Toroidal cores

toroidalToroidal Transformer Basics

A toroid is a doughnut-shaped object whose surface is a torus. Its annular shape is generated by revolving a circle around an axis external to the circle.

A coil of insulated wire in a doughnut shape (usually with a core of iron or similar metal) is an example of a toroidal object. These are used as inductors in circuits such as low frequency transmitters and receivers because they possess higher inductance and carry greater current than similarly constructed solenoids. They are also used as transformers in main power supplies. Toroidal coils reduce resistance, due to the larger diameter and smaller number of windings. The magnetic flux in a toroid is confined to the core, preventing its energy from being absorbed by nearby objects.

In the geometry of torus-shaped magnetic fields, the poloidal flux direction threads the "donut hole" in the center of the torus, while the toroidal flux direction is parallel the core of the torus.

Advantages of Toroidal Power Transformers
Toroidal transformers offer many advantages over standard laminated power transformers. Toroidals provide quiet, efficient operation with very low stray magnetic fields. Their small size and weight support a package that is easy to design into any application.


Manufacturing Toroidal Core Process

toroidalThe manufacturing of strips wound cores is a specialized process, which requires a high degree of precision. These cores are manufactured from selected coils of CRGO electrical steel to yield closely controlled electro-magnetic characteristics and dimensional accuracy.

Cores are wound after slitting is done as per the required shape, on the core winding machine. The Winding Machine automatically stops when the pre-decided dimension is reached. The start and finish ends are firmly spot welded. After winding, the cores are stress-relief annealed to restore the magnetic properties. The cores are bonded where necessary, to provide increased firmness. All cores are spray painted and are tested for magnetic properties.


Strip wound cores, unlike strip lamination, constitute a complete product and every core must meet the specified performance requirement. Consequently, quality control in the manufacturing of wound cores is vitally important at every stage of process.

Dimensional Tolerances:

The coils of CRGO Steel from which the cores are manufactured are carefully selected on the basis of tests carried in our laboratories to ensure that the correct grade of steel is used. Strict checks are made at every stage from winding to the final stage of spray painting to ensure that the finished product is of a high quality. Moreover, each core is subject to inspection and electrical tests to make certain that our customers are provided with the specified performance requirement. Apart from being fully equipped to meet the exacting standards of testing required, EVERGREEN possesses the technical know how, the research facilities and the necessary raw-materials.