CN105761920A - Method for designing oil immersible power transformer - Google Patents

Abstract

The invention discloses a method for designing an oil immersible power transformer and belongs to the field of electrical equipment.According to the method, a high-voltage winding, a low-voltage winding, a ferromagnetic core and an oil tank are provided, a low-voltage output terminal is arranged on the low-voltage winding, a connecting pillar is arranged at the low-voltage output terminal and is partially embedded in the low-voltage output terminal and in interference fit with the low-voltage output terminal, a conductive first columnar part in interference fit with an electricity busbar is arranged on the connecting pillar, a conductive second columnar part is coaxially arranged in the first columnar part, the first columnar part is in interference fit with the second columnar part, and the thermal coefficient of expansion of the second columnar part is larger than that of the first columnar part.The method has the advantages that a larger conduction area can be generated with the same splicing length, so that current density is reduced and low temperature rise of the low-voltage output terminal is achieved; the usage of the busbar is reduced, and resources are saved; electric clearance or safe distance is enlarged, and the electric safety of equipment is improved.

Description

Design method of oil-immersed power transformer

technical field

The invention relates to the field of electric equipment, in particular to a design method of an oil-immersed power transformer.

Background technique

In the power distribution room of the factory, the low-voltage output end of the oil-immersed transformer is usually directly connected with the power busbar, and the power busbar is directly connected to the low-voltage output end. The connection between the low-voltage output end and the power busbar is usually overlapped. Then tighten with bolts. As shown in the upper part of Figure 8, this connection method needs to overlap the busbar and the output end by a certain length, so that the current density of the contact surface can be maintained within a certain range, so that the temperature rise at the connection can meet the relevant standards. In order to reduce the temperature rise at the joint, it is usually necessary to increase the overlapping length of the busbar and the terminal to increase the contact area, thereby reducing the current density at the contact surface, and finally making the joint have a lower temperature rise. Increasing the overlapping length will increase the amount of busbars used, thereby increasing the manufacturing cost. The bolts used for fastening will reduce the electrical clearance or safety distance between conductive parts and non-conductive parts. A large spacing will inevitably result in a larger space occupied by the transformer. How to increase the contact area so that the temperature rise of the connection is low, but the electrical gap is not reduced, and the space occupied by the transformer is not increased.

Contents of the invention

The purpose of the present invention is to solve the above problems and provide a design method of an oil-immersed power transformer.

Therefore, the present invention provides a method for designing an oil-immersed power transformer, which includes providing a high-voltage winding, a low-voltage winding, a ferromagnetic core, and an oil tank, so that the high-voltage winding and the low-voltage winding are coaxially arranged and passed through by the ferromagnetic core, and the The high-voltage winding, low-voltage winding and ferromagnetic core are set in the fuel tank, the high-voltage input terminal is set on the high-voltage winding, the low-voltage output terminal is set on the low-voltage winding, the high-voltage input terminal and the low-voltage output terminal are set outside the fuel tank, and the low-voltage output terminal is set. The connecting column is used to embed the connecting column part into the low-voltage output end and have an interference fit with the low-voltage output end. On the connecting column, a conductive first columnar part that is interference-fitted with the power busbar is provided. On the first columnar part, a Conductive second columnar part, make the first columnar part and the second columnar part interference fit, arrange the second columnar part inside the first columnar part, make the thermal expansion coefficient of the second columnar part greater than the first columnar part coefficient of thermal expansion.

Advantageously, the resistivity of the second columnar portion is greater than the resistivity of the first columnar portion.

Specifically, the material of the second columnar portion is set to be aluminum or aluminum alloy, and the material of the first columnar portion is set to be copper or copper alloy.

Preferably, the ratio of the outer diameter of the second columnar portion to the outer diameter of the first columnar portion is set to 0.5-0.8.

Specifically, the second columnar portion is configured as a solid structure, the first columnar portion is configured as a hollow structure, and the second columnar portion penetrates the first columnar portion.

Advantageously, a second through hole is coaxially arranged inside the coupling column, and a first through hole is radially provided on the outer cylindrical surface of the coupling column, so that the first through hole and the second through hole are communicated, and the first through hole is arranged on the The axial middle of the connecting column.

Beneficial effect

Since the design method of the oil-immersed power transformer disclosed in the present invention is to connect the low-voltage output end to the power busbar in a butt-joint connection, compared with the existing overlapping and lapping method, it can bring the following beneficial effects.

1. The same lap length produces more conductive area, thereby reducing the current density and achieving a low temperature rise at the joint.

2. There is no need to overlap and overlap the busbars, which reduces the consumption of busbars and saves resources.

3. Since the fastening bolts and nuts are eliminated, the electrical clearance or safety distance is increased, and the electrical safety of the equipment is improved.

4. Since fastening bolts and nuts are eliminated, the distance between the joint and the non-conductive parts becomes larger, while the occupied space of the transformer does not increase.

Description of drawings

The invention and its advantages will be better understood in the following description of an embodiment given as a non-limiting example with reference to the accompanying drawings, which follow:

Fig. 1 is a perspective view of an existing oil-immersed power transformer, wherein the power busbars have been lapped;

Fig. 2 is a partial enlarged view of place A in Fig. 1;

Fig. 3 is a perspective view of the oil-immersed power transformer disclosed by the present invention, wherein the power busbar has been butted;

Fig. 4 is a partial enlarged view of place B in Fig. 3;

Fig. 5 is a perspective view of an oil-immersed power transformer disclosed by the present invention;

Fig. 6 is a partial enlarged view at C in Fig. 5;

Fig. 7 is a size comparison diagram between the existing power busbar overlapping method and the power busbar docking method disclosed by the present invention;

Fig. 8 is a partially exploded perspective view of the position of the low-voltage output terminal of Fig. 3;

Fig. 9 is a perspective view of the coupling column disclosed in the present invention;

Fig. 10 is a cutaway perspective view of Fig. 9;

Fig. 11 is an exploded perspective view of Fig. 9;

12-13 are schematic diagrams of the arrangement of the coupling columns disclosed in the present invention;

Fig. 14 is a perspective view of a power busbar.

Explanation of reference signs

1. The first columnar part; 2. The second columnar part; 3. Front side; 4. Back side; 5. End face; 6. First through hole; 7. Second through hole.

detailed description

R in this document stands for radius.

As shown in Figure 1, it is the connection method between the low-voltage output end of the existing oil-immersed power transformer and the power busbar. The two are fastened with bolts and nuts, and such a connection is defined as a lap joint, as shown in Figure 2.

As shown in Figure 5, it is an oil-immersed power transformer disclosed by the present invention, which has a high-voltage winding, a low-voltage winding, a ferromagnetic core and an oil tank, the high-voltage winding and the low-voltage winding are coaxially arranged and passed through by the ferromagnetic core, the high-voltage winding, The low-voltage winding and the ferromagnetic core are located in the fuel tank, the high-voltage winding is provided with a high-voltage input terminal, the low-voltage winding is provided with a low-voltage output terminal, and the high-voltage input terminal and the low-voltage output terminal are arranged outside the fuel tank.

As shown in Figure 6, the low-voltage output end is provided with a connecting column, and the connecting column is partially embedded in the low-voltage output end and has an interference fit with the low-voltage output end. The embedded length is half of the length of the connecting column, and the lower half of the connecting column is embedded in the low-voltage output end. The pins on the front of the low-voltage output end securely connect the connecting column and the low-voltage output end.

As shown in Figure 3-4, insert the prefabricated hole on the power busbar into the connecting column on the low-voltage output end. The power busbar and the connecting column have an interference fit. The pins on the front of the busbar securely connect the connecting column and the power busbar, and this connection is defined as butt joint.

As shown in Figure 8, it is a size comparison diagram between the existing power busbar overlapping method and the power busbar docking method disclosed in the present invention, and the upper part is the low-voltage output end of the existing oil-immersed power transformer and the power busbar. In the lap connection mode, the lower part is the connection mode between the low-voltage output end of the oil-immersed power transformer disclosed in the present invention and the power busbar. The solid line on the right side of the figure is an auxiliary line designed to calculate the electrical clearance or safety distance. In order to enhance the contrast effect of the two connection methods, the connection method disclosed in the present invention is directly arranged below the existing connection method. The overlapping lengths of the two connection methods are the same, both being L5, which is reflected in the following: the overlapping length of the power busbar and the low-voltage output end in the existing connection method is L5, and the length of the connecting column in the connection method disclosed in the present invention is also L5. The intuitive change brought about by the two connection methods is the obvious change of the relevant dimensions. L1 is the electrical clearance or safety distance under the existing connection method, L2 is the electrical clearance or safety distance under the connection method disclosed in the present invention, and L3 is the existing The width occupied by the joint in the joint mode, L4 is the occupied width of the joint in the joint mode disclosed in the present invention. It can be seen intuitively from the figure that L2 is obviously larger than L1, and the increased size is approximately the thickness of the busbar plus the height of the nut plus the height of the protruding nut at the end of the bolt. L4 is obviously smaller than L3, and the reduced size is approximately the thickness of the busbar plus the height of the bolt head plus the height of the nut plus the height of the nut protruding from the tail of the bolt. Therefore, the favorable factor (clearance or safety distance) for electrical equipment is improved, while the unfavorable factor (occupancy space) for electrical equipment is reduced.

As shown in FIG. 9 , a coupling column disclosed in the present invention has a cylindrical shape, and chamfers are provided at the ends to facilitate assembly.

As shown in FIG. 10 , a second columnar portion 2 is coaxially disposed inside the first columnar portion 1 , and the first columnar portion 1 and the second columnar portion 2 are interference fit.

As shown in Figure 11, the first columnar part 1 has a hollow structure, the second columnar part 2 runs through the first columnar part 1, and the ratio of the outer diameter of the second columnar part 2 to the outer diameter of the first columnar part 1 is 0.5- 0.8. Both the first and second columnar parts 1 and 2 have electrical conductivity, the coefficient of thermal expansion of the second columnar part 2 is greater than that of the first columnar part 1, and the resistivity of the second columnar part 2 is greater than the resistance of the first columnar part 1 Rate.

After the connecting column is assembled on the low-voltage output end and the power busbar, since the first columnar part 1 is in interference fit with the prefabricated holes of the low-voltage output end and the busbar, the first columnar part 1 is closely attached to the low-voltage output end and the busbar. Together, the first columnar portion 1 of the connecting column can fully carry the current. Since the first columnar part 1 and the second columnar part 2 are also interference-fitted, the first columnar part 1 and the second columnar part 2 are also tightly fitted, and the second columnar part 2 is also capable of carrying current. Therefore, the thermal effect of the first columnar portion 1 and the second columnar portion 2 can be fully exerted. Since the resistivity of the second columnar portion 2 is greater than that of the first columnar portion 1, the temperature of the second columnar portion 2 will be higher than that of the first columnar portion. A columnar part 1, because the thermal expansion coefficient of the second columnar part 2 is greater than the thermal expansion coefficient of the first columnar part 1, therefore, in the case of relatively high temperature and thermal expansion coefficient, the radial expansion of the second columnar part 2 The large phenomenon will be obviously greater than the radial expansion phenomenon of the first columnar part 1, so the second columnar part 2 will closely fit the first columnar part 1 and apply a radially outward pressure to the first columnar part 1, thereby making the The radial dimension of the first columnar part 1 also becomes larger outwards, which eventually causes the first columnar part 1 to fit more closely with the prefabricated holes of the low-voltage output end and power busbar, and also provides radial outward pressure to the prefabricated holes , that is, the pressure between the connecting column and the low-voltage output end and the busbar is greater than that when the connecting column was just assembled, and increasing the contact pressure can also reduce the temperature rise of the contact part.

It can be seen that the interference fit between various features, the matching of resistivity and the matching of thermal expansion coefficient have a significant effect on reducing the temperature rise at the connection between the low-voltage output end and the busbar, and the effects of the three are complementary. The initial interference fit makes the resistivity and thermal expansion coefficient have a basis to play a role, and the effect of resistivity and thermal expansion coefficient intensifies the interference fit, and finally increases the contact pressure at the joint.

As shown in Figure 12, a power busbar with a square cross section has a prefabricated hole in the middle for receiving the connecting column. The distance from the circumference of the prefabricated hole to the edge of the busbar is R, and the width of the busbar is L6. When using the existing overlapping overlapping method to connect, the conductive area of the connection is

S1=L6xL5=(R+2R+R)xL5=4RxL5 (L5 is the lap length, as shown in Figure 8)

When the connection column is used, the conductive area of the connection is

S2=2πRxL5

therefore,

S2:S1=2πR:4R=π/2≈1.57

Therefore, more contact area can be obtained by adopting the overlapping method of connecting columns. Obviously, under the condition of satisfying the mechanical strength, increasing the diameter of the prefabricated hole and reducing the edge distance of the hole can obtain a larger contact area.

As shown in Figure 13, the power busbar with a rectangular cross section has three prefabricated holes for receiving the connecting columns in the middle. The distance from the circumference of the prefabricated hole to the edge of the busbar is R, the shortest distance between each hole is R, and the width of the busbar for L6. When using the existing overlapping overlapping method to connect,

The conductive area of the junction is

S1=L6xL5=(4R+3x2R)xL5=10RxL5

When the connection column is used, the conductive area of the connection is

S2=3x2πRxL5=6πRxL5

therefore,

S2:S1=6πR:10R=3π/5≈1.884

Therefore, more contact area can be obtained by adopting the overlapping method of connecting columns. Obviously, under the condition of satisfying the mechanical strength, increasing the diameter of the prefabricated hole and reducing the edge distance of the hole can obtain a larger contact area.

Therefore, the connecting column disclosed in the present invention has two positive effects, one is to increase the contact pressure, and the other is to greatly increase the conductive area. Under the joint action of these two positive factors, the temperature rise at the joint is large The amplitude is reduced, and the purpose of the present invention is achieved.

As shown in FIG. 7 , at the low-voltage output end of the oil-immersed power transformer disclosed in the present invention, the material of the first columnar part 1 of the connecting column is copper, and the material of the second columnar part 2 is aluminum. Before the connecting column is assembled on the low-voltage output end, three prefabricated holes for receiving the connecting column are processed on the end face 5 of the low-pressure output end along the length direction of the output end. The diameter of the prefabricated hole is slightly smaller than the outer diameter of the connecting column, so that the connecting column and the prefabricated hole Interference fit in the radial direction; the depth of the prefabricated hole is slightly greater than 0.5 times the length of the connecting column. After the prefabricated hole is processed, insert half the length of the connecting column into the prefabricated hole so that the first through hole in the middle of the connecting column is at 5 places on the end face. The through hole for assembling the pin is vertically processed from the front 3 of the low-voltage output end, so that the through hole runs through the front 3 and the back 4 of the low-voltage output end, and at the same time runs through the connecting column. The axis of the through hole intersects the axis of the connecting column, and the low-pressure Both the output end and the coupling post are tightly coupled.

Before the power busbar is assembled at the low-voltage output end, three prefabricated holes are processed on the end face 5 of the power busbar along the length direction of the busbar. Interference fit; the depth of the prefabricated hole is slightly greater than 0.5 times the length of the connecting column. After the prefabricated hole is processed, insert the prefabricated hole on the power busbar into the exposed connecting column on the low-voltage output end until the end face of the power busbar 5 Fit the end face 5 of the low-voltage output end, process the through hole for assembling the pin vertically from the front 3 of the power busbar, make the through hole pass through the front 3 and back 4 of the power busbar, and at the same time pass through the connecting column, the axis of the through hole It intersects with the axis of the connecting column, and the power busbar and the connecting column are tightly connected by pins, finally realizing the fast connection between the power busbar and the low-voltage output end.

After the low-voltage output terminal and the power busbar are docked, the connecting column and the prefabricated hole are axially clearance-fitted, which is conducive to the close contact between the end face of the low-voltage output terminal and the end face of the power busbar. The head of the prefabricated hole is processed with a convenient installation horn. Due to the interference fit between the hole and the pin, when the pin is assembled in place, the axial movement between the low-voltage output end and the power busbar can be restricted, and finally the low-voltage output end, the connecting column, the power busbar, and the pin are firmly connected together.

As shown in Figure 14, in order to distinguish the various surfaces of the busbar and the low-voltage output end, the end surface 5 is defined as a surface composed of the thickness and width of the busbar (or low-voltage output end), that is, the surface marked 5 in Figure 14. The front and back are defined as the surfaces composed of the width and length of the busbar (or low-voltage output end), that is, the surfaces marked 3 and 4 in the figure, 3 is the front, and 4 is the back.

As shown in FIG. 10 , a second through hole 7 is coaxially provided inside the second columnar portion 2 , the first columnar portion 6 has a hollow structure, the second columnar portion 2 penetrates the first columnar portion 1 , and the first columnar portion 1 A first through hole 6 is provided radially on the outer cylindrical surface. The first through hole 6 communicates with the second through hole 7 . The first through hole 6 is located in the axial middle of the first columnar portion 1 .

Due to the setting of the through holes 6 and 7, when the connecting column is inserted into the prefabricated hole at the low pressure output end, the air in the prefabricated hole can be smoothly discharged from the second through hole 7, so that the connecting column can be smoothly assembled in place. When the power busbar is inserted into the installed connecting column, the air in the prefabricated hole of the power busbar can be smoothly discharged from the first through hole 6 through the second through hole 7, so that the second busbar can be smoothly assembled in place .

Embodiment two

In the first embodiment, the material of the first columnar part 1 is changed to a copper alloy, and the material of the second columnar part 2 is changed to an aluminum alloy. Since the hardness of the alloy is relatively high, the second columnar part 2 can be placed in a low temperature environment ( 5 degrees) for a period of time (5 minutes), while the first columnar part 1 is stored for a period of time (5 minutes) in a high temperature environment (80 degrees), with the help of the effect of thermal expansion and contraction, the inner diameter of the first columnar part 1 Slightly larger, while the outer diameter of the first columnar part 1 is slightly smaller, and then the second columnar part 2 can be easily assembled into the first columnar part 1. After the assembled connecting column returns to normal temperature, the first columnar part 1 Interference fit with the second columnar part 2 can be realized. The diameter and length of the connecting column disclosed in the present invention have different specifications to meet the needs of different busbar sizes or low-voltage output end sizes.

Claims (6)

1. the method for designing of an oil-immersed power transformer, it includes providing high pressure winding, low pressure winding, ferromagnetic core and fuel tank, high pressure winding and low pressure winding is made to be coaxially disposed and be passed by ferromagnetic core, high pressure winding, low pressure winding and ferromagnetic core are arranged in fuel tank, high pressure winding arranges high voltage input terminal, arranging low pressure on low pressure winding is outfan, high voltage input terminal and low-voltage output is arranged on outside fuel tank；It is characterized in that, at low-voltage output, connecting column is set, make connecting column be partially submerged into low-voltage output and with low-voltage output interference fit, first columnar part (1) of the conduction of setting and power bus-bar interference fit on connecting column, first columnar part (1) is coaxially disposed second columnar part (2) with electric conductivity, make the first columnar part (1) and the second columnar part (2) interference fit, second columnar part (2) is arranged at the inside of the first columnar part (1), makes the coefficient of thermal expansion coefficient of thermal expansion more than the first columnar part (1) of the second columnar part (2).

2. the method for designing of a kind of oil-immersed power transformer according to claim 1, it is characterised in that make the resistivity resistivity more than the first columnar part (1) of described the second columnar part (2).

3. the method for designing of a kind of oil-immersed power transformer according to claim 2, it is characterised in that the material of described the second columnar part (2) is set to aluminum or aluminium alloy, the material of the first columnar part (1) is set to copper or copper alloy.

4. the method for designing of a kind of oil-immersed power transformer according to claim 1, it is characterised in that the ratio of the external diameter of described the second columnar part (2) and the external diameter of the first columnar part (1) is set to 0.5-0.8.

5. the method for designing of a kind of oil-immersed power transformer according to claim 4, it is characterized in that, second columnar part (2) is set to solid construction, the first columnar part (1) is set to hollow structure, make the second columnar part (2) run through the first columnar part (1).

6. the method for designing of a kind of oil-immersed power transformer according to claim 4, it is characterized in that, the second through hole (7) it is coaxially arranged with inside connecting column, outer cylinder at connecting column is radially arranged the first through hole (6), make the first through hole (7) connect with the second through hole (6), the first through hole (6) is arranged at the axial middle part of connecting column.