Answer / aju m paulose

0.1, 0.2, 0.5, 1, 3 are Accuracy class
They are used for metering purposes

5P10, 5P15, 5P20 are used for metering and protection purposes

5 indicates Composite error in % and 'P' for protection and 10 means accuracy limit factor...

i.e the CT will have 5% error if the current under measurement is 10 times the normal value

Answer / balakrishna

ct has 3 classes.ie.
0.2,0.5,1
5p10,5p20
ps

here 0.2, 0.5,1 used for metering classes
5p10,5p20 used for protection like overcurrent & earth
fault purpose

ps class used for the differential/distance protection

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