Н. В. Моина ю. Б. Генина т. В. Шульженко чтение английской научнотехнической литературы
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How Is Electric Energy Produced?The first ever public electric power distribution system appeared in the late 19th century and mostly supplied direct currents, with multiple output voltages, or under the form of alternating current, which reverses the polarity of the current every 20 ms (milliseconds). However, the energy demand and the advantages that derive from the use of standard voltage outputs quickly impose the alternating current as the preferred type for production, transport and distribution. Most of the electric energy production process takes place in power plants burning fossil fuel, such as coal, natural gas or crude oil, which accounts for the massive amounts of greenhouse gases emitted daily in the Earth's atmosphere. Heat produced during fuel burning is used to evaporate large amounts of water and create steam that powers a steam turbine, turning the energy extracted during burning fuel into mechanical work. By connecting a mechanical generator to the turbine's drive shaft, the mechanical work can be turned efficiently into electric energy. However, the electric energy cannot be directly supplied to the consumer in this form, thus it must undertake certain transformations in order to meet the required standard, which state that the electric current must have parameters ranging in certain imposed values. The frequency of the alternating current is usually determined by the construction of the generator, however voltage of the current represents a key aspect in the transport and distribution of the electric energy, thus it is uneconomical and unpractical to build generators that produce different voltages. Instead, transformers are used to vary the voltage of the electric current in the required domain. Transformers consist basically of two electric circuits formed of two coils, separate electrically by an inductive coupling used to transfer energy between the two. There are two primary types of electric transformers: high-voltage and low-voltage transformers. High-voltage transformers are used to increase the voltage output, while the low-voltage ones are used to decrease it. The electric energy transport is usually greatly affected by the loss of power in long conductors, as a result of the presence of electrical resistance. Even the best electrical conductors having low electrical resistance can produce enormous power loss over relative small distances. To solve this problem, the electrical current's voltage is being increased with the help of high-voltage transformers, meaning that for a voltage increase of a 10 factor, the current intensity will drop by the same amount, thus reducing the power loss by over one hundred times. Most of the outlets present in our houses have a mono-phase current configuration, consisting of two electrodes, one used as ground and the other to supply the alternating electric current. However, the transport systems mostly imply the use of three-phase currents that consist of four metal conductors, three for alternating electric current supply, while most of the time the fourth conductor is used as ground, though this is not necessarily required. The electric currents through the three-phase metal system are out of phase by 120 degrees and voltages between the lines usually measure an average of 220 V. Static ElectricityTo understand static electricity, one has to know the basics of atoms. An atom has a nucleus consisting of protons and neutrons, and electrons, which move around that core. Protons have positive (+) charge; neutrons are neutral; and electrons have negative (–) charge. Normally an atom has equal number of protons and electrons. In that condition it is without any charge. But sometimes the electrons migrate. This causes a reduction in the negative charge and the atom becomes positive. An atom thus charged is called an "ion". Rubbing materials against each other can create the imbalance between protons and electrons. Electrons cannot pass easily through certain materials that have insulating properties. When such a shield exists, the charge that builds up remains static unless it is grounded or otherwise handled. Sometimes the voltage gradient reaches an intensity that forces the insulator to break down. Lightning is an example of this: here, dry air is the insulator between the clouds that carry static electricity. Industry loses billions of dollars annually because of damages caused by static electricity in several ways. This energy can lead to problems in day-to-day life as well. For instance, static electricity may result in malfunctioning of electronic hearing aids. Gasoline safety rules warn against reentering a vehicle while it is self-filling. There have been reported instances of fire erupting because the person coming out of the vehicle touches the nozzle without defusing static electricity. Touching the metal part of the car away from the filling point when the person gets out can avoid this danger. It is essential to eliminate to the extent possible or control this motionless electric charge to avoid the problems. The first step towards this is to measure and analyze static electricity. Effective instruments are available for this. Next, the appropriate process should be selected and set in motion with the help of experts. Induction in which tinsel is usually used is a simple and effective method. Grounding, where a conductive mat is often employed, is an alternative. Another procedure is to use a static eliminator to neutralize static electricity by ionization. Static electricity is not always a villain. It is energy that can be harnessed. Industry is also finding uses for it. To give one instance – for the In-Mold Labeling process, static electricity efficiently holds up the labels. The ability of opposite charges in static electricity is what's used when designing applications for it. Dust removal. There are some appliances that can eliminate dust from the air, like air purifiers. They use static electricity to alter the charges in the dust particles so that they stick to a plate or filter of the purifier that has an opposite charge as that of the dust (opposite charges attract each other). This effect is also used in industrial smokestacks to reduce the pollution that they generate, although they work in a very large scale, the effect is basically the same as in the home air purifiers. Photocopy. Copy machines use static to make ink get attracted to the areas where we need the information copied. It uses the charges to apply the ink only in the areas where the paper to be copied is darker (usually this means text or other information) and not where the paper is white, this process is called xerography. Car painting. To make sure a car's paint is uniform and that it will resist the high speeds and weather to protect the car's metal interior, it is applied with a static charge. The metal body of the car is submerged in a substance that charges it positively, and the paint is charged negatively with the paint sprayer. This process ensures a uniform layer of paint, since when there is enough negative paint in the car the extra will be repelled by the paint already in the car. It also ensures that the paint won't fall off, since the electrical attraction between the paint and the car is stronger than if it was just sprayed. All of these processes use electronic circuits to generate and control the static charges generated. Many people wonder if static electricity can be used as a source of power for homes and industries. Despite the extremely high voltages that can be generated with static electricity (tens of thousands of volts, compared that to 220 or 110 V of a common power outlet) the amount current it can generate is very low, from microamperes (microamp) to a few milliamperes (mA) and only for very short times. Storing electricity is so inefficient that power plants will just sell the extra energy at a lower price or let it unused and lost instead of storing it because of the cost and also the amount of energy that can be stored is not significant enough to offset the expenses. |