CN210956422U - Improved three-phase high-temperature superconducting transformer - Google Patents

Abstract

The utility model discloses an improved three-phase high-temperature superconducting transformer, which is composed of: a high-voltage bushing (1), a low-voltage bushing (2), a liquid nitrogen conduit (3), a high-voltage tube (4), an iron core (5), Dewar (6), primary/secondary superconducting winding (7), liquid nitrogen cooling system (8), the primary/secondary superconducting winding, the primary side adopts a single solenoid winding, the secondary side Two types of air gaps are used for double-cake windings, and the air gap increases from the middle of the winding to the end, or the primary side solenoid winding is split into a structure in which multiple solenoids are arranged axially, and the double-cake winding with equal air gaps on the secondary side . The technical effect of the utility model: the secondary side double cake winding adopts two kinds of air gaps and three kinds of air gaps respectively, and the air gaps gradually increase and decrease from the middle part of the winding to the end part, and the radial leakage magnetic field is greatly reduced; The side solenoid winding is axially split into two and three-segment windings, and the radial leakage magnetic field is also greatly reduced.

Description

An improved three-phase high temperature superconducting transformer

technical field

The utility model relates to a transformer, in particular to an improved three-phase high temperature superconducting transformer.

Background technique

Compared with traditional transformers, high-temperature superconducting transformers use high-temperature superconducting tapes to replace copper wires, so that the coils operate in a liquid nitrogen environment. High-temperature superconducting transformers have the advantages of small size, light weight, high efficiency, and no potential fire hazards and environmental pollution, which meet the needs of scientific and technological development and the times. The magnitude and distribution of the leakage magnetic field of high-temperature superconducting transformers have a great influence on the characteristics and parameters of the transformer, and play a decisive role in the inductive reactance of the transformer coil, the additional loss and the loss of the transformer metal components. The leakage magnetic field is also closely related to the electromagnetic force acting on the winding under normal and fault conditions, and also has a great influence on the temperature rise of other components of the winding.

In particular, the leakage magnetic field of the high temperature superconducting transformer reduces the critical current of the winding and increases the AC loss. Due to the anisotropy of the strip, the radial magnetic field component has a much larger effect on the critical current and AC losses than the axial component.

Therefore, reducing the magnetic field, especially its radial component, is particularly important for the electromagnetic design of high-temperature superconducting transformers.

Utility model content

The technical problem to be solved by the utility model is that the leakage magnetic field, especially its radial component, should be reduced as much as possible in the single-phase high temperature superconducting transformer.

The utility model solves the above-mentioned technical problems through the following technical solutions:

An improved three-phase high-temperature superconducting transformer, its composition includes: high-voltage bushing 1, low-voltage bushing 2, liquid nitrogen conduit 3, high-voltage tube 4, iron core 5, Dewar 6, primary/secondary superconducting winding 7. The liquid nitrogen cooling system 8 is characterized in that: the primary/secondary superconducting winding adopts a single solenoid winding on the primary side, and two air gaps of a double-cake winding on the secondary side, and the air gap is from the middle of the winding to the end The part is enlarged or the primary side solenoid winding is split into a structure in which multiple solenoids are arranged axially, and the secondary side is equal to the air gap of the double-cake winding.

The iron core 5 is a core-type transformer iron core, which adopts a three-phase three-column type or a three-phase five-column type.

The liquid nitrogen cooling system 8 consists of a heat exchange unit, a main Dewar unit and a liquid pump unit.

Dewar 6 uses fiberglass dewar.

Positive technical effects of the present utility model: The technical effect is only considered from the perspective of reducing leakage magnetic field, especially the radial leakage magnetic field. The double-cake winding on the secondary side adopts two types of air gaps and three types of The middle part of the winding gradually increases and decreases toward the end, and the radial leakage magnetic field is greatly reduced; the primary side solenoid winding is axially split into two and three-segment windings, and the radial leakage magnetic field is also greatly reduced.

Description of drawings

Fig. 1 is the composition diagram of the improved three-phase high temperature superconducting transformer.

Figure 2 is a schematic diagram of primary/secondary superconducting windings.

Figure 3 is a three-phase three-column and three-phase five-column iron core lamination diagram of the transformer.

Figure 4 is a diagram of a liquid nitrogen cooling system.

Figure 5 Schematic diagram of the structure of the FRP Dewar.

In the figure: 1 is high voltage bushing, 2 is low voltage bushing, 3 is liquid nitrogen conduit, 4 is high pressure tube 5 is iron core, 6 is Dewar, 7 is primary/secondary superconducting winding, 8 is liquid nitrogen cooling system.

Detailed ways

The specific embodiments of the present utility model will be further described below with reference to the accompanying drawings.

1. The overall structure of the improved single-phase high temperature superconducting transformer

1) Improved three-phase high-temperature superconducting transformer, its composition includes: high-voltage bushing 1, low-voltage bushing 2, liquid nitrogen conduit 3, high-voltage tube 4, iron core 5, Dewar 6, primary/secondary superconducting winding 7. The liquid nitrogen cooling system 8 is characterized in that: the primary/secondary superconducting winding adopts a single solenoid winding on the primary side, and two air gaps of a double-cake winding on the secondary side, and the air gap is from the middle of the winding to the end The part is enlarged or the primary side solenoid winding is split into a structure in which multiple solenoids are arranged axially, and the secondary side is equal to the air gap of the double-cake winding.

2) The iron core 5 is a core-type transformer iron core, which adopts a three-phase three-column type or a three-phase five-column type.

3) Liquid nitrogen cooling system 8 is composed of: heat exchange unit, main Dewar unit and liquid pump unit.

4) Dewar 6 adopts FRP Dewar.

2. Three-phase transformer core

Three-phase transformers are the most produced and used transformers. Because the price of a three-phase transformer is lower than that of three single-phase transformers to form a three-phase group, and the installation area of a three-phase transformer is smaller than that of three single-phase transformers to form a three-phase group, generally All three-phase transformers are used, and three-phase groups are used only when transportation conditions are limited or there are special requirements. However, if a three-phase transformer needs a backup transformer, a three-phase transformer is required; when a single-phase transformer forms a three-phase group, only one single-phase transformer is required for backup.

1) Three-phase three-column iron core. The most widely used three-phase three-column iron core has simple stacking process and small iron loss per unit mass, that is, the loss coefficient of the transformer is small. Since the three phases are in the same plane, the lengths of the three-phase magnetic circuits are not equal, and the reluctance of the two-phase magnetic circuits on both sides is larger than that of the middle phase. When the applied three-phase voltage is symmetrical, the magnetic flux of each phase is equal, but the no-load loss of the three-phase is not equal, and the no-load current of the three-phase is also asymmetrical. In a large transformer, its unbalance is small. However, since the no-load current accounts for a small proportion when the transformer is running under load, it will not have a great impact on the actual operation of the transformer.

2) Three-phase five-column iron core. Due to the limitation of transportation height, the three-phase three-column iron core cannot meet the transportation requirements, so the height of the iron yoke has to be reduced, and the iron core is made into a three-phase five-column type. A, B, C three-phase windings have three core legs and two iron yokes with vertical and horizontal parts.

3. Complex subcooled liquid nitrogen cooling system

The supercooled liquid nitrogen cooling system is shown in the figure. It consists of three functional units, namely the heat exchange unit, the main Dewar unit and the liquid nitrogen pump unit. Connect each unit with a flexible transfer tube. The heat exchange unit includes two parts, the saturated liquid nitrogen cooled by the vacuum pump and the heat exchanger that subcools the liquid nitrogen; the liquid nitrogen pump unit includes the subcooled liquid nitrogen and the circulating pump, and the circulating pump transfers the liquid nitrogen to the Dewar; the main Dewar The unit contains subcooled liquid nitrogen and a transformer submerged in liquid nitrogen. Below the Dewar level, the temperature is essentially uniform. Compared with the simple supercooled liquid nitrogen cooling system, this system is more complicated, but the use of 108kPa liquid nitrogen greatly improves the insulation performance of the superconducting transformer in the system.

4. Dewar Design

The superconducting winding works in a low temperature environment. If the iron core and the winding are in the same low temperature environment, that is, the so-called cold iron core structure, the superconducting transformer is similar to the conventional oil-type transformer, and it is easier to manufacture. However, the no-load loss of the transformer core always exists, the resistivity of the core material will decrease at low temperature, and the eddy current loss will increase. The power consumption of 1W at liquid nitrogen temperature is equivalent to the power consumption of 15W at room temperature, which brings a great burden to low-temperature refrigeration and reduces the efficiency of the transformer. Therefore, the core and the winding must be separated, and the winding must be placed at a low temperature separated from the core. Dewar container.

There are three basic ways of heat exchange: solid heat conduction, convective heat exchange and heat radiation. The size of the heat conduction of a solid is proportional to its cross section, and reducing the cross section can greatly reduce the heat conduction of the solid; convection heat exchange is the collision of gas molecules with each other, transferring heat to the area with low temperature, and the increase of vacuum degree, that is, the reduction of gas molecules can reduce convection Generated heat transfer; any substance, as long as the temperature is higher than 0, will radiate heat outward through thermal radiation, and the smooth metal foil film can reflect the thermal radiation and reduce radiation heat leakage. The traditional low-temperature Dewar is made of stainless steel, which has high strength. The inner wall of the Dewar can be very thin, which can effectively reduce the solid heat conduction; the stainless steel has high density and no outgassing, and can maintain the vacuum degree and effectively reduce the convective heat exchange. Multi-layer smooth metal foil is wrapped around it as a radiation screen, which can effectively prevent the spread of thermal radiation; at the same time, a certain amount of activated carbon is placed in the middle of the interlayer to adsorb excess gas molecules. Therefore, traditional low-temperature Dewars are generally made of stainless steel, which has the advantages of high strength, long vacuum holding time, and good thermal insulation performance. The vacuum degree of stainless steel Dewars can be pumped to more than 10Pa, and the vacuum degree can be maintained for more than two years. However, the superconducting transformer uses a low-temperature Dewar to surround the magnetic circuit of the iron core, so the Dewar for the transformer cannot use any metal material, and the FRP material with good insulation performance should be selected. In the interlayer of inner and outer Dewar walls, the use of radiation shield is different from that of conventional Dewars. The smooth metal foil of radiation shield should be thin metal foil with a cutout to avoid short circuit rings in the interlayer of Dewar, as shown in Figure 5. Due to the outgassing characteristics of FRP materials, the Dewar vacuum cannot be maintained for a long time, so the low-temperature FRP Dewar for superconducting transformers needs to be evacuated regularly.

The size of the FRP Dewar is related to the size of the winding. The inner wall of the Dewar should keep a certain distance from the iron core and the high-voltage winding, and the outer wall should keep a certain distance from the outermost low-voltage winding. The design height of the 630kVA Dewar is 680mm, and the inner and outer diameters They are 410mm and 760mm respectively.

5. Primary/Secondary Superconducting Windings

1) Pie winding

There are several different types of pie windings, but with the same characteristics as the pie type. It is to arrange the wires into round cakes along the radial direction of the winding, and then connect the round cakes in series in different ways to form different types of windings. The axial compression force of the pie winding is easier to control than that of the cylindrical winding. In general, the axial mechanical strength of the pie winding is greater than that of the cylindrical winding. Therefore, pie windings have been widely used in large and medium-sized transformers. The various types of pie windings are introduced below.

The continuous winding is that when the winding is wound, the wire transitions from the first pie to the second, the third... until the last pie without interruption. This winding method of continuous winding is relatively simple and easy to operate. The wires of the odd-numbered pie are wound from the outside to the inside in turn, which is called the reverse pie. The wires of the even-numbered pie are wound from the inside to the outside in turn, which is called a positive pie.

A reverse pie and a positive pie form a unit, so the number of piecings in a continuous winding must be an even number. The number of bus pie is generally 30-100, and it is an even number, but when the middle is out, it is a multiple of 4. When the number of turns of the wire cake is composed of two or more wires in parallel, the parallel wires should be transposed on the inside of the reverse cake and the outside of the positive cake. The continuous winding can use a wide range of voltages (3-110kVA), the capacity can be large or small (800-10000kVA and above), and high, medium and low voltage windings can be used.

2) Spiral tube winding

When the voltage level of the winding is 10kV and below and the capacity is large, the number of turns of the winding is very small, but the cross-sectional area required by the wire is very large, and the winding is made of a spiral tube. The so-called spiral tube winding is to screw many wires with equal cross-sectional areas that meet the design requirements into one (two, three, four...) group, and then make this group of wires into a winding like a coiled spring. This group of wires rotates once on the winding die to form one turn in the winding. Generally, the total number of turns of the toroidal winding is between tens of turns and 150 turns. The characteristics of the spiral tube winding structure are as follows:

(1) Each turn in the spiral tube winding is shaped like a round cake, so the spiral tube winding is attributed to the pie winding.

(2) It is necessary to choose different ways to transpose the wires in the windings according to the number of parallel windings, so that the circulating current value between the wires in the windings is the lowest.

(3) In order to evenly compress the spiral tube winding in the axial direction, it is necessary to arrange the inside of the spiral tube winding very carefully according to the characteristics of the spiral tube winding - the wire cake of the spiral tube type and different transposition methods.

There are several types of spiral tube windings, such as single spiral tube, double spiral tube, triple spiral tube and quadruple spiral tube.

(1) Single spiral tube winding. The single spiral tube winding is to screw all the wires into a group and wind them into a spiral tube structure.

(2) Double-spiral and quad-spiral windings. Due to the requirements of transposition, the number of parallel conductors per turn should be a multiple of 2 and 4, respectively. Among them, the double spiral tube is to divide all the parallel wires into two columns with the same number of turns, and then wind them together in a spiral tube way. The entire double helical winding should be cross-transposed between the two columns of wires, and the number of complete transpositions is equal to the number of parallel wires. The entire double helix winding can be fully transposed one or more times. The winding method of the four-spiral tube is similar to that of the double-spiral tube, that is, all parallel wires are divided into four columns of equal turns, and then wound in the same way as the double-spiral tube winding. Another method is to divide the four-column wires into two two-column, and cross-transpose each, and determine the number of complete transpositions according to the specific conditions of the winding.

(3) Three rows of spiral tube windings. The three-row spiral tube winding is a type of spiral tube winding, and its structural characteristics are basically the same as those of the double spiral tube. The total number of three-column spiral tube winding wires can be an integer multiple of 3, and in general, an integer multiple of 6 is taken. It performs up and down cross transposition like the double helical tube, but it must follow the unique rule of the three-column spiral tube type, that is, the first transposition is performed between the 1st and 2nd wire cakes of the same turn, and the first wire The top wire of the cake is transposed to the top of the second wire cake, and the bottom wire of the second wire cake is transposed to the bottom of the first wire cake; the second transposition Between the 2nd and 3rd wire cakes of the same turn, transpose the uppermost wire of the 3rd wire cake to the uppermost wire of the 2nd wire cake, and at the same time place the lowermost wire of the second wire cake The first wire is transposed to the bottom of the third wire cake; then the above transposition sequence is repeated until an equidistant complete transposition is completed.

(4) Multi-column spiral tube windings. The multi-column spiral tube winding refers to the spiral tube winding with more than 4 coils wound in parallel. This multi-column spiral tube winding is often used as a voltage regulating winding on a transformer with a large capacity. At this time, the winding may not be transposed, but in order to facilitate the connection of each tap lead, a standard transposition can also be performed in the middle of the winding.

Claims (4)

1. An improved three-phase high temperature superconducting transformer, comprising: high-voltage bushing (1), low-voltage bushing (2), liquid nitrogen pipe (3), high-voltage tube (4), iron core (5), dewar (6), once/secondary superconducting winding (7), liquid nitrogen cooling system (8), its characterized in that: the primary side of the primary/secondary superconducting winding adopts a single solenoid winding, the secondary side of the primary/secondary superconducting winding adopts two air gaps of a double-pancake winding, the air gaps are increased from the middle part to the end part of the winding or the primary side solenoid winding is split into a structure with a plurality of solenoids arranged axially, and the double-pancake winding with equal air gaps is arranged on the secondary side.

2. The three-phase high temperature superconducting transformer of claim 1, wherein: the iron core (5) is a core type transformer iron core and adopts a three-phase three-column type or a three-phase five-column type.

3. The three-phase high temperature superconducting transformer of claim 1, wherein: the liquid nitrogen cooling system (8) comprises: a heat exchange unit, a main dewar unit and a liquid pump unit.

4. The three-phase high temperature superconducting transformer of claim 1, wherein: the Dewar (6) is made of glass fiber reinforced plastic.

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