Patent Application
20240343273
The successful development of the 40 MW series air-cooled turbine generator by totally-impregnated insulation using a combination of domestic and foreign technologies has filled the gap in the company's products. The technical level of this series of generators is still leading in China.
The stator coil of the 40 MW series air-cooled turbine generator adopts VPI (Vacuum Pressure Impregnation) totally-impregnated technology. By reducing the thickness of the main insulation, all wires are embedded into the wire rod wrapped with tape, and the wire rod is vacuum impregnated together with the entire stator core, making a gap between the embedded wires in the stator slot be filled with polyester modified epoxy resin and improving the thermal conductivity, and thus reducing the temperature difference between the stator winding and the core. The insulation system requires a large horizontal vacuum pressure tank, where drying, vacuuming, pressure impregnation, and baking curing are all completed in the same tank, resulting in high production efficiency. Although the initial investment of system equipment is large, it can save time, simplify the manufacturing process, and thus reduce costs. The stator core adopts an external pressing process and adopts an inner and outer frame structure, allowing the stator core to operate parallel to the frame and shortening the entire production cycle [1].
The VPI process has the following advantages:
(1) The stator coils of the 40 MW series generator are drawn using Cartesian coordinates. After half coils are lowered down to the core, it is totally impregnated. The manufacturing process of the half coils is simple, and it is convenient to lower down the coils. The insulation is not easily damaged during the process of lowering down the wire.
(2) After the totally impregnation, the entire stator forms a whole, improving its mechanical strength. When the half coil is lowered down, significant displacement should be avoided to reduce insulation damage caused by displacement.
(3) The stator coil of the 35 MW series generator adopts a single molding technology, and uses the resin-rich mica tape for continuous wrapping and molding, with a thicker insulation. However, the 40 MW series generator uses a less resin mica tape for continuous wrapping with a thinner insulation, which is conducive to heat dissipation.
(4) The gap between the embedded wires in the stator slot is filled with epoxy resin, which reduces the temperature difference between the core and the winding and improves the heat dissipation level.
(5) After the totally impregnation, the gaps are filled, which can resist the invasion of carbon powder and dirt, eliminate accidents caused by the formation of circuits formed by the conductive medium, and improve moisture resistance and chemical stability.
(6) Less prone to corona, enhanced shock resistance, and better adaptability to operating environments.
The cooling method of the 40 MW series air-cooled turbine generator is to use air internal cooling for the rotor and direct cooling for the coils, resulting in high cooling efficiency: however, the 35 MW series air-cooled turbine generator is to use indirect cooling for its rotor, with no ventilation inside the coil and no use of auxiliary slot ventilation, resulting in poor cooling effect.
The rotor winding of the 40 MW series air-cooled turbine generator is composed of concentric copper wires, which are made of electrolytic copper alloy CuAg0.1P containing about 0.1% silver. Silver containing copper wires have higher fatigue strength than ordinary copper wires, and the conductivity is reduced by about 0.5%. At high temperatures, the creep strength and yield limit are significantly improved, which can prevent residual deformation and inter turn short circuits during thermal expansion and contraction processes. The cross-sectional shape of the hollow wire is square, and the end is connected to the straight part, making it easy to process and manufacture. The hollow wire has air inlet and air outlet holes, and cold air flows through the holes to directly cool the rotor wire. The air outlet holes are combined into a V-shape in the slot, and the air volume at each air outlet hole is uniform, without local overheating.
The rotor fan of the 40 MW series air-cooled turbine generator is a single-stage axial flow type. Compared to centrifugal fans, it produces a lower pressure head, sufficient flow rate, and an efficiency of up to 40% to 60%. The fan blades are made of high-quality aluminum alloy AlMgSi112, and the installation angle is strictly controlled, generally not exceeding 30°. If the angle is too large, the air volume will not increase, but it will actually deteriorate the features of the fan. The optimal fan angle for the 40 MW series air-cooled turbine generator is 21°. When designing a fan, the outer diameter should not be too large. If the air volume is insufficient, priority should be given to increasing the width of the fan blades.
In fact, the increase in the capacity of a single generator mainly relies on improving electromagnetic parameters. Due to the magnetic saturation of silicon steel sheets, the increase in magnetic flux density is limited, so the increase in capacity is more dependent on the increase in wire load. Compared with 35 MW, the capacity of 40 MW has increased by 14%, and the stator wire load has also increased by 14%, which means that the internal losses of the generator have increased by 1.3 times, while the volume has remained basically unchanged and the heat dissipation area has also remained basically unchanged. Therefore, it is necessary to find a more efficient cooling method.
The 40 MW series generator adopts stator air external cooling and rotor winding air internal cooling technology. The cold air at the air cooler is fed into the stator and rotor by axial flow fans at both ends of the rotor. The hot air formed after cooling the stator and rotor is cooled by the air cooler and then converted into cold air again, forming a closed loop. The cooling system of the entire motor is symmetrical with respect to the central axis of the generator, corresponding to the axial flow fan.
The stator ventilation is two in and three out, and cold air flows in from the pressure coils at both ends of the stator. After cooling the stator, hot air flows out through three paths at the lower part of the casing. The frame serves as the ventilation duct for the stator, which is divided into the cold air area and hot air area by the middle wall of the generator. The rotor ventilation is divided into two paths, with a part of cold air reaching the center of the rotor through the hollow conductor in the slot, and then entering the air gap through the radial holes on the hollow conductor and slot wedge: The other part of the cold air passes through the hollow conductor at the end of the winding, reaches the magnetic pole axis, is discharged from the hollow conductor, and finally enters the air gap through the crescent slot at the end of the rotor body. This wind path divides the cold air into multiple streams, prioritizing cooling both ends of the stator and rotor whose temperature are high, and then cooling the stator and rotor body, so that all parts of the generator will be cooled well.
The air pressure borne by the wind path of the air-cooled turbine generator is low, and the requirement of sealing is not high. To supplement the leaked air, two air filters are provided on the outer end cover of the stator casing.
The selection of raw materials strictly follows domestic and ALSTOM technical specifications, ensuring the safety and reliability of products from the perspective of raw materials. For example, the stator segment sheets use 50W315, which has a higher magnetic saturation strength than the 50W350 used in the 35 MW series: the rotor body is forged with 25Cr2Ni4MoV/V*JB/T1267 alloy steel, which has high mechanical strength and magnetic permeability: the retaining ring is made of imported anti magnetic steel material X8CrMnN1818, which has strong stress resistance and corrosion resistance: The rotor wire is made of electrolytic copper alloy containing silver, which has strong creep resistance and can eliminate deformation of the rotor winding.
The key insulation materials of the generator are imported from abroad, and F insulation level materials are selected and evaluated according to B insulation level. The selection of insulation materials is one of the key factors affecting the lifespan of generators. For every 12° C. increase in temperature of F insulation level materials, their working life will be shortened by half [2]. Due to the difficulty in detecting the hottest point inside the insulation of the generator, the temperature of the hottest point of the winding is controlled to be 10° C. lower than the allowed 130° C. for B insulation level during design. The stator winding insulation adopts less resin mica tape with high mica content, which has excellent electrical performance, winding performance, and tensile strength.
2.1 Comparison with Similar Products
Compared with the 35 MW and 10.5 kV turbine generator, their parameters are shown in Table 1.
According to Table 1, comparing to the generator manufactured by the 35 MW and 10.5 kV molding process, the capacity of the generator manufactured by the 40 MW and 10.5 kV totally-impregnated process has increased by 14%, the inner diameter of the stator core thereof remains unchanged, the outer diameter of the stator core thereof has increased by 50 mm, the length of the stator core thereof has decreased by 100 mm, and the volume of the stator core thereof has not changed, but the weight of the stator and rotor has significantly decreased, showing the advantages of the design of the totally-impregnated stator and the air internal cooling rotor. With the increase of capacity, the temperature rise of the stator winding and stator core also increases accordingly. The temperature rise of the rotor has decreased due to the fact that air internal cooling technology is capable of taking away more heat, and the 40 MW and 10.5 kV generator is capable of exceeding 10%.
2.2 Comparison with the Specified Indicators in the Standard
Table 2 shows the comparison of 40 MW generator parameters with standard values.
According to Table 2, all electrical parameters of the 40 MW air-cooled turbine generator meet the national standard requirements, and the main indicators reach the standard for premium products in the industry standard.
The 40 MW series new totally-impregnated air-cooled turbine generator is an excellent new product produced by Shandong Qilu Electric Machine Co., Ltd. Based on advanced domestic and foreign technologies, it adheres to the serialization and modularization of new product design, considers the universality and inheritance of the product, utilizes existing fixtures and processes, reduces design and manufacturing difficulties, and shortens the trial production period, laying the foundation for the future development of larger capacity generators.
| Number | Date | Country | Kind |
|---|---|---|---|
| 202320834183.1 | Apr 2023 | CN | national |
| 202311178049.1 | Sep 2023 | CN | national |
