Specification
Characteristics of Aluminum transformers
Source：Original
Editing：frank
Time：2022-03-08 18:00
The development and application of aluminum wire transformer in China has a long history. It has been widely used in distribution transformer as early as half a century ago
Pan application. In the 1960s, aluminum wire transformer has appeared in 110kV transformer, and has passed the sudden short-circuit test, which proves that the aluminum wire transformer has reliable mechanical strength. By the 1970s, aluminum wire transformers had made rapid progress in China. No matter the output or single capacity, they had been in the leading position in the world. Aluminum wire transformer was able to develop rapidly at that time. In addition to the government's vigorous implementation of the decision of "replacing copper with aluminum" and the support of manufacturing departments, some internal characteristics of aluminum wire transformer were also the fundamental reason for its wide application.
At present, aluminum wire transformer has declined in China. In addition to other reasons, there is no objective, accurate and complete understanding of the characteristics of aluminum wire transformer
Sex is also one of the important reasons.
Aluminum wire and copper wire are high-quality conductors, which are widely used in the electrical industry. Therefore, the international standard iec-76 and the national standard gb-1094 do not specify which conductor to use. They can be used if they can meet various performance requirements such as electrical, mechanical and heating.
The insulation structure and test voltage of copper and aluminum transformers are exactly the same, but due to the large wire gauge of a single conductor of aluminum wire transformer, it is difficult to wind
The number of group turns is more, so its electrical strength and insulation margin are better than copper wire transformer.
Including the induction test, the winding potential is distributed linearly, that is, the longitudinal potential distribution is only related to the turn potential and the voltage of each cake (or interlayer)
It is related to the number of turns. As mentioned above, if the core diameter of aluminum wire transformer is 0.91 times that of copper wire, its cross-sectional area is 0.828 times, that is, its turn voltage is 0.828 times. If the turn insulation is the same, its long-term turn to turn working field strength is 18% lower than that of copper wire transformer.
Assuming that the number of turns per cake is similar, the diameter of the core is reduced and the radial width of the winding is increased, it can be approximately considered that the average diameter of the winding is similar
The power frequency field strength of aluminum winding is 18% lower than that of copper winding when the number increases by 1.20 times.
One of the main reasons for the marginalization of aluminum wire transformers in recent years is the arbitrary belief that the mechanical performance is not as good as that of copper wire transformers
Lack of scientific and practical basis. The anti short circuit performance of transformer should include thermal stability and dynamic stability in case of sudden short circuit. The dynamic stability performance includes mechanical strength and stability.
The sudden short-circuit time is very short. It can be considered that all the heat generated by the short-circuit current is used for winding heating. Thermal stability of transformer
It means that the temperature of the winding within the specified short-circuit time (2S) does not exceed the standard.
In recent 30 years, with the increasing progress of calculation technology and experimental research, the understanding of transformer dynamic stability has been further improved
High. Now it is generally believed that the transformer short-circuit accident is mainly due to the inter turn short-circuit caused by winding instability and conductor deformation, not just due to the tensile strength. Winding instability mainly includes radial instability, axial instability and inclined collapse of wire cake. Because the longitudinal leakage flux is greater than the transverse leakage flux, radial instability has become the main fault form of transformer.
The mechanical performance of epoxy cast dry-type transformer completely depends on the performance of epoxy resin. It should be said that there is little difference between aluminum wire or copper wire.
The main problem is that the temperature of the conductor rises suddenly when the transformer is short circuited, which is caused by the inconsistency between the thermal expansion coefficient of the conductor and the epoxy resin
Crack. The thermal expansion system of aluminum wire is 24 × 10-6 / ℃, specific coefficient of copper wire (17) × 10-6 / ℃) is closer to the thermal expansion coefficient of the resin (27 × 10-6 / ℃), so its anti cracking performance is better than that of copper conductor in case of short circuit. Therefore, many countries in the world have made it clear that aluminum wire transformer should be used for dry transformer, which is also the reason.
As for the design principle of aluminum wire transformer, the design scheme was formulated at the national discussion meeting on the design principle of aluminum wire transformer in 1968. After 10 years of development and practice, the design task was put forward at the unified design meeting in August 1979 and implemented in the unified design of aluminum wire transformer in China, which has achieved good social and economic results. After half a century of repeated practice, with the development and progress of materials and processes, especially in the improvement and stability of welding technology, it should be said that now is the time to correct the name of aluminum wire transformer. Based on the experience and lessons of many years and combined with the level of modern technology, the author believes that it is appropriate to use aluminum conductor for transformers with capacity of 25MVA / 110kV and 63mva / 220kV and below. It is suggested to pay attention to the following points in the design.
(1) The loss is controlled according to type 13.
(2) The current density shall be less than 1.8a/mm2.
(3) The thickness (or diameter) of the conductor shall be greater than 2.5mm and the width thickness ratio shall be less than 5.
(4) If combined conductor is used, aluminum alloy wire or self-adhesive semi-rigid conductor is recommended.
(5) High voltage winding uses internal shield instead of tangled type to reduce welding points.
(6) Try to use less transposition wires or self-adhesive transposition wires.
(7) The aluminum foil cylindrical structure is popularized in the low-voltage winding of distribution transformer.
After more than 60 years of repeated practice, it is proved that it is appropriate to popularize the application of aluminum wire transformer in small and medium-sized transformers, and it is even more necessary for countries lacking copper resources.
Pan application. In the 1960s, aluminum wire transformer has appeared in 110kV transformer, and has passed the sudden short-circuit test, which proves that the aluminum wire transformer has reliable mechanical strength. By the 1970s, aluminum wire transformers had made rapid progress in China. No matter the output or single capacity, they had been in the leading position in the world. Aluminum wire transformer was able to develop rapidly at that time. In addition to the government's vigorous implementation of the decision of "replacing copper with aluminum" and the support of manufacturing departments, some internal characteristics of aluminum wire transformer were also the fundamental reason for its wide application.
At present, aluminum wire transformer has declined in China. In addition to other reasons, there is no objective, accurate and complete understanding of the characteristics of aluminum wire transformer
Sex is also one of the important reasons.
Aluminum wire and copper wire are high-quality conductors, which are widely used in the electrical industry. Therefore, the international standard iec-76 and the national standard gb-1094 do not specify which conductor to use. They can be used if they can meet various performance requirements such as electrical, mechanical and heating.
The insulation structure and test voltage of copper and aluminum transformers are exactly the same, but due to the large wire gauge of a single conductor of aluminum wire transformer, it is difficult to wind
The number of group turns is more, so its electrical strength and insulation margin are better than copper wire transformer.
Including the induction test, the winding potential is distributed linearly, that is, the longitudinal potential distribution is only related to the turn potential and the voltage of each cake (or interlayer)
It is related to the number of turns. As mentioned above, if the core diameter of aluminum wire transformer is 0.91 times that of copper wire, its cross-sectional area is 0.828 times, that is, its turn voltage is 0.828 times. If the turn insulation is the same, its long-term turn to turn working field strength is 18% lower than that of copper wire transformer.
Assuming that the number of turns per cake is similar, the diameter of the core is reduced and the radial width of the winding is increased, it can be approximately considered that the average diameter of the winding is similar
The power frequency field strength of aluminum winding is 18% lower than that of copper winding when the number increases by 1.20 times.
One of the main reasons for the marginalization of aluminum wire transformers in recent years is the arbitrary belief that the mechanical performance is not as good as that of copper wire transformers
Lack of scientific and practical basis. The anti short circuit performance of transformer should include thermal stability and dynamic stability in case of sudden short circuit. The dynamic stability performance includes mechanical strength and stability.
The sudden short-circuit time is very short. It can be considered that all the heat generated by the short-circuit current is used for winding heating. Thermal stability of transformer
It means that the temperature of the winding within the specified short-circuit time (2S) does not exceed the standard.
In recent 30 years, with the increasing progress of calculation technology and experimental research, the understanding of transformer dynamic stability has been further improved
High. Now it is generally believed that the transformer short-circuit accident is mainly due to the inter turn short-circuit caused by winding instability and conductor deformation, not just due to the tensile strength. Winding instability mainly includes radial instability, axial instability and inclined collapse of wire cake. Because the longitudinal leakage flux is greater than the transverse leakage flux, radial instability has become the main fault form of transformer.
The mechanical performance of epoxy cast dry-type transformer completely depends on the performance of epoxy resin. It should be said that there is little difference between aluminum wire or copper wire.
The main problem is that the temperature of the conductor rises suddenly when the transformer is short circuited, which is caused by the inconsistency between the thermal expansion coefficient of the conductor and the epoxy resin
Crack. The thermal expansion system of aluminum wire is 24 × 10-6 / ℃, specific coefficient of copper wire (17) × 10-6 / ℃) is closer to the thermal expansion coefficient of the resin (27 × 10-6 / ℃), so its anti cracking performance is better than that of copper conductor in case of short circuit. Therefore, many countries in the world have made it clear that aluminum wire transformer should be used for dry transformer, which is also the reason.
As for the design principle of aluminum wire transformer, the design scheme was formulated at the national discussion meeting on the design principle of aluminum wire transformer in 1968. After 10 years of development and practice, the design task was put forward at the unified design meeting in August 1979 and implemented in the unified design of aluminum wire transformer in China, which has achieved good social and economic results. After half a century of repeated practice, with the development and progress of materials and processes, especially in the improvement and stability of welding technology, it should be said that now is the time to correct the name of aluminum wire transformer. Based on the experience and lessons of many years and combined with the level of modern technology, the author believes that it is appropriate to use aluminum conductor for transformers with capacity of 25MVA / 110kV and 63mva / 220kV and below. It is suggested to pay attention to the following points in the design.
(1) The loss is controlled according to type 13.
(2) The current density shall be less than 1.8a/mm2.
(3) The thickness (or diameter) of the conductor shall be greater than 2.5mm and the width thickness ratio shall be less than 5.
(4) If combined conductor is used, aluminum alloy wire or self-adhesive semi-rigid conductor is recommended.
(5) High voltage winding uses internal shield instead of tangled type to reduce welding points.
(6) Try to use less transposition wires or self-adhesive transposition wires.
(7) The aluminum foil cylindrical structure is popularized in the low-voltage winding of distribution transformer.
After more than 60 years of repeated practice, it is proved that it is appropriate to popularize the application of aluminum wire transformer in small and medium-sized transformers, and it is even more necessary for countries lacking copper resources.
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