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ITGlossary · Power quality
Automatic Voltage Regulator (AVR)
A device that automatically maintains a constant voltage level to protect electrical equipment from fluctuations.
Technical level:Basic
An automatic voltage regulator corrects mains overvoltage and undervoltage without using a battery. In a stabiliser this is done with a transformer that switches taps via relays or electronic switches, or with a servo motor for smoother regulation. In line-interactive UPS units the AVR boosts or bucks the voltage, so the UPS does not switch to battery at every fluctuation.
It is useful in areas with low voltage at peak hours, at the end of long lines or in agricultural installations, where refrigerators, air conditioners and pumps suffer from an unstable supply.
A frequent mistake is assuming that a stabiliser also covers outages. It does not. Also, size it with headroom for the starting currents of motors.
Questions that mention it
All frequently asked questionsHow can I protect my equipment from surges?
Use a UPS, an AVR and surge protection power strips with surge filters.
What is an automatic voltage stabilizer (AVR)? How does it differ from a UPS?
An AVR keeps the voltage stable by filtering out fluctuations and noise, but because it has no batteries it provides no runtime during a power outage.
Can I use an AVR and a UPS together?
Yes. An AVR ahead of the UPS helps where the mains voltage is often out of range, so the UPS does not keep switching to battery. Many line-interactive UPS units already have a built-in AVR and online UPS units regulate their own output, so it is often unnecessary. Never connect an AVR to the UPS output.
Related terms
- Noise (Electrical)Unwanted high-frequency disturbances on the supply voltage, e.g. from motors or power supplies, which UPS systems and line conditioners filter out.
- Power ConditioningTechniques such as EMI/RFI filtering, surge protection and AVR that correct voltage problems before they reach the load.
- Line Interactive UPSA UPS that corrects voltage sags and swells with an automatic voltage regulator and switches to battery only when the voltage is lost or out of range.
- RFI — Radio Frequency InterferenceA subset of EMI: high-frequency noise from electronic equipment that can disturb radio, Wi-Fi and other devices.
- Surge ProtectorA device that limits brief voltage spikes from lightning or grid switching by diverting the excess energy to earth.
- ATS (Automatic Transfer Switch)A device that automatically moves the load from the grid to a generator during an outage and back again when grid power returns.