What are UPSs?
Uninterruptible power supplies (commonly known as UPSs) are electrical devices that will continue to provide emergency power to a load in the event that the primary input power source fails. This emergency power switch over happens almost instantaneously due to the presence of energy-storing batteries or capacitors within the device. UPSs are often utilized in critical applications such as data centers, manufacturing, and process/production, and provide protection against problems such as the nine listed below:
There are several different UPS topologies that provide varying degrees of power protection. The best UPS topology for an application depends on factors such as the desired level of reliability, the type of equipment that requires protection, and the environment where the equipment and UPS will be installed. All four of the below UPS topologies achieve similar functionality; however, the key difference lies in the demand on the battery and how the power switch over happens as a result.
A standby UPS allows equipment to run off utility power until the UPS detects a problem, at which point the UPS switches to battery power to protect against sags, surges, or outages. Because the band of normal operation is typically narrow, the UPS must resort to batteries frequently, which can reduce battery runtime and service life.
A line-interactive UPS regulates voltage either by boosting or decreasing utility power as necessary before allowing it to pass to the protected equipment, or by resorting to battery power. These models typically switch to battery mode with a transfer time of 3-8 ms. Battery usage for line-interactive models is lower than that of a standby model, but still higher than an online model.
An online UPS provides the highest level of protection from raw utility power by converting power from AC to DC and back to AC. When input voltage is within preset UPS tolerances, the output voltage is regulated without going to battery usage. As a result, the UPS uses battery power less often than standby or line-interactive UPSs. Many online UPSs allow an even wider input acceptance window when the UPS is under 100% load.
High-efficiency mode UPSs are among the latest generation of UPS models, successfully combining the benefits of single- and double conversion technologies. Under normal conditions when power falls within acceptable limits, the multi-mode UPS operates as a high efficiency, energy-saving system, regulating voltage and resolving common utility power anomalies.
During erratic power or fleeting disturbances when AC input power falls outside of preset tolerances for line-interactive mode, the UPS switches to online double-conversion mode, completely isolating equipment from incoming power. If power is lost altogether, or the input power exceeds the tolerances of the double-conversion rectifier, the UPS relies on the battery to keep loads operating, converting back to high-efficiency mode when it’s safe.
A ferroresonant UPS operates similarly to line-interactive models, with the exception that a ferroresonant transformer is used to condition the output voltage and hold energy long enough to cover the time between switching from line power to battery power – effectively a no-break transfer. Many ferroresonant UPSs are 82-88% efficient and offer excellent isolation. Although no longer the dominant type of UPS, these robust units are still used in industrial settings such as the oil and gas, petrochemical, chemical, utility and heavy industry markets.
How to correctly size and apply a UPS
Follow the below steps and provided sizing worksheet to correctly size a UPS for any application involving electrical equipment.
- List all equipment to be protected by the UPS – remember to include, PLCs, HMIs, networking equipment, and other sensitive control equipment)
- List the current (in amps/A) and voltage (in volts/V) for each device.
- These ratings can typically be found on the label on the back of the component.
- Multiple amps by volts to determine VoltAmps (VA). Some devices may list their power requirements in watts – to convert watts to VA, divide the watts by the power factor. For servers, the power factor is often 0.9.
- Multiply the VA by the number of pieces of equipment to get the VA subtotals.
- Add the VA subtotals together.
- Multiply the VA total by 1.2 to get the grand total. This step accounts for any future expansion.
- Use the grand total to get the UPS. When choosing a UPS, be sure that the total VA requirement of supported equipment does not exceed the VA rating of the UPS.
The process of selecting the correct UPS (uninterruptible power supply) battery backup for a network closet or intermediate distribution frame for a company’s IT system can be a confusing process. Eaton, an AWC technology partner focusing on power management, has developed several UPS-related resources to guide companies during the planning process during the planning process to ensure the resilience and reliability of their IT networks in the event of power failures.
UPS Buying Guide
Eaton has developed a UPS buying guide that highlights 10 key factors that companies should consider when selecting the correct UPS for an application.
Please click below to download a PDF copy of Eaton’s UPS Buying Guide.
Eaton has also developed a UPS sizing and selection tool that allows customers to answer a brief set of questions to select the correct UPS for a particular application, or replace an existing Eaton UPS with a different or upgraded model.
Please click here to access Eaton’s online UPS selector tool.