Internal structure and working principle of power transformer
Internal structure and working principle of power transformer
A power transformer is a static electrical device that is used to convert a certain value of an alternating voltage (current) into another voltage or current of a different value (current).
A transformer is a kind of static electrical equipment used to convert AC voltage and current to transmit AC power. It is based on the principle of electromagnetic induction to achieve electrical energy transfer. Transformers can be divided into power transformers, test transformers, instrument transformers and special-purpose transformers for their purposes: power transformers are necessary equipment for power transmission and distribution, power users' distribution; test transformers for electrical equipment withstand voltage (boost) Test equipment; instrument transformers are used for electrical measurement and relay protection of power distribution systems (PT, CT); special-purpose transformers include electric furnace transformers for electric smelting, electric welding transformers, rectifying transformers for electrolysis, and small voltage regulating transformers.
A power transformer is a static electrical device that is used to convert a certain value of an alternating voltage (current) into another voltage or current of a different value (current). When the primary winding is energized by alternating current, an alternating magnetic flux is generated, and the alternating magnetic flux is induced by the core to induce an alternating electromotive force in the secondary winding. The level of the secondary induced electromotive force is related to the number of turns of the secondary winding, that is, the voltage is proportional to the number of turns.
The main function is to transmit electrical energy, so the rated capacity is its main parameter. The rated capacity is a conventional value for expressing power. It is a measure of the amount of transmitted electrical energy. It is expressed in kVA or MVA. When a rated voltage is applied to a transformer, it is used to determine the rated current that does not exceed the temperature rise limit under specified conditions. The more energy-efficient power transformer is an amorphous alloy core distribution transformer, and its biggest advantage is that the no-load loss value is extremely low. The ultimate assurance of no-load loss values is a core issue to be considered throughout the design process. When the product structure is arranged, in addition to the effect that the amorphous alloy core itself is not affected by the external force, the characteristic parameters of the amorphous alloy must be accurately and reasonably selected in the calculation.
First, the use of power transformers
A transformer is a stationary power converter that transmits electrical energy without changing its frequency.
Transformers are a very large number of electrical equipment in the power system, and the total capacity of the transformer is about 9 times the total capacity of the generator. Its function is to raise or lower the voltage of the electric energy in the power system to facilitate the reasonable transportation, distribution and use of electric energy.
In the power system, the same power is delivered, the higher the voltage, the smaller the current, and the smaller the power loss on the transmission line; the cross-sectional area of the transmission line can also be reduced, so that the metal amount of the wire can be reduced.
Due to manufacturing difficulties, the generator voltage cannot be very high (currently below 20KV), so in the power plant, the step-up transformer should be used to raise the generator voltage to a high level in order to send a large amount of power to the distant place. Electric areas, such as 35KV, 66KV, 110KV, 220kv, 330kv, 500kv, etc.
At the electrical load, the step-down transformer is used to reduce the voltage to an appropriate value for use by the user's electrical equipment. When power transformers transmit power, they also have some active losses, but the amount is not large, so the transmission efficiency is very high. The efficiency of small and medium-sized transformers is not less than 95%, and the efficiency of large transformers can reach over 98%.
Second, the classification of power transformers
1, by function:
Power transformers are divided into two categories according to their functions: step-up transformers and step-down transformers. Step-down transformers are used in factory substations. The step-down transformer of the terminal substation is also called the distribution transformer.
2, by capacity:
Power Transformers are divided into two categories according to their capacity series: R8 capacity series and R10 capacity series.
R8 capacity series refers to the capacity level is increased by R3 ≈ 1.33 times, China's old transformer capacity level uses this series, such as: 100kvA, 135kvA, 180kvA, 240kvA, 320kvA, 420kvA, 560kvA, 750kvA, 1000kvA and so on.
R10 capacity series means that the capacity level is incremented by R10 ≈ 1.26.The R10 series has a dense capacity rating for easy selection and is recommended by the IEC (International Electrotechnical Commission).China's new transformer capacity grades use this series, such as: 100KVA, 125kvA, 160kvA, 200kvA, 250kvA, 315kvA, 400kvA, 500kvA, 630kvA, 800kvA, 1000kvA.
3. According to the number of phases:
Power transformers are divided into phases, and there are two types of single-phase and three-phase. Factory substations usually use three-phase power transformers.
4. According to the voltage regulation method:
The power transformer is divided according to the voltage regulation mode, and there are two types of voltage regulation (also known as non-excitation voltage regulation) and on-load voltage regulation. Most of the substations in the factory use unloaded voltage regulators.
5, according to the winding structure:
The power transformer is divided according to the winding structure, and has a single-winding autotransformer, a double-winding transformer, and a three-winding transformer. Most of the plant substations use double winding transformers.
6, according to winding insulation and cooling methods:
Power transformers are classified according to winding insulation and cooling methods, such as oil immersed, dry and pneumatic (SF6). Among them, oil-immersed transformers are also oil-immersed self-cooling, oil-immersed air-cooled, oil-immersed water-cooled and forced oil circulating cooling. Most of the plant substations use oil-immersed self-cooling transformers.
The so-called gas-filled transformer refers to a transformer in which the magnetic circuit (core) and the winding of the transformer are both located in a casing filled with an insulating gas. In the past, SF6 gas was generally used, so it is also called gas insulated transformer.
7, according to the winding conductor material:
The power transformer is divided into two categories: copper winding transformer and aluminum winding transformer. In the past, most of the factory substations used aluminum winding transformers, but low-loss copper winding transformers are now more and more widely used.
Third, the type of power transformer