7/5/2023 0 Comments Transmission linesAnyway, back to where that misconception came from. This makes the infrastructure to transmit AC power generally cheaper, and that’s why transmission systems are usually high-voltage AC. Because AC power is compatible with transformers, it’s more easy and cost effective to step AC voltages up or down, as well as isolate power for safety. After all, if DC power has less line losses, then why do most power grids transmit high-voltage AC? The simple answer to this is that AC power won the war of the currents back in the late 19th century (as we mentioned before) because it’s compatible with transformers, and DC power is not. For example, even though losses from the skin effect are considered resistive losses, DC systems are not affected by them.ĭoes this come as a surprise to you? It’s an extremely common misconception that transmitting DC power is less efficient than transmitting AC power. Alternating current (AC) power suffers from all three of these line losses, regardless of voltage, and direct current (DC) power only suffers from some types of resistive power losses (yes, there are subtypes to each of these losses). All three of these types of line losses are caused, in part, by heat loss from power being impeded along power lines. Resistive, capacitive and inductive line losses do not only occur in high-voltage transmission, but also in low and medium voltage scenarios. Introduction to the Three Types of Line Losses This is why electrical cables with lower voltages (and therefore higher currents) need wider gauges. When pressure is reduced (or voltage is lowered), a wider pipe is needed for the same amount of water to flow through. Electrical cables carrying higher voltages can be thought of as pipes with a higher water pressure the higher the water pressure, the faster water will flow through pipes. You can think of this like water flowing through a pipe. Since a higher current means that more heat is generated (and heat is lost energy), we can conclude that transmitting higher voltages reduces the current, thereby also reducing heat/energy lost along power lines.Īdditionally, power lines that carry lower voltages (and higher currents) must also be a heavier gauge. This reduces line losses because (according to the formula for power) the higher the voltage, the lower the current, for the same amount of power. Check out our video on this, or read on, for a full explanation of why this is the case.Īs a general rule, longer power lines carry higher voltages in order to reduce line losses. Essentially, HVDC systems are always more efficient when it comes to power transmission because they only suffer from one of the three main types of line losses (resistive power losses), while HVAC systems suffer from all three types of line losses. The closer power lines carrying AC power are to the ground, the more line losses they suffer because their electric field will more strongly react to the electromagnetic field of the earth. To demonstrate just how efficient HVDC systems are, EE Power points out that the increased efficiency of HVDC over HVAC reduces losses from 5 - 10% in an AC transmission system to around 2 - 3% for the same application in HVDC. However, because HVDC suffers from far less line losses than high-voltage AC transmission (and is therefore much more efficient to transmit), the cost of HVDC transmission systems can be justified at a break-even distance of about 600 km. Mercury arc valves are an additional piece of infrastructure required, so they make HVDC transmission systems generally more costly than high-voltage AC transmission systems (in terms of capital expenses). In the 1950s, however, mercury arc valves were developed, and transmission systems began using them to enable HVDC power transmission. Because HVDC isn’t compatible with transformers, it couldn’t be sent over long distances at the time. In a nutshell, AC power won the War of the Currents because it’s compatible with transformers and the alternative, DC power, is not. Why do we use high-voltage AC power today for electrical transmission? In this article, we’ll break down what the main three types of line losses in transmission systems are, why they occur, and how they affect high-voltage AC and high-voltage DC (HVDC) transmission systems differently. In fact, about 8 - 15% of power is lost between power plants, and consumers in alternating current (AC) transmission and distribution systems. Despite alternating current (AC) power having won the War of the Currents, direct current (DC) power suffers from far less line losses along electrical cables. Not all power transmission systems are created equal.
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