Type of construction of CT's:

Ring type CT or Window type CT:

This is the simplest type of CT. The core has three types of popular shapes (1) Rectangular shape (2) Oval shape (3) Ring shape.

Ring Type CT

Bar primary current transformers:

✥The core is of a Nickel-Iron Alloy, or grain oriented sheet steel.
✥The core is continuously wound type. Before applying secondary winding,
the core is insulated by means of end collars and circumferential wraps.

Bar Primary Current Transformer

✥Recently the continuously wound cores are available in encapsulated form. Synthetic resins are used as encapsulating material.
✥The material is applied by fluidized beds or electrostatic spraying.

(A)Core of A Ring Type CT

(B) Core is taped with insulting tape

(C)Secondary winding wound on core by toroidal winding machine

(D)Exterior taping is completed with circumferential insulating wraps

✥The secondary winding conductor is then wound as the insulated core in the form of toroidal winding by hand winding or toroidal winding machine.
✥The secondary winding is then completely wrapped by external tape with or without exterior ring ends and circumferential insulating wraps.

Current transformers for high voltage installation :

✥Separately mounted post type CT's They are suitable for out door service.
✥They are usually installed in the outdoor switchyard.
✥The primary conductor is at voltage with respect to earth. Hence it insulated by means of an insulator column filled with dielectric oil. Alternatively SF6 gas at a pressure of 2 or 3 atmospheres is now being used.