Due to its simple structure and convenient operation and maintenance, the air-cooled turbo generator has been recognized by more and more users in recent years and has begun to develop rapidly in China. Domestic manufacturers have successively invested in air-cooled steam turbine generators, and 150MW generators have also been successfully manufactured in the factory.
Based on the successful trial production and successful investment operation of the 75MW air-cooled steam turbine generator, our company has made a complete summary of the successful technology that can be inherited and the structure that needs to be improved. Preparations for the production of larger capacity units began. In 2001, our company successively received orders for two 150MW air-cooled generators from four 135MW and two southeast mountain power stations in Linyi and Huasheng, Shandong. I started to work on the development of a larger capacity air-cooled generator based on my own strength.
After thorough technical analysis, our company completed the design of the generator with a large number of model test results. After continuous process testing and improvement, the pilot production of the unit began. At the beginning of September 2002, the 150MW air-cooled steam turbine generator developed by China First Co., Ltd. successfully completed the type test in our company. All technical indicators of the generator fully meet the requirements of national standards, and Wanquan meets the needs of long-term safe operation.
2 The overall technical policy of generator design In foreign countries, the development of air-cooled steam turbine generators from 60MW to 150MW is a key step. It is not only related to the success of this capacity level, but also to the technical basis for the continued development of larger capacity units. Therefore, the overall technical policy needs to be fully considered and demonstrated at the outset.
Due to the low heat capacity and thermal conductivity of air, the key to designing an air-cooled turbo generator is to reduce the loss of effective components and enhance the cooling of these parts. Therefore, we first focus on the research of ventilation in ventilation research. The goal is to use a moderate amount of air to evenly cool the entire generator so that the temperature at each location does not exceed the level allowed by the insulation. Secondly, the heating of the stator bars is one of the keys to limiting the increase in power generation capacity. To this end, we have taken measures to reduce losses, improve insulation and improve cooling. In addition, it is also one of the research projects of air-cooled generators to determine the ventilation cooling mode of the rotor coil through experimental research.
In addition, some measures that need to be taken as the generator capacity increases, such as measures to reduce the end loss of the core to improve the phase-in operation capability, the rated parameters and structural characteristics of the three-string machine 3.1 Main parameters of the generator The main rated parameters are: model rated capacity power factor speed voltage current short circuit than cooling mode stator: air external cooling, rotor: air internal cooling insulation class F (temperature rise according to B level assessment) efficiency temperature limit stator winding çŸ£ 120 (Resistance thermometer) Rotor winding resistance preparation 115 Through the test, not only the factors of the parameters of the beer wind path were understood, but also the relationship between the wind paths was determined, and a reasonable design plan was initially determined. It is a streamline diagram of a set of internal gas measured by experiments.
Finally, we conducted a ventilation test again during the in-plant test of the generator. The head difference before and after the generator fan was measured, and the head distribution data of each part was measured. The air volume distribution and total air volume of each wind generator were also measured. . The test proves that the air volume of each wind road is basically consistent with the design data.
3.2.2 Overall Arrangement The overall layout of the generator is considered in accordance with the purpose of the generator, combined with the overall layout of the plant. Since the generator is matched to the steam turbine (i.e., the steam turbine generator is placed in a high position), an arrangement in which the air cooler is placed in the pit below the generator is employed.
Same as other air-cooled steam turbine generators, with a seated bearing arrangement. Due to the static thyristor excitation system, a brush device is provided at the non-drive end.
3.2.3 Stator base and core The electromagnetic force of the two-pole turbo generator will cause 4-node multi-frequency elliptical vibration in the core. In order to reduce the influence of the stator core vibration on the generator foundation and reduce the noise of the generator, the stator core of the generator and the base should be elastically fixed. The 150MW generator stator adopts the mature stator core vibration isolation structure of our company (see). The belt serves to reduce the base vibration and reduce the noise.
The locating ribs with the elastic rafts separate the core vibration from the frame. In addition, the edge must be taken into consideration when designing the core. The unevenness of the wind volume and wind temperature over the length of the core. In order to make the temperature of the core and the coil as uniform as possible along the length of the core, the length of the core is not uniform. According to the results of the ventilation test, a core length that is much smaller than the wind zones at both ends is selected in the hot air outlet area in the middle to further reduce the temperature of the core and the coil here.
In order to reduce the additional loss of the stator end and minimize the temperature of the area, in addition to the stator pressure ring, the pressure finger and the stator end structure are made of non-magnetic material, and a copper shield is arranged outside the generator stator ring. This is the mature technology of large units (see).
Copper shield outside the generator core ring 3.2.4 Stator coil Since the stator coil of the air-cooled generator is surface-cooled, all losses of the rod must be transmitted through the insulation. In order to reduce the temperature rise of the wire rod, the shape of the wire rod needs to be designed to be narrow and high to increase the heat dissipation area. At the same time, in order to reduce the temperature difference between the inside and outside of the insulation, the insulation should also be appropriately thinned under the premise of safety and reliability. The generator slot current exceeds 7000A, the stator slot depth exceeds 230mm, and the upper layer bar height reaches 120mm. The stator insulation thickness is also slightly thinner than the original generator of the same voltage.
In the online rod design, in addition to lowering the basic loss of the copper wire by selecting a lower current density, the wire rod uses a plurality of thinner strands. And the cross-sectional area of â€‹â€‹the upper layer bar is designed to be about 20% lower than the lower layer, and the lower eddy current loss of the upper layer bar is compensated by the lower resistance loss, so that the temperature of the upper and lower layer bars is closer.
The leakage potential induced by the multiple strands of such large-section stator bars is different, and it is a problem that must be considered by reasonably selecting the transposition mode to reduce the strand circulation. It is difficult to reduce the strand circulation of such a large rod by simply using the 360 â€‹â€‹transposition in the slot. If there is a large number of in-slot 540 transpositions, there will be a large number of strands in the slot, and the pitch of the strand will be too small to produce. difficult. We used a method of transposition at the nose end of the upper and lower wire rods on the 150 MW generator. The strands of the bars are divided into two groups, and the two strands are also insulated from each other throughout the length of the bars, including the nose joints. The upper and lower layer bars are normally connected at the nose end of the steam turbine (see left), and the nose ends of the slip ring are grouped and then transposed (see å‡¼7 right). For the windings in the entire phase band group, the additional induced potential between the two groups is cancelled. Since a group of strands is only equivalent to a rod of very small height, the loop circulation within the group is greatly reduced.
Generator stator bar nose end grouping after transposition connection 3.2.5 Rotor coil 150MW generator rotor winding cooling still uses the axial ventilation cooling structure used on the 75MW generator. The generator rotor winding wire is composed of two U-shaped copper wires, and the upper and lower half grooves are combined to form an axial cooling air passage. In order to reduce the temperature of the rotor windings, the coils along the entire length of the rotor are divided into six separate cooling air sections. After the cooling gas comes out of the fan, it enters through the lower part of the retaining ring, and a part of the airflow enters the sub-groove of the bottom of the trough, and then enters the radial holes of the first and second sets of copper wires respectively, after passing through two independent coil axial air passages respectively. The air gap flows from the radial holes on the wedge. Another portion of the air flows into the air passage at the end of the winding, and after cooling the copper wire through the air passage in the coil, the rotor exits from the air outlet at the end of the rotor body. A plenum is also provided in the large coil with a long end length to further reduce the temperature of the hottest spot.
Other structures of the generator, such as bearings, collector rings, brushes and coolers, are similar to other types of generators and are not described here.
4 Trial production results (see table) Main test parameters and comparison of test values â€‹â€‹and design values â€‹â€‹Project test value Design value Guaranteed value No-load excitation current (A) Excitation short-circuit excitation current (A) Short-circuit ratio Data load Excitation current (A) waveform Distortion rate (% telephone harmonic factor (%) mechanical loss (kW) iron loss (kW) loss of stator copper consumption (kW) consumption and effect additional loss (kW) rotor copper loss (kW) rate excitation device loss (kW) total Loss (kW) efficiency (%) armature winding maximum K) çŸ£ 80 temperature rise constant core maximum K) 80 excitation è…§ average turn K) çŸ£ 75 collector ring temperature (T) bearing temperature (T) 85 September 2002 Our company successfully completed the type test of the first 150MW air-cooled steam turbine generator. The test proves that the efficiency, temperature rise and all technical indicators of the generator fully meet the requirements of national standards, and the completion of school meets the needs of long-term safe operation under rated output.
5 Future development direction At present, there is still a considerable gap between the development of high-power air-cooled steam turbine generators in China and foreign countries. At present, not only has the 260MW air-cooled generator with F-class gas turbine been mass-produced, but the original ABB company also produced the world's largest air-cooled steam turbine generator with a capacity of 500MVA. There is no doubt that our company and other domestic companies will Continue to work on the capacity of air-cooled generators.
The key to developing large-capacity air-cooled generators is still to reduce consumption and enhance cooling. In addition to increasing the size of the generator based on the measures we have taken, some of the following techniques are also considered.
5.1 Advances in insulation technology Improving the heating and cooling of stator bars has always been the key to large air-cooled generators, and how to reduce the temperature drop on the insulation is very important. In the future, we mainly need to improve the electrical performance and manufacturing process of insulation, and minimize the thickness of insulation to achieve the purpose of increasing output. In addition, improving the thermal conductivity of insulating materials is also the goal of further research by the research and production department of insulating materials in China. Although the external vacuum impregnation of the stator is mostly used in the air-cooled generators abroad to reduce the gap between the stator bars and the core, the effect of good heat dissipation is achieved. However, since the overall impregnation of the stator is poor in corona prevention, The insulation quality of the wire rod itself is not as good as that of a single wire rod. In addition, the investment in the overall vacuum impregnation equipment of the stator is large, so the air-cooled generator with larger capacity generally does not use the overall vacuum impregnation of the stator, but uses a single wire rod. Vacuum impregnation.
5.2 Reverse Ventilation Arrangement It is well known that if the cold air flowing out of the cooler is pressurized by the fan and then cooled to the effective part of the generator, the temperature of the effective component of the generator will increase accordingly because the fan first raises the temperature of the gas. Larger capacity generators should consider reverse ventilation. The cold air flowing out of the cooler enters the radial wind ditch from the back of the iron core, and the hot air that cools the iron core and the coil flows out of the iron core into the air gap and mixes with the hot air discharged from the rotor, and is taken out from the air gap by the axial fan on the shaft and then returned to the cooling. Device. This ventilation method allows the stator core and the coil to be cooled by the lowest temperature airflow, which can achieve better cooling effect, and can reduce the air flow through the stator and reduce the ventilation loss.
5.3 Multi-branch stator coil structure Since the heating and cooling of stator bars is the key to large air-cooled generators, in addition to improving insulation and improving ventilation cooling, if the current can be reduced by reducing the current of a single stator bar Rod loss will likely result in more satisfactory results.
Since the capacity of the generator depends only on the voltage and current, if the stator current is reduced by selecting a higher voltage, it will have the negative consequences of thickening of the insulation and greater temperature drop of the insulation. Some foreign companies have thought of reducing the current of a single bar by increasing the number of parallel branches.
However, the two-pole motor can only obtain the symmetry of the branch when one or two parallel branches are used, and there is no circulation between the branches. Through careful analysis, if the number of parallel branches is increased to 3, and then the appropriate connection method is adopted, the asymmetry of the branches can be reduced as much as possible, thereby reducing the circulation between the branches to a negligible extent. The loss of a single wire rod is greatly reduced and the temperature of the coil is lowered. 0 is a schematic diagram of the slot grouping of a phase band group of three parallel branch generators. The I2 slots in one phase band group are divided into three groups, and the potential of each group differs only by 5 degrees in phase. By connecting with three sets of coils under the other pole, the branch potentials can be made in the same phase, and the amplitude difference is different from that of the three stators of the generator stator coil. 6 The development of high-power air-cooled turbo generators is not only in the world. Inevitably, it will become a new growth point in China. Our company will continue to research and develop in this field. The design development, model test, and the development of several 60MW, 75MW and 150MW models have laid a good foundation for further development of larger capacity air-cooled generator sets.
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