After generation of electricity it is important to
transform that voltage at user end/ load end.

__Reason 1 for Transmission at Higher voltage__
During transmission there are losses known as
Transmission losses as heat get generated during transmission, Usually this
loss is known as heat loss.

Heat loss is = I

^{2}R
When Transmission is done at High voltage then Current
drawn will get reduced as:-

Transmission power= Voltage X Current X Power factor

Now Current=

__Transmission Power__
Voltage X Power
factor

From above you will see that higher the transmission
voltage, lower will be the Current so lower will be I

^{2}R losses.
Now let’s take an example; For Power transmission at
11 KV and 33 KV for power of 1 MW, in both cases resistance will be same so
only variable is Transmission voltage.

Current(11KV) =

__Transmission power (1 MW)__---------- (i)
11 KV X Power
factor

Current (33 KV) =

__Transmission power (1 MW)__--------- (ii)
33 KV X Power
factor

Now Heat loss (11 KV)= (

__Transmission power (1 MW))__--------- (iii)^{2}
( 11 KV X Power factor)

^{2}
Heat loss (33 KV)= (

__Transmission power (1 MW))__------------- (iv)^{2}
( 33 KV X Power factor)

^{2}
Now divide (iii) by (iv)

__Heat loss (11KV)__=

__(33 KV)__

^{2}
Heat Loss (33 KV) (11 KV)

^{ }^{2}
Now Heat loss (11 KV) = 9
times the heat loss at 33 KV ---- (v)

You will see how big
difference it will be.

__Reason 2 for Transmission at Higher voltage__
There is one another reason for transmission
at Higher voltage is

**weight**. When Transmitting voltage at low levels then in order to reduce the transmission losses there is often practice to use conductor of big diameter as Resistance is inversely proportional to conductor diameter, so larger the diameter lower will be the resistance of conductor. So lower will be the transmission losses. This will leads to higher weight of conductor. Now when Transmission is done at higher voltage conductor with smaller diameter will be sufficient as thinner wire will have to transmit lower currents.
As conductor is lower this will lead to
smaller snags and leads to more savings. This will also leads to lower number
of towers.

Let’s illustrate this with an example; Now from equation (v)

Heat loss at 11 KV= 9
times the heat loss at 33 kV

Now for same current resistance is to be reduced.

Now
resistance =

__Resistivity X Length__
Area

Now Area is directly proportional to square of
conductor radius/diameter

So
for same heat loss at 11 KV conductor area must be increased to 3 times the conductor
for 33 KV.

You
can see that how there are advantages of transmitting the power at Higher
voltage.

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