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Protection Riddle No.104 - Rating of current transformer secondary
The standard current transformer secondary winding rating is always kept in 5 amps. Why?
Author : soman - From: India
Mon, April 22nd, 2013 - 09:42
Typical values of secondary current of current transformers in compliance with the most protective relay and instrument construction standards are 1 A or 5 A. 
Author : Hamid - From: Iran
Mon, April 22nd, 2013 - 13:28
This is not true.The C.T secondary current is also expressed in 1 Amps. Normally,C.T with 1 Amp is used when the distance between C.T and the instrument to whom C.T feeds is large.The knee point of 1 Amp C.T is at higher valuer for the same VA rating.However, 5 Amps C.T is cheaper than 1 Amp C.T . 
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