Everything is HVDC

March 12, 2014

Stephen OliverThe move to using DC at high voltages has been phenomenally quick. It seems just a couple of years ago that high voltage almost automatically meant AC: despite the efforts of Edison to promote DC, the simplicity of using transformers to set up and down AC voltages meant that Tesla had won (if you don’t know about the battle between Tesla and Edison, learn more in this webinar).

Today, however, everything has changed. It seems that almost everyone in the power electronics community (apart from those working on low-power applications) is talking about using DC at higher voltages. The acronym “HVDC” is being used in a huge variety of different contexts, presenting the possibility of confusion.

Within equipment, HVDC covers a multitude of different voltages: 270 V for aircraft, 400 V (or 380 V) in data centers and building management; 600 V for military vehicles and 800 V for earth moving and construction equipment, to name just a few.

Utility companies, however, have a completely different perspective: the grid is adopting DC power transmission for long-distance links because it is more economic than AC. Using DC also makes it easier to interface the inherently DC outputs of renewable power such as wind and solar. But the voltages used in the electrical grid are hundreds of kilo volts and transmit thousands of mega watts.

With three orders of magnitude difference in the voltages used within systems and in the grid, how can we possibly use “HVDC” to refer to both applications?

In reality this is nothing new. Engineers at utilities have always had a different perspective: AC transmission lines at 69 kV or 100 kV are “low voltage”; an engineer developing industrial control systems might think of 5 V as low voltage and in the world of ultrasound or other sensitive equipment voltages aren’t considered “low” unless they’re a few milli volts or less.

So context is everything. HVDC perfectly describes the technology whether you are discussing power distribution in a data center or transmission across the electrical grid, the term simply works. Just as no one would confuse Axminster lathes with the carpets of the same name, as engineers we’re smart enough to understand the difference between HVDC in different applications.


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