All three basic uninterruptible power supply (UPS) technologies have their place in protecting today’s distributed IT infrastructure especially on the network edge. Each technology has its advantages and each may be necessary for configuring cost effective power protection, especially in complex systems. Selecting a UPS for your particular application requires an examination of a number of factors. The load size, location and criticality of the equipment to be protected are key, as well budgetary considerations, when choosing a UPS for power backup.
The three major types of UPS system configurations are online double conversion, line-interactive and offline (also called standby and battery backup). These UPS systems are defined by how power moves through the unit.
Online Double Conversion
AC power is stable and clean upon generation. But during transmission and distribution, it is subject to voltage sags, spikes and complete failure that may interrupt computer operations, cause data loss and damage equipment. When it comes to safeguarding critical IT loads, only online double conversion technology protects fully against all these power problems, providing the highest levels of security for networks.
An online UPS system is usually called double conversion as well because incoming power is converted to direct current (DC) and then converted back to AC. This AC-DC/DC- AC design ensures an increased degree of isolation of the load from the irregularities on the main supply.
The online UPS takes the incoming AC power supply and converts it to DC using a a rectifier to feed the battery and the connected load via the inverter so that no power transfer switches are necessary. If the main AC input fails, the rectifier drops out of the circuit and the batteries keep the power flowing to the device connected to the UPS. When AC input power is restored, the rectifier resumes carrying most of the load and begins charging the batteries.
Because power runs through an online UPS continually, output is a perfect sine wave. This type of UPS protects the critical load from virtually all power disturbances, including subtle harmonics and waveform distortion.
This means the quality of power from online UPS is significantly better than that of other technologies. Offline and line-interactive technologies reduce the impact of spikes, surges and sags by either clipping the peaks and valleys, boosting power or switching to battery backup. Within the normal track of an electrical sine wave, however, most power fluctuations are left alone. Online UPS regenerates the sine wave, not just conditioning of the raw utility supply.
An online UPS delivers continuous, high-quality AC power to equipment with no break when transferring to battery, protecting equipment from virtually all power disturbances due to blackouts, brownouts, sags, surges or noise interference. A true online, double-conversion UPS provides 100% power conditioning, zero transfer time to battery, no change in output voltage and better transient suppression than line-interactive units.
Online double conversion is the most common UPS mode of operation used for protecting large data centers by providing the highest level of power quality to the load always. Online systems also provide frequency regulation, essential for use with backup generator systems to protect from variations common at generator start up.
Line-interactive UPS systems provide both power conditioning and battery backup. This technology is particularly effective in areas where outages are rare, but power fluctuations are common. Line-interactive UPS systems support a wide range of input voltage fluctuations before switching to battery backup.
Beyond battery backup, line-interactive UPS provides far better control over power fluctuations then offline systems. The critical advantage of line-interactive UPS is the voltage boost circuitry and the range of input voltage that that UPS accepts. The wider the range, the more total protection you will have.
Line-interactive UPS technology provides power conditioning with a 4-6 millisecond break in power when transferring to battery back-up and protects against the most common power problems experienced in a network. Here the UPS also monitors the voltage level and balances under and over voltages. This technology provides a good choice between reasonable protection and moderate operating costs.
With line-interactive UPS, the inverter becomes part of the output and is always on. The inverter can operate in reverse to charge the battery while AC input is normal, and switch to battery power when input fails, which provides filtering and voltage regulation. Line interactive UPS systems rely on the battery to condition power so this type tends to drain its battery more frequently than online UPS systems that condition power through the double-conversion process.
When AC input power fails, the unit’s transfer switch opens and the power flows from the battery to the UPS output. With the inverter always on and connected to the output, line-interactive UPS provides additional filtering and yields reduced switching transients when compared to a standby UPS. Line-interactive UPS systems are typically used in rackmount applications below 5000VA.
Offline UPS, also called standby UPS or battery backup, is a cost-effective choice. Better offline UPS systems switch to battery fast enough to prevent power anomalies and ride out short outages. An offline UPS protects against most spikes, but doesn’t maintain perfect power during minor sags and surges.
The key to offline UPS quality is the range of power the unit will except before switching to battery backup. The wider the range, the less drain on the battery and the more backup time available when the power shuts off. The more times the UPS switches to battery backup, the shorter the battery life.
Offline UPS technology will protect from most power spikes by clamping down on excess voltage and help ride out more than 90% of all outages. An offline UPS system passes utility AC power straight through the unit, past a transfer switch, to the output point where the protected load is connected.
When an input power failure happens, the built-in battery and the inverter, which converts the battery’s DC power to AC, are activated and connected to the output by the transfer switch. There is generally about a 6-8 millisecond break in power when transferring to battery back-up.
This technology is best suited for devices under 1500VA such as small offices, personal home computers and other less critical applications. Offline UPS is a good option for those requiring lower power capacity and cost. Offline UPS technology provides power backup protection for desktop equipment, gaming consoles, workstations, wireless networks and other electronics. During power outage, it provides enough runtime to save work in process and complete an orderly shutdown of equipment. In addition to power backup, most offline UPS systems offers basic surge protection as well.
Vertiv UPS Solutions
Vertiv Liebert APS UPS
The Liebert APS is an online UPS that provides mission-critical availability while reducing costs and maintaining flexibility for the future. A flexible, scalable, modular power solution for room or row-based applications, Liebert APS is available in capacities from 5 to 20kVA. Liebert APS UPS provides mission-critical availability while reducing costs and maintaining flexibility for the future. With low TCO, you can maintain flexibility for the future and ensure the availability of your critical systems – all while obtaining energy efficiency.
Vertiv Liebert GXT5 UPS
The Liebert GXT5 UPS is an online double conversion UPS solution that offers premium power outage protection and continuous power conditioning in a compact and flexible deployment system. It features a full color graphic LCD display with gravity sensing. The Liebert GXT5 is Energy Star 2.0 certified thanks to efficiency up to 95% in on-line mode and even higher efficiency up to 98% in Active ECO mode. Its higher power factor makes more active power available so more loads can be connected. Functions under operating temperatures from 32° to 104°F (0° to 40°C) with no derating. Includes individual receptacle control for runtime management and power cycling of individual connected equipment. Available in 500 to 3000VA capacities, the Liebert GXT5 single phase UPS is ideally suited to protect critical infrastructure in both centralized and edge network applications
Liebert EXL S1 UPS, 300-1250 kW
Liebert® EXL S1 delivers secure power while providing first class load protection and maximum energy saving for medium-large data centers and mission critical applications. The latest high efficiency Dynamic Online mode enables operating efficiency up to 99% without sacrificing availability. Liebert EXL S1 Dynamic Grid Support feature can provide frequency regulation by controlling the input power to support services such as frequency regulation-up, regulation-down, or both via charging and discharging of the battery.
Vertiv™ Edge UPS
Vertiv™ Edge is a family of highly reliable, efficient, manageable and flexible line interactive sinewave UPSs, with models ranging from 500VA to 3000VA in 1U, 2U, 3U, mini-tower, rack tower and rack-mount form factors (depending on model). With a high 0.9 power factor, controllable outlets and extended runtime options, Vertiv™ Edge is a cost-effective choice for protecting server and networking equipment in distributed and Edge IT applications.