I live in a region where nominal mains voltage is 220 volts and state standards permit deviations within 5 percent continuously and within 10 percent for short periods. So if I measure the voltage in a wall outlet in my apartment and see it is 180 volts or anything else out of range I can file a complain with the utility company and the company is expected to somehow treat that voltage anomaly.
My question is - how do companies actually treat voltage deviations? What equipment do they have on the distribution grid that can be adjusted so that the voltage in my wall outlet gets back to permitted range?
Electric utilities traditionally maintain distribution system voltage within the acceptable range using transformers with moveable taps that permit voltage adjustments under load. Voltage regulators located in substations and out on the lines and substation transformers with Tap Changing Under Load are commonly used for voltage control purposes (Load Tap Changer or LTC). These transformers are equipped with a voltage regulating controller that determines whether to raise or lower the transformer tap settings or leave the tap setting unchanged based on “local” voltage and load measurements.
It can depend on where you are. I work at a University, and we've got lots of high drawing things on circuits causing voltage sag. This can really have an effect on certain types equipment that need stability, sometimes to the point that they will just not work.
Our solution has been to use a UPS or a line conditioner that will step the voltage back up. Our electrician guys have been out multiple times and just sort of shrug their shoulders, which doesn't really fix anything. They can cost quite a bit. Unless you are having fuses blown, or things exploding, I generally wouldn't worry about it. Most things have enough tolerance in their supplies to not care.
Many pieces of equipment have a voltage selector switch.
Internally (at least for a linear power supply) the voltage selector just changes taps on the power transformer.
Power distribution utilities have transformers too. These transformers can have several closely-spaced taps at different voltages. If your voltage is too high compared to the rest of the grid, the utility can connect you to the next lower tap.