The end of the plugs and sockets dilemma?

By Gabriela Ehrlich

More than 100 years after the war of currents between Edison and Tesla/Westinghouse, LVDC (low voltage direct current) is being discussed as the possible next evolution of electricity distribution. With distributed energy generation on the rise, this approach may hold significant advantages, not least in terms of energy efficiency. What are those promised advantages and what will it take for LVDC to be adopted widely? IEC SMB (Standardization Management Board) SG (Strategy Group) 4 LVDC is currently exploring these questions and related standardization matters for systems up to 1 500 V DC.

Arcing of trace amounts of escaping electrical energy. Arcing of trace amounts of escaping electrical energy.

Direct current or alternating current?

Direct current, which was Edison’s battle horse for electric power distribution in the late 1880s, and was later abandoned in favour of the AC (alternating current) system advocated by Westinghouse and Nikola Tesla, might have a come-back in the form of LVDC.

Sleeping beauty…

During the early years of electricity distribution, DC was the standard for the US (United States). Incandescent lamps and motors, which were the principal load, worked well with this system. Excess energy produced could be stored directly in batteries. However, voltage drop due to resistance of the system conductors was so high that generating plants had to be located within 1 to 2 km of the load. While, in theory, high voltage DC can be transported over long distances – as is increasingly done today – at the time there were no efficient low-cost technologies available that would allow reducing those high voltages to the 100 or so volts that were needed in a household of the time. Obviously this has changed fundamentally.

…finally wakes up

With increased distributed energy generation and storage, the question of DC has again come to the forefront, especially for buildings and uses that require constant and high levels of quality energy supply. Such is the case in data centres, telecom central offices and could be the case in a later step in hospitals and certain types of commercial buildings.

Huge cost and efficiency advantages

LVDC seems to offer a number of advantages with regard to energy quality, cost, reliability, efficiency, EMC (electromagnetic compatibility) and the ability to store electrical energy while reducing the need for power conversion. This will result in fewer points of failure. More efficient use of DC-based current is predicted to have a positive impact on lighting, variable speed drives, EV charging and more. But all these possible advantages still need to be analysed and confirmed.

For example, in many containerized data centres the dominant design is already DC, obtained through multiple AC/DC power conversions. LVDC distribution at voltages around 400V reduces the need for power conversion, producing better quality power and resulting in fewer points of failure. Compared to AC, there may well be significant reductions in the costs of electricity, operation and maintenance and the space needed for the electrical infrastructure. The approach may also allow for easier integration of renewable energy and direct energy storage.

Tough challenges and little experience

If the advantages seem overwhelming, the hurdles seem equally high. Because nobody has worked with LVDC distribution in houses and buildings in over 100 years, there is currently very little experience with this technology, practically no tests and very few products that are beyond the development stage.

Among the challenges are increased fire hazard and electric shocks due to potential insulation faults and arcing.

New design approaches, specifications and testing

Many of the components that are now used in AC would need thorough analysis and might have to be completely redesigned. For example: because DC is constant, there is no easy way to "break" the current. When a DC circuit is disconnected, the current cannot be turned "off"immediately and a DC arc is produced. This requires a complete redesign of circuit protectors/interrupters and fuses and also of insulation materials. The effect of the constant power supply on individual components – so called corrosion – will need to be evaluated and may require design modifications in products and devices. Overall, new specifications and test methods will need to be developed to ensure the safe and efficient operation of LVDC.

Commercial uses first

And while a number of devices in private households already operate with DC via external or internal power supplies (consumer electronics such as TVs, PCs, cell-phones, electric razors, battery operated vacuum cleaners, etc.) it is unlikely that LVDC will be "coming soon to a home near you". The sheer number of installations that will need to be updated may put off the LVDC revolution in the residential sector for a number of years or even decades.

Accelerating domestic adoption

Hybrid solutions that combine AC for certain end-uses (heaters, ovens and some outlets) and a DC infrastructure made up of low voltage (up to 48V for lighting, PCs, and other small devices) and high voltage (up to 390V for air conditioners, refrigerators and DC outlets) might be able to accelerate the domestic transition process to LVDC. But the need remains to find the right compromise between energy efficiency (high voltage – 400V) and safety (low voltage – 48V).

Standardized plugs and voltages

Ultimately, the broad application of this new technology, standardized globally, might offer the additional benefit of ending the plug and socket dilemma, providing standardized voltages for equally standardized applications. No more transformers, no more travel adaptors. Futuristic…but not utopic.

Thomas Edison Thomas Edison
Arcing of trace amounts of escaping electrical energy. Arcing of trace amounts of escaping electrical energy.
Transformers for high voltage direct current. Source: Siemens Transformers for high voltage direct current. Source: Siemens