Basics of Electrical Transformers Construction

How Are Electrical Transformers Constructed?

The windings of industrial electrical transformers are not placed on separate legs (as shown in Figure 11-1). A more efficient method, which reduces flux leakage, is to place the windings on top of one another (Figure 11-5). If a transformer is wound as shown in Figure 11-1, much of the flux produced by the primary current cannot reach the secondary winding. The leakage flux will induce a back voltage in the primary, causing a primary reactance drop. Similarly, much of the secondary flux will not reach the primary and, therefore, will not neutralize the primary flux but will produce a reactance drop in the secondary. The overall effect is similar to connecting a reactance in series with each winding.

Figure 11-1

An illustration shows the parts of a basic transformer. The transformer core is a rectangular box, where the primary windings are wound on the left side and the secondary windings are wound on the right side. The magnetic flux created passes in clockwise direction from the primary windings to the secondary windings, on the front face of the core.

Figure 11-5

Transformer with two high-voltage windings and two low-voltage windings. The windings may be connected in series or in parallel, depending upon the voltage ratings and the desired results.

In addition to reactance, each winding has resistance. The reactance and resistance of the windings may be represented as shown in Figure 11-6. In each winding of a transformer, there is an drop and an IR drop. The drop is kept to a minimum by placing the primary and secondary windings on the same leg of the core. Frequently, they are made cylindrical in form and placed one inside the other. Another method is to build up thin, flat sections called pancake coils. These sections are sandwiched between layers of insulation. Figure 11-7 shows the cylindrical method; Figure 11-8 shows the pancake method. In the cylindrical method, the low-voltage winding is placed next to the core and the high-voltage winding is placed on the outside. This arrangement requires only one layer of high-voltage insulation placed between the two windings.

Figure 11-6

Diagram showing the resistance and reactance of both windings.

An illustration shows a transformer with resistance and reactance on its windings. Both the primary and secondary windings on the transformer are connected in series with a reactance X_L and a resistor R, each. The resistors are closer to the transformer, compared to the reactance windings.

Figure 11-7

Cutaway view of a transformer. The windings are made in the form of a cylinder and placed inside one another.

An illustration shows the cutaway view of a transformer. The transformer is represented by a main cylinder and two small cylinders each on the left and right side of the main cylinder. The two outer cylinders are labeled high voltage, and the two inner cylinders are labeled low voltage.

Figure 11-8

Cutaway view of a transformer. The windings consist of thin, flat sections sandwiched between layers of insulation.

An illustration shows the cutaway view of a transformer. The transformer is represented by a main cylinder with parallel horizontal sets of five sets of two small parallel lines. There is a pair of 13 rectangular blocks arranged in a vertical manner on the left and the right sides of the main cylinder. The odd rows of blocks are labeled low voltage. The even rows blocks are dark shaded and labeled high voltage.

The above article is an extract from our Fast Trax® Magenta Course for Industrial Electricity. For more information on that course CLICK HERE.

How Are Electrical Transformers Constructed?

Transformer Construction

Comments

Leave a Reply Cancel reply