Before manufacturing of transformers we must know the important parts of transformer which need to be manufactured. Following are the main parts of transformers.
(a) Former or bobbin
(b) Winding wire or coil
(c) Laminated iron core
(d) Shielding and mounting assembly
(a) Former or bobbin: Bobbin is the part of transformer on which the coil is wound. It is also known as coil former. It is made of impregnated paper materials laminated materials, thermosetting and thermo-plastic materials.
(b) Winding Wires: On the bobbin, a low resistivity wire is wound into multi-turn with sufficient insulation to separate the turns. The wires are coated with the suitable quality of varnish. The size of the coil depends upon the current which is to be carried by wires.
(c) Core: The core material should have low hysteresis constant to minimize the hysteresis losses in the core. Silicon steel is the perfect core material. This core is laminated to reduce eddy current losses.
(d) Shield: Shielding is used to suppress electromagnetic interference from or to the inductor. This is done using foil.
MANUFACTURING PROCESS OF SMALL TRANSFORMERS:
In the process of manufacturing a transformer first of all winding of the coil over the bobbin is to be done. Winding of the coil is done by a coil winding machine. This coil winding machine either could be hand operated or it could be driven by a fractional horse power motor. A counter is provided on the winding machine which counts the number of turns wound. To start winding, first the size of the coil former and winding wire required is taken. On the surface of bobbin, a coil former should be checked first to test its smoothness so that it may not damage the insulation of the wire which is to be wound on it. After that, the cross-sectional area, length etc. Of the following are checked for it's uniformly. Then lamination, dimension, etc. Of the laminations of the core should also be checked. Set the counter of the winding machine to zero. Set the machine for required SWG wire. Set the wire in the proper place in the machine. Tighten the wire so that it will attain proper tension. Keep a layer of the impregnated paper on the surface of the bobbin, take the end of the wire and pass it through the opening in the bobbin. Now start rotation the handle of the winding machine uniformly. When entire length of the bobbin is covered, then the direction of rotation of the handle of winding machine is reversed. Wind similarly for the required number of turns. After complete winding of the inner coil of the transformer, cover it with some insulating material such as impregnated paper. Then the outer pin is wound on the bobbin in same manner in which inner coil in wound. After winding the two coils, they are covered with some insulating material. After insulating, the cover is inserted into bobbin. Then fix the terminal plate on the transformers on which terminal wire is soldered. Then the transformer is impregnated. After impregnation it is ready for testing and use thereafter.