Electronic – Where has 150 Vac mains voltage been used

It is to standardise everything on a single fixed voltage. But in practice, mains voltage isn't 230V. It is standardised at 230V +10% -6%, or 216V to 253V. Here, mains voltage measures 249V, which is on the high end of the scale - but we're on a small farm road with not many other customers. Away from home I have measured it at 233V, due to resistive losses from greater demand. Countries have not changed the actual voltage - that would require changing all the generators or all the transformers in the country (at a substantial cost), merely, the allowable range has changed.

Good mains voltage is a clean sinusoidal signal (or several phases thereof, as the case may be) free of dips, spikes and excessive distortion, whose frequency is stable over time, and whose amplitude stays within several percent (say, five) of the nominal value. Also, on good mains voltage, an appliance can draw the maximum rated current for the circuit it is plugged into, without experiencing a voltage drop which takes the voltage out of range.

Good mains voltage is a function of the ability of the grid, as well as the local circuit, to handle the load which is placed upon it.

It is also a function of the quality of the local wiring installation in a building, and also of the quality of the devices that are plugged in. Devices can degrade power quality seen by other devices by spewing noise into the wiring.