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UPS Topology – what does it all mean?

Different types of UPS are available for different applications. Cost is a real everyday life factor that all businesses have to consider when deciding how best to protect themselves, and this is reflected in the range of products we offer. Here we take a look at the various UPS topologies, written in a common-sense plain-English format for those who want to know how it works!

A basic standby orĀ off-line UPS works by a relay contactor switching output power between mains or battery. You might not know this, but these will be used in parking meters as a typical example. There will be a short break in the power whilst switching, usually only a few milliseconds, and many appliances can withstand this. There is no protection against mains voltage fluctuations.

Some of the smaller desktop units like the VCL are the more advanced line-interactive – they filter the incoming mains supply to stabilise the voltage. This is a very cost-effective way of protecting your equipment from power loss and an unstable supply. Examples of use would be PCs, network switches and cash machines.

But businesses need and want more protection. Most of the UPSs we recommend are fully on-line, voltage and frequency independent (VFI), employing double conversion technology. These provide completely uninterrupted protection for even the most delicate electrical components.

What does “double conversion technology” mean? In essence, mains AC (alternating current) charges the battery with DC (direct current). The component that performs this is the rectifier. The DC output from the battery is then inverted to a stable clean 230V AC output. Funnily enough this component is called an inverter. This provides your essential load with a constant steady power supply. If mains drops out, the inverter continues to generate AC until the battery reaches a certain level of depletion.

Hence, Double Conversion = AC – DC : DC – AC

Essentially the UPS generates a fresh output power supply from within, reassuring you that your critical equipment receives the purest electrical input and resilience against mains disruption.

Therefore, VFI = Mains Input 246V 50Hz (variable) : UPS Output 230 50Hz (constant)

The above voltage of 230V applies to single phase equipment. For larger commercial or industrial buildings, they will likely have a three phase supply coming into the premises. Across the phases there will be 415V available. Here is an example of a standard three phase UPS installation:

A client has a 30kVA UPS installed in their server room which provides a constant 3 phase 415V 50Hz output generated from the battery by the DC-AC inverter. Upon mains failure, the UPS continues to provide output power to the supported load albeit the battery is now discharging. Once mains is restored, the rectifier resumes battery charging. The load has seen no interruption of power supply or voltage and frequency fluctuation.