Friday, July 17, 2015

The origin of electrical frequencies – Why 50 or 60 Hz

A couple months ago I decided to emigrate from my home country Venezuela, to the southern country Chile. As an electrical engineer while I was looking for a job I spend some of my free time on studying the local electrical system, the first factor that I have to get used to is that here the system works at 50 Hz and most of the equipment are specify according to the IEC Standard. For the last 8 years I had worked on 60 Hz systems and using mostly ANSI Standard, it is not a BIG deal just have to get used to it.

While studying the electrical system and white all the spare time I started wondering, seriously, WHY? are there two frequencies and so close to each other, true be told never gave much thoughts to the subject always think of that like, its always been like that, obviously there is a story behind. While doing my research I found this article that explain very well the reasons. It was made originally on Spanish so it translate it as precise possible.    

The origin of electrical frequencies – Why 50 or 60 Hz 

Even when today it seems that there is always been a unique frequency for electrical power transportation, on each of the main zones of influence: 50 Hz for Europe and 60 Hz for EEUU, it haven't been like that. Will do a look back through the history of the frequencies that have been used.





In 1891, Westinghouse engineers, in Pittsburgh, took the final decision of considering 60 Hz as the frequency for the future, that same year, the engineers of Allgemeine Elektrizitats Gesellschaft (AEG)  choose 50 Hz.

Since those decisions were taken, those frequencies became the "frequencies for alternative current transmission" standard, in fact this decision keeps affecting us nowadays. The frequency generally depends on each country, one of the most peculiar cases is Japan, when a person travels from Tokio to Osaka have to keep in mind that has come from a 50 Hz to a 60 Hz zone.

With this little review will try to clarify the reasons why the engineers of Westinghouse and AEG didn't agree on an unique frequency and why they choose a different value.  

To know the background of the decisions that set the frequencies of our days we have to go back by the end of the XIX century, for that we need to go through the documents that allows us see the traces of these decisions and this will let us  chronologically review the facts that lead them.



Since early times the electric energy wasn't used as an amusement, it was used as a safe method to light the houses, the boulevards or as a method of energizing electrical motors in factories to produce mechanical movement that will allow us discard the expensive and little efficient mechanic transmission systems: through axis, belts, pulleys, and gears that were used in the industrial revolution Era. The used frequencies have changed from 40 and 53 Hz in Europe, and 133 + 1/3 and 125 Hz in EEUU to 50 and 60 Hz respectively. This article wont cover the transitions period from direct current, promoted by Edison and Kelvin and the alternative current (1887), whose defender was Nikola Tesla. That was a true war, technologically, economically and politically wise.
         
1866 - 1890

Even when it seems incredible in those days each manufacturer, Edison, Thomson - Houston, Westinghouse, Siemens, etc. generated, produced and distributed electrical energy, also they manufactured the motors and lamps that will work it. Where the electricity did not develop to the fullest as a conglomerate and it was attend to be used as individual items one from another, an important technological delay took place like in England, France or Spain.

As a clear example of this situation, in 1878, Edison Machine Works manufactured dynamos, Edison Tube Company manufactured conductors, Edison Lamp Works manufactured lamps and Electric Illuminating Company of New Yorl generated electricity in the Pearl Street Central.  
  


Focusing in AC, by 1884, Dr. Hopkinson demonstrated the possibility of the transmission of AC over short distances, while in that same year Gibbs and Gaulard presented the second version of their called 'Secondary Generator' precursor of the transformer, in the Turin exhibition. Tests were made of transmission from Turin to Lazio. The primary network was around 40 km long, 20 kW and 2.000 V.  In this period, Max Deri, Otto Blathy and Karl Zipernowsky, noticing the defects of Gibbs and Gaulard's machine, improve it closing the magnetic circuit. On September 16th of 1884 was finally completed the installation the transformer, called like that the first time, it characteristics were 120/72 V, 1.400 VA and 40 Hz.

In 1886, Westinghouse bought the transformer patents design by Gibbs-Gaulard and Max Deri, Otto Bláthy and Karl Zipernowsky and with the work of Stanley developed an ironclad transformer used in their Great Barrington exhibition, it was feed from an generator of the kind made by Siemens. It had poles, worked at 1.000 rpm therefore the 133+1/3 Hz.

f (p * n) / 120

Where:
f = frequency  en Hz
p = number of poles
n = spin speed in rpm
In change other manufacturers like Thomson-Houston Company used alternators of 15.000 cicles (p*n), that permitted a frequency of 125 Hz

For this reazon it began in EE.UU the "High Frequency Era" in the generation and transmission of electrical energy. Westinghouse 133 +1/3, Thomson y Houston 125 Hz y Fort Wayne Jenny Electric 140 Hz.



Really, in those years, the main use of electricity was lightning and either frequency perfectly fulfilled the requirements of quality, with lower frequencies the lamps would began to produce an annoying flashing effect.

1890 - 1925

This a period in the one appears an element that will annoy the relative tranquility of manufacturers, the induction motor.

The motors that were used for the development of mechanical power that moved the machines tools were couple directly, motor - machine toll, of the the machine worked at 80 rpm, it will required a 200 poles motor working ar 133 +1/3 Hz. This problem, the elevated pole number, wouldn't appear in Europe since there they used 40 Hz, therefore they required only 60 poles machines.

In 1890, AEG and Oerlikon used 40 Hz for their 175 km three-phase electrical line, from Frankfurt (receptors) to Laufen (production) using an alternator of 50 V phase tension, 32 poles with a spin speed of 150 rpm, that gives 40 Hz frequency. The transmission was made transforming in the origin from 50 to 8.500 V and in Frankfurt it was reduce to 65 V. Later they realize the stroboscopic problems, due the low frequency applied to the lamps and by 1891 they chose to used 50 Hz, that solve both problems. Generators design to feed the motors and lightning systems.



In 1890, the engineers form Westinghouse realize that working with frequencies above 130 Hz was preventing their induction motor development, to many poles in the machines stator. Analyzing the problem, came with the conclusion that 7.200 cicles (p*n), and therefore 60 Hz, was the optimum value for their motors and the coupling of the machines that were manufactured back them.

Steinmetz just before started working at Thomson-Houston Company determined the resonance problems, with the material that Hartford Electric adquied, was due the harmonics of the 125 Hz signal used to supply the energy. The way to solve this was reducing to 62,5 Hz. General Electric kept using 50 Hz that used its European partner AEG. In 1894, General Electric, realize that they where loosing sales in the AC market and drastically change to 60 Hz.

Is wasn't unanimity respect the 60 Hz, one of the biggest projects of the generation in the times, The Niagara Falls project, in 1892, to give electrical energy to Chicago chose a two-phase alternator of 12 poles, rotating at 250 rpm, that gives 25 Hz, Westinghouse was the company that develop the project. Like ways other manufacturers in those times build alternators of 8.000 cicles - 66 +2/3 Hz.

1925 - Actuality

Even when it seems like since 1921 every electrical system in EE.UU used 60 Hz, it wasn't like that. The transformation process to the standard frequency last until 1948. For example the Mili Creek Installations were not modified until the end of WWII.

 In England it was even worse since the Electric Light Act came up, where is was stated that every electrical material that were manufacture had to be able to be used for any person or compay, this prevent the transformer develop by Gibbs and Gaulard to be used in England (this was one of the reasons of their technological delay) this was different in EE.UU or Germany.

A extremely peculiar case is Japan. The Yokohama department sent to EE.UU. engineers so they can study the different technologies about the electricity in the moment, 1889. When they came back to Japan, they were convince of the pros of the "high frequency" and bought and installed an alternator from Stanley-Kelly-Chesney (SKC) that worked at 133 + 1/3 Hz, in Keage Canal. In 1895 sold an alternator of 50 Hz to a company in Tokyo.




Lets Remember that Stanley of SKC then change to General Electric, and was then that determined that 133 +1/3 was to high frequency for AC electrical motor, and changed the alternator production so they generated AC at 60 Hz. When a company of Osaka bought an alternator to AGE, this one manufactured them to generated at 60 Hz and there the frequency division in Japan began to the momment: East 50 Hz and West 60 Hz. 

Summary 

Truly, the determination of the most convenient frequency came from the necessity (like all technology existing) of over come the tech problems that were presenting while the electrical energy spread around the world.  

So, in the first years the electrical energy was used almost exclusively for public lightning, hotels, banks and houses of wealthy people and to avoid the stroboscopic effects high frequencies were used.  
When the electrical energy got into the fabrication process and the energy consume was designated no only to lightning, but also to power in motors the frequency was reduce to the the actual values.

The reason WHY 50 Hz in Europe and 60 HZ in EE.UU, came only and excusably determined for the position of  preponderance of AEG in Europe and GE in EE.UU, whose engineers at some point chose chose on of the actual frecuencies

"The winner sets and tells the history" 


Source: Articulo “El origen de los 50-60 Hz en la transmisión de la energía eléctrica”. Wrote by Eduardo Aznar Colino y Joaquín Royo García, and publish in Técnica Industrial 242 (Septiembre de 2001). Vía afinidadelectrica.com.ar

Translated by: Eg. Aaron Paradas


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