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High-Voltage Direct Current (HVDC) Efficiency
High-voltage direct current (HVDC) transmission is more efficient than alternating current (AC) transmission. This type of power transmission requires a high-diameter cable that reduces losses due to reactive power. Furthermore, HVDC is more environmentally friendly.
While this type of power transmission requires a large diameter cable, it's cheaper, more flexible, and requires fewer insulators and conductors.
Direct current (DC) is a form of electric energy that goes to zero every half-cycle. A circuit breaker can interrupt DC power with 1/20th the force of an AC circuit breaker.
Many modern electronic devices rely on DC current, such as transistors, which use the energy to power their internal components. Such devices include cell phones, computers, and television sets.
High-voltage direct current (HVDC) transmission is more efficient than alternating current ( AC) transmission. The main benefit of HVDC over AC transmission is that it has lower line losses and requires fewer substations to correct power quality.
Furthermore, the technology is cost-effective over a distance of 250 miles. The efficiency of HVDC transmission is also an advantage, especially for offshore wind farms.
While AC and HVDC are equally effective, HVDC is better for the environment. The latter allows for more energy per square metre and over longer distances.
It is also more efficient because it uses less space than AC. Furthermore, HVDC reduces carbon footprint by half. This is due to the fact that it transfers only active power. In contrast, AC transmission has high losses due to its induction of reactive energy.
In addition, HVDC transmission allows power to be transferred between separate AC networks. It also improves system controllability, making it a better option for long-distance transmission.
With these benefits, HVDC will be a necessary part of global renewable energy solutions. It will seamlessly integrate renewable energy into existing power infrastructures. Ultimately, it will make renewable energy more accessible.
It requires a large diameter cable
High-voltage direct current (HVDC) systems have several important factors to consider in a high-diameter cable. For example, the high voltage required by the system affects the design of the conductor, as the thickness of the insulation layer is inversely proportional to the testing voltage and the diameter of the cable conductor.
The Cigre testing protocol recommends an insulation layer thickness of 27 mm. Because this layer occupies a significant portion of the cross section of the cable, it is worth minimizing.
One solution is the use of a “warm dielectric,” which is known for its low cost and long lifespan in electricity grids. The outer cryostat of a thermal shield is typically greater than 150 mm in diameter.
This solution is not suitable for Best Paths due to the difficulty of extruding large diameter cables. However, flexible cryogenic lines with thermal shields have been developed and are now commercially available.
AC and HVDC transmissions require large diameter cables to deliver high-voltage electricity, but the average and peak voltages and currents are similar. AC transmission wastes about 30% of its carrying capacity, while HVDC utilizes 100%.
HVAC also has a wider right-of-way than HVDC transmission. But there are some differences between the two. One major factor is the type of conductor used.
Another important factor is the frequency. High-voltage DC is characterized by a low frequency. While HVDC is less efficient than AC, it does have a low frequency.
AC transmissions are susceptible to inductive loss. The high-voltage cable used for HVDC transmissions will not have these losses. It is also possible to use the same cable for both AC and HVDC systems.
It reduces reactive power losses
In a utility, the co
ncept of voltage control is crucial to maintain system stability. In addition to active power, a portion of the supply must be reactive to meet changing demands while maintaining acceptable voltages throughout the system.
The reactive power component of current is generated by the operation of loads. The amount of reactive power generated by a given load is influenced by everything that occurs on its way from generator to customer. Reactive power loss can occur due to transmission lines, which act as capacitors on the way from the generator to the load.
Reactive power is needed to operate many electrical devices, such as motors, but the excessive amount of energy is harmful to the electrical infrastructure and motorized loads.
Reactive current flows through resistive components in the electrical system, dissipating energy in the form of heat. This energy would otherwise be lost, as it is not converted into useful work. In addition, reducing reactive power losses means that electric bills will be lower.
Reactive power introduced by transmission lines can cause big voltage drops during peak hours, affecting the overall reliability of the system. High voltage lines introduce inductive reactive power and low-voltage lines incur capacitive reactive power.
The power flow Sk on a given line is shown in Figure 1. The higher the transmission power, the greater the proportion of reactive power introduced by each line. This value varies based on the voltage, but a 400 kV line introduces about 32% of total transmitted power.
Depending on the construction parameters, the percentage may differ from 28% to 32%.
The benefits of a HVDC system are numerous. The system is more cost-effective, as it reduces reactive power losses while increasing active power. A typical HVDC system consists of two converters, each requiring a specific amount of power.
In addition, each converter has an optimum DC side equilibrium voltage, which controls the flow of DC current. The resulting system is highly efficient, but there is a high risk of harmonic generation.
It is more environmentally friendly
The benefits of HVDC are far reaching, but the most obvious one is its economic value. This type of energy transmission system supports the profitability goals of power plants, utilities, renewable generation owners, and grid operators.
And because of its efficiency, HVDC helps accelerate the transition to a more renewable energy future with cleaner, cheaper power. Patrick Pla, GE Energy Connections' general manager of HVDC and grid solutions, explains:
Another advantage of HVDC over conventional AC transmission technology is that the system is far more environmentally friendly. HVDC uses two conductors instead of one, which lowers visual impact. This technology also allows for greater power flow over the same ROW without suffering from EMF effects.
HVDC technology enables the construction of more power transmission lines in a more efficient way. The environment is also healthier, and HVDC is much more efficient than AC.
Currently, AC is the primary form of electricity transmission and distribution. However, as new sources of energy and smart devices come online, the demand for electric transmission networks increases.
Therefore, utilities are exploring HVDC conversion potential as an effective solution. It allows power transmission across long distances while minimizing energy losses. HVDC can operate at power levels of over 100 megawatts. And its power potential can extend to 1,000 to 3,000 megawatts.
Although the US has a limited number of HVDC transmission lines, these systems are not designed to enable renewable development. Consequently, the U.S. is far from achieving the integrated nationwide HVDC network needed to achieve net-zero emissions.
Several private-sector efforts to build long-distance HVDC transmission lines have failed, due to multiple challenges. But now, this technology is one of the best candidates for ensuring that renewable generation is connected to power consumers.
Another advantage of HVDC is its reduced environmental impact. HVDC projects can increase rural economies and advance climate action at the same time. The use of HVDC is a smart way to promote renewable energy and accelerate decarbonization efforts.
The technology has the potential to improve rural economies and help the United States meet its goal of decarbonization. When properly developed, it will also support rural economic development and accelerate efforts to combat climate change.
Sources:
https://www.energycentral.com/c/cp/benefits-high-voltage-direct-current-hvdc-transmission
https://www.cleanenergywire.org/news/germany-hvdc-transmission-grid-key-renewable-energy-future
https://www.greenbiz.com/article/hvdc-connecting-renewables-consumers-and-utilities
https://www.powerengineeringint.com/articles/2020/10/highvoltage_directcurrent_transmission_lines
