What is helical winding in transformer?

Helical winding is helically wound around the cylindrical generatrix leaving a duct gap of 4.5-6 mm wide between two adjacent turns around the height.

A turn of helical winding consists of several parallel rectangular conductors flat-wise and close to each other in the radial direction of the winding.

For uniform distribution of current between the parallel branches, transposition of conductors is used.

In the above diagram the transposition of helical winding turns in 3 places along the height: in the middle- the so called middle transposition (a) and the two group transposition (b),(c) are made so that the winding is divided along its height in approximately equal parts.

the no. of parallel conductors in one turn of a helical winding usually varies from 6-20. The helical winding is widely used in low voltage Transformers of medium and especially of high voltage.