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Current Transformer, Protection Type

GENERAL :

‘‘INDOTECH’’ Current Transformer reproduces proportionate primary current on its secondary side required for extending the range of the instruments/protective devices connected in its secondary circuit. CT can also be used for isolating the devices connected in the secondary circuit from the network system into which the C.T. is connected. CT's are available in Tape Wound as well as Cast Resin type. .Basically, CTs are of two types:

1. BAR PRIMARY TYPE :

Coil is wound on a toroidal core of high per-meability silicon steel. The Bar which is passed through the core, acts as single turn on the primary side and the turns on the core act as secondary.BPL CT's are available both for metering as well as for protective purposes.

(a) METERING CT’s :

These CT’s are meant for feeding measuring instruments. Accuracy class of the CT will be selected on the basis of the accuracy class of the instrument to be operated. When the instrument is installed far away from the CT, the secondary is chosen as 1A instead of 5A.

(b) PROTECTION CT’s :

These CT’s are meant for operating the protective devices viz., Circuit Breakers and Relays etc. The magnitude and the nature of fault to be controlled and the electrical characteristic of the device decide the class and type of Current Transformer.

  
   
LIMITS OF ERRORS & PHASE DISPLASEMENT
As per ISS : 2705/81
     
ClassPercentage Current Errors at
          Percentage of Rated Current
Phase Displasement in Minuts
          At percent of Rated Current
       
         
 
0.1
0.2
0.5
1.0
           
5%20%100%120%
0.40.20.10.1
0.750.350.20.2
1.50.750.50.5
3.01.51.01.0
             
5%20%100%120%
15855
30151010
90453030
180906060
Protection Type CT
 
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