How does a UPS system work? | Schneider Electric Singapore

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How does a UPS system work?

The basic function of an Uninterrupted Power Supply (UPS) is to protect and deliver power to critical electrical equipment and to keep the equipment running in the event of a power outage or surge until the grid is restored or back-up power generators are ready to power the load. In case a secondary power source is not available, the UPS provides enough backup time to shut down the critical equipment without losing sensitive data. In most cases, some backup batteries are used. Depending on the UPS size and required backup time, these batteries are installed either internally or externally to the UPS.

A UPS can protect against a variety of power failures or poor electrical quality caused by the power grid or installation environment:

Power outage – blackout is an electric power loss in a given area or section of a power grid. It could affect a single building or an entire city, depending on the extent of the damage or cause of the outage.
Sag & Brownout are both under-voltage conditions; the longer duration of brownout can cause incorrect performance in electrical equipment, like dimming of lights or rebooting of computers.
Over Voltage is an increase of supply voltage to a level higher than the design limits of the electrical equipment and thereby cause equipment damage.
Frequency variation is typically caused by load variations on the public network and can affect electromagnetic loads like motor applications.
Harmonics Distortions are common voltage and current variations and are mainly caused by electrical equipment in buildings having nonlinear loads.
Transients or Surges are a sudden rise in voltage for a very short duration, caused by either lightning strikes on transmission lines or from switching components in the building.

The 3-phase UPSs have several operation modes, including modes for higher efficiency:

Double Conversion Mode is on when the incoming power is converted through an input PFC rectifier stage to the direct current (DC) bus where battery backup is connected and then converted back to AC by an output inverter. This inverter generates perfect output power to the load, independent of any voltage and frequency fluctuations on the mains supply. In this mode, batteries are being charged. This mode provides permanent regulation of the output which uses a high amount of electricity.
Battery Operation Mode is used when the utility/mains supply fails, the UPS transfers to battery operation with zero transferring time and supports the load with conditioned power from the batteries.
eConversion Mode is a patented high-efficiency UPS mode that allows the UPS to supply the active part of the load through the static bypass. The inverter is kept running in parallel with the bypass source and supplies the reactive part of the load to ensure power factor correction and continuously charging of batteries, hereby delivering Class 1 performance similar to double conversion mode, while reducing the electricity use in the UPS by a factor 3 compared to double conversion.
Bypass Operation Mode uses a static switch to supply the load from the bypass source. In the invent of a short-circuit failure on the UPS load at a current level that inverter no longer can provide or by an internal UPS failure the UPS will instantaneously transfers the load to the bypass switch. This mode is also used to transfer the load from UPS to separate maintenance bypass path to isolate the UPS for service maintenance.
ECO Mode is a traditional high-efficiency mode that allows UPS to supply the load through the static bypass without the additional advantages of the eConversion mode.

Discover more on our 3-phase UPS product page and eConversion solution page.