There are numerous types of uninterruptible power supply (UPS) designs on the market, but the most prevalent are line-interactive, double conversion online and multimode.


According to Mike Johnson, vice president of product marketing for the EGS Electrical Group, Rosemont, Ill., a line-interactive UPS uses a constantly running online battery along with an inverter/
converter to keep the battery connected to the output. If the power fails, the transfer switch can shift electrical flow from the battery to the system output. In general, these UPSs work best with linear loads such as motors, heaters and lights. 


“Line-interactive technology is less expensive and more efficient than double conversion UPSs but does not provide quite as much protection,” said Ed Spears, technical marketing manager, power quality group, Eaton Corp., Cleveland.


The double conversion online UPS converts all alternating current (AC) input to direct current (DC) and then back again to AC at the right voltage and frequency. This process, according to Johnson, provides conditioned electrical power along with protection against power outages. The technology is ideal for applications where electrical isolation is necessary or for the electrically sensitive equipment found in data centers or industrial and medical applications.


“This is the most expensive UPS, but [it] offers the best protection,” Spears said.


Multimode technology allows the UPS to operate in multiple modes as it examines the quality of incoming power and changes its operating characteristics to adapt to the electrical conditions of the moment.


“This type of UPS offers the highest efficiency and best performance, depending on the quality of the incoming power,” Spears said.


Regardless of the UPS technology chosen, the goals are simple: to protect devices from power disturbances or disruptions and ensure system availability and integrity of data. 


“Historically, UPSs have been found primarily in the IT [information technology] industry where the creation, transmission and storage of data is critical,” said Ray Munkelwitz, product line manager for Schneider Electric, Palatine, Ill. “However, they may also play a vital role in any process that is susceptible to interruption due to power quality.” 


Safety and other benefits


According to Munkelwitz, a UPS supports safety by providing backup power to systems that rely on the IT network or even some systems outside of it.


“For example, some buildings use UPSs to back up security devices and scanners, or others may use specialized UPSs to provide backup for emergency lighting systems,” he said.


Spears said backup power is necessary for UL 9245 compliance, which requires that lights and emergency signage stay on and that the elevators and ventilation systems keep operating during a crisis and evacuation.


“In addition, UPSs filter out disturbances that can interrupt or damage a life safety system’s sensitive electronics,” Johnson said.


UPS systems also address safety needs in medical applications by supporting critical operating room equipment.


Other benefits of a UPS system include hardware protection from damaging surges and spikes, data protection from corruption caused by noise or minor power anomalies, peace of mind during extreme weather events that have great potential for power disruption, protection from unpredictable utility events, and the time to reroute critical process servers (computers) to more stable locations.


Challenges lie in batteries


“Batteries are the weak links in all UPS installations and are the No. 1 cause of load loss,” Johnson said. 


Today, most UPS systems use sealed valve-regulated lead acid batteries. This technology has proven reliable and economical over time, and they are recyclable.


Recent improvements in lithium-ion batteries promise 30 percent higher power density at 20 percent lower cost, according to Spears. However, making lithium-ion battery technology work with UPS applications today means a larger battery, which does not solve weight or space issues.


“Manufacturers are researching solutions, but it will be up to several more years before the issues are solved,” Spears said. 


Other technologies being researched include nickel-metal hydride, nickel-sodium, super capacitors and fuel cells.


Spears said electrical contractors must be involved with ensuring UPS reliability and eliminating the possibility of human error.


“After battery failures, human error is the most common reason a UPS fails. Contractors need to have design and installation input concerning where breakers are located and the sequence of UPS operations to ensure reliability,” Spears said.


Other challenges include dealing with the overall size and weight of some units, tight spaces and limited ventilation in some environments, different plug types, and operating voltages.


“The contractor’s challenge is to demonstrate that it can provide the required levels of backup power and battery time in the least amount of necessary space,” Spears said.