I was reading about power transmission on wikipedia and came across the explanation of the efficiency of AC power transmission that said power in the load = (I^2)* R while power transmitted= IV. The page then says "Thus, the same amount of power can be transmitted with a lower current by increasing the voltage." What I don't understand is how voltage can be increased without also increasing current, this seems to violate ohm's law. How is this possible?
Electronic – How is current lowered as Voltage is increased in AC power transmission
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Related Solutions
What you do with a current limited power supply is set to maximum properties. The power supply will regulate its output voltage in such a way that the lowest condition is met.
I drew a graph for how a current limited power supply will act with varying resistance connected. Consider a 12V power supply limited to 1A.
- The X-scale varies the load resistor from 1 to 30Ω;
- The left Y-axis and red line represents the ouput voltage of the power supply. Clearly when the resistor is too low, the power supply output voltage drops, to fulfill the 1A max output;
- The right Y-axis and green line represents the output current. Once the maximum output voltage is reached the output current will drop inversely proportional with the resistor value.
- You can clearly see voltage regulation taking over from current regulation at R=12Ω
The magnetic field strength is proportional to ampere-turns. If you hold the field constant, and reduce the resistance (for the same number of turns), then you must reduce the voltage.
The power loss for a given field strength and number of turns is proportional to the resistance.
If R goes to 0, as in a superconducting magnet, no power at all is consumed in the magnet in steady state.
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Best Answer
120The idea is that a different load is used with the different voltages. As a simple example:
In both cases, the load is 120 watts but by doubling the voltage, we get away with 1/2 the current, allowing smaller wires.
Similarly, we could start out with the 240V 1/2A, put that into a 2:1 transformer, and get out 120V 1A for the 120V lightbulb. For the 240V section of the transmission, we can reduce the wire size due to the lower current. Now scale this up to 10KV transmission lines going into 120V/240V residental wiring.