Basic Knowledge of Mains Transformers -

Function and features of mains transformer

The mains transformer is a stationary electrical equipment to transform alternating current, which is used in almost all electronic products. It is simple in principle, but the transformer winding process will have different requirements according to their different use occasions. The role of the mains transformer is to change the voltage, which can upgrade the electricity generated by the power plant to high pressure, in order to reduce the loss in the transmission, to facilitate long-distance transmission of electric power, but also can reduce the high-voltage successively into low voltage in place where the electricity is used, and send to users. Transformer features: voltage conversion; impedance transformation; isolation; regulator (magnetic saturation transformer), the common used core shape transformer is generally available for the E-type and C-type core.

The basic principles

When a sinusoidal AC voltage U1 is applied to both ends of the primary coil, there will be alternating current I1 in the wire and generates an alternating magnetic flux Ф1. It passes through closed magnetic circuit formed by the primary and secondary coils along the core induct the mutual induction potential U2 in the secondary coil, while ф1 also induces a self-inductance electric potential E1 in the primary coil, the direction of E1 is contrary to the direction of the applied voltage U1 and amplitude is similar, thereby limiting the size of the I1. To keep the existence of the flux ф1, certain power consumption is needed, and the transformer itself has a certain loss, despite the fact that secondary does not connect the load, there is still current in the primary coil, this current we called "no-load current ".

Transformer material

1. Core material

The core materials used by transformer are mainly iron sheet, low silicon, high silicon steel sheet. Ad silicon in the steel sheet can reduce conductive, increase the resistivity; it can reduce the eddy current, so that loss is reduced. We often refer the steel sheets added with silicon as the silicon steel sheet. The quality of the mains isolation transformer has a great relationship with the quality of the silicon used in steel sheet; the quality of the silicon steel sheet is usually represented by the magnetic flux density B, generally the black sheet B value is 6000-8000, the low silicon is 9000-11000 and high silicon is 2000-16000.

2. Materials commonly used in wound transformer

Enameled wire (the most common), sandbags wire, silk envelope wire. For the requirements of the wire is good conductive properties, the insulating lacquer layer has sufficient heat resistance, and a certain corrosion resistance. Under normal circumstances, high strength polyester Q2 models enameled wire is preferred.

3. Insulating materials

In winding the transformer, the isolation between the coil frame layer and the resistive isolation need to use the insulating materials. Usually transformer frame material can be made by the phenolic cardboard, interlayer can use polyester film or telephone paper for isolation, winding isolation can use yellow wax cloth.

4. Impregnated material

After the transformer is winded, there is the last step, to impregnate with insulating paint, it can enhance the mechanical strength of the transformer, to improve the insulation performance and prolong life, under normal circumstances, the cresol varnish can be used as impregnating materials.

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