S. Langsdorf - Download as PDF File .pdf), Text File .txt) or read online. good bok. Title: Theory of Alternating Current Machinery Author: A. S. Langsdorf. Theory of Alternating Current Machinery by Alexander S. Langsdorf, , available at Book Depository with free delivery. PRINCIPLES OF ALTERNATING CURRENT MACHINERY - echecs16.info Pages · · (zlibraryexau2g3p_onion).pdf Seven naslovi Seven naslovi.
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As a result, the voltage level also reverses along with the current. AC is used to deliver power to houses, office buildings, etc. Generating AC AC can be produced using a device called an alternator. This device is a special type of electrical generator designed to produce alternating current. A loop of wire is spun inside of a magnetic field, which induces a current along the wire.
Motors and generators are the exact same device, but motors convert electrical energy into mechanical energy if the shaft on a motor is spun, a voltage is generated at the terminals! This is useful for many large appliances like dishwashers, refrigerators, and so on, which run on AC.
Direct Current DC Direct current is a bit easier to understand than alternating current. Rather than oscillating back and forth, DC provides a constant voltage or current. Generating DC DC can be generated in a number of ways: An AC generator equipped with a device called a "commutator" can produce direct current Use of a device called a "rectifier" that converts AC to DC Batteries provide DC, which is generated from a chemical reaction inside of the battery Using our water analogy again, DC is similar to a tank of water with a hose at the end.
The tank can only push water one way: out the hose. Similar to our DC-producing battery, once the tank is empty, water no longer flows through the pipes. Describing DC DC is defined as the "unidirectional" flow of current; current only flows in one direction. Voltage and current can vary over time so long as the direction of flow does not change.
To simplify things, we will assume that voltage is a constant. For example, we assume that a AA battery provides 1. It means that we can count on most DC sources to provide a constant voltage over time.
In reality, a battery will slowly lose its charge, meaning that the voltage will drop as the battery is used. For most purposes, we can assume that the voltage is constant.
However, this was not an overnight decision. In the late s, a variety of inventions across the United States and Europe led to a full-scale battle between alternating current and direct current distribution. Thomas Edison, on the other hand, had constructed DC power stations in the United States by A turning point in the battle came when George Westinghouse, a famous industrialist from Pittsburgh, downloadd Nikola Tesla's patents for AC motors and transmission the next year.
AC vs. DC Thomas Edison Image courtesy of biography. As a result, Edison proposed a system of small, local power plants that would power individual neighborhoods or city sections.
Even though the voltage drop across the power lines was accounted for, power plants needed to be located within 1 mile of the end user.
This limitation made power distribution in rural areas extremely difficult, if not impossible. Nikola Tesla Image courtesy of wikipedia. Transformers provided an inexpensive method to step up the voltage of AC to several thousand volts and back down to usable levels. At higher voltages, the same power could be transmitted at much lower current, which meant less power lost due to resistance in the wires.
As a result, large power plants could be located many miles away and service a greater number of people and buildings. Edison's Smear Campaign Over the next few years, Edison ran a campaign to highly discourage the use of AC in the United States, which included lobbying state legislatures and spreading disinformation about AC. Edison also directed several technicians to publicly electrocute animals with AC in an attempt to show that AC was more dangerous than DC.
In attempt to display these dangers, Harold P. The Rise of AC In , the International Electro-Technical Exhibition was held in Frankfurt, Germany and displayed the first long distance transmission of three-phase AC, which powered lights and motors at the exhibition.
Several representatives from what would become General Electric were present and were subsequently impressed by the display.
The following year, General Electric formed and began to invest in AC technology. The project was completed on November 16, and AC power began to power industries in Buffalo. This milestone marked the decline of DC in the United States. However, due to the high cost and maintenance of the Thury systems, HVDC was never adopted for almost a century.
With the invention of semiconductor electronics in the s, economically transforming between AC and DC became possible. Specialized equipment could be used to generate high voltage DC power some reaching kV. In the end, Edison, Tesla, and Westinghouse may have their wishes come true. AC and DC can coexist and each serve a purpose. AC is easier to transform between voltage levels, which makes high-voltage transmission more feasible. DC, on the other hand, is found in almost all electronics.
You should know that the two do not mix very well, and you will need to transform AC to DC if you wish to plug in most electronics into a wall outlet. With this understanding, you should be ready to tackle some more complex circuitry and concepts, even if they contain AC. It is true that in some cases AC holds no practical advantage over DC.
In applications where electricity is used to dissipate energy in the form of heat, the polarity or direction of current is irrelevant, so long as there is enough voltage and current to the load to produce the desired heat power dissipation.
However, with AC it is possible to build electric generators, motors and power distribution systems that are far more efficient than DC, and so we find AC being used predominantly across the world in high power applications.
To explain the details of why this is so, a bit of background knowledge about AC is necessary. This is the basic operating principle of an AC generator, also known as an alternator: Figure below Alternator operation Notice how the polarity of the voltage across the wire coils reverses as the opposite poles of the rotating magnet pass by.
Connected to a load, this reversing voltage polarity will create a reversing current direction in the circuit. While DC generators work on the same general principle of electromagnetic induction, their construction is not as simple as their AC counterparts.
The diagram shown above is a bit more simplified than what you would see in real life. The problems involved with making and breaking electrical contact with a moving coil should be obvious sparking and heat , especially if the shaft of the generator is revolving at high speed. If the atmosphere surrounding the machine contains flammable or explosive vapors, the practical problems of spark-producing brush contacts are even greater.
An AC generator alternator does not require brushes and commutators to work, and so is immune to these problems experienced by DC generators. While DC motors require the use of brushes to make electrical contact with moving coils of wire, AC motors do not. This relative simplicity translates into greater reliability and lower manufacturing cost.
But what else is AC good for? Surely there must be more to it than design details of generators and motors! Indeed there is. There is an effect of electromagnetism known as mutual induction , whereby two or more coils of wire placed so that the changing magnetic field created by one induces a voltage in the other.
If we have two mutually inductive coils and we energize one coil with AC, we will create an AC voltage in the other coil.