I watched the The American Experience on Tesla this weekend. It was fairly well done. But the issue of why AC was superior at that time to DC was not well done. The documentary shows a circuit flow animation and infers that AC has less loss than DC. It is not entirely accurate. For a given current (and that comparison is interesting – RMS vs. DC) AC actually has more loss due to hysteresis/eddy currents and skin effect. But, at the time, technology was limited for DC transmission. The base reason was that current could be reduced. The basic equation is that losses come from P_loss = I^2*R (Power loss = current squared x resistance of the wires). Therefore, if you can reduce the current for the same power consumed, you can reduce the power lost. Since power is current time voltage (P=IV) generally, if you increase the voltage, you can reduce the power lost. So, at that time, AC power could be generated and transmitted along high voltage lines and then brought down to a safe voltage for use in homes and businesses through transformers. The only real way to do that with DC at the time would be motor-generator sets that converted the voltage. Those were more costly than transformers which have no moving parts. Just as important as Tesla’s AC power generation and his three-phase motors and generators was the invention of the transformer by William Stanley. Without that, there would have been no AC power distribution by Westinghouse.
Today, though, with the advent of high-voltage semiconductor technologies, DC transmission is again realizable. There are already systems in place that use HVDC that are more efficient and cost effective. You can see some at this Wikipedia HVDC article. Of course Wikipedia should not be your sole source of information for anything but it is a start if you are interested in reading more.
My interests are more in Wireless Power Transfer and Energy Harvesting. This is related to the charging stations you see at Starbucks today, RFIDs you use to open your door at work just by touching your id to a sensor and loosely related to the new buzz word of Near Field Communication (NFC).
Another older article from me on Tesla.
Ronald Kollman – RF Hardware Designer and President of Haynes-Bent, Inc.
Haynes-Bent, Inc. – Radiofrequency (RF) hardware design, EMC/EMI analysis and 3D Electromagnetic simulation. We also provide Technology advise for investors and executives and software services from embedded to network servers.
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