Medium Voltage DC Applications And Future Scenarios (That Thomas Edison Has Started…)

The Future Of DC

Although more than a century has passed since the heated dispute between Thomas Edison and George Westinghouse known as the “War of Currents”, the debate as to whether use of direct current (DC) is better than the now widespread use of alternating current (AC) continues.

Development of modern static converters, growing use of renewable energy sources (e.g. photovoltaic generation plants) and new categories of users operating directly in direct current (e.g. distribution on board ships, especially military vessels, data centers and electric vehicles) have re-opened the possibility for direct current to no longer be relegated to merely specific applications but to be used more generally, for electric power distribution.

The purpose of this guide is to provide an overview of how direct current can be applied and an indication as to the state-of-the-art and possible future developments.

However, direct current is now re-awakening the interest of technicians and electricity authorities since, thanks to the developments in power electronics achieved over the last fifty years, the main problem, i.e. voltage variation difficulties, has been resolved.

Modern static converters are now so reliable and efficient as to call into question the possibility of supplying direct current by harnessing its inherent advantages, first and foremost, lower transmission losses.

DC Applications

Since AC distribution has always been predominant, designers of current-using equipment have been obliged to create such devices or their feeders for use with the AC voltage supply available.

Failure to standardize the supply throughout the world, where various voltage levels are used and two or more frequencies, mainly 50 and 60 Hz, has made it even more difficult to develop products since companies have had to differentiate them to suit the market.

Nowadays, and even though progress has been achieved as to the efficiency and control of these rectifiers, the massive presence of such loads is forcing a rethink regarding the structure of the existing power distribution grid.

Loads energized directly in AC are also rapidly decreasing in sectors such as that of electric motors, which has always been dominated by AC supply systems. Our homes and offices contain a huge number of personal computers, printers,
telephones, televisions and Hi-Fi systems.

Considering the increasing use of LED lights, much more efficient than the incandescent ones invented by Thomas Edison, electric vehicles (charged in DC with a considerable load) and all those loads traditionally powered in AC (e.g. washing machines and air conditioners) but which now use static frequency converters or inverters for improved efficiency and to control the speed of their motors:

It is easy to forecast that DC loads will reach 50% of the total consumption within the next few years.