Transformer A transformer is a common electrical device that can be used to transform an alternating voltage of a certain value into an alternating voltage of another value of the same frequency. It can also change the value of the alternating current and change the impedance or change the phase. The significance of the transformer The power plant wants to transmit the electric power of p=3uicosφ to the area where the electricity is used. When p and cosφ are certain values, the higher the voltage used, the smaller the current in the transmission line, which can reduce the transmission line The loss, saving conductive materials. Therefore, it is most economical to use high voltage for long-distance transmission. At present, the highest voltage of AC transmission in my country has reached 500kv. Such a high voltage is not allowed to be directly produced by the generator, regardless of the safety operation of the generator or the manufacturing cost. The output voltage of the generator is generally 3.15kv, 6.3kv, 10.5kv, 15.75kv, etc., so a step-up transformer must be used to increase the voltage for long-distance transmission. After the electric energy is transmitted to the power-consuming area, in order to adapt to the voltage requirements of the electrical equipment, it is necessary to reduce the voltage to the voltage value required by various electrical appliances through the use of transformers at various substations (substations). In terms of electricity consumption, the voltage required by most electrical appliances is 380v, 220v or 36v, and a few motors also use 3kv, 6kv, etc. Transformer classification According to its use, there are power transformers, power transformers, voltage regulating transformers, instrument transformers, and isolation transformers. According to the structure, it is divided into two-winding transformer, three-winding transformer, multi-winding transformer and autotransformer. According to the core structure, it is divided into shell-type transformer and core-type transformer. According to the number of phases, it is divided into single-phase transformer, three-phase transformer and multi-phase transformer. Although there are many types of transformers, the basic principle and structure are the same. The basic structure of the transformer (1) Iron core The transformer is composed of two or more coils (windings) sheathed on a closed iron core. The iron core and the coil are the basic components of the transformer. The iron core constitutes the magnetic circuit required for electromagnetic induction. In order to reduce the eddy current loss caused when the magnetic flux changes, the core of the transformer should be laminated with silicon steel sheets with a thickness of 0.35-0.5mm. The film is separated by insulating varnish. The iron core is divided into two types: the heart type and the guest type. (2) The coil connecting the transformer to the power supply is called the primary winding (or primary side, or primary winding), and its number of turns is n1, and the coil connected to the load is called the secondary winding (or secondary side, or secondary winding). The number of turns is n2. The winding and the winding and the winding and the core are insulated from each other. 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 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 iron core shapes of transformers generally have e-type and c-type iron cores. 1. The basic principle of the transformer Figure 1 is a simplified diagram of the 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, which passes along the core The primary coil and the secondary coil form a closed magnetic circuit. A mutual induction potential u2 is induced in the secondary coil, and at the same time a self-induction potential e1 is induced on the primary coil by ф1. The direction of e1 is opposite to 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 turns of the secondary coil as needed, but it cannot change the power 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 line of magnetic force. 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 "eddy current". 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 wires are needed to wind the transformer. These copper wires have resistance. When current flows through the 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. Since 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, η=output 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 usually uses magnetic flux density.