UPS in Electrical System

Uninterruptible Power Supply 

     An Uninterruptible Power Supply (UPS) is defined as a piece of electrical equipment which can be used as an immediate power source to the connected load when there is any failure in the main input power source.
    When there is any failure in main power source, the UPS will supply the power for a short time. This is the prime role of UPS. 

TYPES of UPS

1. On-line UPS
2. Off- line UPS 
3. Line interactive UPS 
4. Standby on-line hybrid UPS
5. Standby-Ferro on-Line UPS
6. Delta conversion On-Line UPS

Off-line UPS

Block Diagram

      When the power breakage occurs, the transfer switch will select the backup source (shown in dashed path in figure ). Thus the stand by system will start working only when there is any failure in mains.

   
      In this system, the AC voltage is first rectified and stored in the storage battery connected to the rectifier.

     
     When power breakage occurs, DC voltage is converted to AC voltage by means of a power inverter, and is transferred to the load connected to it.

   
     The transfer time can be about 25 milliseconds to detect the utility voltage that is lost.This is the least expensive UPS system and it provides surge protection in addition to back up.

On-line UPS

Block Diagram

     Here, first the AC input is converted into DC by rectifying process for storing it in the rechargeable battery. This DC is converted into AC by the process of inversion and given to the load. 

     This system is a bit more costly due to the design of constantly running converters and cooling systems.

    When there is any power failure, the rectifier have no role in the circuit and the steady power stored in the batteries which is connected to the inverter is given to the load by means of transfer switch. 

    Once the power is restored, the rectifier begins to charge the batteries. To prevent the batteries from overheating due to the high power rectifier, the charging current is limited. During a main power breakdown, this UPS system operates with zero transfer time. 

Line Interactive UPS

Block Diagram

     For small business and departmental servers and webs, line interactive UPS is used. This is more or less same as that of off-line UPS. 

    The difference is the addition of tap changing transformer. Voltage regulation is done by this tap-changing transformer by changing the tap depending on input voltage. 

    Additional filtering is provided in this UPS result in lower transient loss. 

Standby On-Line Hybrid

Block Diagram

       

     The Standby On-Line Hybrid is used under 10kVA which are labeled “online.” The standby DC to DC converter from the battery is switched on when an AC power failure is detected,

     The battery charger is also small, as in the standby UPS. Due to capacitors in the DC combiner, the UPS will exhibit no transfer time during an AC power failure. This design is sometimes fitted with an additional transfer switch for bypass during a malfunction or overload. 

The Standby-Ferro UPS

Block Diagram

        

 The Standby-Ferro UPS was once the dominant form of UPS in the 3-15kVA range. This design depends on a special saturating transformer that has three windings . 

    The primary power path is from AC input, through a transfer switch, through the transformer, and to the output. In the case of a power failure, the transfer switch is opened, and the inverter picks up the output load.

    In the Standby-Ferro design, the inverter is in the standby mode, and is energized when the input power fails and the transfer switch is opened. The transformer has a special “Ferro-resonant” capability, which provides limited voltage regulation and output waveform “shaping”. 

    The Standby-Ferro generates a great deal of heat because the Ferro-resonant transformer is inherently inefficient.Standby-Ferro UPS are generally quite large and heavy. Standby-Ferro UPS systems are frequently represented as On-Line units, even though they have a transfer switch, the inverter operates in the standby mode, 

Delta Conversion On-Line UPS

Block Diagram

                                        

    It is available in the range of 5kVA to 1 MW. The Delta Conversion On-Line UPS always has the inverter supplying the load voltage. However, the additional Delta Converter also contributes power to the inverter output. Under conditions of AC failure or disturbances, this design exhibits behavior identical to the Double Conversion On-Line.

    Delta Conversion technology saves energy by carrying the package, the Delta Converter moves components of the power from input to the output.

    In the Delta Conversion On-Line design, the Delta Converter acts with dual purposes. The first is to control the input power characteristics. This active front end draws power in a sinusoidal manner, minimizing harmonics reflected onto the utility. This ensures optimal conditions for utility lines and generator systems and reduces heating and system wear in the power distribution system. 

  

   The second function of the Delta Converter is to charge the battery of the UPS by drawing power and converting it to the appropriate DC charging voltage.

ADVANTAGES

1.Uncertain Data Loss Can Be Prevented.

2.Emergency Power Supply.

3.Protects the Voltage Sensitive Device from Bad Electricity

4.Provides Surge Protection.

5.Maintains Battery Life.

6.Huge Power Back Up in the Industries.