Friday, May 10, 2013

Battle of the Currents: Is AC better than DC?

A somewhat strange question, isn't it?

If you ask someone in the plywood and wood veneer or paper industry, you would probably hear a lot more  about direct current (DC) applications than those in other sectors. If you are in water production, almost all of your pumps would be driven by induction motors powered by alternating current (AC).

So which system or technology is better?

Two of the pioneers in electrical engineering field have different preference: Thomas Edison is advocating DC and Nikola Tesla on AC. We continue to argue and these gentlemen would have been proud of that long legacy, and the fact that we are still caught in the loop of disagreement.

Image courtesy of ABB

A global leader in both AC and DC technologies, Asea Brown Boveri (ABB), takes a look at pitting these two from the perspective of modern technology, the Data Centres:
(ABB says it didn't take side)

1) DC is more efficient than AC: DC proponents claim 25-30% efficiency improvement, AC advocates counter with data that implies marginal if any differences in power supply efficiencies.
The fact is, if you compare a state-of-the-art AC power supply with a similarly advanced DC power supply, the efficiency improvements for DC are indeed only in the range of 2%.

 However, when comparing true efficiency “from grid to chip,” DC power architecture is typically 8-12% more efficient, depending on the IT power supply. Granted there is no disagreement that other factors such as server loading and cooling have a more profound impact on data center efficiency than the power architecture but every improvement matters.

2) DC is more reliable than AC: Independently collected empirical data as well as laboratory tests give evidence that DC power systems increase reliability over comparable AC systems by a factor of up to 100.Flip that coin, and you could say that DC allows simplification of power systems architecture without jeopardizing availability.

3) DC is cheaper than AC: This angle of the debate has seen a fair amount of cheating but ABB says that, analysis shows that the true cost of a DC power system (including switchgear, UPS, cabling etc.) is at least 20 % lower than that of a comparable AC architecture.

However, as pointed out above, the biggest cost savings lies in the potential to simplify the architecture and achieve the same (or greater) savings with significantly less equipment.

Simplicity is the ultimate sophistication!

Speaking of simplicity, an indisputable advantage of DC is that it allows to connect multiple energy sources such as the utility grid and on-site generated power (e.g. from fuel cells, solar, wind etc.) onto a common bus without complicated controls and synchronization.

This, I agree totally, 100%. Sophistication should simplify things and not make it difficult.

Reference: ABB


brick said...

but electrical devices use AC and convert to DC right?

de engineur said...

but there's energy loss during the conversion process, meaning DC is more efficient.

Adam said...

I guess it's a mixed debated result