The course aims to provide basic knowledge on electrical machines and electrical systems. Furthermore, the appropriate use of machines will be illustrated in real applications such as, for example, the distributed generation of electricity in smart grids and the use of electricity in the industrial, home automation and traction sectors, with particular attention to energy saving. The study of electric machines will provide the conceptual tools to understand the main construction features and their steady-state behavior through analytical and circuit models, evaluating their performance. The study of the electrical systems will allow the student to know the general design criteria of a low voltage electrical system and the protections suitable for preserving the operation and safety of people.
Finally, the aim of the course is to provide the student with basic concepts in the electrical field, which can facilitate his professional communication with highly specialized engineers.
Frontal lectures on theory topics carried out by a video projector. Exercises performed in the classroom by video projector using numerical simulation software. Collective activity of numerical exercises. Test laboratory for electrical machines.
1. ELECTRIC MACHINES
1.1. INTRODUCTION TO ELECTRIC MACHINES. Definition of Electric Machine. Classification of electric machines: Static, Rotating. Classification of rotating machines. Reversibility concept of energy conversion in electrical machines. Definition of effective yield and conventional yield. Role of electric machines for sustainable development. Applications.
1.2 MATERIALS USED FOR THE CONSTRUCTION OF ELECTRIC MACHINES. Magnetic fields in matter. Magnetic permeability. The magnetization of matter. Materials Conductors used in the construction of electric machines. Dependency of the resistivity of the material from the temperature. Some examples of conductors used in the realization of windings of electric machines. Leather effect. Insulating Materials. Thermal solicitation of insulators. Insulation examples. Losses in Isolations. Magnetic Materials: Diamagnetism, Paramagnetism, Ferromagnetism. Magnetization curve. Hysteresis cycle. Sweet magnetic materials. Hard magnetic materials. Losses due to Hysteresis. Parasite current losses in magnetic materials. Rolling process of ferromagnetic materials and grain orientation.
Transformer: Construction features and operating principle. Typical uses for energy conversion in single- phase sinusoidal networks. Relations between voltages, currents and input and output powers. Impedance adaptation. Three-phase transformer.
Real transformer. Link between phase flows and homopolar flow. Transformational Constructive Elements: Magnetic Cores (column, shell - with interleaved joints or facing joints). Transformer windings. The choice of the winding section, their distribution and the arrangement on stepped columns. Winding insulation techniques. Cooling systems.
Analytical / circuit representation of magnetizing and dispersed flows in a transformer. Coefficients of cars and mutual induction. Coupling coefficient. Circuit representation of the losses on the primary and secondary windings. Reduced Equivalent Circuit (T-circuit). Circuit model of the Linear Real Transformer. Operation in sinusoidal regime. Vacuum operation. Transformation Report. Loaded Vector Diagram. Simplified Equivalent Circuits. Magnetic Saturation - magnetizing currents. Transformer Plate Data. Nominal Values. Type of service. Identification of transformer parameters by means of vacuum and short circuit tests. Energy Report. Conventional efficiency of the transformer. Additional losses. Peak Efficiency Index. Transformer in three-phase systems. Types of connection. Timetable Index. Industrial Voltage Fall. Transformer Parallel Operation. Autotransformer. Current (TA) and Voltage (TV) transformers. Applications.
1.4 ROTATING MACHINES
Rotating Electric Machines in AC: Classification. Isotropic and Anisotropic Machines. Characteristic parameters of the windings design. Arrangement Windings on multi-phase machines. Distribution of field lines inside a rotating machine. The trend of the magnetomotive force produced at the air gap in the case of concentrated and distributed windings. Relationship between electric period and mechanical period. Analytical and graphic representation of a rotating magnetic field. Analytical and graphic representation of a pulsating magnetic field.
Asynchronous machines: Construction features and operating principle. Squirrel cage and wound rotor cage. Fundamental relationships. Scrolling. Circuit model of an induction motor. Mechanical speed-torque characteristic. Starting torque and rated torque. Single-phase asynchronous motor. Mechanical characteristic. Starting techniques of an asynchronous motor: star-delta starting, starting with stator impedances and starting with autotransformer. Identification of the characteristic parameters of the machine: vacuum test, locked rotor test. Speed reversal. Applications.
Synchronous machine: Construction features and operating principle. Smooth rotor and salient poles machine. Template. Diagram of Behn-Eshemburg. Synchronous couple. Operating characteristics. Mechanical characteristic. Loading angle. Rotary condenser. Synchronous motor. Starting problems. Parallel to the alternators with the network. Applications.
DC machine: Operating principle. Mechanical characteristics of motors excited in series and in parallel. Applications.
Examples of Electric Machines used in distributed (Wind) generation and in traction (electric vehicles).
2. PRINCIPLES OF STATIC CONVERSION OF ELECTRICITY
2.1. General considerations on static conversion and electronic power components. Power electronics elements: Diodes, Thyristors, Transistors. Rectifiers (c.a.c.c.). Inverter (c.c.-c.a.) Modulation techniques of power electronic converters. Applications.
3. ELECTRICAL SYSTEMS 3.1 GENERAL ASPECTS
Configuration of electrical systems and notes on fundamental technical choices. Production, Transmission, Distribution and Use of Electricity. Classification of electrical systems and nominal voltages.
The thermal problem in electrical systems. Heating and cooling curves. Aging of insulation and insulation classes. Load chart. Types of service.
Determination of conventional loads Conventional power and operating current. Factors of use and contemporaneity. Current of thermally equivalent use.
3.2 ELECTRIC LINES
Construction characteristics of electrical conduits. Overhead lines: types of conductors, insulators and supports. Conducted to bars. Cable lines: classification and structure of electric cables, functional characteristics, types of construction, identification codes, laying method. Thermal behavior of cables. Scope of a cable and factors on which it depends. Criteria for choosing cables.
Electrical calculation of the R-L lines. Project and verification calculations. Design criteria. Criterion of permissible loss of power. Admissible temperature criterion. Criterion of the allowable voltage drop. Notes on the criterion of maximum economic convenience. Minimum sections of the electrical conduits. Electrical calculation of lines with distributed and branched loads.
3.3 OVERCURRENT, AND PROTECTIVE SYSTEMS
Overcurrents. Thermal stress due to overload of an electrical component. Short-circuit current. Crest factor. Thermal short-circuit stress. Electrodynamic stresses.
Operating devices. Classification. Electric arc and its mode of extinction. Switches. Switches. Contactors.
Overcurrent protections. Relay classification. Thermal and electromagnetic overcurrent relay. Magnetothermal protection of maximum current. Automatic circuit breakers for low voltage. Fuses. Short- circuit current limitation. Protection of pipelines against overload and short-circuit. Requirements required by the standards. Determination of the short-circuit current. Serial protection (backup). Unique and distinct protection for overload and short circuit. Protection of phase and neutral conductors.
Selectivity of overcurrent protections.
Rephasing of electrical installations. Theoretical aspects. Causes and effects of a low power factor. Tariff situation. Calculation of the required reactive power and capacity of the rephasing batteries. Power factor correction mode. Functional characteristics of the capacitors. Choice of protection and operation equipment.
3.4 ELECTRICAL SAFETY
Electric current and human body. Overview of electrophysiology. Physiopathological effects of the electric current on the human body. Dangerous limits of the electric current on the human body. Electrical resistance of the human body. Danger of the route.
The electric driving ground / ground system. Earth resistance. Earth potentials. Parallel sinks. Resistance to earth of a person. Total voltage and contact voltage.
General information on protection against indirect contacts. Types of insulation. Mass and foreign mass. Distinction between direct and indirect contacts. Measures to protect against indirect contacts and classification of electrical appliances. Security curve. Danger of voltage as frequency changes. Classification of electrical systems in relation to voltage and ground mass.
Protection against indirect contacts in TT systems. Security requirements. Protection by means of maximum current devices. Differential switch. Protection by means of a differential switch. Multi-outlet common ground system. Selectivity of the protections. Voltage relay.
1. E. Fitzgerald, C. Kingsley, A. Kusko: Macchine elettriche. Franco Angeli
2. G. Conte “Impianti elettrici” vol. I e II - HOEPLI