CN210956422U

CN210956422U - Improved three-phase high-temperature superconducting transformer

Info

Publication number: CN210956422U
Application number: CN201921425125.3U
Authority: CN
Inventors: 张晨丹; 成星辰
Original assignee: Nanjing University of Science and Technology
Current assignee: Nanjing University of Science and Technology
Priority date: 2019-08-29
Filing date: 2019-08-29
Publication date: 2020-07-07
Anticipated expiration: 2029-08-29

Abstract

The utility model discloses a modified three-phase high temperature superconducting transformer, its constitution includes: the high-voltage coil comprises a high-voltage sleeve (1), a low-voltage sleeve (2), a liquid nitrogen guide pipe (3), a high-voltage pipe (4), an iron core (5), a Dewar (6), a primary/secondary superconducting winding (7) and a liquid nitrogen cooling system (8), wherein 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. The technical effects of the utility model: the secondary side double-cake winding respectively adopts two air gaps and three air gaps, the air gaps are gradually increased and decreased from the middle part to the end part of the winding, and the radial leakage magnetic field is greatly reduced; the primary side solenoid winding is axially split into two-section winding and three-section winding, and the radial leakage magnetic field is reduced by a large amount.

Description

Improved three-phase high-temperature superconducting transformer

Technical Field

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

Background

Compared with the traditional transformer, the high-temperature superconducting transformer adopts the high-temperature superconducting strip to replace a copper wire, so that the coil runs in a liquid nitrogen environment. The high-temperature superconducting transformer has the advantages of small volume, light weight, high efficiency, no potential fire hazard, no environmental pollution and the like, and meets the requirements of scientific and technological development and times. The size and the distribution rule of the leakage magnetic field of the high-temperature superconducting transformer have great influence on the characteristics and the parameters of the transformer and play a decisive role in the inductive reactance and the additional loss of a transformer coil and the loss of a metal component of the transformer. The leakage magnetic field is also closely related to the electromagnetic force acting on the winding in normal and fault states, and has great influence on the temperature rise of other parts of the winding.

Especially, the leakage magnetic field of the high-temperature superconducting transformer reduces the critical current of the winding and increases the alternating current loss. Due to the anisotropy of the strip, the radial magnetic field component has a much greater effect on the critical current and the ac losses than the axial component.

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

SUMMERY OF THE UTILITY MODEL

The to-be-solved technical problem of the utility model is to reduce the leakage magnetic field as far as possible especially its radial component in single-phase high temperature superconducting transformer.

The utility model discloses an above-mentioned technical problem is solved through following technical scheme:

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.

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.

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

The Dewar 6 is made of glass fiber reinforced plastic Dewar.

The utility model discloses an actively technological effect: the technical effect is only considered from the angle of reducing the leakage magnetic field, particularly from the angle of radial leakage magnetic field, the secondary side double-cake winding respectively adopts two air gaps and three air gaps, the air gaps are gradually increased and decreased from the middle part to the end part of the winding, and the radial leakage magnetic field is greatly reduced; the primary side solenoid winding is axially split into two-section winding and three-section winding, and the radial leakage magnetic field is reduced by a large amount.

Drawings

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

Fig. 2 is a schematic diagram of the primary/secondary superconducting winding.

Fig. 3 is a laminated diagram of three-phase three-limb and three-phase five-limb iron cores of the transformer.

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

FIG. 5 is a schematic view of a glass fiber reinforced plastic Dewar.

In the figure: 1 is a high-voltage sleeve, 2 is a low-voltage sleeve, 3 is a liquid nitrogen conduit, 4 is a high-voltage tube 5 is an iron core, 6 is a dewar, 7 is a primary/secondary superconducting winding, and 8 is a liquid nitrogen cooling system.

Detailed Description

The following description will further describe embodiments of the present invention with reference to the accompanying drawings.

1. Improved single-phase high-temperature superconducting transformer integral structure

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

4) The Dewar 6 is made of glass fiber reinforced plastic Dewar.

2. Three-phase transformer iron core

Three-phase transformers are the most produced and used transformers. Because the price of a three-phase transformer is lower than that of a three-phase group formed by three single-phase transformers, and the installation area of the three-phase transformer is smaller than that of the three-phase group formed by three single-phase transformers, the three-phase transformer is generally used, and the three-phase group is used only when the transportation condition is limited or special requirements are met. However, if the three-phase transformer needs a spare transformer, a three-phase transformer is needed; when the single-phase transformer forms a three-phase group, only one single-phase transformer needs to be used for standby.

1) Three-phase three-column iron core. The three-phase three-column iron core which is most applied has simple stacking process and small iron loss per unit mass, namely the loss coefficient of the transformer is small. Because the three phases are in the same plane, the lengths of the three-phase magnetic circuits are unequal, and the magnetic resistance of the two-phase magnetic circuits at the two sides is larger than that of the middle one-phase magnetic circuit. When the external three-phase voltage is symmetrical, the magnetic fluxes of all phases are equal, but the no-load losses of the three phases are unequal, and the no-load currents of the three phases are also asymmetrical in the large-scale transformer, so that the unbalance degree is small. However, the proportion of the no-load current in the load operation of the transformer is small, so that the actual operation of the transformer is not greatly influenced.

2) Three-phase five-column iron core. Because of the limitation of transportation height, the three-phase three-column iron core can not meet the transportation requirements, the height of the iron yoke has to be reduced, the iron core is made into a three-phase five-column type, A, B, C three-phase windings are respectively sleeved on three middle iron core columns of the iron core, and the iron core comprises three core columns and two iron yokes respectively provided with a vertical part and a horizontal part.

3. Complex supercooled liquid nitrogen cooling system

The supercooled liquid nitrogen cooling system is shown in the figure and consists of 3 functional units, namely a heat exchange unit, a main Dewar unit and a liquid nitrogen pump unit. Each unit is connected with a flexible transmission pipe. The heat exchange unit comprises a saturated liquid nitrogen cooled by a vacuum pump and a heat exchanger for supercooling the liquid nitrogen; the liquid nitrogen pump unit comprises supercooled liquid nitrogen and a circulating pump, and the circulating pump transmits the liquid nitrogen into the Dewar; the main dewar unit contains subcooled liquid nitrogen and a transformer immersed in the liquid nitrogen. The temperature is substantially uniform below the dewar level. Compared with a simple supercooled liquid nitrogen cooling system, the system is more complex, but the insulating property of a superconducting transformer in the system is greatly improved by using 108kPa liquid nitrogen.

4. Dewar design

The superconducting winding works in a low-temperature environment, and if the iron core and the winding are both in the low-temperature environment, namely a so-called cold iron core structure is adopted, the superconducting transformer is similar to a conventional oil type transformer, and the manufacturing is easier. However, no-load loss of the transformer core exists all the time, the resistivity of the core material is reduced at low temperature, and the eddy current loss is increased. The power consumed at 1W at the liquid nitrogen temperature is equivalent to the power consumed at 15W at the room temperature, which puts a great burden on cryogenic refrigeration and reduces the efficiency of the transformer, so the core must be separated from the winding, which is placed in a cryogenic dewar vessel spaced from the core.

There are three basic ways of heat exchange: solid heat conduction, convective heat exchange and thermal radiation. The solid heat conduction heat quantity is in direct proportion to the section of the solid heat conduction heat quantity, and the solid heat conduction can be greatly reduced by reducing the section; the convection heat exchange is that gas molecules collide with each other to transfer heat to a region with low temperature, and the heat transfer generated by convection can be reduced by increasing the vacuum degree, namely reducing the gas molecules; any substance can radiate heat outwards through heat radiation as long as the temperature is higher than 0, and the smooth metal wave foil film can reflect the heat radiation out to reduce the radiation heat leakage. The traditional low-temperature Dewar is made of stainless steel materials, so that the strength is high, the inner wall of the Dewar can be very thin, and the solid heat conduction is effectively reduced; the stainless steel has high density, does not deflate, can maintain the vacuum degree and effectively reduce convection heat exchange; a plurality of layers of smooth metal foils are wrapped between the inner and outer interlayers of the Dewar to be used as a radiation screen, so that the transmission of thermal radiation is effectively prevented; meanwhile, a certain amount of activated carbon is also placed in the middle of the interlayer to adsorb redundant gas molecules. Therefore, the traditional low-temperature Dewar is generally made of stainless steel materials and has the advantages of high strength, long vacuum maintaining time, good heat insulation performance and the like, the vacuum degree of the stainless steel Dewar can be pumped to be 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 can not use any metal material, and the glass fiber reinforced plastic material with good insulating property should be selected. In the inner and outer dewar wall interlayer, the radiation shield is different from the conventional dewar, and the smooth metal foil of the radiation shield should be thin metal foil with a notch to avoid forming a short circuit ring in the dewar interlayer, as shown in fig. 5. Because the dewar vacuum cannot be maintained for a long time due to the outgassing characteristics of the frp material, the low temperature frp dewar for the superconducting transformer needs to be periodically evacuated.

The size of the glass fiber reinforced plastic dewar is related to the size of the winding, the inner wall of the dewar is kept a certain distance from the iron core and the high-voltage winding, the outer wall of the dewar is kept a certain distance from the outermost low-voltage winding, the design height of the dewar of 630kVA is 680mm, and the inner diameter and the outer diameter of the dewar are 410mm and 760mm respectively.

5. Primary/secondary superconducting winding

1) Cake type winding

There are several different types of pancake windings, but with the same characteristic of pancake type. The wire is arranged in the radial direction of the winding into a round cake shape, and then the round cake-shaped wire cakes are connected in series in different modes to form different types of windings. The axial pressing force of the pancake winding is easier to control than that of the cylindrical winding, and the axial mechanical strength of the pancake winding is generally higher than that of the cylindrical winding. Thus, pancake windings have been used in large and medium-sized transformers. Various types of pancake windings are described separately below.

The continuous winding is that when winding, the conducting wire is continuously transited from the first cake to the second and third … … until the last cake. The winding method of the continuous winding is simple and convenient to operate. The conducting wires of the odd line cakes are wound from the outer side to the inner side in sequence and are called reverse cakes. The wires of the even number of wire cakes are wound from the inner side to the outer side in sequence and are called positive cakes.

One reverse cake and one forward cake constitute one unit, so the number of line cakes of the continuous winding must be even. The number of bus cakes is generally 30-100 and is even, but when the bus is outgoing, the number of bus cakes is a multiple of 4. When the number of turns of the wire cake is formed by connecting two or more wires in parallel, the parallel wires need to be transposed at the inner side of the reverse cake and the outer side of the forward cake. The voltage range of the continuous winding is wide (3-110kVA), the capacity can be large or small (800-.

2) Spiral tube winding

When the voltage level of the winding is 10kV or below and the capacity is large, the number of turns of the winding is small, but the cross-sectional area required by the wire is large, and the winding is made into a spiral tube type. The spiral tube type winding is that a plurality of wires with equal cross section area meeting the design requirement are screwed into one (two, three or four … …) group, and then the group of wires are made into one winding like a rolling spring. The set of wires is rotated once on the winding former to form one turn in the winding, typically a total number of turns in the helical winding of between tens of turns and 150 turns. The spiral tube winding structure is characterized as follows:

(1) each turn in the spiral winding is shaped much like a pie, thus, the spiral winding is integrated into a pie winding.

(2) The wires in the winding must be transposed in different ways according to the number of the windings, so as to minimize the value of the circulating current between the wires in the winding.

(3) In order to compress the spiral tube type winding evenly in the axial direction, the interior of the spiral tube type winding must be arranged very carefully according to the characteristics of the spiral tube type winding, such as spiral tube type wire cakes and different transposition modes.

The spiral tube type winding comprises a single spiral tube, a double spiral tube, a three spiral tube, a four spiral tube and the like.

(1) A single helix tube winding. The single spiral tube winding is formed by winding all the wires into a spiral tube structure by screwing.

(2) Double helix and four helix tube windings. Due to the transposition requirement of the double helix tube and the four helix tube, the number of the parallel conductors of each turn is respectively multiple of 2 and 4. The double spiral tubes divide all the parallel wires into two rows with equal turns, and then the wires are wound together in a spiral tube mode. The whole double-spiral tubular winding needs to perform cross transposition between two lines of wires, and the number of times of one-time complete transposition is equal to the number of the wires connected in parallel. The whole double-spiral winding can be completely transposed one or more times. The winding method of the four spiral tubes is similar to that of the double spiral tubes, namely all the parallel wires are divided into four rows with equal turns, and then the four rows are wound in the same winding mode of the double spiral tube type winding. Another method is to divide the four-column conductors into two columns and perform cross-transposition separately, and the number of complete transposition is determined according to the specific condition of the winding.

(3) Three rows of helical tube windings. The three-row spiral winding is a type of spiral winding, and its structural features are substantially indistinguishable from a double spiral. The total number of the three rows of the spiral tube type winding wires can be an integral multiple of 3, and in general, the total number of the three rows of the spiral tube type winding wires is an integral multiple of 6. The method is characterized in that the method carries out up-and-down cross transposition like a double-spiral tube, but the method must follow the special rule of three-row spiral tubes, namely, the first transposition is carried out between the 1 st and 2 nd wire cakes of the same turn, the topmost lead of the 1 st wire cake is transposed to the topmost of the 2 nd wire cake, and the bottommost lead of the 2 nd wire cake is transposed to the bottommost of the 1 st wire cake; performing transposition for the second time between the 2 nd and 3 rd wire cakes of the same turn, transposing the topmost lead of the 3 rd wire cake to the topmost lead of the 2 nd wire cake, and transposing the bottommost lead of the 2 nd wire cake to the bottommost lead of the 3 rd wire cake; and then repeating the transposition sequence until completing equidistant complete transposition.

(4) And a plurality of rows of spiral tube windings. The multi-column spiral tube type winding refers to a spiral tube winding with the number of wound wire cakes larger than 4. Such multi-row helical tube windings are often used as regulating windings on very high capacity transformers. At this time, the windings may not be transposed, but a standard transposition may be performed in the middle of the windings to facilitate connection of each tap lead.

Claims

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.