Tesla decided that 60 Hz was the right
frequency for AC power distribution,later some British scientist decided that it should be 50 Hz. But we could not find the superior one amongst the both as they both have advantages and disadvantages over places... I'll try to convince you without bringing in technical terms as far as i could..
There two kind of power loss in the form of heat while the AC power is distributed to our home namely constant loss and variable loss due to the resistance and impedance of the transmission lines and transformers.
In those two losses the constant loss is fixed for a particular amount of load but the variable loss is depend on the frequency. if the frequency is more the variable loss will be high when a impedance load connected at home. That why we stick on 50Hz..
You may think why don't we go for 40Hz or less then ! If we still reduce the frequency the efficiency of transmission lines will fall...
that's why tesla recommended 50Hz for distribution.. at where we will get maximum efficiency of the transmission lines with constant and variable losses...
Let's come to the voltage..
While calculating output voltage of a AC generator a constant called form factor is multiplied with the maximum voltage. The value of form factor is 1.1. So the voltage use for distribution will be always multiples of 1.1 . Like 55, 110, 220, 440, 11k, 22k, 33k,.. and so on..
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