Why don't we use high voltage DC lines?

Oh, but we DO use HVDC. Where did you hear that?

It's true that AC power transmission dominates the scene. But when we delve into extra high (EHV) and ultra high (UHV) power transmission—think 500,000V and beyond—DC takes the spotlight for some compelling reasons.

Asynchronous Advantage

DC's lack of frequency makes it asynchronous, meaning it can connect disparate systems without the hassle of synchronization. This flexibility is a game-changer in bridging different power grids seamlessly.

Isolation for Stability

DC lines act as open circuits to AC systems, providing crucial isolation during electrical fault events like lightning strikes or equipment failures. This separation helps contain faults, safeguarding the stability of connected systems.

Economic Efficiency

For long-distance transmission, DC proves more economical. Its transmission towers require less space, reducing land usage for right-of-way. With fewer poles needed (sometimes just one plus ground for return), DC lines trim down on materials and infrastructure costs.

Reduced Losses

DC systems exhibit lower losses compared to AC due to the absence of reactive components. Say goodbye to AC-related losses like capacitive and inductive losses. With DC, it's all about resistive losses, keeping efficiency high and wastage low.

Flexible Power Transfer

DC's ease of power direction switching makes it indispensable in scenarios where seasonal load variations flip the script. Think exporting power from warmer regions in summer to cooler ones in winter, and vice versa. Inverters facilitate instant power direction and quantity adjustments, ensuring smooth operation.

But despite its advantages at high voltages, widespread DC use remains limited in the US, primarily due to:

Cost Considerations

DC installations come with hefty price tags, especially at lower transmission voltage levels. The need for extensive equipment to convert AC to DC and mitigate harmonics adds to the expense, making DC less feasible for sub-transmission and lower voltage applications.

Transformation Troubles

Unlike AC, DC lacks the magnetic field necessary for traditional transformer operation. This absence of frequency-induced current in secondary coils makes DC transformation impractical, posing a significant hurdle in the power system.

Despite these drawbacks, DC transmission finds a more welcoming embrace in Europe, thanks to its asynchronous nature and specific regional needs. In the US, however, its application remains limited, primarily restricted to voltages exceeding 500kV.

In unraveling the enigma of high voltage DC lines, it's clear that while they offer undeniable advantages, their widespread adoption hinges on overcoming cost barriers and addressing transformation challenges. As we navigate the evolving landscape of power transmission, the role of DC may yet see further evolution, driven by innovation and adaptation to changing energy needs.

So, next time you ponder the intricacies of power transmission, remember that while AC may reign supreme, DC continues to carve its niche, shaping the future of electricity transmission in ways both subtle and profound.