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Suppose I increase the voltage supplied to a building from a constant power source substantially by putting a transformer. Doing this would reduce the current substantially as well. So will the building's electronics still work?

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  • $\begingroup$ You've gone from a bulb in the title to an entire building in the detail. But that aside, did you really mean a constant power source because if so then I have an answer that's very different to the ones already there (not got time to write it just yet though). If you meant the power supply was a constant voltage source (with negligible source impedance) then see Elio's answer. $\endgroup$
    – Rodney
    Jun 23, 2019 at 16:11

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$\def\Ip{I_{\rm pr}} \def\Is{I_{\rm sec}}$ You're doing a very common mistake. It's totally false that to

increase the voltage supplied to a building from a constant power source substantially by putting a transformer[...] would reduce the current substantially

The effect would be to burn every electrical equipment connected to that building's mains.

You're not alone in holding the false belief that if a transformer increases voltage than it decreases current. Things are rather different. It's true that in an upward transformer

$V$(secondary) $>$ $V$(primary) and $I$(secondary) $<$ $I$(primary).

But if voltages are given, currents are determined by load.

Assume a simple load, a resistor $R$. If you connect it to primary source $V_1$ the current will be $I=V_1/R$. Now install your transformer, say with an upward ratio $V_2/V_1=k>1$. If $R$ is connected to secondary, current will become $$\Is = V_2/R = k\,V_1/R = k\,I.$$ It will increase, not decrease!

As to primary current you'll have $$\Ip = k\,\Is = k^2 I.$$ Let's compute the dissipated power $W=I^2 R$.

  • without transformer $W = V_1^2 / R$
  • with transformer $W = V_2^2 / R = k^2 V_1^2 / R.$

If $k$ is substantially greater than 1 (say 1.2) the power will increase by a factor $k^2 = 1.44$. Very few appliances - if any - would withstand the test.

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There are some pieces of electronics that need an alternated current to work, so they would not work anymore with a constant voltage. The electronics that uses a transformer already will work if you can connect it without its transformer and if you can provide the exact voltage they need.

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