Classification and Types of UPS


Today, we will start explaining the UPS design and sizing calculations, and as we do usually, we will start by explaining the components and main types of UPS systems.




First: Applicable Standards for UPS Systems



Throughout Our explanation of the UPS systems, we will use the following standards:


1- Standards Relevant to UPS Installations:





Marking in compliance with the following European directives:

• Low Voltage Directive 2006/95/EC

• EMC Directive 2004/108/EC

ISO/IEC 27001:2005

Information Security Standards

BS 25999-1:2006

Business continuity management. Part 1: Code of practice

BS 7698-1:1993, ISO 8528-1:1993

Reciprocating internal combustion engine driven alternating current generating sets. Specification for application, ratings and performance

ER G59/1

Recommendations for the connection of embedded generating plant to the Public Electricity Suppliers distribution systems. Energy Networks Association

BS EN 60529:1992

Specification for degrees of protection provided by enclosures (IP code) BS EN 60439-4:2004: Low-voltage switchgear and control gear assemblies

BS 7671:2001

Requirements for electrical installations. IEE Wiring Regulations. Sixteenth edition

BS EN 50310:2006

Application of equipotential bonding and earthing in buildings with information technology equipment

BS EN 60439-4:2004

Low-voltage switchgear and control gear assemblies

EN 60950:2006

Safety of information technology equipment including electrical business equipments

2- Standards Relevant to Lead Acid Batteries:




BS 6133:1995

Code of practice for safe operation of leadacid stationary batteries

BS 6290-4: 1997

Lead-acid stationary cells and batteries. Specification for classifying valve regulated types

BS EN 60896-1:1992, IEC

Stationary lead-acid batteries. General requirements and methods of test. Vented type

BS EN 60896-2:1996, IEC

Stationary lead-acid batteries. General requirements and methods of test. Valve regulated type

BS EN 50272-2:2001

Safety requirements for secondary batteries and battery installations. Stationary batteries

ANSI/IEEE 450-2002

IEEE recommended practice for maintenance, testing and replacement of vented lead-acid batteries for stationary applications

ANSI/IEEE 1184-1994

IEEE recommended guide for selection and sizing batteries for Uninterruptible Power Supplies (UPS)

ANSI/IEEE 1188-1996

IEEE recommended practice for maintenance, testing and replacement of valve-regulated lead-acid (VRLA) batteries for stationary applications



What is a UPS?


A UPS is a combination of convertors, switches and energy storage devices (for example, batteries), Constituting an alternate or backup source of power for maintaining continuity of critical loads power in case of input power failure.





Why do we need a UPS?


The two main functions of the UPS are:

  1. Ensuring continuity of an alternate power source,
  2. Improving the quality of the power source by keeping it within specified characteristics.




1- Ensuring continuity of an alternate power source:


An UPS can be considered as a source of standby power or emergency power depending on the nature of the critical loads.


Typical critical loads are:

  • Computers – e.g. data processing and control systems
  • Industrial process equipment – e.g. precision manufacturing
  • Medical equipment – e.g. life support and monitoring systems
  • Telecommunications network equipment – e.g. PABX
  • Point of sales (POS) terminals – e.g. retailing environment
  • Online business transactions – e.g. internet shopping.
  • Emergency lighting for evacuation,
  • Emergency perimeter lighting for security.





2- Improving the quality of the power source by keeping it within specified characteristics.


  • Any power system may face a variety of issues either from generation, Transmission & Distribution (T&D) or even within a customer facility which cause disturbance in the quality of power.
  • The Power quality disturbance can be defined as the deviation of the voltage and the current from its ideal sinusoidal waveform.
  • The Power quality disturbance can affect the uninterrupted operation of customer loads, reduce the life of the connected loads and electrical equipment and affect other loads within the facility or even outside the customer facility.


The Power Quality Issues and Causes are summarized in the following table:






Therefore, The UPS can provides the following functions:


  • Protection of load against Line frequency variations,
  • Elimination of power line noise and voltage transients,
  • Protection of load against Voltage regulation.
  • Safe operation of equipment during sags and brownouts.


In addition, some UPS or UPS/software combinations provide the following functions:


  • Automatic shutdown of equipment during long power outages.
  • Monitoring and logging of the status of the power supply.
  • Display the Voltage/Current draw of the equipment.





UPS Rating


  • UPS manufacturers generally use VA (or kVA) to describe the UPS output ratings; this rating determines the maximum load that can continuously be supported by the UPS when the mains supply fails.
  • When selecting a UPS to service a particular load it is important that the combined load does not exceed the UPS output rating, and if the load equipment is specified in Watts it is necessary to convert this to VA in order to assess the UPS/load rating compatibility.





Classification of UPS





UPSs can be classified into many types according to the following:


  1. Voltage range,
  2. No. of phases,
  3. Mobility,
  4. Technological design,
  5. Physical Size/capacity,
  6. Form factor/ configurations,
  7. Topology,
  8. Distribution Architecture,
  9. Use of transformers.





First: According to Voltage Range





The IEC 60038 standard rates voltage ranges as; low 0-1000v, medium 1000v - 35kv, and high as anything over 35kv.


Therefore, according to voltage range, the UPS has two types:

  1. Low Voltage UPS,
  2. Medium voltage UPS.






1-    Low Voltage UPS


  • At low voltage system levels of 400 volts or 480 volts a maximum capacity of approximately 5 MVA at the common bus is reached very soon.
  • The limitation to 5 MVA is given by the current capability of bus bars and breakers of about 6000 amps on one side and the short circuit capability of the switchboards of typically 100 kA on the other side.
  • Higher ratings of both will let the costs and the dimensions of the switchgear increase dramatically while the component availability in the market is very limited. Additionally, high currents require high copper cross sections and cause rather high resistive losses, both resulting in increasing costs for power transmission. A way to reduce the currents and to enable a further increase of the power is the move to a medium voltage (MV) system level.






2-    Medium voltage UPS


  • A medium-voltage UPS is essentially the same as a standard UPS but is designed for a medium-voltage range, ranging from 1000v - 35kV. The major difference between a low voltage (LV) UPS and a medium voltage (MV) UPS is the source voltage. Both systems will store power in the event of a power outage. Both systems filter the incoming voltage to provide clean source voltage to the downstream devices. A typical MV UPS is used for data centers or any mission-critical facility requiring clean, constant electrical power.
Medium voltage ups

  • For example, at a typical MV level of 13.2 kV, the maximum system power rises up to 27 MVA using a standard MV breaker size of 1200 amps and up to 57 MVA with a breaker size of 2500 amps. Medium voltage levels go up as high as 34.5 kV, allowing a system power rating of up to 70 MVA.

  • The transition from low voltage (LV) to medium voltage (MV) level is a natural progression of power protection for large critical power facilities. The approach offers three main benefits as follows:

  1. Increased reliability because the MV design approach comes with larger protected load blocks, lower switchgear count and the operating culture of medium voltage systems.
  2. Reducing the costs because installing the power protection at the MV level provides the most energy efficient configuration as the lower currents at this voltage result in smaller cables and lower losses. 
  3. Reducing the floor space for infrastructure equipment like power supplies results in additional space for IT or manufacturing equipment. Often the available area for the UPS system is given and limited, particularly in existing buildings, but the required power is increasing.





Second: According to No. of phases





The input/output phase configurations of UPS systems are available in:


  1. Single-phase configuration (1/1) or
  2. Three-phase configuration (3/3 and 3/1).


The common phase configurations for UPS are:


ups no. of phases





1-    Single Phase UPS System (1/1)

  • A single phase installation consists of two wires where AC voltage is a single sine wave. The standard voltage of single phase varies in different countries or regions. The standard single phase voltage in America is 120V and Europe, Asia or other regions take 230V as a standard voltage.
  • Single-phase uninterruptible power supplies typically cover requirements up to 20 kVA and are used for smaller installations such as rack-mounted servers, telecoms or computer systems, and network switches, along with any device that runs directly from a standard three-pin plug.  
  • A 20kVA output is generally the largest single phase UPS system available. This is due to the output amperage and cable requirements. 20kVA=20,000VA / 230Vac = 86.9Amps.





2-    Three Phase UPS System (3/3 and 3/1

The three phase UPS can be subdivided into:

  1. Three phase input/three phase output UPS system (3/3),
  2. Three phase input/single phase output system (3/1).

  • If you need to connect to a three phase supply, you must need a UPS with a 3/x configuration. A 3/1 UPS takes in 3 phase power but delivers single phase to the downstream load while a 3/3 UPS not only takes in but also puts out 3 phase power.
  • Three-phase UPS are the standard choice for larger installations with critical loads such as data centers, industrial applications, and medical environments, as well as protecting equipment with motors such as lifts, pumps, and fans.  
  • With a three-phase system, consideration should be given to phase load balancing and load power factors to minimize the imbalance in the output voltage.


Three-phase power

Single-phase power

common in most large businesses and high-density data centers with higher kVA and rack applications.

Used in most residential homes and small businesses.


Used for a wide range of general applications.

Used for applications requiring greater than 1000 watts.

Is the most efficient for units up to 1000 watts.


Used to balance the loads on the utility power of the building.


Is safer and more cost effective to run.


The standard for locations where three-phase power is unavailable.

Delivered in a steady stream at a constant rate.


Not delivered at a constant rate.






Third: According to Mobility





UPS can be classified according to Mobility to:


  1. Movable,
  2. Stationary,
  3. Fixed,
  4. Building-in.





1- Movable UPS (transportable):

An UPS that is either 18 kg or less in mass and not fixed comes usually with wheels, castors or other means to facilitate movement by the operator as required to perform its intended use in different locations.

2- Stationary UPS:

An UPS that that exceeds 18kg and is not provided with a carry handle or wheels.

3- Fixed UPS:

An UPS that is fastened to a support or otherwise secured in a specific location, e.g. open Rack or Stand.

4- UPS for “building in”:

An UPS intended to be installed in a prepared recess such as a cupboards, closed racks etc.





Fourth: According to Technological Design





The design technologies of ups systems are different and can be classified into two main types:


  1. Static UPS,
  2. Rotary UPS.





1-    Static UPS


  • The static UPS is called “static” because, throughout its power path, it has no moving parts (although it has auxiliary moving parts, such as cooling fans).

static ups

  • The rectifier inside of the static UPS converts the incoming utility AC current to DC, and the inverter converts DC back to clean sine-wave AC to supply the load.
  • The DC current interfaces with the “energy storage” medium – most commonly batteries, in which case it charges the batteries and receives power from the batteries when the utility power supply is distorted or fails.





2-    Rotary UPS


  • The rotary UPS is called “rotary” because rotating components (such as a motor-generator) within the UPS are used to transfer power to the load.

rotary ups

  • Rotary technology has been utilized for many years especially in the following conditions:

  1. When loads would commonly exhibit a low power factor (which resulted in increased losses in the power distribution system and thus, an increased energy cost),
  2. When loads would commonly exhibit high harmonics (which prematurely shortened the life of transformers and capacitors),
  3. When loads would commonly exhibit high voltage dips and sags for example when large motors turned on, Users would experience the dimming of lights

Thus, the introduction of the rotary UPS to address this issues.





2.1 Types of Rotary UPS

The rotary UPS has two main types as follows:


  1. Motor-generator / battery rotary UPS,
  2. Engine-coupled rotary UPS.





2.1.1 Motor-Generator / Battery Rotary UPS

  • When the utility power quality (voltage and frequency) falls within an acceptable range, then the motor component of the rotary UPS is driven directly from the utility. That motor then provides mechanical power to the generator component of the motor-generator to support the critical load with clean power. Also, the rectifier / inverter unit operates in stand-by mode during the time the utility is stable. That is, the rectifier is in “battery float” mode (the batteries get charged).

Motor-Generator / Battery Rotary UPS

  • When utility voltage and frequency parameters fall outside of preset limits, then the rectifier / inverter unit begins to provide controlled power to the motor which is coupled directly to the generator to support the critical load. When a blackout occurs, the battery bank provides necessary power via the inverter to the motor-generator to support the load. The stored energy within the batteries provides sufficient ride-through to sustain the load until the standby generator (outside of the UPS) comes up to full operating speed.





2.1.2 Engine-Coupled Rotary UPS

  • The key components of an engine-coupled rotary UPS include the following: a motor-generator, a choke, a flywheel, a mechanical clutch, and a diesel engine.

Engine-Coupled Rotary UPS

  • Under normal operation, the utility feeds power to the critical load via the filter (made up of the choke and motor). The same motor also provides the necessary power to the flywheel to retain kinetic storage of energy in case of emergency.
  • During failure mode, power is supplied by the flywheel to the motor-generator unit, which in turn supports the critical load for a few seconds before the diesel engine runs up to full speed. The clutch is then engaged to provide mechanical power to the motor-generator to supply continuity of power to the load.





2.2 Comparison Of Static and Rotary UPS Architectures


The range of applications for static UPSs is broad while the application ranges of rotary UPSs are more limited. In the domain of the data center, static UPSs represent the technology of choice. Rotary UPSs become more competitive in very large multiple megawatt data centers.



Comparison Of Static and Rotary UPS Architectures



In the next Article, I will continue explaining other classifications of UPS. So, please keep following.



  1. Thanks Eng. Hassan For All your Effort. Very Interesting Information. Hope you More Successful

  2. I have learned some useful specifications details to consider when am planning on buying a UPS device. Thanks for sharing.

  3. Very Useful technical Artical, Thanks Eng. Hassan.