Uninterruptible Power Supply | UPS Systems Guide

Uninterruptible Power Supply (UPS)

Introduction

Information explaining uninterruptible power supplies and a list of UPS manufacturers

You will learn:

What is an Uninterruptible Power Supply?
How Uninterruptible Power Supplies are Made
Uses for Uninterruptible Power Supplies
Regulations Regarding Uninterruptible Power Supplies
How to Select an Uninterruptible Power Supply
And much more …

Chapter 1: What is an Uninterruptible Power Supply?

An uninterruptible power supply is a source of electrical power that activates when the main input power fails or goes out. They are designed to deliver power instantaneously from energy stored in batteries, super capacitors, or a mechanical storage method. Sensitive electronics, such as computers, data centers, and mission critical devices, require a reliable and consistent power supply and can be harmed by sudden outages. UPSs, for a few minutes, fill the gap between a power outage and the restoration of a stable power supply.

Since energy can be stored in different ways, uninterruptible power supplies take different forms. The most common type is rechargeable batteries, which are plugged into an alternating current (AC) outlet. When there is a voltage drop, power outage, surge, or frequency variation, a UPS activates immediately to prevent damage to electrical equipment.

While supercapacitors and battery UPSs are quite common, mechanical non-battery UPSs are also used. The types of mechanical UPSs include motor generators, rotary UPSs, and flywheel UPSs that activate like battery UPSs using mechanical systems. These three mechanical methods are vacuum fault interrupters that use vacuum technology to interrupt electrical faults to protect power distribution systems.

Chapter 2: How Uninterruptible Power Supplies Work

One of the factors that is critical to the operations of today's connected technologies is clean continuous power, which requires the use of reliable backup power systems that help companies avoid the negative consequences of downtimes. Uninterruptible power supplies are backup solutions that supply power in the event of a power failure. They make it possible to properly shut down sensitive equipment and prevent data loss.

In addition to being a form of safety device, UPSs have other aspects that ensure the stability of a power system. They shield electronics from voltage surges and sags, complete power failures, and unsafe output voltage fluctuations. Each of these factors can damage electronics, affect equipment performance, and endanger the life span of critical devices.

Uninterruptible power supply systems are important tools that guarantee reliability and the protection of essential electronics. The ultimate goal of UPSs is the protection of all forms of electrical devices against any form of power supply anomalies.

Types of Uninterruptible Power Supplies

Three of the general categories of UPSs are standby, line interactive, and online or double conversion. Standby and line interactive UPS systems are referred to as single conversion systems with standby being the most basic of the two. Online double conversion UPS systems are designed for complex power support and are constantly activated. A unique form of UPS is multi-mode UPSs that combine the features of two of the basic UPS types.

The three types of UPSs are capable of meeting the needs of a wide range of applications, devices, and electronic processes. Their objective is to maintain the operation of devices during power failures prior to long term or temporary power being restored.

Standby UPS – A standby UPS is the most basic form of UPS that provides short term battery power during outages. When incoming power changes, a standby UPS provides direct current (DC) power from batteries that is converted to AC power by an inverter that is used to run connected equipment.
Line Interactive UPS – Line interactive UPSs correct power fluctuations without the use of their battery using an auto transformer that regulates low voltages and over voltages. They automatically regulate voltage and support systems during outages. As with standby UPSs, line interactive UPSs convert battery power to AC power using an inverter.
Online UPSs – Online UPSs, also known as double conversion UPSs, are UPSs that convert incoming AC power to DC power and back to AC power. They operate on isolated DC power and have a zero transfer time. With online UPSs, incoming AC power travels to a rectifier where it is converted to DC power. From the rectifier, the DC power goes through an inversion before it is delivered to electronic equipment.

Delta conversion online UPS units are a variation of online UPSs that provides highly efficient power correction. They are used in high density computer situations, large data centers, and mission critical applications. Part of the efficiency of Delta online UPSs is their ability to regulate input current for charging of their battery system.

Multi-Mode UPS – Multi-mode UPSs use features from single and double conversion systems to produce higher protection and more efficiency. They act as line interactive UPSs under normal input power conditions. When there are fluctuations in the main power supply, they change to double conversion mode to better isolate affected equipment. Multi-mode systems achieve 99% efficiency by operating in different modes.

Multi-mode systems turn to the best operating mode per the needs of electronic devices. There are variations in the design of multi-mode UPS systems with some having a double conversion mode and multi-mode while others have a high efficiency eco mode and a premium power protection mode. In all cases, systems switch between the various modes when they detect problems with the main power supply.

Three level insulated gate bipolar transistor (IGBT) UPS technology reduces switching and power conversion losses. New multi-mode technologies use precision disturbance analyzers and responsive monitoring for highly accurate and seamless switching between main power and UPS conditioned power. In these systems, UPSs operate for a shorter time and have a higher transfer speed.

How an Uninterruptible Power Supply Works

A UPS constantly monitors received voltage from the main power supply. If the supplied voltage is lost or unstable, the UPS automatically switches to an alternate supply. The overall purpose of a UPS is the protection of electronic devices and equipment from electrical surges, sags, and power spikes, which is essential for modern business and industry. The amount and length of the alternate power supply is dependent on the size of the UPS and the load it is supplementing.

Power outages are always a potential threat. According to the United States Energy Information Administration (EIA), on average, a loss of power can last up to six hours. The response that most businesses use in regard to power outages is the installation of generators that provide power when the main supply is interrupted. Although this is a logical solution, it is not sufficient protection for sensitive equipment.

Generators provide power support for mission critical devices, such as IT, AC, heating, and various forms of electronics. Frequent changes in load requirements are difficult for generators to maintain consistent output. These types of variations can be handled by an online double conversion uninterruptible power supply that regulates power and is able to accept variations in power frequency.

Components of a UPS System

The types of UPS systems vary from ones for data centers and hospitals to single phase UPS systems that protect industrial operations and other types of applications. Although the sizes of UPS systems vary, all types have four basic components, which are batteries, automatic transfer switches (ATSs), a rectifier, and inverter. Around these four basic components are other features of UPSs that offer extra aspects to a system to enhance its performance.

Batteries

The heart of all UPS systems is their battery that supplies power during a power outage or shut down. Batteries automatically connect to the load during utility power failure or when there are anomalies that cause power fluctuations. All UPS systems have at least one battery with some systems having strings of several batteries to increase run times and redundancy. The unique structure of battery strings provides protection for a system through the use of multiple batteries that cover the potential failure of any one or multiple batteries.

Automatic Transfer Switch (ATS)

The ATS automatically transfers power from the primary power supply to the UPS when there is a power outage. They are ideal for smaller UPS units that are below 10 kilovolt ampere (kVA) and are unable to operate in a parallel configuration. An ATS has two AC power input sources, ‘A’ and ‘B’, with one providing power should the first one fail. They can be used in place of power distribution units (PDU) for plug and play loads. ATSs protect against short circuits and can switch output on and off remotely.

The configuration of an ATS can take three forms. ‘A’ can be supplied from the output of the UPS while ‘B’ is supplied from the main. ‘A’ and ‘B’ can be supplied from two separate UPS outputs or from separate main supplies. Multi switch ATSs provide power distribution to eight 10A IEC utilities or one 16A IEC in a system with two power supply lines from two mains or two UPS systems.

Rectifiers

A UPS rectifier converts AC power to DC power and can accept a wide range of input voltage fluctuations, which enables a UPS system to handle overloads or surges without activating the battery. They are responsible for recharging the battery or batteries when DC power routes to the inverter. With larger UPS systems, a rectifier may have a battery charger while smaller systems, below three kVA, the battery charger and rectifier may be separate components.

The normal functions of a rectifier are charging batteries and keeping them in optimum working order and providing DC power to other loads. Rectifiers are installed with the kind of battery a UPS system uses, which can be a lead acid battery (Pb), lithium ion battery, or nickel cadmium battery (NiCd). Pb batteries have two current levels, float and charge, while three current levels are used for open Pb and NiCd batteries, which are float, fast charge, and deep charge. Lithium ion batteries are widely used batteries for their superior energy density, fast recharging, and long lifespan.

Inverter

For online UPS systems, the inverter is an essential aspect of the double conversion process and serves as a filter for power surges, spikes, and electrical noise. The DC power converted by the rectifier is routed to the inverter that converts the DC power back to AC output, that is required by the load. With inline UPS systems, the inverter is part of the output. The inverter recharges the battery and relies on battery power during input failures.

Although inverters can stand alone receiving DC power from solar power or batteries and converting it to AC current, in UPS systems, they are a utility interactive inverter that is one part of the power supply unit. The difference between stand alone inverters and UPS system inverters is their response time with UPS systems changing over in 10 milliseconds while stand alone inverters change over in around 500 milliseconds.

Insulated gate bipolar transistors (IGBTs) are a form of inverter that use insulated gate bipolar transistors to convert DC current to AC current. IGBT inverters are able to handle large power ratings with low losses and are the common choice for use with UPS systems. They ensure stable and fast switching that is quick and efficient.

Integrated gate commutated thyristors (IGCT) inverters are capable of handling voltage levels that are higher than those of IGBT inverters. They are rugged and known for being robust and resilient. The turn off speed of IGCTs is another factor that differentiates them from IGBT inverters, which is important in UPS systems in minimizing switching losses and ensuring precision power flow. Due to their ruggedness, IGCTs last longer, a factor that keeps UPS system replacement costs down.

Static Bypass Switch

Static bypass switches are ATSs that perform as a fail safe measure for UPS systems if there is an internal fault or failure in a system. If a UPS system runs on bypasses, it circumvents the rectifier, batteries, and inverter to ensure power continuity as the UPS is being fixed. Static bypass switches are known as safe failure to mains. When a system is operating on a bypass switch, the input and output supply is not filtered, which is typical with online double conversion UPS systems. Static bypass switches ensure that continuous power is provided regardless of any changes in the main system by seamlessly switching between on UPS or off UPS, depending on the condition of the UPS.

Although static bypass switches may be positioned internally in a UPS system, some systems have external ones that are mechanical wraparound or rotary switches or a set of circuit breakers. This type of static bypass switch is commonly used with line interactive and offline UPS systems, which can have external static bypass switches that have an automated transfer feature.

UPS Components with a Static Bypass Switch

Capacitors

Capacitors are simple electrical devices that store and release electrical energy. They vary in size in accordance with their voltage rated capacity. Capacitors consist of metal plates that have a conducting surface, which are insulated and separated by a dielectric material. The thickness of the dielectric material determines the capacitance or how much charge can be stored in a capacitor.

In UPS systems, capacitors serve three purposes. They are part of the AC input filter and power correction stage where they smooth input transients and reduce harmonic distortion. They are also part of the UPS’s output filter, connecting the load output and controlling the waveform of the output voltage. As part of the rectifier, DC capacitors smooth voltage fluctuations for supply voltage filtering.

UPS Fans

As with every aspect of a UPS, fans play an important role in keeping UPS inverters and rectifiers cool for safe operation. Fans are strategically placed to provide enough cooling to avoid component deterioration and failure since UPS components operate at very high temperatures. As the size of UPSs increase, larger bigger fans are needed for protection of components and UPS performance.

As with capacitors, UPS fans have a set service life, which can be 5 to 7 years when operating under optimal environmental conditions. Manufacturers recommend replacing fans in advance of their service life to prevent the risk of system failure. In many cases, fans and capacitors should be replaced at the same time, a process that is described as UPS overhaul. Smart cooling systems have fans that adjust their speed in accordance with the load of a UPS.

UPS cooling fans only operate when required and are activated by internal thermometers. When a UPS is idle and not using its battery, the fans do not run, except in the case of online UPS models that have fans that run all the time.

Components of UPS systems wear out with normal use, which makes them susceptible to failure. As with all types of industrial equipment, UPS equipment have maintenance schedules where they are checked regularly for any issues that could lead to failure. UPS manufacturers offer maintenance plans with their contracts to assist in ensuring the proper performance of their equipment, which include repairs, maintenance and battery recycling and monitoring that is performed by manufacturer technicians.

Chapter 3: UPS System Output Waveforms

The three different types of uninterruptible power supply waveforms are sine wave, square wave, and modified square wave, known as a stepped shaft. Output waveform is an important part of selecting a UPS system. It affects the compatibility with connected devices and the stability and efficiency of the power supply. Each type of waveform has its advantages and disadvantages, which need to be understood in order to choose the right UPS system.

UPS manufacturers work closely with their clients to understand their needs and help in the selection of a UPS system that best fits their requirements. They categorize their equipment in accordance with the types of power related problems the units prevent, eliminate, and will endure.

Sine Waveform

Sine waveform is the most common type of waveform. It is a smooth, repeated oscillation of AC current and is the finest quality waveform output. Sine waveform is the same type of waveform that is produced by a network and meets the requirements and specifications of modern electronics. Output voltage produced using sine waveform has high stability. High quality UPS systems have pure sine waveform output, which requires expensive components in the inverter. The purity of sine waveform is especially important for online UPSs that have loads that are always running.

Sensitive electronics function with a sine wave power supply. In most cases, precise voltage and frequency levels are necessary for proper functioning of sensitive equipment. Sine waveform is compatible with nearly all electronic equipment and prevents spikes, surges, and voltage sags. Sine wave UPSs have filtering mechanisms that reduce noise, known as electromagnetic interference (EMI) or radio frequency interference (RFI) that can disrupt the function of sensitive equipment.

Square Waveform

Square waveform is the least desirable waveform. It has the appearance of a flattened version of sine waveform. Unlike sine waveform that shifts smoothly from negative maximum to positive maximum, square waveform suddenly leaps from negative to positive, where it stays for a cycle, which is followed by a jump to full negative. While sine waveform UPS systems are expensive, square waveforms are used due to their affordability.

As a pulse wave, square waveform has arbitrary durations at maximum and minimum amplitudes, the ratio of which is referred to as a duty cycle. A true square waveform has a 50% duty cycle with equal high and low periods. The peak voltage for a square wave is lower than sine waveforms. Unlike sine waveforms that have a single frequency, square waveforms contain multiple high frequencies called harmonics that cause buzzing. The existence and use of square waveforms is due to their low cost, which is the reason they are used in cheap equipment.

Stepped or Modified Square Waveform

Stepped waveform is a compromise between square waveform and sine waveform. Square waves are thinned and separated to make it possible for them to match the peak of sine waveform and have a shape that is similar to sine waves. The circuitry used to form stepped waveform is close to the cost of square waveform and less expensive than sine waveform. Stepped waveform can be produced by adding two square wave forms that slightly shift in phase from each other.

Electronic equipment that uses stepped square waveform has fewer problems than ones using square waveform. Stepped square waveform is used in midrange UPSs and advertised as a stepped approximation of sine waveform. Although stepped waveform attempts to replicate sine waveform, it does not have sufficient sensitivity to work with highly technical and critical devices.

The waveform of a UPS determines the quality of the power being delivered to connected electronics. Sine waveform mimics standard utility power and is crucial to the safety, longevity, performance, and proper functioning of modern devices. Although square and modified square waveforms are available and less expensive, they are not sufficiently sensitive for highly technical equipment. The choice between sine, square, and modified waveforms is dependent on the types of electronics being powered and the required level of reliability.

Chapter 4: Non-Battery and Battery Mechanical UPSs

Uninterruptible power supplies rely on batteries and provide backup power for a short time during power failures and outages. They ensure that critical systems remain online by instantly providing power when the main power goes down. They are very commonly used by businesses that have sensitive and precision equipment that can be damaged by the loss of power. UPSs are connected directly to a company’s main power supply.

Mechanical non-battery UPS systems are voltage frequency independent (VFI) devices that are referred to as mechanical uninterruptible power systems. They are double conversion units where power conversion is mechanical with motors that act like rectifiers.

Motor Generator (MG)

Motor generators combine a motor with a generator with the motor performing like a rectifier in the UPS system. Main power drives a rectifier that runs a DC motor that charges a set of batteries. When main power fails, the batteries power a generator that continues to deliver power to the load. Motor generator sets are designed to power mechanical equipment, such as air conditioners and refrigerators, and not IT equipment.

In a motor generator set that is connected to a UPS system, the generator’s power can be delivered to sensitive critical systems. Since generators produce frequently changing loads, the UPS system regulates the generator’s power using an online double conversion UPS system. Since UPS systems are constantly converting incoming power to AC power into DC power and back to AC power, they can adjust power from the main or a generator.

UPS systems instantly activate when there is a deviation in the input power. They are designed to provide power for a short time to protect critical systems. Generators do not respond as quickly as UPS systems but provide power for a longer period of time. The inconsistencies and fluctuations in generator voltage and frequency changes necessitate an online UPS system to adjust the unstable generator power to deliver consistent clean power to sensitive equipment.

Rotary UPS

Flywheel driven rotary UPSs do not include batteries and provide electrical support in a few seconds up to a few minutes. Unlike other UPS systems, rotary UPS systems can provide power for extended periods of time for air conditioning and lighting loads. As with mechanical generator sets, they are not ideal for IT support. The gas or diesel engine of a rotary UPS starts and maintains power. Its flywheel turns long enough for its generator to stabilize before a clutch attaches it to the generator. Rotary UPS systems are a cost effect alternative to separate generators and ensure uninterrupted cooling of critical equipment.

Flywheel UPS

A flywheel is a device that stores rotational kinetic energy to provide backup power during an outage or system shutdown. A rotary flywheel spins at speeds up to 37,000 rpm as it converts electrical energy into stored kinetic energy. When a power outage occurs, the stored kinetic energy is converted into DC power that is sent to the UPS that releases AC power. Flywheel UPSs discharge their capacity in a few seconds, which allows the changeover to backup power.

The footprint of flywheel systems is normally that of a battery system that weighs less than lead acid and nickel zinc batteries and has a weight that is similar to lithium-ion batteries. Most flywheel systems rely on mechanical ball bearings to rotate the flywheel, which need to be replaced every year. Magnetic flywheel systems use magnetic interaction where the magnets move closer or farther away to create varying degrees of resistance.

Flywheel setups have a rectifier and static bypass. When there are power changes, over voltage or power failures, the flywheel turns kinetic energy into DC power that goes through a DC bus and into an inverter where the DC energy is converted to AC current that is sent to connected devices. The provided power lasts for a few seconds and allows for an alternate power source to take over. After which, the flywheel recharges in 15 minutes with some units able to recharge in 2 minutes.

Leading Manufacturers and Suppliers

Chapter 5: UPS Batteries

Uninterrupted power supply batteries are an essential part of a UPS system. They are the stopgap measure designed to briefly supplement power when the main power source fails. UPS batteries are a key feature in the instantaneous response to power outages and are critical to the protection of sensitive electronics and devices.

There are three types of batteries that are used in UPS systems, each of which has a different cost, life expectancy, and maintenance requirements. Understanding these factors is critical to the selection of a UPS system. It is important to note that battery technology is constantly changing as new and innovative ways to use batteries are being introduced. When examining battery options, it is important to understand the difference between battery design life and battery service life, factors that UPS manufacturers explain.

Battery Design Life – Battery design life is in regard to cell design, which is determined by a UPS manufacturer and varies according to the type of battery. The design life of a battery is impossible to guarantee since it is influenced by the battery service life factors of environment, temperature, maintenance cycle, discharge cycles, and charging. Good quality batteries last 9 to 10 years but may need replacement in 6 to 8 years.
Battery Service Life – A battery’s service life is the most important factor in regard to battery selection and is influenced by real life usage of a battery. Battery service life is critical for UPS systems since it determines when a UPS battery will need to be changed. In sensitive and critical situations, UPS batteries need to be regularly checked and monitored.

UPS manufacturers work with their customers to design a UPS system that fits the specific requirements of their customers. Since battery life is an essential aspect of UPS systems, manufacturers clearly outline the advantages of each type of battery and its relevance to the customer’s operation.

Lead Acid Batteries

The two types of lead acid batteries are valve regulated (VRLA) and vented (VLA), which vary in their structure and performance. VRLA batteries are batteries that have been sealed with polypropylene to prevent leakage. They have a valve for releasing gas pressure. The service life for VRLA batteries is around five years.

VLA batteries are normally encased in a clear enclosure that makes it possible to check levels of liquid electrolytes and the condition of their lead plates. They have a much longer life than VRLA batteries, up to 20 years, and are resistant to overcharging. VLA batteries are seldom used due to their large footprint and high cost. They require special housing and present significant safety concerns.

Nickel Cadmium (NiCad) Batteries

Nickel cadmium batteries consist of nickel oxide hydroxide, metallic cadmium electrodes, and a potassium hydroxide electrolyte solution. They are very popular with emergency backup systems. NiCad batteries have a high energy density, which is lower compared to newer batteries, but can still store significant amounts of energy. The long-life cycle of NiCad batteries provides consistent support for UPS systems.

An attribute that enhances the usefulness of NiCad batteries is their resistance to temperature shifts, which enables them to survive in hostile environments. Their fast charging makes them ideal for UPS system usage. NiCad batteries are large and bulky, a factor that prevents them from being used in tight spaces. In addition, they contain toxic chemicals that present safety concerns and make their disposal and recycling difficult.

Lithium-Ion Batteries

Lithium-ion batteries are smaller, lighter, and have fast charging times due to their high-power density. They have built-in monitoring systems that check every cell to provide data on the health of the battery and its performance. Lithium-ion batteries generate less heat and can operate at significantly high temperatures without the need for air conditioning or fans for cooling. They are the newest form of UPS battery and the highest priced. Lithium-ion batteries have a longer service life than any other form of battery and require very little maintenance.

With lithium-ion batteries, lithium ions move between the cathode and anode of the battery as electrons move in the opposite direction. The movement creates electrical current. When the battery is charging, the movement is in the opposite direction where the lithium ions are released by the cathode and accepted by the anode. Although lithium-ion batteries can use a variety of materials for their electrodes, the most common combination is lithium cobalt oxide for the cathode and graphite for the anode.

Factors that Affect Battery Life

As stable and strong as UPS batteries may be, they are affected by external factors that reduce their useful life and lead to failures. Batteries with an advertised life of 5 years normally are replaced after two or three years of use. Having knowledge regarding the factors that shorten the life of batteries assists in ensuring the performance of a UPS.

Temperature – As with many types of equipment, ambient temperature is the most common reason for battery failure. High temperatures cause quicker chemical reactions and increase water loss and corrosion. The accepted paradigm is that service life is reduced by 50% for every 10°C (50°F) increase above a battery’s recommended temperature.
Frequency of Discharge – After a UPS runs during a power outage, it recharges, which is known as the discharge and charge cycle. All UPS batteries are designed for a set number of discharge and charge cycles. The number of cycles a battery completes reduces its capacity depending on the depth of the discharge with slightly discharged batteries lasting longer than ones that are fully discharged.
Operational Voltage – UPS batteries have a charging voltage rate. Charging them beyond that rate leads to damage and a shorter service life. Overcharging produces excessive hydrogen and oxygen gases that cause internal dry out or thermal runaway. By comparison, undercharging causes sulphate crystals to form on a battery’s plates that harden and damage a battery.
AC Ripple Current – AC ripple current, generated by the rectifier, charger, or inverter, causes overheating in a UPS that speeds up the deterioration of battery poles and failure of a UPS battery. Ripple current is a non-sinusoidal waveform and is due to the incomplete suppression of the alternating waveform.
Battery Left Totally Discharged – Batteries that are left on 0% after discharge can be damaged if not recharged. It is one of the reasons for sulphation, which prevents recharging.
Battery Application – Different batteries are designed for different applications. Those for UPS systems deliver a high rate of voltage for a short period of time, which is a few minutes. Other forms of batteries provide hours of power and work independently. If long lasting batteries are used in a UPS system, they won’t perform as well as ones designed for that purpose.

Chapter 6: Types of Power Supply Problems

In the event of a power outage, electric current or waveform changes from its normal operational mode to a deviation, which differs in accordance with the type of power supply problem. Although the most common form of power problem is a black out, there are other, more common ones that produce unconventional power currents or waveforms.

Power Surges or Spikes

During a power surge, there is a sudden increase in voltage that is way higher than normal. Surges cause overloads that damage electronics by overheating internal components. They happen for various reasons, which include power grid switching, transformer malfunctions, or lightning strikes. UPS systems react to power surges in the same way they react to blackouts by switching to battery power to protect sensitive equipment. Such a reaction is necessary since mains are susceptible to any type of disturbance that can cause damage.

Brownout

A brownout is a drop in voltage for an extended period of time. They are like sags but last much longer and are serious. Brownouts occur when the main supply is unable to cope with the load demand, which causes generating companies to drop network voltage. Depending on the circumstances, brownouts can last several hours. The main reason for brownouts is to reduce strain on power resources and to avoid blackouts.

Sags

Sags are drops in the main power supply that can last for several cycles. They are caused by negative spikes, but last longer. Sags are common occurrences and are due to switching on large loads. If the main voltage falls very low, sags can cause computers to shut off. The drop in voltage of a sag is 10% or more below the nominal main supply. If the sag is low enough, it causes data and voice processing hardware to fail or reboot. During a sag event, power supply units (PSUs) draw down more current, which places additional stress on components and leads to a buildup of heat.

Over Voltage

Over voltage is when an electrical circuit exceeds its normal level, causing damage to components. Circuits and circuit elements have a design limit. When voltage exceeds that limit, a circuit is experiencing an over voltage. The duration of over voltages varies from passing through to being permanent. The causes of over voltages are lightning strikes, switching surges, or faults in the main power supply. The results of an over voltage take many forms from insulation breakdowns to damage to highly sensitive equipment.

Harmonic Distortion

Harmonic distortions are caused by non linear loads that draw peak currents from the main. They are generated by rectifiers, switched mode power supplies, and rotating machines, which include computers, copy machines, laser printers, and variable speed motors. Harmonic distortions cause a rise in current that increases temperatures and component failures due to overheating.

Electrical Noise

Electrical noises are unwanted electrical signals that get into circuits. They occur in power and signal circuits where they disrupt signals. Data and signal circuits are most vulnerable to electrical noise because of their operating speed and low voltage level. As signal voltage gets lower, they are less capable of enduring electrical noise. Signal to noise ratios indicate the level of noise a circuit can tolerate before a valid signal becomes corrupted.

Blackout

A blackout is a total failure of the main supply shutting down every aspect of a system and comes without warning, lasts for long periods, and is caused by severe weather or catastrophic equipment failures. They are a major inconvenience that disrupts working conditions and social functions. Aside from being inconvenient, blackouts can be dangerous in that they interrupt the function of medical devices, shut down utilities, and damage computers and IT functions.

Unlike other electrical disruptions, blackouts affect large areas and regions and have several causes with heavy winds and severe storms being the most common. Other causes are accidents on a power grid, such as power poles and power lines being knocked down or when too many high powered appliances are running. The danger of black outs is due to the time it takes to rectify the results of a black out, making work and living conditions difficult.

Chapter 7: Regulations Regarding UPS Systems

The regulations for uninterrupted power supplies take several forms and include Electromagnetic Compatibility (EMC) compliance, performance standards and limitations on the impact of a UPS on a network. For UPS systems that use lead acid batteries, there are a separate set of regulations regarding selection, safe operation, testing, maintenance, and replacement. Other oversight regulations include UPS installation, environmental protection standards, writing regulations, equipotential bonding, and earthing.

UPSs must comply with low voltage EMC directives and regulations that fall under that purview. UPS Standard EN62040 or International Electrotechnical Commission Standard IEC62040 is in regard to movable, stationary, fixed, pluggable, and permanent UPSs. The UPS topologies covered by EN62040 are offline - VFD, line interactive - VI, and online - VFI.

The testing of UPSs is broken into two types of environments, which are classified as first environment and second environment. First environment classifications is for UPSs that are used in homes, commercially, and light industry while second environment classifications is for light industry and heavier industrial locations.

EN60240 - IEC60240

The three parts of EN60240 are general and safety requirements, electromagnetic compatibility, and performance and test requirements.

EN 62040-1:2008 - General and Safety Recommendations

General and safety recommendations relate to electrical storage devices in a DC link and are used in combination with EN60950, safety of information technology equipment including electrical business equipment, which is a reference document (RD). It stipulates that the primary function of a UPS is to ensure the continuity of an AC source and improve the quality of the power source by meeting specified characteristics. This standard ensures the safety of the UPS units as they adhere to manufacturer installation, operating, and maintenance specifications.

En 62040-2:2006: Electromagnetic Compatibility (Emc) Requirements

This EMC standard is in regard to single UPSs that are operator accessible and connected to industrial or public low voltage networks. UPSs, under this standard, ensure a sufficient level of EMC compatibility in public and industrial locations. It allows for tests that include physical size and power ratings. EN 62040-2:2006 is for standalone products not connected to a larger system.

En 62040-3:2011: Method of Specifying the Performance and Test Requirements

EN 62040-3:2011 is for movable, stationary, and fixed UPSs that deliver single or three phase AC output voltage that is less than 1000 VAC and have energy storage systems connected by a DC link. The purpose of this standard is to ensure the purity of the AC power source. This standard applies to:

Single or three-phase, fixed frequency, 50/60 Hz AC output voltage
Single or three-phase input voltage
Storage devices in the DC link
Rated voltage less than 1000 VAC
Movable, stationary or fixed equipment

The standard includes equipment characteristics, testing methods, and the various levels of acceptable performance.

Conclusion

An uninterruptible power supply is a short term backup power supply for critical systems during a power outage to ensure components and devices can continue to operate or be shut down safely.

A UPS is a safety device that is designed to protect equipment from damage and is used to provide power to sensitive electrical devices that can be damaged by power loss.

UPSs are typically used in settings that have computer systems, data servers, and mission critical equipment, such as medical devices and laboratory systems.

The energy for UPS systems is stored in different ways with rechargeable batteries being the most common. Mechanical devices that produce stored kinetic energy are also used as a stopgap during power losses.

Battery powered UPSs have a rectifier, inverter, one or several batteries, a static bypass, and control unit all of which are plugged into the main power supply and activate when a power fluctuation is detected.

The three types of UPS systems are single conversion, double conversion, and multi-mode, which are also known as standby, online, and line interactive with multi-mode being a combination of two of the three basic types.