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معمای الکتریکی شماره 46 - فلسفه برق سه فاز
فلسفه این که برق بصورت سه فاز تولید و انقال پیدا کرده چیه؟
چرا دوفاز یا چهار فاز نشده؟
یسری مطالب مثل زاویه 120 درجه ای که سه فازباهم دارم و همچنین سهولت در انتقال و تولیدش پیدا کردم ولی قانع کننده نبود.
به صورت علمی چطوری میشه جواب داد؟
نویسنده : علی - از: ایران
 
#1
ساعت: 11:31 - تاریخ: 1 آذر 1393
از ویکیپدیا :
در سیستم های قدرت سه فاز که عموما هم متعادل هستند با توجه به اختلاف فازی که دارند سیم برگشت نداریم لذا هزینه سیم کشی در خطوط انتقال نیرو کاهش یافته است.
برای اینکه تصوری اقتصادی داشته باشید ما در یکی از پروژه ها برای یک خط انتقال 100 کیلومتری 3 باندله نزدیک به هزار کیلومتر سیم نیاز داریم . سیم های این خط انتقال کرلو هستند وزن تقریبی هر متر سیم "کرلو" در حدود 2 کیلوگرم است یعنی بعبارتی 2 هزار تن سیم لازم است. حال اگر قیمت هر کیلو سیم را در حدود 10 هزار تومان فرض کنیم. ( البته در بازار در حدود 11 هزار تومان است) .   می شود در حدود 20 میلیارد تومان.
اگر می خواستیم به این خط یک سیم نول هم اضافه کنیم بایستی در حدود 2 میلیارد اضافه خرج می کردیم.  
نویسنده : برقندان - از: تهران
 
#2
ساعت: 11:35 - تاریخ: 1 آذر 1393
بنده در محاسبات ارسالی قبلی تعداد باندل های سیم نول را یکی فرض کردم اگر سیم نول را مشابه سیم فاز در نظر بگیریم اختلاف قیمت به نزدیک 6 میلیارد خواهد رسید. 
نویسنده : برقندان - از: تهران
 
#3
ساعت: 14:01 - تاریخ: 6 آذر 1393
پاسخ به این سوال همه جانبه است و نیازمند تجارب عملی و تئوریک زیاد است. در مورد دو سیستم تکفاز و سه فاز تجربه شده از نقطه نظر عملی و تئوری می توان برخی موارد را به شرح زیر بیان کرد. همچنین پس از آن تاریخ شکل گیری اختراعات مرتبط با برق متناوب را می توانید ببینید.

1- بطور کلی مولدهای سه فاز از مولدهای تکفاز هم توانشان کوچکتر، سبکتر و ارزانتر خواهند بود.
2-  انتقال برق سه فاز نیازمند مس یا آلومینیوم کمتری نسبت به تکفاز است.
3- موتور های القایی سه فاز خود راه انداز هستند، اما موتورهای تکفاز نیازمند سیستمهای راه انداز می باشند.
4- در موتورهای القایی سه فاز گشتاور الکترومغناطیسی یک سویه است، در موتورهای تکفاز این گشتاور تنها در سرعت نزدیک سنکرون می تواند به شرایط سه فاز نزدیک شود، بنابراین در موتورهای تکفاز میزان لرزش بویژه با افزایش بار و لغزش افزایش می یابد.
5- موتورهای سه فاز از ضریب قدرت بهتری نسبت به تکفاز برخوردارند، زیرا در شرایط مشابه از سیم پیچی کمتری در آنها استفاده می شود.
6- یکسو سازی برق سه فاز و بالاتر بسیار آسانتر از برق تکفاز است.

AC Power Development Timeline:
1835 - Hippolyte Pixii builds the first alternator. Pixii builds a device with a rotating magnet. He doesn't know how to make his creation useful since all the other experimenters of the time were building DC devices. Others like Faraday and Henry were experimenting at the time with primitive electric motors using electromagnets.

1855 - Guillaume Duchenne uses alternating current in electrotherapeutic triggering of muscle contractions. (Paris, France) AC power is not viewed as useful for anything else at the time.

1878 - Ganz Company starts working with single phase AC power systems in Budapest, Austro-Hungary
1879 - London: Walter Baily makes a copper disc rotate using alternating current (this is a weak early AC motor) which was not effective for bearing any load.
The 1880s: This decade proved to be an exciting time for the development of electric power, read below to find out some of the major developments by year.
1882 - London, Sabastian Ferranti (Englishman with an Italian parent) works at Siemens Brothers firm in London with Lord Kelvin (William Thompson), and Ince. With the help of Lord Kelvin Ferranti pioneers early AC power technology, including an early transformer. Later on John Gibbs and Lucien Gaulard would base their designs off of Ferranti.
1884

1884 - Turin, Italy: Lucien Gaulard develops transformers and the power transmission system from Lanzo to Turino. The demonstration of AC power includes a 25 mile trolley with step down transformers that allow low power Edison incandescent lights to light the path along with arc lamps. Galileo Ferraris was head of the Electrical Department. The next year Ferraris would invent the polyphase motor.
1885
1885 - Ferraris conceives the idea of the first polyphase AC motor: " In the summer of 1885 he conceived the idea that two out-of-phase, but synchronized, currents might be used to produce two magnetic fields that could be combined to produce a rotating field without any need for switching or for moving parts. "
1885 - Elihu Thomson at Thomson-Houston starts experimenting with AC power (the first company in the US to start work on AC)
1885 - George Westinghouse is intrigued by AC power and buys North American rights to Gaulard and Gibbs system for $50,000
1885 - George Westinghouse orders a Siemens alternator (AC generator) and a Gaulard and Gibbs transformer. Stanley begin experimenting with this system.
1886
An important year for AC power
1886 - Great Barrington, Massachusetts - the first full AC power system in the world is demonstrated using step up and step down transformers. The system was built by William Stanley and funded by Westinghouse.

1886 - November - Buffalo, New York receives the first commercial AC power system in the USA. This system designed by George Westinghouse, William Stanley, and Oliver B. Shallenberger
1886 - William Stanley designs an improved version of the Siemens single phase alternator

1886 - Fall - Elihu Thomson's AC power system is rejected by the patent office. Westinghouse is already far ahead, having sold its system commercially already.
1886 - Nikola Tesla tries to sell his AC power system to investors in New York City, but it fails to be of interest in a city which is already heavily invested in DC power systems. Other inventors around the world also promoting AC power have similar problems. This is especially due to the fact that no one has yet to invent an AC electric motor which is efficient.
1886 - Otto Blathy comes to the USA and Thomas Edison buys options on the Z.B.D. Transformer. This would put him in the position to rival Westinghouse that controlled the Gaulard and Gibbs transformer patent. Later Edison decides that it is not worth going into AC and drops his options on the Z.B.D. Transformer.
1887
1887 - C.S. Bradley builds the first AC 3 phase generator. Up until this time Siemens and Westinghouse had been producing single phase AC generators. The 3 phase system would be a great improvement.
1887 - F. Augus Haselwander develops the first AC 3 phase generator in Europe. He is behind Bradley by a couple months and it is generally believed that he built his design independently of Bradley.

1887 - Sabastian Ferranti designs Depford Power Station in London. When it is completed in 1891 it would be an important early site in AC power history.
1888
1888 - Mikhail Dolivo-Dobrovsky in Germany builts his first AC polyphase generator. He works for AEG. (Allgemeine Elektricitäts-Gesellschaft)l

1888 - April - Galileo Ferraris makes public his AC polyphase motor first conceived in 1885. His motor works without a commutator, this development finally makes the AC motor efficient, and therefore competitive with DC motors. The A motor report was first published at the Royal Academy of Sciences in Turin. Westinghouse read the report of Ferraris and saw a chance for AC systems to become much more marketable

1888 - May 15 - Tesla stands before the AIEE showing his polyphase motor. Elihu Thomson was there and some in the group seemed to be impressed. One week later Westinghouse sent out a recruiter to get Tesla to join him. Tesla's progress on the motor is slightly ahead of Oliver Shallenberger's 3 phase electric motor. Shallenberger was already working for Westinghouse.
Tesla claims he "dreamed up" the first polyphase motor before Galileo Ferraris. Later at a trial a US court sides with Tesla despite the fact that Tesla has no proof besides witness testimony.Read more here

1889 - Dobrovolsky builds his first transformer and motor to work with his 3 phase AC system
1891 - Frankfurt, Germany: First distance power transmission (for electric power utility) Lauffen to Frankfurt 109 miles. The entire system was designed by Dobrovsky from generator to electric motor. Many important figures of AC power were invited to the event, at the Congress Dinner Galileo Ferraris was hailed as “the father of three-phase current.”
1892 - Charles P. Steinmetz goes before the AIEE and presents his paper on hysteresis, or the delay effect in 3 phase AC power. Steinmetz was the first person to understand AC power from a mathematical point of view. After his paper he is hired by General Electric Company and joins forces with Elihu Thomson and William Stanley. Steinmetz would go on to improve and troubleshoot future AC power systems.

1893 - Redlands Power House - the first commercial installation of 3 phase AC power, 40 hz.
1895 - Folsom Power House - The first installation of modern AC power in the USA: 3 Phase AC at 60 Hz.
1895 - Westinghouse builds the power system for the Adams Power Station at Niagara Falls. Benjamin Garver Lamme is the principal engineer of the operation. General Electric builds the 25 mile power transmission system from the Niagara power house to Buffalo, NY which is made operational in 1896.
1897 - Mechanicville Power Station - Charles P. Steinmetz experiments with a unique single phase AC power transmission system.
1900s - Three Phase AC power is fully established as the principle source of power for the world

 
نویسنده : حمید - از: فیروزآباد فارس
 
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