Monday, July 30, 2012

war of currents

Power distribution is a key technology for increasing the efficiency of work, thus increasing life quality and improving the human condition. Early factories had extensive belt systems to transmit the mechanical force of a water wheel to the workstations in a plant. In the industrial revolution the water wheel was replaced with the more predictable and powerful steam machine, but the inefficient and inconvenient mechanical distribution through belts remained.

There was strong interest in building a distributed system where the mechanical energy can be produced near where it is needed. The problem was solved with the development of electrical energy, which could not only be used to drive motors at each workstation, but also to illuminate factories, offices, hotels and homes.

Edison was an early developer of this technology. He invented the incandescent light bulb, which could be driven safely at 100 V. He build a distributed power generation system where small neighborhood generators would produce 100 V electricity and distribute it locally where power was needed. To compensate for transmission losses, the generated and distributed power was actually at 110 V. One drawback of Edison's system was that when a higher voltage was required to drive powerful motors, a separate distribution system was necessary.

The transmission loss is given by Joule's laws and is proportional to the square of the current, so for transmission purposes it is better to use a high-voltage low-current system. A little later the transformer was invented, which allowed changing the current on a transmission line, viz. generating and consuming at lower voltage while transmitting at higher voltage. The transformer was based on a different electrical system called alternating current (AC), and mostly in Europe (Lauffen–Frankfurt transmission), transmission systems, dynamos, and motors where invented for AC.

Edison was a tinkerer and could not understand AC because he did not have the necessary theoretical education, so he hired Nikola Tesla to develop this technology for him. However, after a year they had a fight and Tesla left for Westinghouse. Thus began a standards war of DC vs. AC, which was mostly a patent war. The term "war of currents" is not historical, it is modern. At the time it was mostly about standards and patents.

In the 1960s, the thyristor was invented, which allows to change the current in a DC transmission system. Today, high voltage transmission occurs again in DC through high voltage direct current (HVDC) systems, because they have higher power ratings (hence lower cost) and allow better control of power flows, especially in transient and emergency conditions that can often lead to blackouts. One of the leading companies in this sector is ABB.

And now, something completely different.

Today most electricity in the home is consumed by solid state technology: LED lamps and TV BLUs, microprocessors and other computer & appliance gadgets, electric cars, etc. Also in businesses, server farms and clouds consume a large portion of the power. Most these devices sit behind uninterruptible power supplies (UPS), which are essentially batteries. Finally, due to the uncertainty of industrial power generation, we are increasingly using solar power (PWC) located a few meters from the consuming devices.

These are all DC and low voltage devices. Today, a large percentage of the consumed power is wasted to heat transformers, inverters, and rectifiers. Should we not have a low-voltage network in every home and building? We still need AC for the transition and to bridge over peak periods, but hey, is it not time for another paradigm shift?