Current Transformers (CT) Ratings Methodology Rating methodologies exist for Normal Summer Peak and Normal Winter Peak ratings without accelerated loss of life (defined in part by IEEE C57.13-1993) Free-standing current transformers (CTs) and other non-bushing type CTs 24-hr ambient temperature cycle, constant load, and no accelerated loss of life. Methodologies Needed for: Emergency ratings for all types of CTs (particularly 4-hr ratings) Normal ratings for all types of breaker bushing and transformer bushing CTs Both rating methodologies should be tested and include the effects of an ambient temperature cycle, rating factor (RF), and chosen CT tap position Different types of non-bushing, breaker bushing and transformer bushing CTs should be surveyed for various existing and projected types of CTs Industrial Advisory Board Meeting July 31 – August 3, 2005

Purp0se and Scope Develop a technically-based, practical, simple method to calculate the rating of free-standing and bushing CTs and the condition of these CTs in terms of remaining life or loss of life. Review of normal and emergency ratings for different possible types of free-standing, breaker bushing and transformer bushing CTs Survey of different types of free-standing, breaker bushing and transformer bushing CTs Include ambient temperature cycle, tap position, and RF Load cycle is desired but not required for normal ratings For emergency ratings, a constant pre-emergency normal loading for a defined time period followed by an emergency loading for a defined period taken into account, as well as accelerated loss of life For the 4-hr emergency ratings, consider 20 hrs at the normal rating followed by 4 hrs at the emergency rating. CT voltage ratings should include 115, 161, 230, and 500 kV. Develop a methodology for normal ratings for bushing CTs, and emergency ratings for non-bushing, breaker bushing and transformer bushing CTs. Test (benchmark) at least one type of free-standing, one type of breaker bushing, and one type of transformer bushing CT at both 161 and 500 kV by experimentally exposing the CTs to lab tests. This is a minimum of six types of CTs. Both normal and emergency ratings must be lab tested for these six CTs.

Desired Outcome Normal ratings equations developed for breaker bushing and transformer bushing CTs similar to Normal Summer and Winter Peak ratings methodologies for relevant-types of free-standing CTs Verified equations by lab tests on representative CTs. Emergency ratings equations for free-standing, breaker bushing and transformer bushing CTs for relevant types with a method to determine a quantified loss of life. Verified equations by lab tests on representative CTs of the same type as those described above in item 1.