Basic knowledge of transformer

Transformers are used in almost all electronic products. Its principle is simple, but the winding process of transformers will have different requirements according to different applications (different purposes). The main functions of the transformer are: voltage transformation; impedance transformation; isolation; voltage stabilization (magnetic saturation transformer), etc. The commonly used iron core shapes of transformers generally have E-type and C-type iron cores. 1. 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 use occasions (different purposes). The main functions of the transformer are: voltage transformation; impedance transformation; isolation; voltage stabilization (magnetic saturation transformer), etc. The commonly used core shapes of transformers generally have E-type and C-type cores. 1. The basic principle 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 wire and an alternating magnetic flux ф1 is generated. It passes through the primary coil and the secondary coil along the iron core to form a closed The magnetic circuit. A mutual induction potential U2 is induced in the secondary coil, and ф1 will also induce a self-induction potential E1 on the primary coil. The direction of E1 is opposite to the direction of the applied voltage U1 and the amplitude is similar, thus limiting the size of I1. In order to maintain the existence of the magnetic flux ф1, a certain amount of power consumption is required, and the transformer itself also 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. This current is called 'no-load current'. '. If the secondary is connected to a load, the secondary coil will generate a current I2, and therefore generate a magnetic flux ф2, the direction of ф2 is opposite to ф1, which acts to cancel each other, so that the total magnetic flux in the core is reduced, so that the primary The self-inductance voltage E1 decreases, and as a result, I1 increases. It can be seen that the primary current has a close relationship with the secondary load. When the secondary load current increases, I1 increases and ф1 also increases, and the increased part of ф1 just supplements the part of the magnetic flux offset by ф2 to keep the total magnetic flux in the core unchanged. If the loss of the transformer is not considered, it can be considered that the power consumed by the secondary load of an ideal transformer is the electric power obtained by the primary from the power supply. The transformer can change the secondary voltage by changing the number of turns of the secondary coil as needed, but it cannot change the power that is allowed to be consumed by the load. 2. Loss of the 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, an electric potential will be induced in the plane perpendicular to the magnetic force line. This electric potential forms a closure on the cross section of the iron core. The loop generates electric current, like a vortex, so it is called 'vortex'. This 'eddy current' increases the loss of the transformer and increases the temperature rise of the transformer's core heating transformer. The loss caused by 'eddy current' is called 'iron loss'. In addition, a large amount of copper wire is needed to wind the transformer. These copper wires have resistance. When current flows through the resistance, this resistance will consume a certain amount of power. This part of the loss is often consumed as heat. We call this loss 'copper loss' . Therefore, the temperature rise of the transformer is mainly caused by iron loss and copper loss. Because the transformer has iron loss and copper loss, its output power is always less than the input power. For this reason, we introduce an efficiency parameter to describe this, ηu003doutput power/input power. Third, the material of the transformer To wind a transformer, we must have a certain understanding of the materials related to the transformer. For this reason, I will introduce this knowledge. 1. Core material: The core materials used in transformers are mainly iron sheet, low silicon sheet, high silicon sheet. The addition of silicon to the steel sheet can reduce the conductivity of the steel sheet and increase the resistivity. It can reduce the eddy current and reduce the loss. . We usually call silicon-added steel sheets as silicon steel sheets. The quality of the silicon steel sheets used in the quality of the transformer has a great relationship. The quality of the silicon steel sheets is usually expressed by the magnetic flux density B. Generally, the B value of black iron sheets 6000-8000, low silicon wafers are 9000-11000, high silicon wafers are 12000-16000. 2. The materials commonly used for winding transformers are enameled wire, sand-bag wire, silk-covered wire, and the most commonly used enameled wire. The requirements for the wire are good electrical conductivity, sufficient heat resistance of the insulating paint layer, and a certain degree of corrosion resistance. Generally, it is best to use Q2 type high-strength polyester enameled wire. 3. Insulating materials In winding transformers, insulating materials are used for the isolation between coil frame layers and the isolation between windings. The general transformer frame materials can be made of phenolic cardboard, and the layers can be isolated by polyester film or telephone paper. , The winding room can be isolated by yellow wax cloth. 4. Impregnating material: After the transformer is wound, the last process is impregnated insulating varnish, which can enhance the mechanical strength of the transformer, improve the insulation performance, and prolong the service life. Under normal circumstances, cresol varnish can be used as impregnation. Material