At the end of the 19th century, Edison and Tesla’s victory in the electricity wars made alternating current the standard for power delivery due to its efficiency over long distances. But with recent advances in high-voltage direct current (HVDC) transmission technology, direct current has overcome the limitations of alternating current and is emerging as a viable alternative for the power grid of the future, with greater efficiency and reliability.
At the end of the 19th century, when electricity was first invented, humanity was at a historic crossroads to set the standard for how electricity would be delivered. It was clear that electricity would become the power source for industry and homes, and the way it was delivered efficiently would determine the power system of the future. Two geniuses faced off at this crucial time: Edison, who advocated direct current (DC), and Tesla, who championed alternating current (AC). Edison argued for direct current, where the direction and magnitude of the current is constant, and Tesla argued for alternating current, where the direction and magnitude of the current changes periodically. The battle was more than just a technical debate; it was a choice that would shape the way we power and live our lives, and it sparked an in-depth discussion of the pros and cons of different methods of power transmission.
Edison’s insistence on direct current was closely tied to his invention, the incandescent light bulb. The incandescent light bulb required a stable voltage and a steady flow of current, and direct current was perfect for this. Edison defended direct current by claiming that his invention and direct current were inextricably linked, but technically, direct current had the disadvantage of losing power when transmitted over long distances. Tesla, on the other hand, advocated for alternating current, which would solve the problem of efficiency over long distances. Power losses were a big problem at the time, and alternating current had the advantage of reducing losses over long distances because the voltage could be easily raised through transformers. Tesla’s alternating current eventually won out, and today it’s common to see alternating current used in transformers and outlets.
But lately, there’s been a push to switch back to direct current, which has been the standard for power delivery for over 130 years. But what is the reason for this shift?
Just as humans bend or stretch to get around obstacles, electricity changes its flow when it encounters resistance in a circuit. An obstacle that gets in the way of electricity flowing in a circuit is called a resistance, and it causes some of the electricity’s energy to be lost. Reducing this resistance during the transmission of electricity is a key challenge in increasing efficiency. In direct current, this resistance is constant, but in alternating current, the direction of the current changes periodically, creating additional resistance. This is called reactance, and the power lost is called reactive power. Reactive power is the surplus power contained in the current that is not actually available as an energy source. This is not a big problem when the transmission distance is short, but as the distance increases, the resistance and reactance of the line increases and the reactive power also increases, which reduces the transmission efficiency. In other words, alternating current can be inefficient for long-distance transmission.
In addition, it is not only the amount of power lost in the transmission process that matters, but also the economical way to send power. With alternating current, the magnitude of the current and voltage is constantly changing, so the design must account for every fluctuation. Direct current, on the other hand, flows in a constant direction, reducing design complexity and lowering equipment and installation costs. In addition, reactance, which is only present in alternating current systems, does not exist in direct current systems, making them relatively stable and suitable for large-capacity transmission. From this perspective, direct current has the potential to deliver power more reliably and economically.
High-voltage direct current (HVDC) transmission is an emerging technology. It involves taking high-voltage alternating current power generated at a power plant, converting it to direct current through a converter, and then converting it back to alternating current at the receiver. Although it is difficult to convert the voltage of direct current itself, it has become possible to generate high voltage direct current through semiconductor devices such as thyristors and IGBT devices that convert alternating current into direct current. The direct current method is stable because the current direction is constant and no reactance occurs, and it is more efficient than the alternating current method because there is no reactive power.
With these various advantages, HVDC technology has been utilized in various fields. In Korea, Jeju Island, Jindo Island, Haenam Island, and Jeju Island have been connected by submarine cables since the late 1990s to transmit power using direct current, and in Europe, power grids between countries are being connected to build a continent-wide power supply system. In addition, it is also suitable for power transmission from offshore wind farms, a renewable energy source, enabling stable power supply.
Of course, it is difficult to convert the power grid based on alternating current to direct current in a short period of time because it has already been built over the past 130 years. There are also challenges to commercialization, such as harmonics that occur when converting high voltage alternating current to direct current. Nevertheless, with continued research and technological advancements, direct current will be a key technology for a greener and more efficient power grid in the near future.
Edison may have lost the War of Currents 130 years ago due to the limitations of direct current, but today, with the revitalization of direct current power delivery with advanced technology, Edison’s revenge is beginning.
