Posted: 3/1/2009 3:34:48 PM EDT
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Is there any difference in required wire size for AC versus DC at the same voltage?
In other words, 240VAC and 240VDC - can the same size wire be used? Assume the amperage draw is the same. Also, most utility transmission lines are AC, correct? It's always been my understanding that AC was better for long distance transmission - true? |
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Is there any difference in required wire size for AC versus DC at the same voltage? In other words, 240VAC and 240VDC - can the same size wire be used? Assume the amperage draw is the same. Also, most utility transmission lines are AC, correct? It's always been my understanding that AC was better for long distance transmission - true? That is my understanding... |
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No difference. As long as bothe are rated for the same voltage. Wire size (copper) is determined by the current.
Yes most transmission lines are AC. There are a few ultra high DC transmission lines around the world. AC is easier to transform so that is it's main reason for being used. If you are only taking into account loss then a DC line will easily beat out an AC line. |
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Is there any difference in required wire size for AC versus DC at the same voltage? at 60hz (low frequecy) vs DC there is no difference, at very high frequencies there can be due to skin effects. That is to say at high frequncy the voltage travels at the outside of the conductor and limits the area that the current can travel through, so you need a bigger conductor. In other words, 240VAC and 240VDC - can the same size wire be used? Assume the amperage draw is the same. yes Also, most utility transmission lines are AC, correct? It's always been my understanding that AC was better for long distance transmission - true? yes, AC is used because it allows for the use of transformers, transformers use coils and magnetic fields to step up and down an AC voltage. A simplistic explanation is that the total power being transmitted is P=VI, or voltage x current. In a long stretch of cable the resistance of the cable is high, and from ohms law V=IR it loses voltage proportional to the resistance times the current. So with AC you can use a transformer to step up the voltage and use a smaller current to transfer the same ammount of power, and you get less IR drop and power loss. You can't do this with DC. This ignores capacitive and inductive loads, but is a good enough explanaiton. here toy go. |
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No difference. As long as bothe are rated for the same voltage. Wire size (copper) is determined by the current. Yes most transmission lines are AC. There are a few ultra high DC transmission lines around the world. AC is easier to transform so that is it's main reason for being used. If you are only taking into account loss then a DC line will easily beat out an AC line. So for a given wire size, line losses would be the same? The frame of reference I am using is an article about small hydroelectric turbines used for off the grid energy. The article suggested different wire sizes for different run lenghts, and I get the whole "bigger wire is better, to a point" thinking. Just wondering if line losses would be the same for AC as DC since the article didn't differentiate. Based on what you said above, I guess that's the case. |
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No difference. As long as bothe are rated for the same voltage. Wire size (copper) is determined by the current. Yes most transmission lines are AC. There are a few ultra high DC transmission lines around the world. AC is easier to transform so that is it's main reason for being used. If you are only taking into account loss then a DC line will easily beat out an AC line. So for a given wire size, line losses would be the same? The frame of reference I am using is an article about small hydroelectric turbines used for off the grid energy. The article suggested different wire sizes for different run lenghts, and I get the whole "bigger wire is better, to a point" thinking. Just wondering if line losses would be the same for AC as DC since the article didn't differentiate. Based on what you said above, I guess that's the case. Yes. The power lost due to a wire's resistance is the current squared times the resistance. For a given resistance (set by the size of the wire) and given power transferred, doubling the voltage halves the current which reduces the power loss by a factor of four. |
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No difference. As long as bothe are rated for the same voltage. Wire size (copper) is determined by the current. Yes most transmission lines are AC. There are a few ultra high DC transmission lines around the world. AC is easier to transform so that is it's main reason for being used. If you are only taking into account loss then a DC line will easily beat out an AC line. So for a given wire size, line losses would be the same? The frame of reference I am using is an article about small hydroelectric turbines used for off the grid energy. The article suggested different wire sizes for different run lenghts, and I get the whole "bigger wire is better, to a point" thinking. Just wondering if line losses would be the same for AC as DC since the article didn't differentiate. Based on what you said above, I guess that's the case. In your refernced case yes they are the same. The longer the line, the higher the resistance. The higher the resitance the more line loss you have and the corresponding voltage drop. V = IR and P = I^2 X R. |
