why the voltage ratings are in multiples of 11?

Question

ex:11kv,22kv,33kv,66kv etc

Answer 1

Just in case an electrical engineer does not answer your question I can try. (from an electronics background)

Basic House voltage is 110volts and when you multiply that by 2 you get 220volts used for large appliances like electric dryers and furnaces.

That basic 110volts when multiplies by 10 = 11kv or 11,000volts. that doubled is 22kv, that doubled is 44kv. Sometimes it is only increased or decreased by 1/3. But they will all be some multiple of the 110volts.
The higher the multiple the farther it can travel across town or country without loss. (or loosing energy.)

Answer 2

This is completely dependent on where you are located geographically. In the really big (i.e worldwide) picture, the 'multiples-of-eleven' theory isn't true.

North America has standard 3-phase transmission voltages of:
240 - 460 - 600 - 2400 - 4160 - 6600 - 6900
7500 - 13200 - 13800 - 26000 - 75000
150000 - 315000 - 375000 - 500000
and 750000.

Europe has standards more like:
208 - 400 - 600 - 900 - 1500 - 3300 - 4400
6600 - 10000 - 11000 - 15000 - 25000
50000 - 90000 - 115000 - 250000
400000 - 500000 and 750000

South America has combinations of the two, as does Australia and most of Asia.

For some equipment, certain voltages work better than others - this is particularly true for special 'custom built' machinery for industrial applications. This means the internal voltage on the facility bus can be pretty much anything ... it's all based on transformer turns' ratios. However, the voltage on the line coming from the utility to the plant is most likely one of those listed for either North America or Europe.

Note that almost all 'generators' class as custom-built equipment; this means there's a often a votlage-changing transformer located just outside the utility's generation facility to bring the 'custom' generated voltage in accordance with the standard transmission voltages of the local lines.

Answer 3

110 Volts is nominal and may vary when measured by a voltmeter. That said, power is supplied using sets of three separate parallel wires that you can see up on most power poles. The very high voltage there is stepped down using a transformer to supply most houses and businesses with a usable lower voltage. The voltage between any one of the three wires to ground in a house is 110 Volts for example to light a light bulb. The voltage between any two wires is 220 Volts and is used for example to power a clothes dryer or kitchen range. Houses do not use all three wires. A machine shop may power a large motor by connecting all three wires (in a delta or Y configuration) to obtain 440 Volts. Therefore the progression of 110, 220, and 440 Volts stems from the use of single, two and three-phase wiring circuits. Electrical power is conducted cross-country at very high voltages using high tension lines strung in sets of three wires or phases which produces the multiple of 11 you mention. Incidentally there may be an additional single wire above all the rest to arrest lightning strikes and according to that insulators are made.

Answer 4

Hmmm. I've been in the electric utility industry for 26 years and I've never noticed that. You learn something new every day!! But to answer your question - I would think it might have something to do with the windings of the transformers.

Answer 5

its because of this equation
E=4.44*f*T*phi
E -Induced emf per phase
T -number of turns
f -frequency
phi -maximum flux per pole
from the equation we see that E is proportional to 11.So we get in multiples of 11.