P-UPS: Stop Calling It a UPS

Brian Olsen is the Eastern Regional Sales Manager for E1Dynamics.

The critical infrastructure industry relies on uninterruptible power supplies (UPS) as an integral part of any mission critical system. The problem with static UPSs and referring to them as such, is they are not uninterruptible. This moniker has led to reliance on an outdated topology, with functional limitations, that newer technology has made irrelevant.

A vast majority of installed mission critical infrastructure have static UPSs as a major component, and this continues to be common practice. However, for mission critical applications, the static UPS needs to be used in conjunction with either automatic transfer switches or paralleling switchgear as well as engine generator sets. These components comprise the complete system. Referring to a power converter and string of batteries as uninterruptible is where the industry goes wrong, and it’s exacerbated by the manufacturers of the equipment.

A recent study conducted by Emerson Network Power cited the static UPS as the No. 1 cause of unplanned data center outages, accounting for one-quarter of all events. For something to be referred to as both “uninterruptible” and a source of “supply” it must truly be both of those things.

The reason for this argument is very simple … what’s commonly referred to as a UPS is really a P-UPS, or partially uninterruptible power supply. It’s both part of a larger system, and only capable of supplying power for as long as the batteries can support the load.

Therefore, this designation as a P-UPS is important. Advances in diesel rotary uninterruptible power supplies (DRUPS) clearly show the limitations of the P-UPS. It’s like comparing apples to oranges. The result is that end-users and facility owners are the ones left dealing with the shortcomings of a system believed to be uninterruptible, and ironically the leading cause of load loss. By understanding that a partially uninterruptible power supply (P-UPS) is completely dependent on other components comprising a system, only then will the owner realize that higher availability can be achieved.

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