1.2 Million Volt Circuit Breaker

By Steve McCollum; posted October 24, 2013

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From the May 2012 issue of IEEE Spectrum magazine. This is the text that accompanied the picture: This unit is the world's first circuit breaker capable of switching on and off power lines that carry 1.2 megavolts. The circuit breaker was created by Siemens at the behest of the Indian government, which will test it at a transformer substation in Bina. India wants to replace the 800-kilovolt transmission lines that presently carry current from generating facilities in the country's mountainous regions to its largest cities. Because resistive power losses diminish as the voltage is stepped up, a 1.2 MV transmission line can carry more than twice as much power as the 800-KV lines [at the same current].

Clarification by Steve: That last statement can be misleading. Resistive losses depend only on current, not voltage. Yes, I presume we're talking AC here. Please don't wander off into the weeds with a discussion of real vs. imaginary power.

The resistive losses equal R times I squared, so at a constant current, a conductor will dissipate the same amount of power irrespective of the potential voltage. But the number of Watts transported by the conductor rises with the voltage. For a given cross-section of cable, raising the voltage at constant current raises the delivered power while the losses remain constant.

Maybe what the Indian engineers are planning is to re-insulate the existing conductors and simply raise the voltage. I'd like to see the insulator strings for a 1.2 million volt line!