Helical winding of Transformer and Double helical winding of Transformer

Q. Draw neat sketches and discuss the special features of following windings used for 3 phase transformer : Cylindrical winding, Helical winding, Crossover winding, Disc winding. List the typical voltage and current ranges over which they are used.

• Different type of windings are used depending upon voltage, current and capacity of transformer.
• Transformers with core type construction uses concentric type of windings. Both primary and secondary winding coils are wound on the limb concentrically. Generally LV winding is placed near the core (Due to less insulation requirement).
• Depending upon voltage, current, temperature rise, short circuit strength following types of windings are used for core type of transformer :

Types of Transformer Winding
     1. Cylindrical winding of Transformer
     2. Helical windings of Transformer

• These are used for low voltage winding of high capacity transformers (high current). In this conductors are wound in an axial direction along a screw line. (Due to high axial mechanical strength these windings are used in low voltage windings of large power transformers which are exposed to high short circuit currents).

• In this number of conductors are used in parallel to form one turn. As parallel conductors are used it. becomes essential to transpose the conductors (i.e. changing the relative position of individual conductors). Transposition makes length of each conductor in parallel conductor same, as well as flux embracing becomes same and hence equalizes the impedance of parallel conductors.

     3. Double helical winding of Transformer

• Similar to helical winding this is used in low voltage winding of high capacity transformers where current and number of parallel conductors required are very large.

     4. Multilayer helical winding of Transformer
     5. Cross over winding of Transformer
     6. Disc and continuous disc winding of Transformer