A brief overview of uninterruptible power supplies (UPS)

An uninterruptible power supply, also known as the UPS, is a term that can be applied to several types of systems whose end goal is to provide uninterrupted power to a load. The load can be anything from: lights, servers, air-conditioning, industrial equipment, anything that uses electricity. For most of our readers, the load powered by UPS will be servers and possibly air-conditioning and security equipment.

Another term used to describe a UPS is SEPSS (Stored Energy Power Supply System). The principle is the same: the unit stores enegy (kinetic, chemical, electrical) and in the event of a power failure, releases that energy to the load so the load receives continuous power.

Why do we need UPS?

There are countless examples of equipment that needs a constant supply of power. We call such equipment “mission-critical” because that equipment is critical to the mission of an organization. If your organization's mission is providing 24/7 uptime for servers that host websites, and it is critical that those servers stay online and connected to the network. If your organization supports ATM transactions, banking transactions, and investment transactions, that is your mission and it is critical that it is in operation all the time.

What are the main types of UPS?

Since the purpose of an uninterruptible power supply is to provide constant electrical energy to a load, any device that can store electrical energy and provide energy to the load during a utility power outage can be considered UPS. There are two main types of UPS: static UPS and Rotary UPS. As the name implies a static UPS has no moving parts other than cooling fans. A rotary UPS, on the other hand, may have several moving parts that are integral to the operation of that UPS.

Static UPS

Most commonly, a static UPS relies on chemical energy stored in batteries to provide electrical energy to the load during a power outage. This type of UPS system has been around for nearly a century, is widely accepted, and has a very mature design. Here's an interesting tidbit: have you ever heard someone refer to a battery as “jar”? Do you know the reason why? Streetwise because the batteries were first invented, they were actually made in glass jars. The jars contained the acid solution and metal which made up the first rudimentary batteries.

The common static UPS sits in line with the incoming power, monitors that power, and in the event of a power issues such as a sag or complete outage, pulls electrical energy from the batteries to power the load.

Rotary UPS

The goal of a Rotary UPS is the same as the static UPS, however it is accomplished in a different way. Instead of having batteries store chemical energy, a Rotary UPS has a flywheel or rotor which stores kinetic energy. Through illegible circuitry, a Rotary UPS converts this kinetic energy intellectual energy to power alone during a utility outage.

Rotary UPS is also have a long lineage. Some of the first Rotary UPSs have been around since the 1930s and 40s, although they didn't go mainstream until the 60s. One major advantage is that Rotary UPS systems have over their static UPS counterparts is that they are more robust and can handle a wide range of loads. Most static UPS systems were not designed to support large, reactive loads such as pumps and motors. Therefore a static UPS is not a good match if you also want to backup your air-conditioning equipment and chiller plant. A Rotary UPS can handle these highly reactive loads.

Runtime

One of the biggest variables to consider when selecting a UPS system is the amount of runtime provided by the UPS system. The runtime is how much time the UPS can provide power to your load without utility or another source of power. The design of many electrical systems in a data center includes incoming utility power, a backup generator, a transfer switch, in the UPS. Should utility power fail, UPS provides instantaneous ride through, uninterrupted power, to keep the critical load online. In the second that follow a power failure, the backup generator detects this failure and begins its start up procedure.

So the minimum runtime that UPS system needs to have should be sufficient to allow the generator to come online and to begin to support the load. Modern generators can be online within 7 to 10 seconds, although 15 to 20 seconds should be assumed for any generator to come online. A UPS should also provide a safety margin which will allow a few restart attempts of the backup generator.

Several decades ago there was a recommendation that the minimum runtime UPS should provide was 15 minutes. The reason behind this is because in the days of the mainframe, the shutdown process of a mainframe was long and complicated. The minimum shutdown time of a mainframe computer was generally believed to be 15 minutes. Additionally data center technicians had have sufficient time to shut down other systems and components of the data center.

These days, however, fewer and fewer clients are opting for that 15 min. run time, which can get quite costly. In the static UPS system that relies on batteries, the only way to increase your runtime is to connect more batteries to UPS. Batteries are quite expensive, require maintenance, and take up floor space. Many organizations do not have the required floor space or budget to purchase a UPS system that provides 15 min. of runtime. Experience shows, however that these days 15 min. is more than enough runtime. Many facilities get by with 5 to 10 min. of run time without any problems.

Efficiency

Efficiencies of UPS equipment vary drastically. In the 1970s 80s and even into the 90s, most UPS equipment was very inefficient. The electrical components in a UPS system were often SCRs, also known as silicon controlled rectifier's. A silicon controlled rectifier could handle a lot of current but it was very inefficient. Typical efficiency seen in the early days of static UPS equipment were as low as the 60% to 70% range. Since your UPS will be running 24 hours a day, seven days a week, it's efficiency should be very important to. If you have an inefficient UPS in your system, it will be wasting a significant amount of electricity.

These days, static UPS equipment easily reaches 96% efficiency and higher. The efficiency of Rotary UPSes is typically between 93% and 95% efficient. Although the latest generation of static UPS has pushed beyond efficiency of Rotary UPS equipment, there still is one advantage that Rotary UPS systems have over static UPS systems in the efficiency department: Rotary UPSes do not need as many support systems as static UPS. Static UPS with batteries typically needs to be indoors in a condition space. These extra support systems required for static UPS with batteries also use electricity, leading a decrease in the overall total system efficiency.

A Rotary UPS, on the other hand, can be located outdoors, may not need air-conditioning, and may not need other support systems. So the total system efficiency of a Rotary UPS is often on par or perhaps even greater than the static UPS system. But believe the nitty-gritty up to the marketing department!

A word about expandable UPS systems.

The past several years, we have seen an increase in the number of companies that manufacture “expandable” UPS systems. The basic premise behind the systems is that you can purchase UPS with X kVA capacity today, and by purchasing expansion modules, that UPS can have XX capacity tomorrow. It really works like this: you purchase of expandable UPS cabinets that has been populated with a single power module.

As your load increases, you can purchase additional power modules that slide into the original UPS. On day one, UPS may have had 40 kVA capacity. If you purchase two additional power modules, you can expand the capacity of 120 kVA. This flexibility and scalability is certainly appealing to many IT professionals. It allows a lower initial cost outlay, so that capital can be allocated for other purchases.

When purchasing an expandable UPS system, you and your design team must take into account the future load in the future capacity of that UPS. If you purchase an expandable UPS and populate with a single 40 kVA power module today, but you expect to populated with several more modules in the years to come, you must size your eventual system to accommodate future capacity of that UPS. This includes over sizing components such as wires, breakers, panel boards, and transformers. If you size these electrical system components based off the initial 40 kVA capacity of your UPS, it will become incredibly costly to increase the capacity of your electrical system to fully support the future capacity of the UPS once you have expanded it.

The future of UPS technology

Over the years, UPS manufacturers have been continually pushing the boundaries of UPS design. Deficiencies have increased, physical size has decreased, reliability has increased. We're beginning to see integrated power systems where a UPS is only one component or module of a greater, larger, more complete power system.

We've also seen the trend of “building a better mousetrap” where some UPS systems have become a commodity. In years past, it was easy to see the difference between one UPS brand and design and another. Some UPSs have high efficiencies and low harmonic distortion, while others have low efficiencies and high harmonic distortion content.

As the industry matures, the technology is experiencing a convergence, and there is much less that separates one brand from another. While it is hard to go wrong with any of the top name brands in the market today, we do recommend that you consult with a professional to make sure you're getting the right UPS system for your facility and your needs. You can always contact the sales team at DataCenterStore.com for recommendations and information.