Hello, and welcome to Introduction to Electric Power Systems. We will start with basic electricity concepts. Let's talk about nature and effects of electricity. Electricity is a term that covers all the phenomena caused by either electric charge or by movement of charge and the electrical and magnetic fields associated with that. Electricity is commonly understood to be a form of energy, comparable to other energy forms such as heat, light, mechanical, or chemical energy. Electrical energy has some major advantages over other forms of energy. First of all, electrical energy can be easily conveyed over long distances. Power stations supply large areas via overhead transmission lines. Electrical energy can easily be converted into other forms of energy such as heat, light, or mechanical energy. It is therefore used commonly both domestically and in industry. Let's talk about atomic models. All electrical states and processes are linked to the presence of the tiny elementary particles known as an electron. An electron carries a charge that corresponds to the smallest amount of electrical charge possible to have. It is the elementary quantum of electricity. Electrons are a constituent of the atoms that make up any chemical element, an atom from the Greek "atomos", meaning "indivisible", was long thought to be the ultimate indivisible component of matter. Nowadays, it is known that atoms are not indivisible. They actually possess a rather complex structure that we have tried to envisage using atomic models. The atomic model developed by Niels Bohr is still the most important of these. It perceives that structure of an atom as being in the nature of our solar system. At the center lies the atomic nucleus in the way that the sun lies at the center of the solar system, electrons that move in orbit around this nucleus like planets, atoms of various elements differ in terms of the size of the nucleus, and the number of electrons that surround it. The electron orbits can be elliptical or circular and are of different diameter and in different planes, they make up the shell of the atom. The diameter of an atomic nucleus is about 10,000 times smaller than the diameter of the atom as a whole. Atoms consist of an atomic nucleus and an electron shell, and this is a fundamental principle, electrons are negatively charged while the nucleus is composed of uncharged neutrons, and positively charged protons. It's overall charge is thus positive. For this reason, an atom should possess an equal number of electrons and protons to make it electrically neutral. The following graphic depicts the atomic model in its entirety. That leads us to conductors and insulators, the conductivity of a material is effectively related to the number of free electrons in it. A distinction is usually made between conductors, insulators and semiconductors which will have a special role of their own. Let's talk about conductors in more details. Electric current can only occur in materials that contain charge carriers, usually free electrons that are free to move within the substance. Those materials that contain many such free electrons, that are able to move with little resistance are called conductors of electricity. Solid conductors are most likely to be metals such as gold, silver, copper, aluminum, or iron. One non-metallic conductor is the graphite or a specific form of carbon. Liquids can also conduct electricity for instance metallic mercury. Indeed, any molten metal or aqueous solution of salts or acids can do the work. Insulators, these are materials that contain very few free electrons and usually are called non-conductors or insulators, they can't conduct next to no current. Let's take a look at the graphics that illustrates that. You can see that while node just few free electrons compared with conductors that have many. Among the solid materials that do not conduct well in fact, are glass, porcelain, amber, rubber, paper, cotton, and plastics. They are suitable for insulating one conductor from another. These substances do however possess a certain but slight conductivity. So, in fact there are no perfect insulators. For this reason there is no actual well-defined boundary between conductors and insulators, instead there exist a continuous spectrum of conductivity. That brings us to semiconductors, these are materials that fall into the category of semiconductors and occupy a special position between conductors and insulators. They are particularly important in the manufacture of electronic components such as diodes, transistors, and integrated circuits. The main materials with the requisite properties are silicon and germanium, the conductivity of these materials can be altered by a process called doping. Which introduces impurities into a substance that can lead either to a surplus of free electrons or a relative absence of them. The absence of an electron, results in the so-called hole in the atomic structure.
