i want to ask that "our household supply is 220V , somewhere in industries it is 440V......i also found out that somewhere from where high transmission line is going it is written 11KV, 33KV etc................these all are multiples of 11 " i want to ask that what is the reason behind it?
1 comment:
Since form factor for sinusoidal wave is 1.11 which is a multiple of 11 so generation and transmission is supposed to be done at 11,33,66kv
First let us define form factor before we go into the question:
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 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.
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.
Answer for the transmission of power at high voltages
Power loss during power transmission is predominantly due to the current drawn, which heats the wires. Power dissipated is current x voltage and voltage is current x resistance, so in any wire with fixed resistance the power loss is proportional to the square of the current flowing. The higher the voltage you use to transmit the power down the distribution network the lower is the current, hence power is distributed at the highest voltage that is practical, then the voltage is dropped to the domestic level at the destination sub-station or by a transformer on the power line pole. Major distribution systems operate at over 100 kV, with regional ones at lower voltage.
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