Why do we have AC power line transmission, why can’t DC power?

AC and DC are the two ways of power transmission used. But, AC is most commonly used power transmission mode over long distances.

Here are some true reasons pointed out why AC power line transmission is preffered over DC transmission:

Why AC transmission? Not DC?

-AC voltage is capable of converting voltage levels with just one transformer, making large-distance transport much easier than DC, which requires more complex electronic circuitry to be converted.

Power = Volts X Amps X PF

-The higher the voltage level for the same amount of Current, the more power can be supplied to the customers.

-Only so much Current can pass through a heating-up cable. That’s why today’s power companies are using voltage levels above 1,000,000 volts.

-AC can use transformers to raise the voltage at the power station and push it down at the consumer

-DC is used with the Unity Power Factor when the Power Transmission range reaches 500 Miles. This is because the Resistance is conducting AC, and the Transmission Line’s Capacitive and Inductive Reaction Losses, DC is only caused by the Cables ‘ Resistance Losses. DC includes the power company’s converters and the customer’s inverters.

-Transformers hold up better when Lightning strikes than do Power Electronic Devices.

-Power converters are safe enough not to cause house fires when they fail, it doesn’t matter whether the house is wired for AC or DC, or both.

-To save money and keep it simple, AC is going to be around for a very long time, in Homes, Businesses, and Factories.

Reason why DC transmission is used for Ultra high voltage transmission:

It is asynchronous:

That is, because DC has no frequency, two different systems can be connected without thinking about synchronizing the systems.

The DC connection is a open circuit to AC systems

This is important when it comes to system stability, since this separation helps to isolate two separate systems, such as lightning or equipment failure, in the event of an electrical fault.

The DC circuit restricts the direction of the fault, shielding basically the unfaulted part of the system to which it is connected.

For long distances, it is more economical

DC transmission towers take up less space, meaning less land can be used as a way right. Because DC uses only a total of two poles (sometimes one pole is used and the ground is used as a return), less wire is needed. Towers are also more economical as there are three different wires they do not have to bear.

Fewer losses:

There are less losses with a DC system–there is no reactive component to a DC circuit, so there are no losses associated with AC system such as capacitive, inductive or skin effect. Also, since there is no AC, there is no concern with losses and other issues related to electrical coupling / induced currents.

Easy to transfer large blocks of power:

Power route can be modified more easily with DC. It makes DC invaluable in areas where summer loads and winter loads are opposite, such as a country that is colder in one area in winter and hotter in another area in summer.

The DC circuit could be used in winter to export power from the warmer region to the colder region, and in summer from the cooler region to the warmer region.


DC installations are very costly, which is one reason why they are not currently being used below the voltage rate of transmission.

AC power is easier to step up and down:

As transfomers allow an alternating magnetic field to operate, there is no such thing as a DC transformer. Since there is no frequency, DC current can not generate the induced current in the transformer’s secondary coil. Transformation is an essential part of the AC power cycle, which renders this incapacity a very important negative.


Instrumentation Engineer

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