Current Transformer Rating 2

[Zahi1]

Hello,

What does it mean for a current transformer to be ext. 100%? Does that mean it allows for a continuous current of double it's rated current without any damage?

Thanks.

 

[7anoter4]

Current Transformer Rating:
1) Maximum current value in order to limit the measuring accuracy [usually 5-10%] for a very short duration [seconds]. The limit in the IEEE standard is 20 times the CT primary current rating. Twenty times is also the preferred limit in the IEC standard.
2) Normal Current Rating (Ia) =Current which can be carried continuously without any current transformer part exceeding its normal and allowable maximum temperature.
3) Emergency Current Rating (Ie) =Current which can be carried for a specified period of time without any current transformer part exceeding its emergency allowable maximum temperature. For instance:
Percent of Adjusted Rated Continuous Current [Normal Allowable Maximum Temp.85 C degrees]:
Season: winter summer
Normal 120 100
Emergency: Greater Than 24 Hours 141 125
2 to 24 Hours 149 129
15 Minutes 175 159
For more information see:

http://www.pjm.com/planning/design-...-standards/20011108-current-transformers.ashx

 

[randyman]

Typically that would be the maximum continuous current the CT can handle and maintain its accuracy class, and at the same time not exceed its thermal rating. In your case it means the CT can only be used at its nameplate current ratio continuously, and no higher. Anything higher than 100% of its rated current ratio may overheat the winding(s) or yield higher errors or both.