110425-1031 EDT
iwire:
Most equipment today is designed around a nominal voltage of 120 V. If for whatever reason the supply at a given location has a nominal value of 105 V instead of 120 V and it normally varies within a 5 V range and source impedances are comparable, then why should you not boost that voltage somewhat?
Gar, that is IMO very poor advice as that will cause an over voltage to the small loads when the higher loads are on.
I believe that you meant to say when the higher loads are off. Assuming that is what you meant, then if one boosts an unloaded nominal low voltage to a somewhat higher voltage, more near what the nominal voltage should be, how does this create an excessive voltage for the light loads when the heavy load is removed? The relatively unloaded supply voltage just rises to near a more correct unloaded nominal voltage.
Basically as a first approximation for a linear circuit you can represent a circuit as a series circuit consisting of an ideal voltage source (means it is invariant), a series source impedance that is constant, and a load impedance that will vary. If there are no resonance effects, then the load voltage will never be larger than the ideal voltage source. That equivalent source impedance is made up of everything from the internal impedance of the real voltage source, and all the distribution system impedances from the voltage source to the load.
At a user point in a large distribution system if you measure the noload voltage, then this is a good approximation of the ideal source voltage. The internal impedance of the pole transformer and the wiring from the transformer to the load is the source impedance. The transformer internal impedance is usually large relative to the impedance of the primary supply to the transformer when that primary impedance is reflected to the secondary of the transformer. So you can probably ignore the primary source impedance. This is because on the primary side of the pole transformer it is a large system designed for many loads.
Only if the supply voltage was temporarily low would there be a problem with boosting it, and no way to automatically unboost it when the voltage returned to normal.
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