Why is Electric Power Transmission Multiple of 11 i.e 11kV, 22kV, 66kV etc?
Obliviously, this is an interview type question for electrical engineers especially related to power engineering. Now, we are going to explain the simple logic behind the story.
First of all, It is not true that all the transmissions and distribution voltages are multiple of 11. In most case, they are multiple of 11 such as 11kV, 22,kV, 33kV, 66kV & 132kV. But 400kV, 765kV and 800kV etc are not multiple of 11 in case of electric power system (generation, transmission and distribution) in power lines from the generation station to the receiving point.
It is not due to the Form Factor (1.11)
Most of you may opt for form factor (1.11) which is nothing to do related to this question. How? Lets see below:
What is Form Factor?
Form Factor is the ratio between the R.M.S (Root Mean Square) value and average value of electric quantity (Current or Voltage). Mathematically, It can be expressed as
For a sinewave, the form factor is given below:
This way, the value of form factor is 1.11.
Now, we know that 400kV and 800kV are not the multiple of 11. Also,
- 10kV x 1.11 = 11.1kV
- 20kV x 1.11 = 22.2kV
- 30kV x 1.11 = 33.3kV
- 60kV x 1.11 = 66.6kV
- 120kV x 1.11 = 133.2kV (But the transmitted voltage are 132kV)
The above calculation clearly shows that the results are different then the general values i.e. in case of 132kV, with the from factor multiplication, it is 133.2kV.
In addition, We use 230V instead of 220V (Single Phase) and 400V instead of 440V (Three Phase).
Also, alternator and generator with terminal voltages are available i range of 10kv – 15kV which is not to do with multiple of 11.
If it is not related to the form Factor, What is it then?
Now back to the point, the voltage at the receiving end are generally:
- 10kV
- 20kV
- 30kV
- 60kV
- 120kV and so on…
Sending Voltage = 10kV x 10% = 11kV. While the receiving end voltage are 10kV due to voltage drop. More examples are given in below table.
| Sending Voltage | Receiving Voltage |
| 10kV x 10% = 11kV | 10kV |
| 20kV x 10% = 22kV | 20kV |
| 30kV x 10% = 33kV | 30kV |
| 60kV x 10% = 66kV | 60kV |
| 120kV x 10% = 132kV | 120kV |
| 200kV x 10% = 220kV | 200kV |
FAQs
Why is electricity in forms of 11kV, 22kV, 33KV, 66kv, and 132kv transmitted in India?
Why is supply voltage always generated in 11KV, 33KV and 132 kV? The supply voltage is generated in 11kV, 33 kV, and 132 kV due to economical reasons. Generation At higher voltage is more economical than lower voltage but at the same time cost of the Generator also increased.
Why is transmission line 11kV 33KV 66kv not is 10KV 20KV 30KV?
10KV, 20KV, and 30KV are not used as often as the other voltages because they are not as efficient or as safe. Basically , we can say that transmission line voltage is in multiple of 11. This is because of induction property of transformer. Transformer induced voltage equation contains factor of 4.4.
Why is the voltage rating always multiple of 11?
Those with a voltages around 110–120V 120V is more common than 110V. The form factor of a sinusoid is 1.1 . Because of this factor, the magnitude of voltages are the multiples eleven.
What is the difference between 11kV and 22kV?
The main difference between 11kV and 22kV electric distribution voltage is the amount of voltage being transmitted. 11kV refers to a voltage of 11,000 volts, while 22kV refers to a voltage of 22,000 volts. This means that 22kV has a higher voltage capacity and can transmit more energy than 11kV.
Why is electricity transmitted across the country at high voltage?
Why High Voltage. The primary reason that power is transmitted at high voltages is to increase efficiency. As electricity is transmitted over long distances, there are inherent energy losses along the way. High voltage transmission minimizes the amount of power lost as electricity flows from one location to the next.
Why is electric power generated at 11kV?
Electricity is generated at 11000 V or 11 kV at the generating stations. It is cheaper to generate electricity at a relative lower voltage and then step it up for transmission. Hence, most power generating plants are designed to operate at 11kV across the world.
Why is the electric power transmission multiple of 11 ie 11kV 22kv 66kV etc?
Transformer Induced voltage equation contains 4.44 factor. 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.
Why do we use 11kV to 33kV?
The 11kV lines are used in residential areas and are what feed the local transformers, which then distribute power to the buildings in the area. 33kV lines, on the other hand, involve much higher voltages and are used to distribute power from one small sub-station to another.
