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How do power lines have a high voltage and a low current? | All About Circuits
Actually, you're missing several things, not just one. You've got V=IR, the relationship between voltage, resistance and current right; but you've managed to get yourself thoroughly confused as to which voltage, which current, and which resistance you should be looking at.

Here's the real deal: the amount of current flowing through the transmission wires, times the resistance of those wires, will determine how much voltage is lost along the transmission wires from the generator end to the load end. The higher the resistance, the more voltage will be lost; and likewise, the higher the current, the more voltage will be lost. Now here's the key: the voltage applied by the generator to the transmission line-- that is, the voltage between one conductor of the transmission line and the other conductor-- has absolutely no bearing whatsoever on that calculation. It is completely irrelevant. V=IR determines how much voltage is lost due to that current going through the transmission line's resistance, NOT the voltage applied to the line by whatever is driving it.

For example, suppose I have a hydroelectric generator that delivers 500,000 volts to a transmission line stretching a hundred miles, and that transmission line has a resistance of 10 ohms from one end to the other; and at the far end of the transmission line, the load (a city, for example) has a nominal power demand of 500 megawatts and therefore draws a thousand amperes. 1000 amperes times 10 ohms equals 10,000 volts, which is the voltage lost going down the transmission line from the generator to the load. The generator is delivering 500,000 volts to the line, but only 490,000 volts appears a the other end where the load is.

The problem, of course, is that since power equals voltage times current, that lost voltage represents 10 million watts of wasted energy-- 10,000 volts times 1000 amperes equals 10,000,000 watts. Still, at this high voltage, the transmission system is losing only 2% of the power being pumped into it. Not bad.

Now lets try to send that same 500 megawatts down that exact same transmission line, but at a much lower voltage-- say, 100,000 volts. This time, 5,000 amperes are needed to transmit the same amount of power. What happens to the voltage drop along the transmission line? The line drop is equal to 5000 amps times 10 ohms, or 50,000 volts; and 50,000 volts times 5,000 amps is 250 megawatts. Now, we're losing fully 50% of our power in the transmission line!

And there you have the basic reason why we try to transmit electrical power at the highest voltage practical: it minimizes power loss in the transmission wire.

voltage  highvoltage  power  powertransmissions
yesterday
Have You Forgotten Your Childhood? — The Learning Scientists
it seems important to keep reminding students that retrieval practice is hard for everyone, and having to make an effort to retrieve doesn’t mean that their memory of a subject is poor.
learning  retrieval  practice  students
november 2018
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