Variable-section combined shielding structure of stator end

Abstract

The present invention relates to the field of steam turbine generators. Disclosed is a stator end variable-cross-section combined shielding structure. A stator end shielding structure and a ventilatio

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of turbo-generators, and in particular to a variable-section combined shielding structure of a stator end. BACKGROUND

[0002] The design of large turbo-generators is limited by many factors, so the cooling demands can be satisfied using high parameters, high air gap magnetic density and high specific electric load. For full-speed generators, the pitch of stator coils is large, the number of coils in each phase is large, the size of the stator end is long, and there is a large rotating leakage magnetic field at the end. A leakage magnetic field rotating with the rotor is also formed at the rotor end, and the stator leakage magnetic field and the rotor leakage magnetic field are synthesized into the end leakage magnetic field. The end leakage magnetic field, which is mainly based on the stator leakage magnetic field, is complicated in distribution and affected by many factors, such as specific electric load, short circuit ratio, end structure, material and size. The stator end leakage flux passes along a path with the minimum magnetic resistance, so the stator and rotor leakage flux is concentrated at an inner ring of the stator pressing ring, pressing fingers and tooth heads of iron core at the edge section, leading to the increase of additional loss and temperature rise in these parts. When the generator is in over-voltage operation, especially when the generator is in leading power factor operation, the synthetic flux of stator and rotor is added, and the end leakage flux is increased, which makes the temperature of these structures exceed an allowable limit, seriously endangering the operation of the generator, and even burning down the end structure of the generator, resulting in a major shutdown accident. Therefore, there are usually strict restrictions on the leading power factor operation and over-voltage operation state of generators in the operation conditions of generator sets.

[0003] However, due to the operation demands of grids, some generators are often required to operate at the leading power factor to stabilize the grid voltage, and large generators are required to have a certain ability to operate at the leading power factor. For a direct-current extra high voltage power transmission and transformation system, a synchronous phase modifier is required to be provided, which is specially used for leading or lagging power factor operation, so as to adjust the reactive power of the grid, improve the quality of the grid and strengthen the response ability of the grid to sudden short circuit accidents. Therefore, in the design of large generators and synchronous phase modifiers, necessary measures must be taken on the stator end structure of the generator to meet the operation requirements. For example, the copper shield, aluminum pressing ring and magnetic shunting structure at the generator end are the measures taken in the past to strengthen the leading power factor operation ability of the generator, and certain results have achieved.

[0004] However, there are some shortcomings in the application of the copper shield, aluminum pressing ring and magnetic shunting structure in the past, i.e., the application of the copper shield and aluminum pressing ring is limited by self-heating, and an external pressure plate of the magnetic shunting structure is affected by leakage flux, resulting in excessive temperature and increased end leakage reactance, and the stator tooth head is not effectively shielded, which is prone to overheating, burning loss, and loosening. The operation of the generator is limited by the problems of overheating, burning loss and loosening at the dovetail part of the locating rib on the back of the iron core. The operation temperature of the previous single-layer copper shield is subjected to finite element simulation. As can be seen from the simulation nephogram, the concentrated heating spot of the previous single-layer copper shield is at the end tip of the inner edge arc region, and the finite element analysis results show that the high point temperature has far exceeded the allowable value of the structural temperature. In order to ensure the ability of large generators and synchronous phase modifiers to cope with extreme working conditions, the temperature of key structure of the stator end is reduced to guarantee reliable operation of generators or synchronous phase modifiers. Some improved stator end shielding structures have been applied in recent years, i.e., the patent End Loss Reduction Ventilation Device of High-capacity Synchronous Phase Modifier (202011369810.6). However, this structure does not change leakage flux heating distribution of a copper shield at a concentrated heating spot in an inner edge arc region, and still has the characteristics of concentrated heating like the traditional structure. As the heating is reduced to a limited extent only using a method of improving ventilation, the local overheating problem cannot be completely eliminated. The main structure of the device different from the previous one is that an auxiliary shielding layer composed of double-layer fan-shaped plates is added at an outer edge of the copper shield. Because the double-layer circular rings composed of the fan-shaped shielding plates cannot form an annular conductive structure, the shielding efficiency is greatly reduced, and moreover, a rectangular groove exists at a joint of the fan-shaped shielding plate and the single-layer shielding layer and an insulating structure is provided between the fan-shaped shielding plate and the single-layer shielding layer, a shielding dead zone is formed in this region, which forms a leakage flux concentration channel, and another overheating spot is generated due to the fact that the pressing ring structure at the corresponding position is harmed by the leakage flux. As can be seen from the finite element simulation nephogram, the structure has not effectively alleviated the overheating spot problem at the inner edge region of the traditional structure, and has also caused a new overheating spot on the pressing ring structure. In the patents Combined Stator End Leakage Flux Barrier Structure (201610739054.9), Laminated Leakage Flux Barrier Structure (201620944415.9), Stator End Leakage Flux Barrier Structure (201610739051.5), Tooth Head Leakage Flux Barrier Structure (201620944544.8), Copper Shield Structure of Stator Core End of Turbo-generator (201921269420.4), and Iron Core Back Leakage Flux Barrier Structure capable of being Assembled in Segmentation" (201620946243.9), these stator end shielding structure are greatly improved compared with the past structures, but the temperature rise at the stator end of the generator and the improvement of hot spot temperature are not obvious, and there are also some limitations and shortcomings. For example, the structural schemes are all around the aspects of increasing the size and range of shielding or increasing the number of shielding layers to reduce the harm of leakage flux, and adding ventilation ducts to enhance the cooling effect and avoid overheating of copper shield, and the hot spot temperature problem of the copper shield is not solved. This is because the shielding current has the characteristics of skin effect and edge effect, the loss of the copper shield is always concentrated on the outer surface of the inner edge of the copper shield, and the excessive heating density causes local overheating region in this part. The prior art cannot effectively and reliably solve this problem, for example, increasing the thickness of copper shield or increasing the number of layers is affected by the skin effect, so the shielding current cannot enter the increased thickness, and the method of increasing the number of layers cannot be realized due to the limitation of mechanical stiffness and strength, this is because the best material for the copper shield is pure copper, power frequency penetration depth of which is about 12 mm. If the effect that the outer copper shield bears 50% or less shielding is to be achieved, the thickness of the outer copper shield must be equal to or less than 3 mm. For large turbogenerators, if the thickness of the outer copper shield is equal to or less than 3 mm, the stiffness and strength requirements of the own structure cannot be satisfied, there will be the problems and hidden dangers such as resonance and fatigue cracks, making this scheme unable to be effectively implemented and unable to achieve the purpose of reducing the hot spot temperature. The measures of increasing the cooling and ventilation speed and ventilation volume are limited by the internal structure of the generator and the air volume distribution, and the increase of the heat dissipation surface in the overheating region is limited by the structure, manufacturing technology and cost. As can be seen from the finite element simulation nephogram of operation temperature, these structures cannot alleviate the overheating spot problem at the inner edge region of the traditional structure. As also can be seen from the nephogram, the provided inner shielding has no effect on heat dissipation due to the characteristics of skin effect and edge effect. Moreover, in the patent Flux Shield for Electric Motor (201480053345 .1), the essence is still the traditional ring-plate structure, the only change is in the position and other aspects, and thus it is also impossible to change the leakage flux heating distribution of the copper shield at a concentrated heating spot of the inner edge arc region, and there is still the problem of concentrated heating in the traditional structure. Further, in some of these stator end shielding structures appeared in recent years, there is also the problem that the service life of the shielding structure is reduced caused by a situation that an air guide insulating structure is close to the local overheating region of the copper shield, and there are shortcomings such as great difficulty in manufacturing and assembly, high cost and the like. SUMMARY

[0005] An objective of the present disclosure is to provide a variable-section combined shielding structure of a stator end. Under the combined action of an inner edge arc variable-thickness region of a main shielding ring and a variable-thickness copper ring, the shielding efficiency to the stator end can be guaranteed, and the distribution of a shielding current in the shielding structure can be effectively improved to eliminate the problem of over-concentration of the shielding current, such that the shielding current can be spread evenly between the main shielding ring and the copper ring, the local overheating phenomenon of the shielding ring is eliminated, and the operation reliability of the generator is improved.

[0006] The technical solution of the present disclosure is as follows: a variable-section combined shielding structure of a stator end is composed of an iron core clamping plate, a main shielding ring, and a copper ring. The main shielding ring is of a three-dimensional ring-plate structure made of a copper plate, and a ventilation gap is provided between the main shielding ring and an outer surface of the iron core clamping plate to form a cooling main ventilation duct. A thickness of an inner edge arc region of the main shielding ring is gradually reduced from outside to the inside from a basic thickness, and a thickness at the minimum diameter is 1 / 4 to 1 / 5 of the basic thickness. The copper ring is arranged between the inner edge arc region of the main shielding ring and an inner hole region of the iron core clamping plate, and a thickness of the copper ring is gradually reduced from inside to outside, and a thickness at the maximum diameter is 1 / 4 to 1 / 5 of the basic thickness. A gap is provided between the copper ring and the inner hole region of the iron core clamping plate to form an inner ventilation duct, and a gap is provided between the copper ring and the inner edge arc region of the main shielding ring to form an outer ventilation duct.

[0007] In the variable-section combined shielding structure of a stator end above, each of the main shielding ring and the copper ring is subjected to surface sandblasting treatment after machining is completed.

[0008] In the variable-section combined shielding structure of a stator end above, a mechanical fixation structure among the iron core clamping plate, the main shielding ring and the copper ring is made of a non-magnetic material.

[0009] In the variable-section combined shielding structure of a stator end above, a heat-resistant electrical insulation structure is adopted between each of the iron core clamping plate, the main shielding ring and the copper ring and the mechanical fixation structure, such as a bolt, a nut, and a pad.

[0010] In the variable-section combined shielding structure of a stator end above, each of an inner surface and an outer surface of the copper ring is provided with air guide grooves which are spirally distributed, and a spiral direction is the same as a rotation direction of a generator rotor.

[0011] Compared with the prior art, the present disclosure has beneficial effects as follows:

[0012] The main shielding ring is of an annular structure made of a copper plate and is used to cover an outer surface of the iron core clamping plate, so as to play a role in shielding the leakage flux of the stator end and preventing the iron core clamping plate from heating. Due to the fact that the shielding current has a skin effect, in consideration of cost element and structural space limitation, the basic thickness of the main shielding ring is selected according to the theory of a penetration depth, and is equivalent to the penetration depth. The thickness of the inner edge arc region of the main shielding ring is gradually reduced from outside to inside from the basic thickness, and the thickness at the minimum diameter is 1 / 4 to 1 / 5 of the basic thickness. The copper ring with gradually reduced thickness is arranged between the inner edge arc region of the main shielding ring and an inner hole region of the iron core clamping plate, the thickness of the copper ring is gradually reduced from inside to outside, and the thickness at the maximum diameter is 1 / 4 to 1 / 5 of the basic thickness. The main shielding ring and the copper ring complement each other to form a double shield to jointly complete the leakage flux shielding protection for the inner hole region of the iron core clamping plate. Compared with a constant-thickness main shielding ring structure in the previous structure, the leakage flux distribution on the iron core clamping plate and the inner hole region of the iron core clamping plate is better than that in the previous structure, and a magnetic field line penetrating into each region of the iron core clamping plate remains unchanged or decreases, but the shielding current distribution in the shielding structure has changed. As the thickness at the minimum diameter of the inner edge of the main shielding ring is 1 / 4 to 1 / 5 of the basic thickness, that is, equivalent to 1 / 4 to 1 / 5 of the penetration depth. According to finite element analysis, the heating power of eddy current is only about 50% of the constant-thickness main shielding ring structure in the prior art, and the temperature is obviously reduced due to the improvement of the surface heat dissipation condition, and the penetrating leakage flux is located at the region with the maximum thickness of the copper ring, which is equivalent to the penetration depth, and when the main shielding ring and the copper ring are combined together, the equivalent thickness is greater than the penetration depth, which can ensure the leakage flux shielding requirements of the inner hole region of the iron core clamping plate. The main shielding ring covers the outer surface of the iron core clamping plate, a gap for ventilation and cooling is provided between the main shielding ring and the iron core clamping plate to form a main ventilation duct, a gap is provided between the copper ring and the inner hole region of the iron core clamping plate to form an inner ventilation duct, and a gap is formed between the copper ring and the inner edge arc region of the main shielding ring to form an outer ventilation duct, so the heat dissipation surface area of a shielding eddy current heating concentration region is increased. A ventilation cooling duct is formed to further improve the heat exchange efficiency of ventilation and cooling and further reduce a hot spot temperature, thus making the temperature rise of the main shielding ring tend to be balanced and eliminating the overheating spot of the main shielding ring. According to the present disclosure, the problems of deterioration of shielding effect, concentrated heating at the end of the thinned region and insufficient structural stiffness and strength caused by simple thinning of the main shielding ring are avoided, the shielding eddy current concentration region is effectively dispersed, the eddy current density is reduced, and the disadvantages that the hot spot temperature cannot be effectively reduced by using a constant-thickness double-layer main shielding ring, the structural space is wasted and the construction cost is high are also avoided. On the premise of ensuring the proper shielding protection efficiency, the shielding current is evenly diffused to increase the heat dissipation surface area and form a smooth cooling air path, thus improving the heat dissipation effect, reducing the temperature rise, eliminating the concentrated heating problem that harms the reliability of the generator, and eliminating the local overheating phenomenon of the shielding ring in the prior art.

[0013] The main shielding ring and the copper ring are machined and then subjected to surface sandblasting treatment, so as to produce microscopic convex-concave texture, which can aggravate the turbulence of cooling airflow and enhance the heat exchange efficiency.

[0014] A mechanical fixation structure among the iron core clamping plate, the main shielding ring and the copper ring is made of a non-magnetic material, which can reduce the eddy current loss caused by the stator end in the mechanical fixation connecting structure and reduce the structure temperature rise.

[0015] A heat-resistant electrical insulation structure is adopted between each of the iron core clamping plate, the main shielding ring and the copper ring and the mechanical fixation connection structure, which can avoid electric circulation between each of the iron core clamping plate, the main shielding ring and the copper ring and the mechanical fixation connection structure, and prevent the structure from overheating.

[0016] Each of an inner surface and an outer surface of the copper ring is provided with air guide grooves which are spirally distributed, and a spiral direction of the air guide groove is the same as a rotation direction of a generator rotor. The rotating airflow formed by the generator rotor intensifies the flow and turbulence of a cooling gas, which enhances the ventilation and cooling conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG. lisa schematic diagram of the present disclosure;

[0018] FIG. 2 is a schematic diagram of a copper ring.

[0019] In the drawings: 1-iron core clamping plate; 2-inner edge arc region; 3-main shielding ring; 4-cooling main ventilation duct; 5-copper ring; 6-inner ventilation duct; 7-outer ventilation duct; 8-inner hole region; 8-air guide groove. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The present disclosure is further described below with reference to accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present disclosure, and cannot be used to limit the scope of protection of the present disclosure.

[0021] Many specific details are set forth in the following description, for example, the terms "inside", "outside", "clockwise” and the like are based on the orientation or positional relationship shown in the drawings only for convenience of description of the present invention and simplification of description rather than indicating or implying that the device or element referred to must have a particular orientation, be constructed and operate in a particular orientation. However, the present disclosure can be implemented in a variety of manners different from those described herein, and it may be similarly generalized by those skilled in the art without departing from the concept of the present disclosure. Therefore, the present disclosure is not limited to the specific embodiments disclosed below.

[0022] Totally, as shown in FIG. 1, a variable-section combined shielding structure of a stator end is disclosed by this embodiment of the present disclosure, which is composed of an iron core clamping plate, a main shielding ring 3 with an inner edge arc region 2 having a gradually reduced thickness, a main ventilation duct 4, a copper ring 5 with a gradually reduced thickness, an inner ventilation duct 6, and an outer ventilation duct 7. The main shielding ring 3 is an annular structure made of a copper plate and is used to cover an outer surface of the iron core clamping plate I, and a gap for ventilation and cooling is provided between the main shielding ring 3 and the iron core clamping plate 1 to form the main ventilation duct 4. The thickness of the inner edge arc region 2 of the main shielding ring 3 is gradually reduced from outside to inside from the basic thickness, and the thickness at the minimum diameter is 1 / 4 to 1 / 5 of the basic thickness. The copper ring 5 with the gradually reduced thickness is provided between the inner edge arc region 2 of the main shielding ring 3 and an inner hole region 8 of the iron core clamping plate 1, the thickness of the copper ring 5 is gradually reduced from inside to outside, the thickness at the maximum diameter is 1 / 4 to 1 / 5 of the basic thickness, and the thickness at the minimum diameter is the same as that of the main shielding ring 3. According to a power frequency penetration depth requirement of 50 Hz, the basic thickness is about 16 mm, a gap is provided between the copper ring 5 and the inner hole region 8 of the iron core clamping plate 1 to form the inner ventilation duct 6, and a gap is provided between the copper ring 5 and the inner edge arc region 2 of the main shielding ring 5 to form the outer ventilation duct 7. The main shielding ring is of an annular structure made of a copper plate and is used to cover an outer surface of the iron core clamping plate 1, so as to play a role in shielding the leakage flux of the stator end and preventing the iron core clamping plate 1 from heating. Due to the fact that the shielding current has a skin effect, in consideration of cost element and structural space limitation, the basic thickness of the main shielding ring 3 is selected according to the theory of a penetration depth, and is equivalent to the penetration depth. The thickness of the inner edge arc region of the main shielding ring 3 is gradually reduced from outside to inside from the basic thickness, and the thickness at the minimum diameter is 1 / 4 to 1 / 5 of the basic thickness. The copper ring 5 with gradually reduced thickness is arranged between the inner edge arc region of the main shielding ring 3 and an inner hole region of the iron core clamping plate 1, the thickness of the copper ring 5 is gradually reduced from inside to outside, the basic thickness is about 16 mm, and the thickness at the maximum diameter is 1 / 4 to 1 / 5 of the basic thickness. The main shielding ring and the copper ring complement each other to form a double shield to jointly complete the leakage flux shielding protection for the inner hole region of the iron core clamping plate 1. Compared with a constant-thickness main shielding ring structure in the previous structure, the leakage flux distribution on the iron core clamping plate 1 and the inner hole region of the iron core clamping plate 1 is better than that in the previous structure, and a magnetic field line penetrating into each region of the iron core clamping plate 1 remains unchanged or decreases, but the shielding current distribution in the shielding structure has changed. As the thickness at the minimum diameter of the inner edge of the main shielding ring is 1 / 4 to 1 / 5 of the basic thickness, that is, equivalent to 1 / 4 to 1 / 5 of the penetration depth. According to finite element analysis, the heating power of eddy current is only about 50% of the constantthickness main shielding ring structure in the prior art, and the temperature is obviously reduced due to the improvement of the surface heat dissipation condition, and the penetrating leakage flux is located at the region with the maximum thickness of the copper ring 5, which is equivalent to the penetration depth, and when the main shielding ring and the copper ring are combined together, the equivalent thickness is greater than the penetration depth, which can ensure the leakage flux shielding requirements of the inner hole region of the iron core clamping plate 1. The main shielding ring 3 covers the outer surface of the iron core clamping plate 1, a gap for ventilation and cooling is provided between the main shielding ring 3 and the iron core clamping plate 1 to form a main ventilation duct, a gap is provided between the copper ring 5 and the inner hole region of the iron core clamping plate 1 to form an inner ventilation duct, and a gap is formed between the copper ring 5 and the inner edge arc region 2 of the main shielding ring to form an outer ventilation duct, so the heat dissipation surface area of a shielding eddy current heating concentration region is increased. A ventilation cooling duct is formed to further improve the heat exchange efficiency of ventilation and cooling and further reduce a hot spot temperature, thus making the temperature rise of the main shielding ring 3 tend to be balanced and eliminating the overheating spot of the main shielding ring 3.

[0023] According to the present disclosure, the problems of deterioration of shielding effect, concentrated heating at the end of the thinned region and insufficient structural stiffness and strength caused by simple thinning of the main shielding ring are avoided, the shielding eddy current concentration region is effectively dispersed into the copper ring 5, the eddy current density is reduced, and the disadvantages that the hot spot temperature cannot be effectively reduced by using a constant-thickness double-layer main shielding ring 3, the structural space is wasted and the construction cost is high are also avoided. On the premise of ensuring the proper shielding protection efficiency, the shielding current is evenly diffused to increase the heat dissipation surface area and form a smooth cooling air path, thus improving the heat dissipation effect, reducing the temperature rise, eliminating the concentrated heating problem that harms the reliability of the generator, and eliminating the local overheating phenomenon of the main shielding ring 3 in the prior art.

[0024] The main shielding ring 3 and the copper ring 5 are machined and then subjected to surface sandblasting treatment to produce microscopic convex-concave textures, which can aggravate the turbulence of cooling airflow and enhance the heat exchange efficiency. A mechanical fixation structure, including a bolt, a nut, and a pad, among the iron core clamping plate 1, the main shielding ring 3 and the copper ring 5 is made of a non-magnetic material, which can reduce the eddy current loss caused by the stator end in the mechanical fixation connecting structure and reduce the structure temperature rise, and thickness of the pad is determined according to ventilation demands. A heat-resistant electrical insulation structure, including an insulation gasket and a sleeve, is adopted between each of the iron core clamping plate 1, the main shielding ring 3 and the copper ring 5 and the mechanical fixation connection structure, which can avoid electric circulation between each of the iron core clamping plate 1, the main shielding ring 3 and the copper ring 5 and the mechanical fixation connection structure, and prevent the structure from overheating.

[0025] As shown in FIG. 2, each of an inner surface and an outer surface of the copper ring 5 is provided with air guide grooves 9 which are spirally distributed, and a spiral direction of the air guide groove is the same as a rotation direction of a generator rotor. A rotating airflow formed by the generator rotor intensifies the flow and turbulence of cooling gas, which enhances the ventilation and cooling conditions.

[0026] The above is only the preferred embodiment of the present disclosure, and is not used to limit the present disclosure. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. A variable-section combined shielding structure of a stator end, composed of an iron core clamping plate (1), a main shielding ring (3), and a copper ring (5), wherein the main shielding ring (3) is of a three-dimensional ring-plate structure made of a copper plate, and a ventilation gap is provided between the main shielding ring (3) and an outer surface of the iron core clamping plate (1) to form a cooling main ventilation duct (4); a thickness of an inner edge arc region (2) of the main shielding ring (3) is gradually reduced from outside to the inside from a basic thickness, and a thickness at the minimum diameter is 1 / 4 to 1 / 5 of the basic thickness; the copper ring (5) is arranged between the inner edge arc region (2) of the main shielding ring (3) and an inner hole region (8) of the iron core clamping plate (1), and a thickness of the copper ring (5) is gradually reduced from inside to outside, and a thickness at the maximum diameter is 1 / 4 to 1 / 5 of the basic thickness; a gap is provided between the copper ring (5) and the inner hole region (8) of the iron core clamping plate (1) to form an inner ventilation duct (6), and a gap is provided between the copper ring (5) and the inner edge arc region (2) of the main shielding ring (3) to form an outer ventilation duct (7).

2. The variable-section combined shielding structure of a stator end according to claim 1, wherein each of the main shielding ring (3) and the copper ring (5) is subjected to surface sandblasting treatment after machining is completed.

3. The variable-section combined shielding structure of a stator end according to claim 1, wherein a mechanical fixation structure among the iron core clamping plate (1), the main shielding ring (3) and the copper ring (5) is made of a non-magnetic material.

4. The variable-section combined shielding structure of a stator end according to claim 1, wherein a heat-resistant electrical insulation structure is adopted between the mechanical fixation structure among the iron core clamping plate (1), the main shielding ring (3) and the copper ring (5) and each of the iron core clamping plate (1), the main shielding ring (3), and the copper ring (5).

5. The variable-section combined shielding structure of a stator end according to claim 1, wherein each of an inner surface and an outer surface of the copper ring (5) is provided with airguide grooves (9) which are spirally distributed, and a spiral direction is the same as a rotation direction of a generator rotor.

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