Why Three Phase?
Why Three Phase
Why three phases? Why not more?
What are the phases in electricity?
Electric current, which we know as alternating current, is electrical energy that has a certain wavelength and therefore is produced at a certain frequency.
While electron flow occurs in direct current, alternating current occurs when electrons vibrate in the form of a wave on the conductor.
For this reason, while direct current suffers a large voltage loss depending on the resistance of the conductor, this voltage loss in alternating current is much lower than direct current and alternating current can be transmitted to much longer distances with lower cable cross-sections.
In alternating current, this fluctuating movement is in the form of a sine wave. A sine wave is a circular wave. By circular wave I mean that the current has a peak value and a base value. Depending on the wavelength, the current takes positive and negative values at a certain frequency, that is, over a certain period of time.
Now imagine that we divide this fluctuation into three separate phases by giving phase differences. Carry each phase with a separate cable.
Here is three-phase alternative electrical energy for you.
You know the turbines used in alternating current generation, these turbines produce electricity in a circular motion, you can think that for three-phase electricity, we take one phase lead from three separate 120-degree sections of the circular turbine and transmit the current with three separate conductors.
This is how three-phase electricity is produced. A circular turbine of 120 to 360 degrees produces electrical energy in three separate phases with a phase difference of 120 degrees. We can also say that the energy produced by the turbine is collected from all parts of the circle without being wasted.
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Well, can't four phases be taken from the turbine with a phase difference of 90 degrees?
Yes, it is taken. In fact, since four cables will carry more power than three cables, we can say that four cables are better than three cables if the energy capacity produced is high enough.
However, since the production capacity is fixed, we need to calculate the calculation by dividing the total power by four instead of three. Therefore, logically, we will need to reduce the cable cross-sections in a four-phase power line. In addition, insulators and other equipment will increase by 4/3. Moreover, you will need to run 4 cables instead of 3 cables.
All this means additional costs.
In fact, this issue is not a matter of three phases at 120 degrees, but four at 90 degrees, or six phases at 60 degrees, but it is actually a standard issue since electricity is transported through a network spread all over the world.
The standard for this was decided as three phases at the time.
This decision was taken to avoid the confusion caused by both the costs of the equipment used at these high voltages and the phase differences.
After all, carrying electrical phases with four or more cables instead of three also creates cable costs.
Moreover, if necessary, it is possible to increase the power by increasing the voltage while calculating the power to be carried. So there is no need to lay extra cables.
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As you know, it is the same at dam outlets or other power plant outlets; voltages can be carried through 380,000 volt and 200 ampere lines.
This voltage is later adjusted to different voltages and amperes depending on the need and transported to the cities via high voltage lines at lower voltages. In the cities, it is reduced to 380 Volt and three-phase current, called low voltage, by transformers and distributed to our homes.
Each phase is distributed in a balanced manner in our homes, some of us are supplied with electrical energy from the first phase, some from the second, and some from the third phase. As you know, the voltage of single phase is 220 Volt.
Three-phase electrical energy is supplied to industrial buildings because three phases are generally needed for motors. This means 380 Volts. Three-phase energy is actually a much more advantageous form of energy for industrial buildings, with both higher capacity and more economical cable costs.
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Since voltage is a vector value, the voltage between phases changes according to the phase difference.
There are quite complicated formulas for calculations, but I do not want to tire you with the formulas in this article.
Since there is an inverse proportion between increasing the voltage and the current, and the resistance of the conductor is directly proportional to the current, energy is carried to long distances as high voltage. Low current, low resistance, low resistance, less energy loss. Thus, since losses are less, long-distance energy transmission lines are always high voltage.
In cities, these lines are distributed within the city with medium voltage and used for road lighting and electrical energy in residences with low voltage.
These high, medium and low voltage values vary by country. Although there are international standards on electricity, each country has its own electrical standards.
For example, 110 Volt is still used in America. As far as I know, 110 volts is available in Canada. While most countries use a voltage of 220 or around (220, 230, 240) (the voltage frequency is 50 Hz. Some countries prefer a voltage around 110 volts (100, 110, 127) and a frequency of 60 Hz.
When it comes to standards, for example, there is no definition of medium voltage in Russia. Russians define voltages as high and low voltage.
In fact, in Russia, we even use 24 Volt for security purposes at some construction sites, especially for night lighting and on the sides of pedestrian roads.
In other words, each country's electrical specifications may contain changes.
However, an international standard has been established regarding three-phase and single-phase. All countries produce electricity in three phases.
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So who determined this three-phase standard?
So how did it happen that they decided on three rather than four or more?
In fact, Nikola Tesla is the inventor of the alternating current that we use today.
Before him, there was William Stanley, who produced alternating current with an induction coil, but Nikola Tesla succeeded in producing the alternating current we use today for the first time in a laboratory environment in 1886.
Tesla later sold the patent to George Westinghouse.
In those years, there were other scientists working on this subject besides Tesla.
However, the first person to install high voltage lines on a dam is Almirian Decker.
Decker designed a hydroelectric power plant at the Mill Creek dam in California in 1893, and his design was a 10,000 volt and 3-phase system.
Most likely, it continued the same way it started, and this is how three-phase electricity spread around the world.
Three phase is logically the most suitable alternative electricity generation method.
Today's cost efficiency analyzes show that the choice in those early days was probably the right choice, and the whole world still continues to produce and use three-phase electricity.
Electricity is a dangerous form of energy, especially when there is high voltage.
That's why, as far as I understand, there are not many people who have an opinion on this subject other than experts.
Even after it is so widespread, the ideas of those who produce different ideas must not be of much importance.
However, a six-phase high voltage line was once installed on the island of Malta as a trial.
In a video I found on the internet, an experienced electrical engineer named Lionel Barthold, who is also the owner of an electrical company, touched upon this issue in an interview.
The interviewer asks why this trial was conducted in six phases. Why six and not four or five? Why not twelve?
Because it was very easy to give a 60 degree phase difference on a three-phase line, says Mr. Barthold.
Then, by adding three new lines with this phase difference between the existing three phases, you get a 6-phase energy line with phase differences of 60 degrees.
However, he says, establishing the infrastructure of this job based on six lines was quite complicated, including equipment, cable costs, specially produced insulators, etc. Since the system was quite costly and complicated, the continuation of the line was immediately abandoned.
Yes, you can transfer approximately twice the power this way, but why spend twice as much on cables when you can handle the same power with three cables by increasing the voltage? Why spend money on insulators and other equipment?
Additionally, when going from six to twelve phases, the power transfer also doubles, says Mr. Barthold. In other words, twelve-phase electricity production is also possible, he says.
For example, mathematical formulas mention that transferring all the power produced through a tube-shaped energy transmission line without any losses other than the resistance losses of the conductors as energy through such a line will be the maximum possible power transfer method.
In short, practical attempts to carry electricity with more phases were once made.
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Of course, let me finish this topic by examining the last question that comes to my mind on this subject.
Since it is cost-effective to install a three-phase system by dividing the 360-degree angle into three equal parts, then let's divide the 360-degree angle into two and draw two phase lines everywhere with a phase difference of 180 degrees.
Won't two phases be even more advantageous?
Since we can transfer the power we want by increasing the voltage, why don't we make the alternating current lines two-phase? Why are we doing three?
To be honest, I don't know if there is any problem with this technically, as the two phases will be opposite to each other, there may be problems when using them together. Maybe electric motors do not work at full efficiency with such two phases. Maybe it's not working at all. As a result, it is possible to produce a rotation movement with three-phase electricity. But it is probably not possible to do this with two phases.
In short, three is good, three is balance, so far so many lines have been built on three-phase electricity, all kinds of industrial equipment, starting from the motor industry, have been produced and are in use on three phases.
Probably even if we look at it from this perspective, it is no longer possible to change this standard.
Moreover, if the two-phase system has some technical problems, then we can say that it was not possible anyway and that is why they did not make it two-phase.
Yes, conclusion: it is technically possible to use more than three phases, but there is no point! I think two phases involve technical problems.
In summary, three phases are sufficient, there is no need for more, as the number of phases increases, you have to spend much more money, so more than three phases is costly and more than three phases are much more complicated in terms of engineering solutions.
I always say, three is better!
Thank you Tesla, without you I would have to write this article by candlelight.
