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UPS - Uninterruptible Power Supply

UPS - Uninterruptible Power Supply

Today, a continuous power supply is the basic necessity of humans. The application of electricity is wide and seen in all industries, domestic appliances, and hospitals. If a power supply is hindered, it causes a delay in production and inconvenience that causes loss to the organization. Hence, it is necessary to have an alternative power supply to avoid such a situation in case of power failure. Therefore, the Uninterruptible Power Supply (UPS) is invented to be used in a power failure. It saves everyone from the losses that occur if there is a sudden power disruption.

What is Uninterruptible Power Supply?

UPS, also known as the Uninterruptible Power Supply, is an electrical device used to maintain a continuous power supply to any electrical device in case of a power failure.

UPS saves us from the power surges by continuously establishing a connection to the computer and keeping it running even after power failure. It differs from the other power backup devices like batteries and supercapacitors. The UPS can supply power only for a short period sufficient to keep the device safe or facilitate it to shut down properly to avoid damage.

The Main Components of a UPS System

The four main components of the UPS system are listed below:

  1. Rectifier: The function of the rectifier is to convert the AC (Alternating Current) to the DC (Direct Current). Another function of the rectifier is recharging the batteries. The battery chargers are separately added to the rectifier module in an uninterrupted power supply greater than 3 KVA. In an uninterrupted power supply of less than 3 KVA, the rectifier and the battery charges are a single unit.
  2. UPS Batteries: The role of the battery is to provide an emergency power supply in case of failure. Rectifiers or chargers are used to keep the batteries charged. A string of batteries or batteries connected in series is used in the UPS system. Hence, failure of a single battery means failure of the string. Small UPS systems consist of internal batteries, whereas large UPS systems have separate cabinets for batteries.
  3. Inverter: The inverter converts the DC voltage to the AC output. AC output is then used to power the critical loads. Inverters help in smoothening the surges, electrical noise, sags, spikes, etc. As a result, the output obtained is a pure sine waveform.
  4. Static Bypass Switch: The main function of the static bypass switch is to act as a safeguard in case the UPS system fails. In such a condition, a static bypass switch will bypass the rectifier, inverters, and batteries, and hence it will connect the system to the main supply. However, this arrangement is not ideal as it will have unfiltered power, but it is useful to continue the functioning while the UPS system is being repaired.
  5. Other components of UPS system: Other components of a UPS system vary depending upon its size and type, and it may include components such as fans and capacitors.
    1. External Maintenance Bypass is used to keep the load uninterrupted while the UPS is being replaced or removed.
    2. Transient Voltage Surge Suppressors
    3. Simple Network Management Protocol
    These can be used for monitoring and communications applications.

How Does a UPS Protect Computer?

Certain specifications are necessary for the computer to function continuously, and deviation in these specifications causes the power supply to fail, and the computer stops working. The use of a UPS is to protect the data and any work on the computer while there is a power problem. These power problems are:

  1. Voltage Surges and Spikes: Greater voltage on the line than the desired voltage.
  2. Total Power Failure: In cases when the fuse blows or the line goes down.
  3. Voltage Sags: Line voltage is less than the desired voltage.
  4. Differences in the frequencies: When the frequency of oscillation of the power supply differs from the desired frequency.

Different types of Uninterruptible Power Supply

UPS system accommodates a complete range of applications using its three types which cater to the demands of enterprises and the customers. The three types are;

  1. Standby UPS
  2. Line Interactive UPS
  3. Online UPS

All three devices operate during power failure; however, they may differ in their operations.

1. Standby UPS:

UPS - Uninterruptible Power Supply

Standby UPS is a type of UPS that is an offline unit. It can detect an electrical failure and automatically switches to the battery-powered mode. Through a direct AC connection, in normal conditions, hardware receives utility power. Common uses of standby UPS include computers, modems, VoIP equipment, etc. Standby UPS is the least expensive among the three UPS types.

2. Line Interactive UPS:

UPS - Uninterruptible Power Supply

UPS is capable of regulating voltage automatically; it also responds to the conditions of high and low voltage. It supports the system at the time of outages. During outages, it converts the battery power into AC for the continuation of the operations.

IT Applications of Line Interactive UPS System: The line interactive system safeguards sensitive equipment during burnouts or blackouts. In this system, units are expensive as compared to the standby system. However, these are cost-effective when compared to the online UPS system. It protects in situations such as short-term power failure or low voltage conditions. Additionally, in cases of a long outage, the battery power of the line interactive UPS system allows the device to shut down safely.

3. Online UPS:

UPS - Uninterruptible Power Supply

Double or Delta conversion technology is used in the Online UPS system. AC power is carried to the rectifier to become DC power. Hence the network does not receive electricity from the AC outlet directly. It is then carried to the inverter. Afterward, its inversion takes place to AC, and this power is delivered to the equipment. The online UPS system provides continuous clean power to the equipment. Online UPS system costs more as compared to the standby and line interactive UPS systems.

Online vs Line Interactive UPS

Knowing the difference between the online and line interactive UPS is a must before buying it as an alternative for outages. The line interaction UPS is a version of basic standby UPS with an autotransformer.

Comparison of Different Types of Uninterrupted Power Supply

Standby / Offline UPS
  • The battery is not used continuously. Hence, high efficiency.
  • Less cost due to simple design.
  • The simple design of the controller.
  • Sag and spike protection is limited.
  • If the main fails, there will be transfer time from the main to the inverter, usually 5-10 milliseconds.
  • The output is not reliable.
Line Interactive UPS
  • It is best suitable for the light sags and surges that range from 10% to 20%.
  • Less cost of operation due to less consumption of electricity.
  • The switching time is zero.
  • It is larger and heavier as compared to the online and offline UPS.
  • Battery power will be used frequently in case of unstable AC power.
Double Conversion / Online UPS
  • The switching time is zero.
  • It is a completely reliable option in the cases of spikes, electrical noise, sags, and power failure.
  • Cost is higher due to complicated design.
  • UPS heats more.
  • Inverter remains on always. Therefore the overall efficiency is low.

Advantages and Disadvantages of UPS


  • The zero-time delay between the power supply switching and UPS.
  • Critical instruments are supported better as compared to the generators.
  • The customers can choose the type and size of the UPS according to the power they wish to supply to a device.
  • UPSs are easier and cheaper to maintain as compared to generators.


  • UPS runs on battery; hence these are not useful to run heavy appliances.
  • Battery replacement is required on a regular basis if substandard batteries are used.
  • Installations of UPS must be done by professionals.

Choosing an Uninterrupted Power Supply

We may sometimes need to buy a new UPS or replace the existing one. In such conditions, we must know how to choose an appropriate UPS for our devices. Choosing a proper uninterrupted power supply is extremely important, and it depends upon the load required and battery autonomy.

  1. Required Load: To establish the power required, it is required to separate the critical loads from the non-critical ones. Hence for determining the UPS topology, it is essential to establish the load requirement.
  2. Battery Autonomy: It is the second factor that must be considered while selecting a UPS. It includes parameters such as runtime required for the safe shut down and space for installing the batteries.

Other Factors

Following are some of the other factors that must be considered before choosing a UPS:

  1. Installation configuration: Installation configuration must be decided before choosing your UPS. Such as a parallel system N+1.
  2. Installation environment: The location and environment are important considerations when choosing a UPS, and UPS can be rack-mounted or a freestanding tower. However, the best environment for the UPS is a well-ventilated room with a controlled and consistent temperature.
  3. Maintenance of UPS: Front panel access and side panel access of maintenance should be identified to choose the UPS.
  4. Warranties: UPS systems have two to three years of warranty according to the industry norms.
  5. Accessories: Other accessories such as bypass switch, BMS connection, depending on the requirement of the networking and communications.
  6. Features: Features such as touch screen display and different operating modes such as smart active mode must be considered when choosing a UPS.

Alternatives of UPS

There are many alternatives to the UPS which will help keep your computer running during power failure. Some of these are discussed below in brief:

  1. Generator: Devices that convert mechanical energy into electrical energy are known as electric generators, also known as a dynamo. It is used to power devices such as automobiles, aircraft, ships, etc.
  2. Surge Protectors: These devices are used to protect electrical appliances during power surges and voltage spikes. It protects the device by blocking voltage at a constant value which is known as the safe threshold.
  3. Power Inverters: Power inverters are used in automobiles to enable the use of large electronic devices in the vehicle. These are useful, especially for the devices that require a proper plug for its operation or charging. The main function of a power inverter is to convert the direct current (DC) into alternating current (AC). Nowadays, the application of power inverters has increased in other areas such as air conditioning.
  4. Automatic Surge Protectors: Surge protectors are used to protect devices against overvoltage conditions. Generally, it is used in parallel with the power supply of the device, which is to be protected against overvoltage.

Comparison of UPS with Alternatives

There are many alternatives to supply power to devices when power surges, spikes, or power loss occurs. However, UPS has advantages over some of the alternatives. Therefore, it can be used if the requirement of the system matches the features of UPS.

UPS VS Generator

Generators are useful to keep the device running for a long period of time, whereas UPS keeps the device running for a short period of time. The reason behind this is that the UPS is powered by batteries, whereas the generator is powered by fuel. Another difference between UPS and the generator is that the UPS starts after the power is lost, and however, the generator takes time to start. Therefore, UPS is useful when a continuous power supply is required and generators can be used where power loss is often and for a long time.

UPS VS Surge Protectors

The use of surge protectors is in conditions such as voltage spikes, power surges, etc. However, Suppressors or power surges cannot be used during power outages and main supply power cuts. UPS, unlike surge protectors, work in the condition of supply cut from the mains.

UPS VS Inverters

Power inverters are used for the conversion of the direct current to the alternating current. These take input as the DC and produce output as AC. One or more batteries are used to store power for the power inverters to function at the time of power failure. Using power inverters during power failure will cause a delay in the power transfer from one source to another.

AVRs, also known as automatic voltage regulators, are used to control fluctuations in the voltage. It is used in power converters and inverters.

Single Phase and Three Phase UPS System

Single-phase UPS: Single-phase UPS is the one that has single input and output. It requires only conductor and neutral wire to complete the circuit along with one sine waveform. The 1-phase type of uninterruptible power supply is used for installations that are small such as network switches, rack-mounted servers, and telecoms or computer systems. In addition to this application, it can also be used for devices that require a three-pin plug.

Three-Phase UPS: This type of UPS system is a 3-phase system. Three-phase UPS utilizes three out of phase sinewaves for providing continuous power to load, and these waveforms are spaced at 120-degree to each other. Hence, a three-phase system requires three conductors and a neutral wire, and it supports single-phase and three-phase output.

Applications of three-phase UPS generally include large installations such as industrial applications, data centers, hospitals, and protection of lifts, pumps, and fans. Such equipment needs to be protected as they have motors.

Comparison of Single-Phase and Three-Phase UPS

  • The Single-phase UPS system is of rating 10 KVA whereas, in UPS of three-phase, the rating is dependent on the number of output phases. It is 20 KVA or 3:1; 200 KVA or 3:3.
  • Single-phase UPS has one conductor, and three-phase UPS has three conductors.
  • The number of sinewaves is three in three-phase UPS compared to the single-phase UPS with one sinewave.
  • The voltage of the three-phase is 415V whereas that of the single-phase is 230V.
  • Three-phase UPS is much more complicated than single-phase UPS.
  • The efficiency of three-phase UPS is greater than that of single-phase UPS.

The comparison of the single-phase and a three-phase UPS is presented above. It will help evaluate both and choose the UPS according to the requirement.

Working of a Transformer-based and Transformer-free UPS

The use of a transformer in a UPS system is to step up the levels of AC voltage, provide protection during load disruption and galvanic isolation. In the traditional type of UPS. The flow of power to the output is via rectifier, inverter, and transformer.

The operation of the transformer-less UPS is similar to that of the transformer-based. However, insulated-gate bipolar transistors (IGBTs) are used in transformer-free UPS. These are advantageous as they eliminate the need for a transformer after the inverter. They are also capable of dealing with high voltages, improving the efficiency of the uninterruptible power supply.

Although advancement in technology has increased the energy efficiency of transformer-based UPS, transformer-less UPS systems are extremely beneficial for lower load conditions. Transformer-based UPS are now 95-96% efficient.

Advantages of Transformer-based UPS

The transformer-based UPS is advantages as in such a system, the points of failure are fewer. Additionally, it provides separation between input and output, known as galvanic isolation. The galvanic isolation provides protection from spikes, surges, and electrical noise if these are generated. Transformer-based UPS is the choice for 100 KVA and above. It is generally used for large installations. Some of the benefits of the transformer-based UPS are listed below:

  • Dual load protection
  • Galvanic isolation
  • Increased robustness
  • The mains power supply is independent
  • Phase-neutral inverter short circuit current is higher than a phase-phase short circuit current
  • Power protection is superior
  • Reduced power quality problems

Advantages of Transformer-less UPS

Transformer-less UPS is beneficial because it doesn't require a bulky and large transformer. Therefore, the heat generated is also less as compared to the UPS with a transformer. Moreover, transformer-less UPS is cost-effective as the transformer costs more. Some of the other benefits of a UPS without a transformer include the following:

  • Size and weight are significantly reduced. Hence, more space will be available at the data centers.
  • Energy efficiency is high as compared to that with the transformer.
  • Noise level and heat are lower.
  • The cost of installing, running, etc., is lower.

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