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Why is it that distribution and tra

Why is it that distribution and tra

Why is it that distribution and tra

Why is it that distribution and transmission voltage levels are mainly in multiples of 11
for example: 11KV, 33KV, 66KV, 88KV, 132KV ?

RE: Why is it that distribution and tra

Not where I come from; [sub]transmission phase-to-phase voltages here are typically 13.8 kV, 27.6, 44, 115, 230, 500, and distribution is commonly 2400, 4800, or 8000 volts.


"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Why is it that distribution and tra

System voltages are standardized by IEC 60038. Note that they are just suggestions, with local / historical practice overriding.

For 1kV through 35kV, there are three series of voltages. Two for 50Hz and one for 60Hz. For UK influenced voltages, the "11" multiplier fits - 3.3kV, 6.6kV, 11kV, 22kV and 33kV. For French / German influence, the standard voltages are 3kV, 6kV 10kV, 20kV and 35kV.

Above 35kV there isn't a differentiation of 50/60Hz.

RE: Why is it that distribution and tra

When I was in the college one of our professor while explaining the form factor for the pure sinusoidal wave he was mentioning that this factor is used as the basis for selecting the voltage levels.
Form factor = RMS Value/Average Value

For the pure sinusoidal wave, Form factor = 0.707/0.637 = 1.1

So the average voltage value is in the multiples of 10.

But in reality, I don't find any application of this. But due to the usage, I am now habituated to these multiples of 1.1, as I am in IEC world.

ANSI standard has different basis, which I believe all the North American standards followers use.

RE: Why is it that distribution and tra

Is it a Spinal Tap thing?

RE: Why is it that distribution and tra


Look at the maximum voltages of your voltages and then look at the maximum voltages in IEC rated equipment.

RE: Why is it that distribution and tra

I was going to guess that it had to do with voltages you could insulate comfortably to with different number of bushings. If I am unsure of the voltage of a transmission line, I just count the bushings.

RE: Why is it that distribution and tra

To me, the whole thing is formed on a false premise. Yes, we have a smattering of 11kV, but it is archaic. The actual voltages are more along the lines of 13.2kV, 57.5kV, 115kV, 230kV, and 500(525)kV. The 13.2 just doesn't fit into the 57.5/115/230 pattern. The 500, or 525, is just a different number and doesn't fit with anything.

Many of the European countries had the opportunity (?) to start over from scratch in the mid-20th century on a whole country basis. Much of the developing world started, to a large extent, no earlier than that. In the US, on the other hand, we live on a daily basis with decisions made well over 100 years ago. The gurus in this area made one set of voltage level decisions and the gurus in that are made a different set of decisions. Those of use in the business today still live with those decisions. All of my voltage levels are A-B-C, but as I understand it a company to the south with similar initials as A-B-C at some voltages and A-C-B at other voltages. My 115kV would be entirely incompatible with the 110kV system a couple of states away. Heck, sometimes one 115kV system doesn't really coordinate with somebody else's 115kV system when one operates at 115kV and the other operates a few kV higher.

There are no universal rules, rather there are a lot of very specific local rules. Consider yourself lucky if your local rules are the same as the local rules of all of your adjacent systems.

RE: Why is it that distribution and tra

The utility that employs me has over the years absorbed a number of smaller entities whose operating voltages deviate from "the company standard" and we power system controllers have just had to learn to deal with it.

And although all of our facilities are operated under the same corporate banner the geographic distances and virtually autonomous history of the different regions of the company become problematic when the desire arises to harmonize standards; for instance, in the far-flung diaspora where the response time to dispatches is typically a few to several hours, one trade is very accustomed to being asked to perform the rudimentary tasks of another trade group, provided it's within the scope of their training, whereas in the closely compacted together urbania such a request would get you laughed out of the room.


"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Why is it that distribution and tra

The story of transmission voltage evolution is briefly covered in IEEE Red book-141-1986,1993 (Clause 3.2.6) I hear color books are going to be scrapped by IEEE 3000 series standards.
In 1882,September, Thomas Alva Edison commissioned Pearl Street power station (72kW DC) in New York for feeding 1300 numbers of his 16 candle power incandescent lamps. That was the beginning of commercial sale of electricity in the world. He selected 100V as rated voltage for his lamps to deliver 16 candle power. But he soon started getting complaints from consumers at fag end of the street of poor light due to voltage drop. He could not change the voltage of bulb,but only the generator voltage to 110V ,so his lamps were seeing a voltage band of 110-90 V depending on the distance from the station and consumers were satisfied. ( I have no reference to this story but hearing for many years!)Thus 110V became standard distribution voltage. Soon Edison increased it to 220V by grounding the middle point. Then the voltages started doubling. Probably the reason for 1:2 may be the ease of using auto-connection with AC transformers. Soon the voltages raised up as demand soared -440 V,1.1,2.2,4.4,6.6, 13.2 kV etc followed by 11,22,33,66,110,220 kV etc. Up to 1919, at least in US,110 V was universally followed as basic distribution voltage. But then to take care of higher voltage drop, 115 V &120 V were also adopted.
This resulted in 115,230,460 V- 2.3,4.6,6.9,13.8- 23,34.5,46,69,115,138,230 kV and
120,240,480,600 V + 2400,4800,12000,12 470,7200 V series.
But transmission voltages were not affected much by 115 &120V.
So those days,transformer manufacturers had to make multi circuit transformers (some times 4-6 voltages) to cater to plethora of voltage levels adopted in various parts of each country.

RE: Why is it that distribution and tra

Quote (prc)

But then to take care of higher voltage drop, 115 V & 120 V were also adopted.
Actually 115V was a transition voltage on the way to 120 Volts.
I saw this written many years ago and have been searching in vain ever since for the reference.
A decision was taken to raise the utilization voltage from 110 Volts to 120 Volts.
This was to be phased in at the rate of 1/2 Volt per year.
When I was young new appliances were rated at 112 Volts for about 5 years. Then new appliances came out rated for 115 Volts. Five years later we had 117 Volt appliances for 5 years.
As a school boy intensely interested in electricity I lived through those transition years.
Our standard utilization voltages are now multiples of 120 Volts.
120V, 240V, 480V and in Canada 600 Volts.
115 Volts? That is the standard rating for motors. This incorporates an allowance for the voltage drop from the 120 Volts at the transformer terminals to the motor.
So our standard motor ratings are 115V, 230V, 460V and in Canada 575 Volts.

"Why not the best?"
Jimmy Carter

RE: Why is it that distribution and tra

I remember seeing one of those travel kits you can buy for hand-held appliances referencing 117/200V appliances, which the packaging stated was used in Indonesia, IIRC.


"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

RE: Why is it that distribution and tra

Thank you friends for your answers. I have been enlightened here.

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