Which type of current transformer is the least common?

The least common type of current transformer is the wound current transformer. Wound current transformers are designed with a specific turns ratio and are constructed by winding a number of turns of wire around a magnetic core. This design is generally utilized for measuring current in applications with lower current ratings, and it offers the advantage of higher accuracy and better performance under certain conditions, especially for intermediate voltage levels.

However, wound CTs are less commonly used compared to other types, such as bar, bushing, and window current transformers. The bar CT is more widely used in high-current applications, while bushing CTs are typically integrated into the bushings of high-voltage equipment, facilitating easier installation and maintenance. Window CTs, which are characterized by their open design that allows for direct insertion of electrical conductors, are also favored for their simplicity and ease of use.

Thus, the wound current transformer stands out as the least prevalent among these options due to its specific application, cost considerations, and the availability of alternative types that may be more suitable for various electrical systems.