Why are all the Transmission Line Voltages Multiple of 11kv? Not 10kV?
It is not due to 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 asFor 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% = 120kV | 200kV |
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