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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?

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  • \$\begingroup\$ They have generators on the grid that turn off, on, or vary in someway (Depending on the technology) in order to achieve a fixed voltage. \$\endgroup\$
    – Kellenjb
    Jan 31, 2012 at 15:18
  • \$\begingroup\$ @Kellenjb: I'm talking about much smaller scale. Suppose it's 180 volts in one apartment building and 220 volts in a building across the street and they definitely share most of the connection to the 110 kilovolts grid. How would the deviation be addressed? \$\endgroup\$
    – sharptooth
    Jan 31, 2012 at 15:22
  • \$\begingroup\$ How would such a situation arise? If it did I would assume they would be on different transforms, one of which was malfunctioning. \$\endgroup\$
    – Kellenjb
    Jan 31, 2012 at 15:38
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    \$\begingroup\$ There is therapy for such deviations. \$\endgroup\$
    – user3624
    Jan 31, 2012 at 16:05
  • \$\begingroup\$ A bit late to this party, but on-load tapchangers on transformers are only one tool that can be used for voltage regulation. There are also capacitor-based solutions and power electronics solutions, coming under the banner of "Flexible AC Transmission Systems" or "FACTS". I don't know enough about how these work to write an actual answer. \$\endgroup\$
    – Li-aung Yip
    Feb 27, 2015 at 16:04

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From this wiki page:

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.

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See also this website primer from UST Power that explains a lot of different techniques for automatic voltage regulation.

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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.

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Many pieces of equipment have a voltage selector switch.

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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.

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  • \$\begingroup\$ The utilities have circuits that automatically adjust the taps. \$\endgroup\$
    – Jason S
    Feb 1, 2012 at 3:17

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