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What does it all mean

When choosing a UPS for your business, it’s often too easy to only pay attention to the more obvious decision making factors, such as required autonomy, physical size and price.

However, one key factor that is often overlooked is choosing the right type of UPS topology to protect your critical equipment. We find that the most common reason for this is that customers do not fully understand which of the topologies best suits their needs.

Here at UPS Buyer, we like to keep things simple, and hope that the following comparisons will give any organisation the confidence to choose the right power protection equipment for their organisation.

Offline UPS (VFD – Voltage/Frequency Dependent)

During normal operation, an offline UPS will supply raw mains to the critical load via its bypass line and static switch. In the event of a power failure, the static switch will transfer the load to the UPS inverter and batteries. In a offline UPS, this transfer time will typically last between 4ms and 10ms. In industries such as IT and Telecoms, this changeover time is deemed unsuitable for the high sensitivity of modern equipment.

  • Low initial purchase cost
  • Small form factor
  • Lower running costs
  • Lengthy changeover time
  • Limited autonomy
  • Limited communication options
  • Leaves load equipment subject to varying supply voltages
  • Only available up to 2kVA
  • Protects against the least of the 9 major power anomalies

Line-interactive UPS (VI – Voltage Independent

This topology operates in a similar way to an Offline UPS, but with the addition of a built in voltage stabiliser. The voltage stabiliser ensures that the output voltage from the UPS stays within a predetermined window, regardless of fluctuations in voltage from the incoming mains supply. This offers a greater level of protection fo sensitive equipment that have pre-set voltage parameters. In the event of a power failure, or variation of the mains supply

outside of the pre-set window, power is transferred to the inverter by the static switch. Changeover time for this topology is approximately 2-8ms.

  • Offers voltage stabilisation
  • Lower cost than online double conversion UPS
  • Quicker transfer time compared to offline UPS
  • Extended runtime options
  • Communication Cards available
  • High Efficiency
  • Protects against more power anomalies than offline UP
  • Still involves a changeover gap when transferring to inverter
  • Only available up to 5kVA
  • Protects against less power anomalies than online UP

Online Double Conversion UPS (VFI – Voltage/Frequency Independent)

Online UPS consist of four key components; rectifier, batteries, inverter and a static switch. The rectifier converts incoming mains power in to stable DC voltage, which is used to charge the batteries. The stable DC voltage also supplies the inverter, where it is converted in to stable AC supply to power the critical load. This “double conversion” process creates a zero break transfer in the event of a mains failure, as the battery set is always connected to the inverter. The instantaneous switch between mains supply and battery power makes Online UPS the most comprehensive topology for protecting mission critical equipment

  • Zero break transfer between mains supply and battery power
  • Available for UPS applications above 5kVA
  • Options for parallel and redundant systems
  • Protection against all 9 major power anomalie
  • Most expensive topology under 5kVA
  • Less efficient than VI Technology
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