*Advantages of high voltage transmission line*

*( a ) Volume of Conductor Material*

Let
us consider that the electrical power transmitted through transmission line is

P
= √ 3 V_{L}I_{L} Cos Φ

I_{L
} = P / √ 3 V_{L} Cos Φ….
( 1 )

Where

V_{L}
= Line voltage

I_{L}
= Line current

P
= Power transmitted

Cos
Φ = Power factor of the load

Resistance per conductor R = ρL / a………
( 2 )

Total power loss W = 3I^{2}R

= 3 ( P / √ 3 V_{L} Cos Φ
)^{2} ( ρL / a )

= 3 ( P^{2} / 3 V_{L}^{2} Cos ^{2}Φ
) ( ρL / a )

W = ( P^{2} ρL / a V_{L}^{2} Cos ^{2}Φ ) …….. (
3 )

Cross section area a = ( P^{2} ρL / W V_{L}^{2}
Cos ^{2}Φ )

Volume of conductor = Area of conductor
× Length of conductor

= aL

= ( P^{2}
ρL^{2}
/ W V_{L}^{2}
Cos ^{2}Φ )……..( 4 )

**Volume of conductor α ( 1 / V _{L}^{2}
Cos ^{2}**

**Φ )**- The volume of conductor is inversely square of supply voltage and inversely proportional to square of power factor if power transmitted, length of conductor, transmission line losses and resistivity of material is remains constant.

*( b ) Decrease in voltage drop*

Voltage drop = IR

= I ( ρL / a )

= I ( ρLJ / I ) ( Current density J = I / a )

=
ρLJ

*% Voltage drop = [ ρLJ / V ] × 100%*

**We can say that If the voltage increases, percentage voltage drop decreases.**

*( c ) Transmission line efficiency*

Input power = Pi

Output power = P

Input power = Output Power + Losses

= P + ( P^{2}
ρL / a V_{L}^{2}
Cos ^{2}Φ )

= P + ( P^{2}
ρLJ / I V_{L}^{2}
Cos ^{2}Φ ) (
current density J = I / a )

As P = √ 3 V_{L}
I_{L} Cos Φ

= P + { P^{2}
ρLJ ( √ 3 V_{L}
Cos Φ
) / P V_{L}^{2}
Cos ^{2}Φ }

= P + { P
ρLJ ( √ 3 ) / V_{L} Cos Φ
}

= P + { ( √ 3 ) P
ρLJ / V_{L} Cos Φ
}

= P { 1 + [ √ 3 ρLJ / V_{L} Cos Φ
] }

Transmission line efficiency = [ Output
power / Input power ] × 100%

=
P / P { 1 + [ √ 3 ρLJ / V_{L} Cos Φ
] }× 100%

= { 1 – [
√ 3 ρLJ / V_{L} Cos Φ
] }× 100%

**If current density, resistivity and length of line is constant the efficiency of the transmission line is inversely proportional to line voltage and power factor of the load.**

__Conclusion__

If the transmission line voltage
increases,

- Transmission line efficiency increases
- Percentage voltage drop decreases
- Volume of conductor material decreases

*Disadvantages of high voltage
transmission line*

- High cost of insulator of conductors
- High cost of transformer, switchgear and other protective equipments

*You may also like :*

Right of way ( ROW ) in the
transmission line

Minimum clearance between transmission
line

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