Greeting's all. Ron here, an electrician who just passed his licensing exam and it's me first post here.
Three questions in this thread I'd like to consolidate into one coherent post.
Q1) Why three phase and not more?
A1) Because adding more phases doesn't appreciably add more efficiency to a motor. The original reason why three phases was adopted in the first place. Adding more phases would add more cost of wire, however.
Q2) Why is residential called single phase instead of a two phase system?
A2) Years ago there was a two phase system in existence. The phases were 90 degrees out of phase with each other for running motors, etc.. It's obsolete now. It's called "single phase" because most of the loads are actually single phase and unlike the ~original~ two phase sytem, single phase systems are 180 degrees out of phase with each other. Perhaps if the system were perfect to begin with then it would have been called a two phase system, because the *other* two phase system wouldn't have ever come to be. That phrase was already used so the new name is the one we have now and the new nomenclature stuck. It's as accurate a phrase as calling it as an 'opposing asynchronous bifurcated phasing system'.
Q3) Why 60Hz to begin with and Europe uses 50Hz instead of our 60Hz?
A3) Using 60Hz utilizes power most efficiently for, shall I say, 'man's use'. 50Hz is just a bastardizaion of what Nikola Tesla figured what was right all along. The Europeans didn't understand why changing the frequency by 10Hz would make much difference. Perhaps this is myth, but I heard that the Europeans changed the Hz to 50 because it fit better with the metric system. Who knows, but the fact remains they changed it and their power supply system isn't as efficient as the American 60Hz system.
Someday I'd like to figure out just how less efficient that 10Hz difference really is. Maybe do some calculations to see how much energy they've wasted for being so "smart".
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Nikola Tesla figured all about AC/Transformers/Hz/three phase systems and many other things by himself! We could have been stuck with a vastly inferior system still in use today if we had started off wrong. What a genius he was and our text books still credit Edison for our modern way of life. Even when Edison was resoundedly proven wrong he still held on to his ideas that DC was better than AC, even going so far as to invent the electric chair to prove how much more dangerous AC was.
Edison really hated learning and using his mind to uncover things, rather than just endless experimentation. He was more of a showman IMHO. That, unfortunately, is much more celebrated in America than anything resembling the art of inventiveness.
One thing is for sure: without Tesla our carbon footprint -- ahum, energy usage -- would have been much greater than it is today!
P.S.
I've no references, just from what I have in me memory from school and all.