UtilityGy
Electrical
- Mar 5, 2010
- 35
Hello,
I have done my homework well before asking this questions and also read posts here as well. Because, I am not an expert so need your final opinion,
Q#1 Why in most of the cases, we d'nt consider DC offset value of current in to calculation when the whole point of calculating the saturation point is avoid its impact. Most of the tutorial on web and books just calculate the fault p.u. value, burbden and then calculate the voltage drop. If this value is less than the CT class voltage like incase of C400, if it is 383 V then CT is good. Other wise not.
Q#2 I have never tested a CT my self but sure read about it. I was asked a question during a casual discussion by some field techs regarding excitation test on some rewound CTs on 27 kV outdoor breakers. CT's are C200 class and were getting excitation voltage of 926V. These are very big CTs. I think I am confused. When we do excitation test there is no load so how can we actually verify correctly that particular burden voltage poingt of 2 ohms or 4 ohms.
Kindly advise.
I have done my homework well before asking this questions and also read posts here as well. Because, I am not an expert so need your final opinion,
Q#1 Why in most of the cases, we d'nt consider DC offset value of current in to calculation when the whole point of calculating the saturation point is avoid its impact. Most of the tutorial on web and books just calculate the fault p.u. value, burbden and then calculate the voltage drop. If this value is less than the CT class voltage like incase of C400, if it is 383 V then CT is good. Other wise not.
Q#2 I have never tested a CT my self but sure read about it. I was asked a question during a casual discussion by some field techs regarding excitation test on some rewound CTs on 27 kV outdoor breakers. CT's are C200 class and were getting excitation voltage of 926V. These are very big CTs. I think I am confused. When we do excitation test there is no load so how can we actually verify correctly that particular burden voltage poingt of 2 ohms or 4 ohms.
Kindly advise.