« on: 13/04/2016 17:25:23 »
i know that transmitting electricity at high voltages makes the mediums of transportation to be smaller, but how does the inductance an transformers correlates to this?   A transformer has relatively little inductance when it's carrying current; the secondary windings carry, in a sense, the same amount of 'current' around the iron core (specifically the amp-turns is nearly the same) and opposes the input side's inductance, and consequently transformers when carrying current have very low inductance.
When the output side isn't carrying current, the inductance goes really high, since the inductance on the input side isn't being opposed, and this means that the transformer then has high inductance, which means high impedance, and because it's high impedance, the input side ends up carrying relatively little current, so the resistive losses on the input side are small, and transformers are still fairly efficient when nothing is drawing current.
If that didn't happen, every time we turned off all the power in the house, the transformer at the substation would glow red hot!
So, a lot of the efficiency is about what happens when you're not using power as much as when you are.
Still, some power is still lost like that. Those 'fat' power supplies that you plug into the wall, they step the mains down to 12v or 5V. But even if they not carrying any current, if you touch them they're often slightly warm; that's the current that's not being blocked by the transformer's inductance. The modern slimline ones are much more clever, and the transformer inside is much smaller, and they disconnect the transformer from the mains when they're not in use, and so they are cold to the touch when they're not powering anything.
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