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ITGlossary · Power quality
Frequency
The number of AC cycles per second, measured in hertz (Hz); the mains frequency in Europe is 50 Hz.
Technical level:Basic
In Greece and throughout Europe the grid runs at 50 Hz, while North America and part of Japan use 60 Hz. Grid frequency is very stable; the same is not true of generators, especially small or overloaded ones, where frequency can drift as the load changes.
A UPS monitors its input frequency and switches to battery if it goes out of limits. Online double-conversion UPS units deliver a stable output frequency regardless of the input, and some can also work as 50/60 Hz frequency converters.
If a UPS fed by a generator keeps switching to battery, check whether it offers a setting for a wider input frequency tolerance or a dedicated generator mode.
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.
- RFI — Radio Frequency InterferenceA subset of EMI: high-frequency noise from electronic equipment that can disturb radio, Wi-Fi and other devices.
- BlackoutA complete and sudden loss of grid power, lasting anywhere from seconds to several hours.
- Input Voltage WindowThe range of mains voltage within which a UPS keeps powering the load from the grid without switching to battery.
- OvervoltageA voltage above normal that lasts from seconds to hours and can stress or damage connected equipment.
- UndervoltageA sustained drop of mains voltage below normal that can cause malfunctions or overheat motors.