Multiple Factor for Voltage

It goes back in history. Edison was trying to find the ideal distribution voltage for his DC power.

from wikipedia:
The 110 volt level was chosen to make high-resistance carbon filament lamps practical and economically competitive with gas lighting. While higher voltages would reduce the current required for a given quantity of lamps, the filaments would become increasingly fragile and short-lived; Edison selected 100 volts as a compromise between distribution costs and lamp costs. Generation was at 110 volts to allow for a voltage drop between generator and lamp.

Other voltages were then chosen as a multiple of the original 110 volts to make transformer design easier.

My feeling is that #2 is unlikely, since Edison was all for DC. It was Tesla that popularised AC, and then came sine waves and form factors.

The Magic of the multiples of 11

Question: Why Transmission, distribution and utilization voltages are in multiples of 11, as in 110V, 220V, 440V, 1.1kV, 3.3kV, 6.6kV, 11kV, 22kV, 33kV, 66kV, 110kV, 132kV & 220kV?

Answer: It is true only with respect to AC power systems. The first known man-made source of electricity is a cell, which is DC in nature. But, after realizing the disadvantages of the DC electric equipments, AC Electricity generating machines were invented. When these AC Machines were developed, the power of these machines was to be compared with the already available DC electricity, as it is human tendency to compare anything new with the existing ones. As in the case of steam engines.

When steam engines were invented, the power of the steam engines was compared with that of the horses, which were the power sources before the invention of the steam engine.

So, a value called RMS Value for AC Electricity was derived which compared the effectiveness of the AC Electricity with that of the DC Electricity. This value is the Effective Value of AC Electricity. As we were more interested in knowing the effect of AC electricity, all measuring instruments were and are designed to measure only the RMS value of AC electricity – may it be Voltage, Current, Power, etc.

But, for the designer sitting in the design lab, more than the effective value, the average value over a period on one sinusoidal cycle of AC Electricity was important. So, he designed an AC electric Generator, which would produce, on an average, a voltage over a period of one cycle, of say, 10kV (10 is a round figure, you know).

But, when this machine was built to the design and put to operation and when the output voltage was measured, it was found to be 11kV, as the meter was measuring NOT the average value but the effective or the RMS value. This relation existed for any voltage. So, a factor was arrived at – relating the RMS value and the average value, called Form Factor, which is the ratio of RMS value to the Average value, which for a sinusoidal wave form was about 1.1. Then, when the voltage was to be transformed, it was easy to have a whole number for the turns ratio of the transformer and hence all subsequent AC voltages became multiples of 11.

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Oh nooooo... not this #@*% AGAIN!!!

I think this is the 2nd most repeated (and #1 most annoying) question in this forum. Someone needs to make a filter that auto-redirects people to an FAQ...

It is not true, there is no "factor of 1.1" or "factor of 11", its a coincidental myth that applies only to certain parts of the world, and even then, it only appears to exist if you ignore evidence to the contrary. For example 110V? no such thing. 115, 117, 120, 125, 110, they are all considered "nominal" voltages, the official standard for the US is 120V. Everything else is nominally within tolerance. 220? Try 208, 220, 230, 240, 250V as standards in different places. 440V, again, no such thing. Officially it is 480V for distribution, 460V for utilization, but anything from 440-480V is considered within tolerance. 3.3kV, 6.6kV 11kV, etc. etc.? What about 2300V, 4160V, 6900V, 7200V, 10kV, 12.47kV etc.? the "1.1/11 factor" only holds true if you pay no attention to the fact that these other INDUSTRY STANDARD voltages are all currently in use around the world.

It's a myth based on coincidence and ignorance, get over it already people...