solutions in industrial contexts, with reference to the cases covered in the course, including machine applications, line sizing and the selection of protective devices. Justify these choices in relation to operating conditions, energy efficiency and safety.

These skills are developed through discussion of exercise solutions, comparison of analytical and numerical results, and interpretation of laboratory tests on electrical machines.

4 Communication skills

Interact with working groups to achieve project objectives. Communicate the results of their work both concisely, through schematics and drawings, and through written reports and technical notes. Explain the operating principles of electrical machines and installations using appropriate technical terminology. Present and explain equivalent circuits, schematics, diagrams and operating characteristics.

These skills are developed through practical exercises and discussion of laboratory activities. Clarity of expression and the appropriate use of technical terminology are also assessed during the oral examination.

5 Learning skills

Adapt their knowledge to technological developments in electrical engineering and its applications. Independently use reference textbooks and teaching materials to consolidate and deepen their understanding of the course topics. Interpret nameplate data, schematics and technical documentation relevant to the topics studied, identifying the information needed to address practical problems and recognising aspects that require further investigation.

These skills are developed through independent study, further analysis of exercises and laboratory activities, and comparison of teaching materials, models and practical results.

Lectures on theoretical topics are delivered using a video projector. Classroom exercises are conducted using a video projector and the MATLAB/Simulink programming and numerical computing environment. Laboratory sessions involve testing electrical machines. Numerical problems are also solved collectively in class.

If the course is delivered in blended or distance-learning mode, the necessary adjustments may be made to the arrangements described above to ensure that the programme set out in the syllabus is covered.

Lectures aim to develop knowledge of operating principles, models of electrical machines and power converters, and criteria for the design and protection of electrical installations. Analytical and numerical exercises enable students to apply this knowledge to performance assessment, sizing and verification problems. Laboratory tests include the analysis of relevant electrical and mechanical quantities and the processing of acquired signals. Laboratory tests and collective discussion of exercises foster critical interpretation of results, comparison between models and machine behaviour, independent judgement and the use of technical terminology. Independent study and further analysis of the activities undertaken contribute to the development of autonomous learning skills.

If the course is delivered in blended or distance-learning mode, the necessary adjustments may be made to the arrangements described above to ensure that the programme set out in this syllabus is covered.

To benefit fully from the course, students should possess the following background knowledge, understood as subject-specific prerequisites.

Essential: Basic knowledge of electromagnetism, particularly electric and magnetic fields and electromagnetic induction; knowledge of electrical circuit analysis, Kirchhoff’s laws, sinusoidal steady-state operation, phasor representation, impedance, electrical power and three-phase systems.

Important: Proficiency in calculations involving complex numbers, systems of linear equations, and the fundamentals of differential and integral calculus, as required to understand the models and solve the exercises.

Useful: Familiarity with numerical computing tools and the MATLAB/Simulink environment to support practical exercises.

1. ELECTRICAL MACHINES

1.1 INTRODUCTION TO ELECTRICAL MACHINES (Lectures: 4 hours; Practical exercises: 0 hours)

Definition of an electrical machine. Classification of electrical machines: static and rotating machines. Classification of rotating machines. Reversibility of energy conversion in electrical machines. Definition of actual and conventional efficiency. The role of electrical machines in sustainable development. Applications.

1.2 MATERIALS USED IN THE CONSTRUCTION OF ELECTRICAL MACHINES (Lectures: 3 hours; Practical exercises: 2 hours)

Magnetic fields in matter. Magnetic permeability. Magnetisation of materials. Conducting materials used in electrical machines. Temperature dependence of electrical resistivity. Examples of conductors used in electrical machine windings. Skin effect. Insulating materials. Thermal stress on insulation. Examples of insulating materials. Dielectric losses. Magnetic materials: diamagnetism, paramagnetism and ferromagnetism. Magnetisation curve. Hysteresis loop. Soft and hard magnetic materials. Hysteresis losses. Eddy-current losses in magnetic materials. Lamination of ferromagnetic materials and grain orientation.

1.3 TRANSFORMERS (Lectures: 6 hours; Practical exercises: 8 hours)

Transformers: construction features and operating principles. Typical applications for energy conversion in single-phase sinusoidal AC systems. Relationships between input and output voltages, currents and powers. Impedance matching. Three-phase transformers.

Non-ideal transformers. Relationship between phase fluxes and zero-sequence flux. Transformer construction: magnetic cores, including core-type and shell-type configurations with interleaved or butt joints. Transformer windings. Selection of winding conductor cross-sections, winding distribution and arrangement on stepped core limbs. Winding insulation techniques. Cooling systems.

Analytical and circuit representation of magnetising and leakage fluxes in transformers. Self- and mutual inductances. Coupling coefficient. Circuit representation of losses in primary and secondary windings. Reduced equivalent circuit (T-equivalent circuit). Linear circuit model of a non-ideal transformer. Sinusoidal steady-state operation. No-load operation. Transformation ratio. Phasor diagram under load. Simplified equivalent circuits. Magnetic saturation and magnetising currents. Transformer nameplate data. Rated values. Duty types. Identification of transformer parameters through no-load and short-circuit tests. Energy balance. Conventional transformer efficiency. Additional losses. Peak Efficiency Index. Transformers in three-phase systems. Winding connections. Clock notation for phase displacement. Transformer voltage regulation. Parallel operation of transformers. Autotransformers. Current transformers (CTs) and voltage transformers (VTs). Applications.

1.4 ROTATING MACHINES (Lectures: 18 hours; Practical exercises: 20 hours)

AC rotating electrical machines: classification. Magnetically isotropic and anisotropic machines. Main winding design parameters. Winding arrangements in polyphase machines. Magnetic field distribution within a rotating machine. Air-gap magnetomotive force distributions produced by concentrated and distributed windings. Relationship between electrical and mechanical periods. Analytical and graphical representation of rotating magnetic fields. Analytical and graphical representation of pulsating magnetic fields.

Induction machines: construction features and operating principles. Squirrel-cage and wound-rotor machines. Fundamental relationships. Slip. Equivalent-circuit model of an induction motor. Torque–speed characteristic. Starting torque and rated torque. Single-phase induction motors and their torque–speed characteristics. Induction motor starting methods: star–delta starting, starting with stator impedances and autotransformer starting. Identification of machine parameters through no-load and locked-rotor tests. Reversal of the direction of rotation. Applications.

Synchronous machines: construction features and operating principles. Cylindrical-rotor and salient-pole machines. Machine model. Behn-Eschenburg phasor diagram. Synchronous torque. Operating characteristics. Torque–speed characteristic. Load angle. Synchronous condensers. Synchronous motors. Synchronisation and parallel operation of alternators with the grid. Applications.

DC machines: operating principles. Torque–speed characteristics of separately excited and series-wound motors. Applications.

Examples of electrical machines used in distributed generation (wind power) and traction (electric vehicles).

2. PRINCIPLES OF STATIC ELECTRICAL POWER CONVERSION (Lectures: 8 hours; Practical exercises: 10 hours)

2.1 General introduction to static power conversion and power electronic devices. Basic power electronics: diodes and transistors. Rectifiers (AC–DC). Inverters (DC–AC). Modulation techniques for power electronic converters. Applications.

3. ELECTRICAL INSTALLATIONS

3.1 GENERAL ASPECTS (Lectures: 4 hours; Practical exercises: 0 hours)

Electrical system configurations and an overview of fundamental technical choices. Generation, transmission, distribution and utilisation of electrical energy. Classification of electrical systems and nominal voltages.

Thermal behaviour of electrical installations. Heating and cooling curves. Insulation ageing and insulation classes. Load profiles. Duty types.

Determination of design loads. Design power and design current. Utilisation and coincidence factors. Thermally equivalent design current.

3.2 ELECTRICAL LINES (Lectures: 6 hours; Practical exercises: 10 hours)

Construction features of electrical wiring systems. Overhead lines: types of conductors, insulators and supports. Busbar trunking systems. Cable lines: classification and structure of electrical cables, operating characteristics, construction types, identification codes and installation methods. Thermal behaviour of cables. Cable current-carrying capacity and the factors affecting it. Cable selection criteria.

Electrical calculations for lines. Design and verification calculations. Design criteria based on permissible power loss, permissible temperature and permissible voltage drop. Introduction to economic optimisation criteria. Minimum conductor cross-sections. Electrical calculations for lines with distributed loads and branches.

3.3 OVERCURRENTS AND PROTECTION SYSTEMS (Lectures: 6 hours; Practical exercises: 10 hours)

Overcurrents. Thermal stress caused by overloading electrical components. Short-circuit current. Thermal stress caused by short circuits. Electrodynamic stresses.

Switching devices. Classification. Electric arcs and arc-extinction methods. Switches. Disconnectors. Contactors.

Overcurrent protection. Classification of relays. Thermal and electromagnetic overcurrent relays. Thermal-magnetic overcurrent protection. Low-voltage circuit breakers. Fuses. Short-circuit current limitation. Protection of wiring systems against overloads and short circuits. Requirements specified by technical standards. Calculation of short-circuit currents. Back-up protection. Combined and separate protection against overloads and short circuits. Protection of phase and neutral conductors. Selectivity of overcurrent protection devices.

Power factor correction in electrical installations. Theoretical principles. Causes and effects of a low power factor. Electricity tariff arrangements. Calculation of the required reactive power and the capacitance of power factor correction capacitor banks. Power factor correction methods. Operating characteristics of capacitors. Selection of protective and switching devices.

3.4 ELECTRICAL SAFETY (Lectures: 4 hours; Practical exercises: 0 hours)

Electric current and the human body. Introduction to electrophysiology. Physiological and pathological effects of electric current on the human body. Thresholds for hazardous effects of electric current. Electrical resistance of the human body. Risks associated with different current paths through the body.

Earth as an electrical conductor. Earthing systems. Earth resistance. Earth potentials. Parallel earth electrodes. Resistance between a person and earth. Earth potential rise and touch voltage.

General principles of protection against indirect contact. Types of insulation. Exposed-conductive-parts and extraneous-conductive-parts. Distinction between direct and indirect contact. Protective measures against indirect contact and classification of electrical equipment. Safety curve. Effect of frequency on voltage-related hazards. Classification of electrical systems according to voltage and earthing arrangements.

Protection against indirect contact in TT systems. Protection requirements. Protection using overcurrent devices. Residual current devices (RCDs). Protection using RCDs. Earthing systems shared by multiple circuits. Selectivity of protective devices. Voltage relays.

Contribution of the course to the Sustainable Development Goals of the 2030 Agenda

- GOAL 7: AFFORDABLE AND CLEAN ENERGY

- GOAL 11: SUSTAINABLE CITIES AND COMMUNITIES

- GOAL 12: RESPONSIBLE CONSUMPTION AND PRODUCTION

- GOAL 13: CLIMATE ACTION

TESTI DI RIFERIMENTO 

1.   E. Fitzgerald, C. Kingsley, A. Kusko: Macchine elettriche. Franco Angeli 

2.   G. Conte “Impianti elettrici” vol. I e II – HOEPLI

ALTRO MATERIALE DIDATTICO

l materiale didattico prodotto dal docente è disponibile sul Portale Studium, all’indirizzo web associato al modulo didattico Macchine e Impianti Elettrici.

Oral examination.

The examination covers the topics included in the syllabus and assesses knowledge and understanding of the operating principles of electrical machines, static power converters and electrical installations, as well as the ability to apply the models and criteria for analysis, sizing and protection covered in the course.

The discussion includes the interpretation of equivalent circuits, schematics and operating characteristics, together with a reasoned approach to practical problems. Students are required to state their assumptions, justify their reasoning and choices, and discuss the physical meaning and limitations of their results, including with reference to practical exercises and laboratory tests.

Assessment takes into account the relevance, accuracy and completeness of answers; the ability to make connections between different syllabus topics; the ability to apply knowledge to practical cases; independent reasoning and judgement; clarity of expression; and the appropriate use of technical terminology.

The final mark is awarded on a scale of 30. To pass the examination, students must demonstrate at least a satisfactory understanding of the fundamental topics and the ability to formulate a correct approach to basic practical problems. Higher marks reflect more comprehensive and precise knowledge, greater independence and rigour in applying methods, and a stronger ability to connect topics and discuss them critically. Honours (lode) are awarded for complete and thorough mastery of the subject matter, together with outstanding independence of judgement and clarity of expression.

Learning assessment may also be conducted online if circumstances require it.

To ensure equal opportunities and compliance with current legislation, students may request an individual meeting to discuss any compensatory measures and/or exemptions based on the learning objectives and their specific needs. Students may also contact the departmental CInAP representative (Centre for Active and Participatory Inclusion — Services for Disabilities and/or Specific Learning Disorders).

Operating principles of electrical machines

Conventional efficiency of transformers

Losses in electrical machines

Equivalent circuits of electrical machines

Torque–speed characteristics of rotating machines

Earthing systems

Protection against direct and indirect contact

Circuit breakers, fuses and their operating characteristics