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frankdawnz • Jun 7, 2008

# Why do we use multiples of 11 as voltage in transmission lines?

Why do we use multiples of11 as voltage in transmission linesππ
rammohan.gubba • Aug 7, 2008
Hi,
Its simple... π
Transformer comes into picture when you talk about transmission.

Transfomer Induced voltage equation contains 4.44 factor.

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 4.4 and it is in turn multiple of 11.
So always transmission voltage is multiple of 11.
might be so,but we can also transmit voltage in other multiples too
cutiermn • Aug 9, 2008
then how others countries are having some other volages like 1050........ there where transformer come into picture
cutiermn • Aug 9, 2008
if transformer is a one means, then how other countries are having other voltage like 500kv , 1050 kv...........

and also it may not be due to transformer output equation ok....... transformer eequation also derived from form factor (1.11)........ it should not because of transformer.
cutiermn • Aug 9, 2008
y our porcelain insulator discs are designed for 11 kv
prestonee • Aug 11, 2008
Considering there have been what 3 different posts asking the exact same thing within a couple of days I'm starting to think the Indian students use this forum as a means of having Engineers do their homework for them...
anupi87 • Aug 19, 2008
hey actually its not mutiple of 11. its the multiple of 1.1
u may be knowing that its form factor.
we use multiples of form factor
jayant shakya • Oct 18, 2008
thankssssssssssssss
kpengineer • Apr 24, 2011
The reason is some thing historical. In olden days when the electricity becomes popular, the people had a misconception that in the transmission line there would be a voltage loss of around 10%. So in order to get 100 at the load point they started sending 110 from supply side. This is the reason. It has nothing to do with form factor (1.11). Nowadays that thought has changed and we are using 400 V instead of 440 V, or 230 V instead of 220 V.

β
Mr.Don • Apr 24, 2011
@Good question Frankdawz. Have the same doubt in my mind when I first came across it.

@all thanks.
Chandrakiran • Jun 16, 2011
Power can be transmitted at any voltage we designed, consider 400kV EHV and 750kV EHV lines where the multiple of 1.1 has not come. Form factor is one consideration for 11kV but it is not mandatory to have a multiple and also voltage in grid should be same in grid so a standardization is followed.
Naman Agarwal • Aug 2, 2012
it is only in india that we r using voltage ratings of multiples of 11...actually its makes our calculations easier..nothing special..
[Prototype] • Aug 2, 2012
There are somethings which are just there and has became like standard. Another good example is satellite communication. The up-link frequency is 6GHZ while down-link is chosen to be 4GHZ. Its not like that if you reverse their frequencies they will not work, but because it has been like that always.

Its there just for sake of standardization ( and that's why form factor exists).
vinod1993 • Aug 2, 2012
This one has a better answer..! But I suppose in India we follow the same standardization..! Not sure though..!
Killer_smile • Aug 3, 2012
kpengineer you have a good information but its not related to your major π
rajk. sharma • Aug 10, 2012
i think this is due to form factor which is 1.1 and multiple of 11
sndgpr26 • Aug 11, 2012
its not like that
other countries have some other voltage too.........
rajk. sharma • Aug 11, 2012
i think its based on transformer rating how much it stepdown
rajk. sharma • Aug 11, 2012
but also we use a form factor or rms value in emf of transformer it based on it
g.ananda kumar • Aug 12, 2012
well one answer might be that its is just a practise and also it has to do with 1.11(form factor)
g.ananda kumar
well one answer might be that its is just a practise and also it has to do with 1.11(form factor)
• The form factor of an alternating current waveform (signal) is the ratio of the RMS (Root Mean Square) value to the average value (mathematical mean of absolute values of all points on the waveform). In case of a sinusoidal wave, the form factor is approximately 1.11.
• The reason is something historical. In olden days when the electricity becomes popular, the people had a misconception that in the transmission line there would be a voltage loss of around 10%. So in order to get 100 at the load point they started sending 110 from supply side.
• This is the reason. It has nothing to do with form factor (1.11).
• Nowadays that thought has changed and we are using 400 V instead of 440 V, or 230 V instead of 220 V.
• Also alternators are now available with terminal voltages from 10.5 kV to 15.5 kV so generation in multiples of 11 does not arise.
• The Basic Idea behind a desired transmission voltage was still the form factor. In ancient times when we needed to use 10 kV at destination, simply multiplied the form factor to it Say 1.11X10=1.11 =11KV aprox.(we had taken 10% losses as standard thumb rule) similarly for 30 & 60 KV.
• Form Factor = RMS voltage/Average Voltage For AC sine wave Form Factor is 1.11.
• Now a days when, we have voltage correction systems, power factor improving capacitors, which can boost/correct voltage to desired level, we are using the exact voltages like 400KV in spite of 444KV
The real reason is not form factor. Because now 400kv, 765kv, 1200kv(yet to commission) are transmitted.
The real reason is actually due to a misnomer that started in the olden days. According to them, some voltage was always lost and they accounted it to be 10% of the transmitted voltage. So they always transmitted voltages 10% above what they required. For example if they wanted to transmit 100kv, they used to transmit 110kv, similarly 200kv - 220kv; 10% higher than what is actually required. That is why this multiple of 11 was there.
But now a days with advance protection schemes, people are transmitting voltages of the order 400kv, 765kv etc
SUbratDAsh • Mar 17, 2015
frankdawnz
Why do we use multiples of11 as voltage in transmission linesππ
We Indians are good listeners and after china we are the 2nd country to be good in copying.so we used what Britishers taught us...so they derived the form factor as 1.11 so we kept on using it.but now the good thing is PGCIL is creating a 1200 kv transmission line..and we have a misconception that we use only the 11 multiples..