The transformer is used in almost all electronic products. Its principle is simple, but the winding process of the transformer will have different requirements according to different applications (different purposes). The functions of the transformer mainly include: voltage transformation, impedance transformation, isolation, voltage stabilization (magnetic saturation transformer), etc. The core shapes commonly used in transformers are generally E type and C type.

1、 Basic principle of transformer:

It is a simplified schematic diagram of the transformer. When a sinusoidal AC voltage U1 is applied to both ends of the primary coil, there is an alternating current I1 in the conductor and alternating magnetic flux is generated ф 1. It passes through the primary coil and secondary coil along the iron core to form a closed magnetic circuit. The mutual inductance potential U2 is induced in the secondary coil, and ф 1 will also induce a self induced potential E1 on the primary coil. The direction of E1 is opposite to the applied voltage U1, but the amplitude is similar, thus limiting the size of I1. To maintain magnetic flux ф 1 requires a certain amount of power consumption, and the transformer itself has a certain loss. Although the secondary is not connected to the load at this time, there is still a certain current in the primary coil, which is called no-load current. If the secondary is connected to the load, the secondary coil will generate current I2, and thus generate magnetic flux ф 2， ф 2 direction and ф On the contrary, it counteracts each other, reducing the total magnetic flux in the iron core, thus reducing the primary self inductance voltage E1, which increases I1 as a result. It can be seen that the primary current is closely related to the secondary load. I1 increases when the secondary load current increases, ф 1 also increases, and ф 1 The added part just supplements the quilt ф 2 The part of magnetic flux offset to keep the total magnetic flux in the iron core unchanged. If the loss of transformer is not considered, it can be considered that the power consumed by the secondary load of an ideal transformer is the electrical power obtained by the primary power supply. The transformer can change the secondary voltage by changing the number of turns of the secondary coil as required, but cannot change the power consumed by the allowable load.

2、 Loss of transformer:

When the primary winding of the transformer is energized, the magnetic flux generated by the coil flows in the iron core. Because the iron core itself is also a conductor, the potential will be induced on the plane perpendicular to the magnetic line of force. This potential forms a closed loop on the section of the iron core and generates current, like a vortex, so it is called eddy current. This eddy current increases the loss of the transformer, and increases the temperature rise of the transformer core heating transformer. The loss caused by eddy current is called iron loss. In addition, a large number of copper wires need to be used to wind the transformer. These copper wires have resistance, which will consume a certain amount of power when the current flows. This loss is often consumed as heat. We call this loss copper loss. Therefore, the temperature rise of transformer is mainly caused by iron loss and copper loss. The transformer has iron loss and copper loss, so its output power is always less than the input power. Therefore, we introduce an efficiency parameter to describe this, η= Output power/input power.

3、 Materials of transformer:

1. Core material: The core materials used in the transformer mainly include iron sheet, low silicon sheet and high silicon sheet. Adding silicon to the steel sheet can reduce the conductivity of the steel sheet and increase the resistivity, which can reduce eddy current and reduce its loss. We usually call the steel sheet with silicon as silicon steel sheet. The quality of the silicon steel sheet used for the quality of the transformer has a great relationship. The quality of silicon steel sheet is usually expressed by magnetic flux density B. Generally, the B value of black iron sheet is 6000-8000, that of low silicon sheet is 9000-11000, and that of high silicon sheet is 12000-16000,

2. The commonly used materials for winding transformers are enamelled wire, sand covered wire, silk covered wire, and the most commonly used enamelled wire. The requirements for conductor are good conductivity, enough heat resistance of insulating paint layer and certain corrosion resistance. Generally, Q2 type high-strength polyester enamelled wire is preferred.

3. In the winding transformer, the insulation materials shall be used for the isolation between the layers of the coil frame and the winding resistance. The general transformer frame materials can be made of phenolic cardboard, the layers can be separated by polyester film or telephone paper, and the winding resistance can be separated by yellow wax cloth.

4. Impregnating material: after the winding of the transformer is completed, the last process is to impregnate the insulating paint, which can enhance the mechanical strength of the transformer, improve the insulation performance, and extend the service life. Generally, cresol varnish can be used as the impregnating material.

5. Baoying Power strictly produces high-efficiency energy-saving transformers according to requirements. It can save the loss caused by machine failure and improve work efficiency.