A Study On Electric Machines Engineering Essay

A Study On Electric Machines Engineering Essay The classical set of machines represents the asynchronous induction, synchronous, DC machines, and variable reluctance machines. Among these classical machines, the asynchronous machine is most widely used in a large range of applications and is able to operate as a motor (converting electrical power into mechanical power) or as a generator (converting mechanical power into electrical power). The machine can be fed via a power electronic converter or connected directly to an AC or DC supply. Electric machines are majorly based on 4 principles. The first principle is that an electrical current produce a magnetic field around it that can be strengthened by more than a thousand times when passing through iron. The second principle is called motor action and is defined by a force perpendicular to both the direction of the electrical current and the magnetic field. This induced force is given by: F= i (L) B: magnetic flux density L= length of wire i= magnitude of current in the wire The third principle is that an electrical conductor moving in a magnetic field has an electrical current induced in it creating an electromotive force. The induced voltage is expressed by the following formula: ?ind= (v) L v: velocity of the wire L: length of conductor in the magnetic field B: magnetic flux density The fourth principle is that a change in the magnetic field in a circuit can cause an induced voltage to this circuit. This effect is based on the Faradays law that states that when a flux passes through a turn of coil, a voltage proportional to the rate of change of the flux will be induced. ?ind = N: number of turns of wire in coils ?ind: voltage induced F: flux passing in the coil (http://mysite.du.edu/~jcalvert/tech/elmotors.htm) An electric machine has two essential electrical parts: The stator and the rotor. The stator (derived from the word stationary) is the stationary part of the machine forming a hollow cylinder consisting of individual electro-magnets shaped towards the middle. The rotor (derived from the word rotating) is located inside the stator and consists of a group of electro-magnet arranged around a cylinder, mounted on the motors shaft with its poles facing toward the stator poles. The rotor is the rotating component of the machine. (http://www.reliance.com/mtr/mtrthrmn.htm) (http://www.reliance.com/mtr/mtrthrmn.htm) In general, when the change of flux is associated with mechanical motion, it is the case of electromagnetic energy conversion. Regarding the rotation machines, the voltage is generated in groups of coils, often called windings, by three different ways. The first technique is by mechanical rotation of the windings through a magnetic field, the second is mechanical rotation of the magnetic field past the winding, and third by the design of the magnetic circuit so that the reluctance varies with the rotation of the rotor. So these methods generate a time-varying voltage caused by the cyclic charge of the flux linking a specific coil. The armature winding of a machine is a combination of such coils interconnected so that their generated voltage is close to the desired. In a DC machine, the armature is the rotating member or rotor. As for the AC machine, the armature is the stationary member or stator. The coils pointed out previously are wound on iron cores in order to maximize the coupling between the coils, to increase the magnetic energy density associated with electromechanical interaction, and to shape and distribute the magnetic fields according to the requirements of each particular machine design. Eddy currents will be induced in the armature iron since it is subjected to a time varying magnetic flux. To minimize this eddy-current loss, thin laminations for the armature of AC machines construct the armature iron. The magnetic circuit is completed through the iron of the other machine member, and excitation coils, or field windings, may be placed on that member to act as the primary source of flux. Permanent magnets may be used in small machines, and developments in permanent magnet technology are resulting in their use in larger machines. In variable reluctance machines, there are no windings on the rotor, and the operation depends on the non uniformity of air-gap reluctan ce associated with variations in rotor position. (electric machinery fifth edition (LIBRARY)) AC electric machines AC machines are motors converting AC electrical energy to mechanical energy and generators that convert mechanical to AC electrical energy. AC electric machines are divided into two types: Asynchronous (induction) and synchronous machines. The difference between these two types is that induction machines have their field currents supplied by magnetic induction while the field current in synchronous ones are supplied by a separate DC source. (Electric machinery fundamentals). The principle of rotating magnetic fields is the main rule of the operation to most ac motors. The magnetic field created by the poles will make the rotor rotate making the stator poles progressively change. This change will make the rotor follow and rotate with the magnetic field of the stator. As each change is made, the poles of the rotor are attracted by the opposite poles on the stator, forcing the rotor to rotate with the stator field. (http://www.reliance.com/mtr/mtrthrmn.htm) The rotor is rotating within the stator at angular velocity ?n, the magnitude of the flux density vector B at any angle a around the stator is given by B= BM cos(?t-a). Then the voltage induced in the stator that has N turns of wire is expressed by eind= NF?cos(?t). The voltage induced is sinusoidal with amplitude depending on the flux, angular velocity and a constant depending on the construction of the machine. In a three phase set of coils, the voltages induced will have same magnitude but they are shifted by 120 degrees. eaa'(t)= NF? sin(?t) ebb'(t)= NF? sin(?t-120) ecc'(t)= NF? sin(?t-240) The rms voltage of each phase is: EA= pNFf

Fall of Man Depicted in Atwoods Backdrop Addresses Cowboy Essay

Fall of Man Depicted in Atwood's Backdrop Addresses Cowboy The sexual politics of the man-woman relationship, or more specifically the sexual exploitation of women by men, is a clear concern in Margaret Atwood's "Backdrop Addresses Cowboy." Although the oppressor-as-male theme is by no means an original source of poetic inspiration, Atwood's distinction is that she views the destructive man-woman relationship as a metaphor for, symptom and symbol of, bigger things. From the vantage-point of feminine consciousness, Margaret Atwood empahsizes the "backdrop" as being not only the woman, but also the land and the spiritual life of the universe; the "cowboy" is both a man bent on personal gain (possibly an American based on Atwood's strong anti-American sentiments in her novel, Surfacing) and an emissary of technological progress. The structure of the poem logically supports the theme of conflict and "imperialism" in that it is clearly divided into two sections or "camps." The first four stanzas offer a description of "you", the "righteous and heroic" cowboy who brutalizes life without creating new life. The perspective shifts then from predator to prey in the final five stanzas as "I", presented as victimized woman and exploited nature, "addresses" her antagonist. The tone or mood of "Backdrop Addresses Cowboy" also undergoes a change after the first four stanzas when the reader enters the tragic, joyless experience of one who is paying the price of "slaughter and desecration." At this point in the poem, it seems futile to consider whether or not the price should be paid and the metaphoric man-woman tension remains distrubingly unresolved. In terms of form, "Backdrop Addresses Cowboy" is written in open (org... ...esecrate", the emphatically placed word of the climactic line in "Backdrop Addresses Cowboy", emphasizes again the "backdrop" as being not only the woman, but also the land and the spiritual life of the universe. As an emissary of technological progress, man has committed a sacreligious act against nature and humanity and his "fall" embodies the fall of the spiritual, the historical and the rational. In Margaret Atwood's poem, then, the troubled man-woman relationship is symptom and symbol of a greater alienation within humanity. Man's past and present curelties to human, natural and spiritual life are expressesed metaphoricall in terms of a cowboy "winning the West" on a movie set, against a backdrop "supporting" his heroism. "Backdrop Addresses Cowboy" offers a vision that is both desolate and conscious-expanding but it does not present answers.

Connecting Nazi Propaganda poster to Hitler’s rise to power

After the Great Depression in the early 1930’s, it resulted in economic and political instability for post ww1 Gremany. Adolf Hitler utilized fascism to promote his rise to power. Nazi propaganda posters were being used as â€Å"Art of Persuasion† during this time. Hitler was no fool, and used every opportunity to his advantage provied by the depression. The Propaganda posters were used as a tool to promote Hitlers beliefs. He used this as a way to sell his ideas to the people of Germany. Hitler was trying to gain the German peoples trust through emotions. The propaganda poster helped promote Hitler’s rise to power. He related to the peoples wants and needs to gain his power. Each poster related to everyone in Germany in some way. This helped secure his rise in power. If one poster did not relate to someone, another did. By utilizing the â€Å"Art of Presuation†, he gained all the power one would need to rule. Personally, it is devostaing how one person can gain that much power over that many people during a time of crisis. It makes perfect sense as to why so many people allowed Hitler so much power. He took initiative when no one else would. He took matters into his own hands. Hitler gave the people what they needed at a time of crisis. Hitler’s rise to power came at the perfect time. Germany was in turmoil, and they were in need of a hero to save them. Propaganda posters related to everyone, and Hitler made the best use out of them.

5 Top Tips on Travel Writing

5 Top Tips on Travel Writing 5 Top Tips on Travel Writing Travel writing is one of the most popular types of non-fiction. And if you’re someone with a love of both literature and globetrotting, travel writing offers a fantastic opportunity to combine the two! Here, then, are a few top tips for budding travel writers to help get you started. 1. Read Other Travel Writing The best starting point if you’re new to travel writing is to read other authors. There are many types and styles of travel writing out there. So we suggest reading a little bit of everything, from blog posts to book-length travelogues, to find inspiration if you’re not already sure what to write. 2. Picking a Subject To stand out from the crowd, your travel writing needs to offer something unique. Part of this will be your written voice, but what you are writing about is equally important, so you’ll want to pick a great destination to focus on. Finding somewhere interesting that nobody has written about before is the dream, so you might want to look beyond the famous beaten track for strange or unusual attractions. Alternatively, if you are writing about a familiar place, look for an angle that nobody has used before. It helps if you do more than just lie on the beach, too. 3. Paint a Picture Your writing should conjure an image of the places you describe, so use sensory language wherever possible. If you can communicate some of the views, sounds and smells you’ve experienced, your reader will feel more like they’ve been there. Rich, descriptive writing is therefore crucial. Of course, a literal picture can help as well, so don’t forget to pack a camera! 4. Tell a Story Travel writing is about more than just facts. It’s about your experience of a place or journey. As such, you need to take your reader on a journey, too! One tip in this respect is remembering that the best travel writing is more than just descriptive. It may also have: Characters (e.g., people you meet along the way or travel companions) Themes (e.g., issues or events that recur throughout your journey) A plot (e.g., your goal, such as visiting every museum in Cumbria) Make sure not to miss the Derwent Pencil Museum, especially if you like big pencils.(Photo: Stinglehammer/wikimedia) Keep in mind that travel writing is creative writing, even if it is non-fiction. You may even want to twist the facts to tell a better story. Or go full Hunter S. Thompson and blur the lines between fact and fiction entirely. We wouldnt suggest taking as many drugs as he did, though. 5. The Benefits of Fact Checking Assuming you’re not fictionalizing your journey too much, you may want to do some fact checking on things you’ve learned when you get home. For instance, before repeating what that odd man in the plaza told you about Piacenza being founded by a champion chicken farmer as a luxury resort for poultry, get online and do some reading. You can still include the anecdote if it turns out to be untrue. You just don’t have to present it as a fact. And if you handle the fact checking, we’ll be happy to help with the proofreading once you have a first draft ready!

Free Essays on Sex ED

Who’s Entitled Sex, sex, sex it’s so prevalent in everyday society. The media, television, movies, video games, advertisements, books, magazines; all of these and more not only condone sexual promiscuity but glorify it. The children of America are subjected daily to these explicit thoughts and images. Yet one third of school districts in the U.S. teach abstinence-only-until-marriage which not only tell kids that they should just wait, but the program also limits the information about contraceptives (Rollins). Many people argue that teaching kids about safe-sex is sending them mixed messages. They feel that the message being sent is telling kids it’s okay to be sexually active, so long as one protects him/her self. But what about all the explicit imagery and actions that the media portrays as being normal and cool, is this not also sending kids a mixed message? Unfortunately most of the media doesn’t provide the information of safely protecting oneself from diseases or pregnancy. In the majority of movies and television shows they don’t show the guy slipping on a condom before he performs sexual intercourse; or the girl taking birth control weeks in advance. The after effects are failed to be presented in much of today’s media. Very few of the sexual acts being performed are by couples that are married. This is in return sending kids a mixed message. Television, and movies are showing them it’s okay to be sexually active with out marriage, but their schools are telling them just wait until marriage because it’s better that way. Who’s sending the mixed message now? Educating the youth efficiently about all aspects of sex in public schools starting in middle school until high school should be a number one priority in every school in America: Teaching kids abstinence only is unhealthy and unreal istic in today’s society; by teaching youth safe-sex methods a reduction in the number of teen pregnancies and... Free Essays on Sex ED Free Essays on Sex ED Who’s Entitled Sex, sex, sex it’s so prevalent in everyday society. The media, television, movies, video games, advertisements, books, magazines; all of these and more not only condone sexual promiscuity but glorify it. The children of America are subjected daily to these explicit thoughts and images. Yet one third of school districts in the U.S. teach abstinence-only-until-marriage which not only tell kids that they should just wait, but the program also limits the information about contraceptives (Rollins). Many people argue that teaching kids about safe-sex is sending them mixed messages. They feel that the message being sent is telling kids it’s okay to be sexually active, so long as one protects him/her self. But what about all the explicit imagery and actions that the media portrays as being normal and cool, is this not also sending kids a mixed message? Unfortunately most of the media doesn’t provide the information of safely protecting oneself from diseases or pregnancy. In the majority of movies and television shows they don’t show the guy slipping on a condom before he performs sexual intercourse; or the girl taking birth control weeks in advance. The after effects are failed to be presented in much of today’s media. Very few of the sexual acts being performed are by couples that are married. This is in return sending kids a mixed message. Television, and movies are showing them it’s okay to be sexually active with out marriage, but their schools are telling them just wait until marriage because it’s better that way. Who’s sending the mixed message now? Educating the youth efficiently about all aspects of sex in public schools starting in middle school until high school should be a number one priority in every school in America: Teaching kids abstinence only is unhealthy and unreal istic in today’s society; by teaching youth safe-sex methods a reduction in the number of teen pregnancies and...

Law of international organisations Essay Example | Topics and Well Written Essays - 2750 words

Law of international organisations - Essay Example The idea of human rights receives formal universal recognition that the international community strives to maintain and enforce encoded through the United Nations Charter signed on June 26, 1945 with the main objective of saving generations of humans from war and reaffirms the faith in fundamental rights and freedoms. The main objective of the United Nations is to achieve international cooperation, through promoting and encouraging respect for human rights and the fundamental freedoms that accrue to them without the discrimination in terms of aspects such as sex, race, language or religion. It is important to note that the enforcement of these rights and freedoms can be undertaken through joint or separate actions by the member states. The provisions of the Articles of the United Nations Charter have the force of prudent international law as the charter is a treaty and binds to those nations that have ratified it. Therefore, state parties are required to fulfil the obligations and th e responsibilities enshrined in the Charter including the obligations to defend human privileges and the major liberties, the promotion of the observance of the civil liberties and the cooperation with the United Nations in attaining these inherent obligations. ... Since the Universal Declaration became international law there have been other conventions and treaties that create regional courts that also help in the enforcement of fundamental rights and freedoms. Due to the dramatic increase of human rights activities in the twentieth and twenty first century, there has been need to combine the monitoring of the human rights violations and matters concerning their enforcement. The establishment of the International Criminal Court formed a vital part of an emerging system of international human rights protection in that it is empowered to take legal action and castigate individuals liable for offenses against humankind. The growing international awareness of the need to protect human rights and guarantee freedoms has rejuvenated the need for upholding them. Yet, serious violation and deprivation of human rights and fundamental freedoms still exist that require a remedy in the shortest time possible. To remedy this situation, there have been regi onal courts with the jurisdiction to protect human rights and fundamental freedoms. However, these courts must strive and adhere to the already established norm that the supremacy of the United Nations Charter. In Britain, for example, the Human Rights Act of 1998 is an act of Parliament, whose main aim is to ensure that it gives further force the laws concerning human rights, contained in the European Convention and the United Nations Charter. It gives the courts in the United Kingdom the power to deal with those issues, which might cause the citizens of this country to go to the European Court of Human Rights. The act makes it illegal for all public bodies

The Railroad Era and Economic Growth Paper Research

The Railroad Era and Economic Growth - Research Paper Example The only means of transport was either by wagons, stagecoaches or by the ocean, this discouraged immigration of children and women (Norris, 2008). Fortunately, in 1862, The Central pacific Railroad emerged from California’s need for a remedy to its transportation crisis as well as socio economic challenges. Construction of the railroad began at Sacramento in 1863 after the congress authorized it the previous year. The businesspersons who combined efforts to finance the project named themselves the ‘octopus’ and the profits from the project rewarded them greatly years later. With the development and opening of the railroad, traveling time from the state to other states and within the cities greatly reduced. From travelling for months and several weeks, the people of California could now use just a week or days to reach their destinations. The Central Pacific Railroad was labelled the safest means of transport, most attractive site for tourists as well as the most direct means for transport for the immigrants across the American continent. Transport of goods and services developed as the machinery, mails, manufactured goods, as well as human resources begun moving to the west. In addition, natural resources, and food rolled eastward hence feeding almost half of the Eastern populace. Along the Central Pacific Railroad as well as its terminals, towns emerged and developed quickly because of the strategic location. Among the towns that developed along the lines of this railroad were North Plate, Lexington, Julesburg, Cheyenne, LA rime, Rock Springs, and Eva nston. People begun purchasing land that the had been given to the railroads as grants and they established settlements in the new town, constructed houses, began business activities as well as ranches and farms (Norris, 2008). The Octopus used agents to market the area