[Clayart] DC power

Girrell, Bruce bigirrell at microlinetc.com
Mon Jul 25 10:22:34 EDT 2016


> At least somebody won the electricity feud.

Edison may get the last laugh. At least he is still kicking.

Driven primarily by environmental concerns, moving power from cleaner sources, notably hydro, to more distant locations is being considered. To do so, high voltage DC cables are planned. These are like giant pipelines for electricity. There are few, if any, offtakes (substations) along the way, so the transformation back to AC and usable voltage levels generally happens in only once. 

Both DC systems and AC systems suffer resistive losses, and high voltages are used to minimize those effects in both worlds. But because of a thing called "power factor" in AC systems, not all the power* you put in one end of the line comes out the other end. DC systems do not suffer from power factor losses, and when you're shipping very large volumes of juice around, small inefficiencies add up. Power factor losses are simply money down the drain. Since the expensive part of a DC power distribution system is recreating AC from the DC and that is done in a very limited manner, the payback for the more expensive equipment comes quickly and there are some strong incentives to use DC in this sort of application. These cables are practical for distances of at least a couple hundred miles which would, for example, allow hydro power from the St. Lawrence to be fed to New England states. DC as a power distribution means is definitely not dead.

Bruce Girrell
(currently trying to keep myself out of the design of one of these systems at work, and not being too successful at it)


* The power available in an AC system equals the power of a DC system only when the current and voltage are exactly in a specific phase relation with one another, which is true only for resistive loads like light bulbs and electric kilns. Other things, especially motors, cause the voltage and current to be out of phase resulting in loss of usable power. This is where it is important to understand the difference between volt-amperes and watts.

-----Original Message-----
From: Clayart [mailto:clayart-bounces at lists.clayartworld.com] On Behalf Of L TURNER
Sent: Sunday, July 24, 2016 3:53 PM
To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>
Subject: Re: [Clayart] DC power

Jim,
Your retelling of the Edison-Westinghouse  AC-DC electricity battle reminds me of the potter  battles of kick wheels vs electric wheels and wood kilns vs electric kilns.
At least somebody won the electricity feud.

LT



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