When a particular amount of power has to be transmitted over a certain distance the following aspects need to be considered to decide the best voltage.

A lower voltage the need higher size conductors to withstand the high current is involved. There is a physical limitation to the size of conductor. Also, the percentage voltage drop may become excessive.

A higher voltage will make the conductor size manageable and reduce the voltage drop (% value) but the cost of the line becomes high due to larger clearances needed.

The best voltage will be one in which the total operational cost which the sum of the annualized capital cost (of the line) and the running cost due to power loss in the line is the lowest.

In practice, it is found that transmitting bulk power over long distances is economical if done in the HV range. The actual voltage will vary based on the distanceand quantum of power. Distribution circuits where typically the amount of power and distance involved are both lower, the best voltage is in the MV range (11, 22 or 33 kV).

For the same reason, low voltage circuits are found only in local sub-distribution circuits.

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