Research on Corona Prevention of 600MW Turbogenerator
The anti-halation structure is a very important aspect of the design of the motor insulation structure. The anti-halo effect directly affects the preventive test and safe operation of the motor. With the continuous increase of the motor capacity, the rated voltage of the motor is correspondingly increased. The anti-halation at high voltage is even more important in the design and manufacture of the motor insulation structure. The following will discuss in detail the anti-halo structure, materials, and test results of our 22kV 600MW turbine generator. 2 Selection of raw materials Motor coil anti-halation molding method A variety of samples, most of our company's large-scale motor coil mold hot press molding method, that is anti-halation layer and the main insulation at the same time a hot-press molding, and then the second treatment. Therefore, anti-halation materials include anti-halation tape substrates, semi-conductor anti-corona coatings, and insulating covering lacquers. 2.1 Glass Ribbon In view of the actual situation of our company, the anti-halation of 600MW steam turbine generator starts with the materials. Because the asbestos products are harmful to the human body, they have been completely eliminated in foreign countries and are rarely used in China, and the supply is unstable. Therefore, we decided to use glass ribbons for the anti-halation tape substrates of 600 MW turbine generators. We use the pre-treatment yarn for the webbing, which eliminates the need for a dewaxing process after the glass ribbon is introduced into the factory, improves the impregnation of the glass ribbon, and also increases the mechanical strength of the glass ribbon. 2.2 Low-resistance anti-halation paints We have made improvements to the imperfect parts of the original low-resistance anti-halation paints. For example, the original 134 anti-halo paint problems are: high resistance and poor adhesion. In response to these problems, we changed the conductive material graphite in the original low-resistance paint to acetylene black, which can reduce the content of the conductive material in the paint and increase the adhesive content to increase the adhesion. In addition, the particle size of acetylene black is smaller than that of graphite. After uniformly mixing, the resistance can be stably controlled within the range required by the standard. 2.3 High-resistance anti-corona paint High-resistance anti-halation paint The anti-halation principle is to use the non-linear characteristics of carbonization, and the electric field at the coil end is automatically distributed evenly under the action of an electric field. Therefore, the most critical raw material for high-resistance anti-corona paints is silicon carbide. In this research, we prepared different components of abrasive silicon carbide and electrician silicon carbide from several different manufacturing plants, and screened for the anti-halation 22kV 945 high-resistivity belt anti-halation paint and 947 high-resistance anti-corona paint . 3 anti-halation structure design based on the stator coil of high-voltage motor in the ventilation slot and the end of the slot surface at the outlet surface of the insulation surface is uneven, when the local field strength reaches a certain value, the gas is generated by local ionization corona. 3.1 The principle of the prevention of the corona of the crotch The corona of the groove is caused by the gap between the insulating surface and the wall of the groove. When the field strength in the gap exceeds the critical value, the corona field intensity is generated. According to the distribution parameter circuit calculation can be drawn out of the groove for the vibrated field strength 8.lkV/cm. Groove corona prevention method is to make the coil insulation surface stable grounding, eliminating air gap voltage. The specific method is to perform anti-corona treatment on the surface of the coil to form a whole body of the coil groove with a semiconductor material. The resistance value of the semiconductor material can also be determined by the distribution parameter circuit calculation method. Considering the loss of the stator core, the resistance value is usually controlled between 102~15fl. This can not only prevent the occurrence of corona, but also does not affect the loss of iron core and cause unnecessary temperature rise. 3.2 Prevention of end corona The field strength of the insulation surface of the stator coil end increases in the direction of the core, so the voltage drop at the insulation surface at the outlet of the notch is the largest and the axial field strength is also the highest. The ultimate goal of end anti-halation is to evenly distribute the electric field at the ends of the coil and make the surface field strength lower than the corona onset field strength. A non-linear material carbide carbide provides this possibility. Experiments have shown that when the field strength reaches the haze field strength, the anti-halation layer will start to halo. After exceeding a certain value, the anti-halation layer at that location will be superheated and carbonized. By adjusting the resistivity and non-linear coefficient of the anti-halation material, the effect of neither hazing nor overheating can be well achieved, and the theoretical calculation combined test proves that the surface resistivity of the end anti-halation material should be 18~11 ( > The non-linear coefficient should be between 1 and 2 more appropriate. 3.3 Anti-halation treatment length 3.3.1 Groove length anti-halation treatment length The length of the groove anti-halation treatment needs to consider the structure of the motor to reduce the non-uniformity of the electric field, and does not happen to other parts (such as copper shielding, bracket screws, etc.) Discharges are as short as possible from the notch. 3.3.2 End anti-halation treatment length The end anti-halation treatment length is based on limiting the electric field strength on the surface of the coil end below the inflaming field strength. Based on the rated voltage of our company's 600MW turbine generator is 22kV, the minimum length of anti-halation at the end of the coil can be obtained through calculation. Considering a certain margin, we finally determined the length of the anti-halation of the end of the turbine generator that was suitable for our company. 4 Tests verify that the finalization of motor anti-halation is not enough only through theoretical design. Due to the large dispersion of raw materials and high voltage, the anti-halation structures and materials must be verified through a large number of tests before they can be finalized. . 4.1 Verification of raw materials 4.1.1 Glass fiber belts with anti-corona glass fiber belts for 600 MW turbine generators are ordered to glass fiber production plants according to special requirements. The original glass fiber weaving is used for weaving pre-treated glass filaments. After entering the factory, There is no need to de-wax treatment, change the warp and weft density and the twist of the original yarn to improve the impregnation of the glass fiber tape. With the exception of the domestic glass fiber tapes, the remaining indicators meet and exceed Hitachi's technical requirements. Fully meet the needs of 600MW turbo generator anti-halation. 4.1.2 Low-resistance anti-halation paints For low-resistance anti-corona paints for low-resistance anti-corona paints for anti-aliasing and brushing purposes, the graphite is acetylene black, and the test is repeated for a number of tests to obtain the desired low-resistance anti-smoke paint. . Its performance fully meets domestic standards and Hitachi's technical requirements. 4.1.3 High-resistance anti-halation paints High-resistance anti-halation paints are made from silicon carbide as the main raw material at home and abroad. Therefore, its performance mainly depends on the properties and content of carnauba in the anti-halation paint. We have applied tests on carbide carbides produced by different manufacturers, and will use acetylene black as the front-end graphite conductive base. Through a large number of tests and conclusions, high-resistance anti-halo paints suitable for 600 MW turbine generators were selected. Through tests, it was proved that this high-resistance anti-corona paint is also the same (turning to page 110). However, because the specific speed of the ultra-high head pump turbine is small, the thrust generated by the small pressure difference between the outside back pressure of the runner and the side pressure part of the runner will change the total water thrust. Because it includes the transient operating state, it is difficult to accurately calculate the pressure distribution around the runner. Therefore, Mitsubishi Corporation tries to maintain the water thrust balance on the structure design of the real machine, considering the structure of the pump turbine. Its characteristics are as follows: Make the clearance of the outer back pressure chamber and side pressure chamber of the runner as much as possible. Set the inner balance tube (secondary balance tube) and the outer connecting tube (primary balance tube) to balance the water pressure in the back pressure section and the lateral pressure section of the runner. When the manpower is interrupted, the guide vane adopts a closed mode with a small influence on the countercurrent zone. The water thrust changes before and after the load rejection and the force interruption are shown. The results of site tests show that under all operating conditions, including normal operation and transient operation, excessive water thrust will not be generated and the operation is very stable. Generator output (MW) pumping water thrust characteristics 4 Conclusion This paper presents the design and test overview of the world's highest head ultra high head pump turbine in the Gegencheon pumped storage power station in Japan. The test results on the site are basically consistent with those predicted in advance and studied on the microcomputer and meet the design requirements. From the viewpoint of further pursuit of economy, the technical problems of high-head, high-speed pump turbines have not been completely resolved. In the future, research must continue to be carried out to improve analytical techniques. Lin Xiuzi and Fu Zhiyue (above page 98) can fully meet the requirements of 22kV motor anti-halation. 4.1.4 Covering Paint The antifogging overlay of 600 MW turbine generators is basically the same as that of Hitachi and meets the technical requirements. 5 Structural tests Through the screening and testing of raw materials, all the anti-corona materials used in 600 MW turbine generators can meet and exceed Hitachi's requirements in terms of main performance. The test results of the Al row anti-halation test specimen and the real machine coil anti-halation test have shown that the anti-halation performance meets and exceeds the requirements of Sanli Corporation. 6 Conclusion 6.1 motor anti-halo structure process is simple, reliable, anti-halo performance and stability. Machine anti-halation requirements. In comparison, the 600MW turbo-generator of our company has a second-time treatment after anti-halation, which makes the anti-halation performance more reliable. 6.4 The reduction of the length of the low-resistance anti-halation layer has obvious advantages for improving the reliability of the motor operation and smoothly passing through the process withstand voltage test.
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