Power transformer (transformer for short) is an electrical equipment used to change the AC voltage. According to the principle of electromagnetic induction, it exchanges one level of AC voltage with another level of AC voltage to meet the needs of different loads. Therefore, transformer plays a very important role in power system and power supply and consumption system.
The output voltage of the generator is usually 6.3kV, 10.5kv and no more than 20kV due to the limitation of the insulation level of the generator. It is difficult to carry out long-distance transmission with such a low voltage. Because when transmitting a certain power of electric energy, the lower the voltage, the greater the current, and most of the electric energy may be consumed in the resistance of the transmission line. Therefore, the step-up transformer can only be used to increase the terminal voltage of the generator to tens of thousands of volts to hundreds of thousands of volts, so as to reduce the transmission current and reduce the energy loss on the transmission line without increasing the conductor section to transmit the electric energy over a long distance.
After the transmission line transmits tens of thousands of volts or hundreds of thousands of volts of high voltage to the load area, the high voltage must be reduced to a low voltage suitable for electrical equipment through a step-down transformer. Therefore, in the power supply and consumption system, step-down transformers are needed to convert the high voltage transmitted by the transmission line into various levels of voltage to meet various composite needs.
Function of power transformer
1. Transmission and distribution of electrical energy. If it is a step-up transformer, it can send out electric energy. If it is a step-down transformer or distribution transformer, the electric energy can be transmitted or distributed respectively;
2. The rated voltage at the primary and secondary sides can be changed;
3. The phase angle of the primary and secondary sides can be changed;
4. Mainly the above items, of course, can also include: improving or protecting the role of the power grid, reducing or increasing the number of phases, etc.
Purpose of transformer
Current converter is a kind of transformer with closed core and no air gap. The advantage is that when the core is unsaturated, the waveform of the secondary current is the same as that of the primary side. The disadvantage is that it is easy to saturate and has poor linearity under the action of aperiodic component of current. Current converter is generally used in microcomputer protection. This equipment shall be used in the voltage forming circuit of input current by microcomputer protection device. The working principle is to convert the current into a linear DC voltage signal through impedance for use by the measuring circuit.
A transformer is an element that converts voltage. In our daily work, we often need to get voltages of different amplitudes, so we need to use transformers. For example, the voltage amplitude commonly used in our Chinese families is 220 V, that is to say, most household appliances are equipped with 220V voltage. For mobile phones used in our daily life, we need to reduce the voltage of 220V to a safe voltage relative to human body, which requires a transformer. In addition, when our students do some electrical experiments, for the sake of safety, we need to use a transformer to reduce the voltage to a safe voltage. When we transmit voltage, in order to reduce power loss, we need to use a transformer to increase the voltage.
The power transformer is composed of a closed iron core and two coils (also known as windings) wound around the iron core. One coil is connected to the power supply, which is called the primary coil (also called the primary coil); The other coil is connected to the load, which is called the secondary coil (also known as the secondary coil). Both coils are made of insulated wires, and the iron core is made of silicon steel sheets coated with insulating paint. With different turns of the coil, we can make various step-up transformers and step-down transformers to achieve different purposes.
Application of transformer in various aspects
There are many classifications of transformers. Different transformers are used in different places. as
Oil immersed distribution transformer is mainly applicable to pole erection, box type substation and distribution room and substation with separate distribution transformer room; Thousand type distribution transformer is mainly suitable for indoor distribution; The single-phase distribution transformer is easy to go deep into the load center for power supply because of its small volume and single pole erection. The single-phase distribution transformer has low loss and can supply power near the residential end, which greatly reduces the loss of low-voltage line, so it has also been widely used. Because some rural areas have the characteristics of small villages, few power users and relatively concentrated load, the use of transformers is very important. In rural areas, if a distribution transformer is needed for power supply, according to the existing load and development planning, we should consider that the distribution transformer should be installed in the center of the load as much as possible. For places with large population and large number of electricity users in rural areas, multiple distribution transformers are needed to supply power and distributed in different places, so as to achieve better power supply effect.
In the classification of transformers, there is a kind of transformer called box type, which is generally used in power engineering construction. According to the specific construction engineering requirements, it generally fluctuates between 102% 125% of the power consumption, so as to prevent the transformer from being burned out due to excessive voltage. Appropriate voltage switch shall be installed at the high-voltage end of the box transformer. The power consumption in the project construction shall be obtained through calculation at the high-voltage end. At the same time, voltage monitoring device and useless power compensation equipment with O.95 power coefficient shall be installed. In addition, it should be operated in strict accordance with the instructions.
There are many types of transformers, which can be classified according to voltage rise and fall, phase number, purpose, structure, cooling mode, etc.
Classified by voltage rise and fall: there are two types of step-up transformer and step-down transformer.
Classification by phase number: there are three types of single-phase transformer, three-phase transformer and multiple transformers.
Classification by purpose: there are power transformers used in power supply system; Instrument transformers (voltage transformers and current transformers) for measurement and relay protection; Pressure transformer for withstand voltage test of high voltage power supply equipment; There are special purpose transformers such as electric furnace transformer, welding transformer and rectifier transformer.
Classification by cooling mode and cooling medium: there are dry-type transformers cooled by air; Oil immersed transformer with oil cooling; There is a water-cooled transformer cooled by water.
The 21st century is an era of rapid development of high technology. Electricity is generally used in all aspects of people's life, so the status of transformer is becoming more and more important, especially the demand for electronic transformer is particularly strong. In daily life, the demand for low-voltage electronic transformers is relatively large. In other words, the development prospect of transformer is still relatively good. Therefore, it is necessary for us to have a certain understanding of the transformer. We should pay close attention to its principle, application and problems needing attention.
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