What is a UPS? And why should I care?

03/15/2012 | By Ed Spears

What is a UPS?

Budgeting for electricity, securing adequate supplies of it, and finding ways to use less of it are all common topics of conversation for facility managers and building owners. However, ensuring that power resources are both dependable and clean can sometimes be an afterthought.

This can be an inconvenient reality for businesses, as power sags, surges and outages are not only unavoidable, but also more than capable of damaging valuable electrical equipment, bringing productivity to a halt.

That’s why planning and deploying a robust power protection solution is an absolutely vital aspect of business continuity. But, any well-designed power protection architecture is incomplete without its central component, which is… you guessed it, an uninterruptible power system, affectionately known in the industry as a “UPS.”

 Now, what exactly is a UPS?  At its most basic level, a UPS performs two primary and complementary functions:

1.  Conditioning incoming power to smooth out the sags and spikes that are all too common on the public utility grid and other primary sources of power

 2.  Providing ride-through power to cover for sags or short-term outages (say, five minutes to an hour), by dynamically selecting and drawing power from the utility grid, batteries, backup generators and other available sources

Why should you care?

The answer is simple, because no company can afford to leave its IT assets unprotected from power issues, and here are just a few of the reasons why:

Even short outages can be trouble. Losing power for as little as a quarter second can trigger events that may keep IT equipment unavailable for anywhere from 15 minutes to many hours. And downtime is costly. Some experts believe the U.S. economy loses between $200 billion and $570 billion a year due to power outages and other disturbances.

Utility power isn't clean. By law, electrical power can vary widely enough to cause significant problems for IT equipment. According to current U.S. standards, for example, voltage can legally vary from 5.7 percent to 8.3 percent under absolute specifications. That means that what utility services promising 208-phase voltage actually deliver can range from 191 to 220 volts.

Utility power isn't 100 percent reliable. In the U.S., in fact, it's only 99.9 percent reliable, which translates into a likely nine hours of utility outages every year.

The problems and risks are intensifying. Today’s storage systems, servers and network devices use components so miniaturized that they falter and fail under power conditions earlier-generation equipment easily withstood.

Generators and surge suppressors aren’t enough. Generators can keep systems operational during a utility outage, but they take time to startup and provide no protection from power spikes and other electrical disturbances. Surge suppressors help with power spikes but not with issues like power loss, under-voltage and brownout conditions.

Availability is everything these days. Once, IT played a supporting role in the enterprise. These days it’s absolutely central to how most companies compete and win. When IT systems are down, core business processes quickly come to a standstill

Availability is everything, but power costs must be managed. The cost of power and cooling has spiraled out of control in recent years. Data center managers are typically held responsible for achieving high availability while simultaneously reducing power costs. Highly-efficient UPS systems can help with this goal, and products are available today that were not an option even a few years ago.

What types of UPSs are there?

UPSs being marketed for data center applications provide functions to meet the requirements of IT power supply units as set forth in industry standards and specifications. However, there are differences in the degree of protection they provide and the way they provide it. Most commonly, three different UPS topologies are sold to protect IT equipment:

Single-conversion systems

In normal operation, single-conversion systems feed incoming utility AC power to IT equipment. If the AC input supply falls out of predefined limits, the UPS utilizes its inverter to draw current from the battery, and also disconnects the AC input supply to prevent backfeed from the inverter to the utility. The UPS stays on battery power until the AC input returns to normal tolerances or the battery runs out of power, whichever happens first. Two of the most popular single-conversion designs are standby and line-interactive:

Standby UPSs allow IT equipment to run off utility power until the UPS detects a problem, at which point it switches to battery power. Some standby UPS designs incorporate transformers or other devices to provide limited power conditioning as well.

Line-interactive UPSs regulate input utility voltage up or down as necessary before allowing it to pass through to protected equipment. However, like standby UPSs, they use their battery to guard against frequency abnormalities.

Double-conversion systems

As the name suggests, these devices convert power twice. First, an input rectifier converts AC power into DC and feeds it to an output inverter. The output inverter then processes the power back to AC before sending it on to IT equipment. This double-conversion process isolates critical loads from raw utility power completely, ensuring that IT equipment receives only clean, reliable electricity.

In normal operation, a double-conversion UPS continually processes power twice. If the AC input supply falls out of predefined limits, however, the input rectifier shuts off and the output inverter begins drawing power from the battery instead. The UPS continues to utilize battery power until the AC input returns to normal tolerances or the battery runs out of power, whichever occurs sooner. In case of a severe overload of the inverter, or a failure of the rectifier or inverter, the static switch bypass path is turned on quickly, to support the output loads.

Multi-mode systems

These combine features of both single- and double-conversion technologies while providing substantial improvements in both efficiency and reliability:

Under normal conditions, the system operates in line-interactive mode, saving energy and money while also keeping voltage within safe tolerances and resolving common anomalies found in utility power.

If AC input power falls outside of preset tolerances for line-interactive mode, the system automatically switches to double-conversion mode, completely isolating IT equipment from the incoming AC source.

If AC input power falls outside the tolerances of the double-conversion rectifier, or goes out altogether, the UPS uses the battery to keep supported loads up and running. When the generator comes online, the UPS switches to double-conversion mode until input power stabilizes. Then it transitions back to high-efficiency line-interactive mode.

Multi-mode UPSs are designed to dynamically strike an ideal balance between efficiency and protection. Under normal conditions, they provide maximum efficiency. When problems occur, however, they automatically sacrifice some efficiency to deliver maximum levels of protection. The end result is that data centers can save tens of thousands a year on energy without compromising data center performance or reliability.

What now?

Businesses today invest large sums of money in their IT infrastructure, as well as the power required to keep it functioning. They count on this investment to keep them productive and competitive. Leaving that infrastructure defenseless against electrical dips, spikes and interruptions, therefore, is a bad idea.

A well-built power protection solution, featuring high-quality, highly efficient UPS hardware, can help keep your business applications available, your power costs manageable and your data safe. By familiarizing yourself with the basics of what a UPS does, facility managers and building owners can ensure that mission-critical systems always have the clean, reliable electricity they need to drive long-term success.

Ed Spears is Product Manager, Power Quality Solutions Operation, Eaton Corporation

Related Coverage