Increased ratings of overhead transmission circuits using HTLS and compact designs

High temperature low sag (HTLS) conductors offer the option of higher transmission capacity for a given right of way (ROW). The basis of an HTLS conductor is its ability to operate at long term high temperature, thereby allowing higher long term current ratings. The lower sag characteristics are obtained by managing conductor design and thermal properties of the conductor. Concomitantly, power ratings are increased in HTLS designs. HTLS lines can also improve the security limits through decreased phase spacing and resulting decrease in positive sequence line reactance. Utilization of HTLS as a transmission option, and compact designs as a configuration option can be used separately or together to achieve desired transmission objectives. This paper discusses the advantages and disadvantages of HTLS compact line designs. The focus is on increased ratings, re-conductoring circuits, and the identification of application sites. The paper introduces a method to approximate the positive and negative sequence reactances using the mutual and self reactances.