Electrical Engineering ⇒ Topic : Advantage and disadvantage of high transmission voltage

HIGH TRANSMISSION VOLTAGE

Advantages

(1) Reduces volume of conductor

The transmission of electric power is carried by the three-phase line. Let us assume that P is power transmitted in watts, V is line voltage in volts, cos Φ is power factor of the load, l is length of the line in metres, R is resistance of conductor in ohms, ρ is resistivity of the conductor, a is area of cross-section of conductor, and I is the load current

                                             ............. (1)

                   ............. (2)

                        ........ (3)

From Eq. (3), we have

                      ................ (4)

Total volume of conductor required is given by

                                              ................ (5)

From Eq. (5), it is clear that for a given value of P,  ρ, l and W, the volume of copper material is inversely proportional to the square of the voltage and power factor. So, the greater is the transmission voltage, the more is the reduction in volume of the conductor.

(2) Increase of transmission efficiency

Input power = P + Total losses

             [using equation (1)]

            ............... (6)

                 ........... (7)

For constant ρ, I, and j, transmission efficiency increases.

(iii) Decrease percentage line drop

               ............ (8)

For constant ρ, I, and j, percentage line drop also decreases for high transmission voltage.

 Limitations

• The insulation cost of the conductors increases.
• Cost of transformers, switchgear, and other terminal apparatus also increase