Construction of a Transformer The Core and Coils

The actual energy conversion in a transformer takes place in its core and coils.

For better energy conversion, the coils are placed on, or enclosed in, a magnetic circuit fabricated from a ferro-magnetic material having a high permeability, which

Transformer cores mostly come in any one of two de­signs, the core type and the shell type. In a core-type single-phase transformer, the core consists of two vertical limbs around which the preformed circular windings are placed. The windings consist each of two coils which may be con­nected in series or parallel and are placed on different limbs. The top and bottom members, called the yokes, join the two limbs into a closed magnetic circuit

In a core-type three-phase transformer, a primary and a secondary winding of one phase are wound on each limb. The three equal limbs are joined by the two yokes into a closed magnetic path.

In a single-phase shell-type transformer, the core is divided so that parallel magnetic paths encircle the single group of coils on two sides as if by a shell. As is seen, the yokes are built up to a cross-sectional area half as large as that of the limb carrying the coils.

To reduce height and to facilitate transit by rail, high-power transformers have five-leg core-type circuits called the core-and-shell type in usage. A core-and-shell transformer is lower in height because the yokes have to carry half as large a flux and may therefore have a lower height, too.

At the corners of a core, the yokes and limbs may be joined in any one of two manners. One gives butt joints; and the other, interleaved (or imbricated) joints.

With butt joints, the limbs and the yokes are stacked up separately, the coils are put on the limbs, and the top yoke is then placed on (joined with) the limbs to form a closed magnetic circuit. The butt joints are filled by insulating spacers to avoid eddy currents at those places. The spacers form a virtual air gap which absorbs reactive power over and above that required by the iron itself. Because of this, butt joints are seldom used, although they simplify assembly and disassembly.

Interleaved (or imbricated) joints are used on a wider scale. in this case, the successive layers of laminations in the yokes and limbs are interleaved so as to give an overlap at the corners to reduce the joint reluctance

The function of the structural parts in any transformer is to provide electrical insulation between the windings, to hold the core and coils in place, to cool the transformer, to provide connection between the transformer windings and the associated electric lines, and the like. Actually, the yoke clamps and the other clamping and packing-out parts may also be classed as structural parts.

2. Make up a plan in the form of questions.

3. Give the summary of the text according to your plan in a written form.

IV Comprehensive skills.

1. Read and remember.

1. occur – траплятися, приходить

2. steady – стійкий, твердий, безперервний

3. undergo – переносити

4. disregard – неуважність, нехтувати

5. intentional – навмисний