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Limitations of AC Transmission

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Limitations of AC transmission: Compared to DC transmission, AC transmission has many advantages but AC transmission also has some limitations, today we will see 4 limitations of AC transmission. Which is discussed below-

4 Limitations Of AC Transmission

1. Corona and Radio Interference

As we know, corona only causes power loss. Not only this, it sometimes creates unwanted noise and signals in radio-television as well. This problem is very common in electric high-voltage AC transmission. When crossing the conductors at 2-3 kV/mm, the voltage rise between the conductors causes the oxygen in the air to ionize to ozone (O_3) and cause the faint, often invisible, violet glow with a jim jim sound around the conductor.

If the conductors can be kept at about 1.5 kV/mm, the unwanted noise and corona of radio and television can be kept low. And for this, it becomes necessary to increase the size of the conductor, that is, the diameter.

In overhead transmission lines, ACSR conductors of the large cross-sections are used for this, and its manufacturing cost is high and it is difficult to move. Hence high voltage transmission in AC transmission is often not possible. which is subject to the limitations of AC transmission.

2. Problems with tall supporting structures

Since the conductors are thick or bundled in case of AC transmission, their weight is much greater than that of DC lines, so the mechanical design of the tower to hang these conductors has to be large. Because the tower may collapse due to excessive wind and pressure. The installation of these lines requires highly skilled manpower and the financial cost of moving goods to these large towers is high.

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3. Current carrying capacity

As the voltage increases in AC, the charging current increases, and hence in transmission it is not feasible to draw multiple conductors carrying high voltages together. Which is the main limitation of AC transmission.

4. Ferranti effect

In a medium or long AC transmission line open circuit or running under no load or light load conditions, it is observed that the voltage at the receiving end is higher than the voltage at the sending end. Such phenomena in supply lines are called the Ferranti effect.

1.5 percent for 160 km long lines, 13 percent for 500 km long lines, and about 100 percent for 960 km long lines. Sometimes this condition appears suddenly, which is very harmful to the line.

So in long and medium power transmission systems, the receiving end voltage (Vr) is greater than the sending end voltage (Vs) at zero or low load. which is one of the considered limitations of AC transmission.

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