Classification (Types) of Uninterrupted Power Supply (UPS Wiki)

Types Of UPS
UPS is an acronym for Uninterrupted Power Supply which is an alternative source of power supply which provides an interruption free supply to sensitive electronic equipment like Personal Computers and Super Computers etc.  You can read this article to know more about U.P.S.
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Now we are going to discuss the types of UPS, that is classification of Uninterrupted Power Supply. Uninterrupted Power Supply can be classified as:
  • On the Basis of their Output Power
  • On the Basis of their Working
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  1. On the Basis of their O/P Power: On the basis of output power, the UPS system may be classified into two types:
    (1) Low Power Rating UPS and
    (2) High Power Rating UPS
    The output power of a UPS is rated in KVA i.e. Killo Volt Ampere. The UPS system can be classified on the basis of power to be handled by it. For a single personal Computer or any other single sensitive device, we can use UPS of small rating. But if we have to install a UPS system in a lab or for a network of
     computers then we have to select one having high power rating. The power rating simply determines the maximum power to be handled by UPS.  We should choose power rating of the UPS according to our need. For example if we uses low power rating UPS for a number of Computers then it can't handle the power flow through it and thus lead to destruction.
  2. On the Basis Of Working: On the basis of working, the UPS System may be classified into three types, given as:
  • On line UPS
  • OFF line UPS
  • Line Interactive UPS
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Online UPS:  In online UPS, the internal circuitry of UPS is sorted as:
AC Mains->Rectifier (Charger)->Battery->Inverter->Load
As shown above, we can see that there is no link between Mains AC Supply and Load in ON line UPS . The load get power supply from Inverter whether the main supply is ON or OFF.(Although, we can draw an AC line directly from AC mains to load, in case our inverter stop working due to any reason. Then we have to use transfer switch which will transfer control of power from inverter to direct AC mains)  In this type of UPS, the inverter works continuously therefore this type of UPS are also called Continuous mode UPS.
When the Mains AC Supply is ON, the rectifier circuit converts incoming AC into DC, which is fed to battery. Battery gets charged by this DC supply and the output of rectifier is also fed to the inverter. Inverter circuit do the invert of rectifier. That is it converts incoming DC signal to AC. Then this output of inverter is fed to the load. In this type of UPS, the load is isolated from AC mains so there is no affect of interrupted (mains) power supply on the load.
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When the Main supply is OFF. Then rectifier stop its operation as there is no incoming AC signal to convert into DC. But the whole process takes place similarly. The bank or batteries provides power to inverter. As the output of batteries are in DC, So the inverter converts DC into AC and this inverted AC is fed to load for its operation. Now depending on the type and quantity of batteries, the UPS can give power to the load for a specific time. This time is called Back up time. The back up time of commonly used UPS is 15 to 40 minutes.
Advantages of ON-line UPS: They gives very good continuity of power supply and protection.
Dis-Advantages of ON-line UPS: Following are the main dis-advantages of ON-line UPS:
  • Heavy in Weight
  • Requires Large Space
  • More Costly
OFF-Line UPS: The only difference between ON Line and OFF line UPS is that in Offline UPS load has a direct link to ac mains via a static switch, while having other same circuitry. In case of  OFF line UPS, the inverter doesn't remains it ON state as ON line UPS, Instead it comes to On only when the Main supply gets OFF. When the main supply is ON the load derives power directly from AC supply. When the Mains AC  supply gets OFF, then inverter come to play and convert incoming DC supply from Batteries to AC. This inverted ac is then fed to load. Here we make use of static switch which immediately switches from one supply to another in case ac mains gets off. The switching time of OFF line UPS is almost equal to five mili seconds.
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Advantages Of OFF-line UPS: 
  • Less Expensive
  • Light Weight
  • Requires Less Space.
  • This type of UPS is mostly used for our personal computers.
Line Interaction UPS: Line interaction UPS is similar to OFF line UPS. In this type of UPS, the inverter circuit works only when there is no AC Power supply. When AC Mains are ON, the load derives current directly from Mains power supply. In case when there is some failure in AC mains then the inverter goes ON and inverts incoming DC signal from battery to AC. This Inverted AC signal is then fed to load. The switching time of this UPS is large than both previous UPS. This type of UPS is commonly used at our homes. The main advantage of this type of UPS is that its back up time is very high(almost 1 hour to 4 hours). So this type of UPS are used where switching time does not matter for example: Fans, Lights, TV , DVD and other home appliances.