MACHINERY AND ELECTRICAL INSTALLATIONS

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.

1. ELECTRICAL POWER SYSTEMS

1.1 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.

1.2 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.

1.3 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.

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

Oral examination.

Verification of learning can also be carried out electronically, should the conditions require it.

To guarantee equal opportunities and in compliance with the laws in force, interested students can ask for a personal interview in order to plan any compensatory and / or dispensatory measures, based on the didactic objectives and specific needs.

It is also possible to contact the referent teacher CInAP (Center for Active and Participatory Integration - Services for Disabilities and / or SLD) of our Department, prof. A. Pagano.

1. Danger of electric current

2. Ground system

3. Types of distribution.

4. Sizing and verification criteria for electrical conduits

5. Protection from direct and indirect contacts

6. Circuit breakers, fuses and tripping characteristics.