1 Introduction The 300MW dual-water internal-cooled steam turbine generator is popular because of its high efficiency, low temperature rise, simple operation and maintenance, and small amount of motor materials and small size. However, the stator core of such a motor is air-cooled, and the anti-halation problem of the stator end windings when operating in a high-altitude environment is a subject that needs to be studied intensively. In order to improve the corona voltage of the winding, this paper analyzes the causes of corona and the technical solutions to solve it theoretically, and develops a simulation test plan for experimental research. The main cause of corona is that small gap discharge and creeping discharge of the contact portion between the end insulating structural member and the high voltage bar under high altitude and low air pressure conditions. The anti-halation measure is to insulate and process the end-to-phase gap and other related small gaps. At present, there are relevant research reports in China, but there is no successful practical experience. The former Soviet Union has an anti-halation technology that describes the stator end windings of high-voltage motors (= 24kV) in its air-cooled medium. The 900MW turbo generator of Siemens has a rated voltage of up to 27kV. It uses the fixed and anti-corona technology of the entire end winding (which is patented by Siemens), and its tweezers are operated under pressure-tight hydrogen pressure, so the operation time The problem of anti-halation is not outstanding. The process of electrical aging and ozonation accompanying corona is extremely detrimental to the insulation life of the winding, so corona is a problem that must be avoided in the operation of the motor. The corrugated corona of the stator winding of the high voltage motor has been effectively controlled. The end corona problem, in addition to the straight line and end anti-corona problem of a single bar that has been the focus of attention and has been well solved in the past, has recently found that the end must be raised. The overall anti-halation capability of the winding. Solving this problem is not only important for the repair and market expansion of high-voltage motors in high-altitude areas of 20kV, but also for the development of end-side anti-corona technology for higher voltage grade generators. 2 technical theory analysis 2.1 technical goals At present, the anti-halation level of a single stator bar has greatly exceeded the technical indicators specified in the relevant standards. This paper aims to study the overall anti-halation technology of the stator end windings. According to the national machinery industry standard B8439-96 for high-altitude high-voltage motor anti-corona technical requirements, the high-voltage motor machine's corona voltage value (Rs) should meet not less than lfVF, the motor's rated phase voltage, F and installation site It is related to the altitude of the test site. The motor (t/N = 20kV) installed in this paper has an altitude of more than 2000 meters. Its test at Shanghai is about 19kV at an altitude of nearly zero meters. 2.2 High-altitude motor is prone to halo. The essence of analyzing corona is the phenomenon of localized glow discharge of gas under the action of electric field. For a dual-water internal-cooling generator with a capacity of 300MW and a rated voltage of up to 20kV, the cooling method is water and water, that is, the core is air-cooled, and the main insulation of the entire stator winding is in the air medium. When the motor is running, the air medium participates and constitutes the stator. 7 The field strength and voltage calculated by the filling medium between the phase-locked coils of Table 2-1 are calculated. The interval between the dielectric constants of the medium filled with the medium is 5, kV The /mm phase medium is subjected to the main insulation to withstand the field strength. The main insulation is subjected to the main insulation to withstand the field strength. Part of the winding insulation structure. In general, the dielectric strength of air is lower than the dielectric strength of the solid insulating material and is therefore easily broken down or discharged. Taking the standard state (p = 201, (0=llg/m3) as an example, when the electrode distance is lcm, the breakdown field strength of the air under a uniform electric field is about 3.2kV/mm, which is about 2.3kV/mm of the power frequency AC. The breakdown field strength of air depends on temperature and pressure and depends on the density of the gas. At a certain temperature, the lower the air pressure, the larger the average free path (X) of the charged particles passing through the air without collision, the more charged The kinetic energy obtained by the acceleration of the particle g when it is moved in the direction of the electric field (the greater the knowledge, the greater the kinetic energy accumulated between the two collisions of the charged particle is enough to generate the impact free to cause the air to break down to form a corona, thus reducing the air pressure. Small, its breakdown field strength also declined. High altitude air is thin, such as 2,200 meters above sea level in Qujing, Yunnan, the atmospheric pressure is only about 0.786X103, and the breakdown field strength under uniform electric field is /=, if tt/kh =1.94kV/mm, which is about 16% lower than the air breakdown field strength under the standard state. Considering the high operating temperature when the generator is running, the local air state changes, the end structure is complicated, and the electric field distortion and environmental cleanliness are caused. And other factors, the air breakdown field will be strong 2.3 High-altitude high-voltage motor stator winding end anti-halation of the air is less than any other insulating material, when there is an electric field, the electric field strength in the air medium is higher, which is extremely unfavorable for anti-halation. For the end corona mainly occurs in the same layer phase region, the electric field distribution of the region is analyzed in detail below. -1 is the schematic diagram of the ends of the two coils in the same layer of the stator winding of the generator. The insulation structure parameters are: =5.5, the dielectric constant is £11=5; the interphase distance of the coil is a; the dielectric constant of the interphase filling medium is ea. The field strength and voltage values ​​of the filling medium between the phase-separated coils can be calculated, see Table 2-1. When the air is interphase filled medium, as shown in the box in Table 2-1, when the phase separation coil is separated When a is respectively, the field strength of the air medium is 1.16, 1.4kV/mm, and the voltage is 17.4kV and 16.9kV respectively. As mentioned above, the breakdown field strength of the air between uniform electric fields at p = 20 is 1.94kV/mm; according to reports, if the operating temperature is corrected, the breakdown field strength is reduced by 15% to 1.63kV/mm, only slightly exceeding E = a = 12mm; and, due to unavoidable process variations and coil ends The influence of the spacers in the interval will result in an electric field distortion that does not conform to the calculation, so that the actual average breakdown field strength in the region is reduced to =, <1, which is a coefficient of the degree of electric field inhomogeneity, which is about 0.4 to 0.5. , b substantially field strength and voltage calculation (simplified to uniform electric field) phase coil and end hoop bracket The spacing between a and mm is small. The dielectric constant of the medium is small. The gap medium is subjected to field strength EaVS/mm. Small gap dielectric bearing-2 stator winding end fixing structure (cross-sectional view) Table 2-3 Filling material performance index and test data material The code HYC ratio is low, which inevitably leads to air discharge. The 800MW/T3B series full-water-cooled steam turbine generator (rated voltage of 24kV) produced in the Soviet Union from the late 1970s to the early 1980s also has the problem of halo in the end-phase isolation zone. One of the solutions is to use e=20. The material fills the spaced-apart bar spacing area. In this paper, the two-water internal-cooled turbo generator with rated voltage of 20kV is considered. Considering that the five b is about 0.65, the visible phase interval is a=12 to 15, and the filling medium is e 10-15, which can reduce the interphase field. Up to 0.42~0.6kV/mm, it can fully meet the requirements of anti-halation. If the phase-to-phase distance is greater than 15, the dielectric constant e is 5, which can reduce the interphase field strength to less than 0.77kV/mm, which can also meet the application requirements. Table 2-2 The medium between the phase coil and the end hoop bracket is received by the medium. In addition, the fixed structure of the end of the stator winding (such as -2) causes a local irregular small gas between the phase coil of the high potential end and the end hoop bracket and the pressure plate. There are creeping (spaced spacers) in the gap and phase separation zones, which are all factors that cause corona. For the former, it mainly leads to small air gap discharge. The data in Table 2-2 is the calculation result of simplifying the electric field at the small gap (the surface potential of the end hoop bracket is approximately zero). When the gap S=1 circle is visible, the field strength of the medium is 6.25kV/mm. Even if the electric field distortion is not considered, the breakdown field strength of the air in the average electric field is far exceeded. If the medium at the gap is replaced with a filler material having a higher dielectric constant such as 10 to 15, the field strength of the dielectric material is greatly reduced by about 0.87 to 0.59 kV/mm, and the dielectric material itself is required to have a dielectric strength high enough not to be high enough. It is broken down so that the small gap problem can be solved. For the latter, it mainly leads to creeping discharge. According to the general experimental experience, the creeping discharge formed by the epoxy laminate has the following relationship: when the creeping voltage is 10 mm apart, the AC creeping surface discharge voltage is about 12 kV; when the surface voltage is 12 mm apart, The AC creeping discharge voltage is about 20kV. It can be seen from Table 2-1 that when the phase-to-phase distance is 10 and 12mm, the phase-to-phase voltages are 16.4kV and 16.9kV, respectively, when there are no spacers and the like. When there are spacers, etc. When it occurs, the creeping discharge seems to be inevitable. To avoid creeping discharge, first try to increase the creeping distance, such as increasing the distance between the bars or making the bevels or step faces along the surface. Second, cancel the creeping surface, that is, fill the interphase regions with a specific filling material to eliminate the short distance. Avoid creeping discharge along the surface. 2.4 Performance requirements of the filling material As mentioned above, in order to achieve the purpose of anti-halation at the end of the high-altitude motor, the end of the stator winding of the high-voltage motor can be filled with a material having a dielectric constant of 5-15. Moreover, the filling material must also have excellent heat aging properties; and because the end portion is subjected to electric power during operation, the material must have sufficiently good mechanical properties, especially the bonding strength must meet certain requirements. In addition, since high dielectric materials generally have large dielectric loss and are prone to cause more heat generation during motor operation, which is not conducive to the normal operation of the motor, the dielectric loss of the material must also be required, which will inevitably lead to the development of materials. Bring more difficulties. The performance indexes prepared for the filling materials during the simulation test are shown in Table 2-3. Table 2-3 also lists the relevant performance test data of the two materials used in the simulation test. 3 Test 3.1 Simulation Rule According to the above analysis, the simulated stator windings were designed and fabricated, and the insulation materials with dielectric constants of 5 to 15 were used for specific insulation treatment between the phases. The contents of the two simulation tests and the results are summarized in the following table. 3-1. Table 3-1 Simulation of the implementation of the ruled content Simulation of the structure of the interphase filler material under the pressure plate and the two sides of the phase and other small gap simulation test (a) the stator wire rod embedded in the stator core in the shape of the felt dip Paint YQ, laminate, untreated epoxy filler HYC-1, etc. Untreated conformal felt dipping paint FK, laminate, etc. Untreated simulation test (2) Stator wire rod embedded in wooden simulation mold Epoxy filler HYC-2 Treatment of untreated epoxy filler HYC-2, conformal rope and other treated laminates, conformal felt and epoxy filler HYC-1, etc. Table 3-2 First simulation test results End corona observation point scheme "S (Shanghai), kv treatment effect evaluation phase between the region, the pressure plate on both sides and other parts 118 poor 228 good 320 poor 418 local difference 5> 32 good 6> 30 good table 4-1 generator stator end anti-halation treatment Halo voltage test results pressure repair products (installation site t altitude 2KB meters) new Product (manufacturer, Shanghai) phase group "S (pre-treatment) S (after treatment) B8439 requirements S (measurement data after the end of the r-excited winding after cleaning; 2) repair products and new products ( After the treatment, the corona test results after the anti-halation treatment, that is, no corona was observed when the voltage was raised to 20 kV and 26 kV for 1 minute, respectively; the boost was ended when the motor insulation test was maintained. Note: The voltage of the corona test only rises to 30kV. 4 The end of the anti-corona treatment of the generator is based on the results of the above simulation test and research, summed up a set of high-voltage motor end anti-corona technical scheme and process measures for the elevation stator The end-to-phase spacing region was simulated by a conformal high dielectric ring 3.2 corona test. The end of the stator winding was insulated and fully cured, and then subjected to a halo voltage test. In order to thoroughly examine the level of anti-halation at the rear end of the insulation treatment, the test was carried out under no light conditions at night, and the halo was observed with the naked eye. During the test, one wire rod copper wire is connected to high voltage, and the other wire rods are grounded. When boosting, the voltage is boosted step by step by 18, 20, 23, 25, 28, 30, 321 and the voltage of each gear is kept for 15 seconds. 3.3 Corona test results The corona test results of the two simulation tests are shown in Table 3-2. In contrast, the anti-halation effect of the schemes 5 and 6 is ideal, and the stun voltage can be higher than that in the Shanghai test. 30kVQ 20mV generator repair products and new product stator end anti-halation treatment. After the treatment, the halo voltage test was carried out at the installation site and the manufacturing plant respectively. The result is that the halo voltage is greater than 20kV (standard requirement is 15kV) at the installation site, and the halo voltage is greater than 26kV in the manufacturing plant (Shanghai), which is much higher than the standard requirement. (19kV more), that is, the anti-halation level of the generator reaches the specific requirements in a high altitude environment. Test results and indicators requirements are shown in Table 4-1. Oxygen composite fillers for anti-halation technology treatment can significantly improve the overall machine's corona voltage, making it far exceed the technical specifications of B8439, effectively meeting the high-altitude high-voltage motor defense Halo technical requirements. Hydraulic Cutter Frame,Synchronous Servo Drivers,Cnc Turning Machine Parts,Electric Hydraulic Cutter Frame Ningbo junfa CNC Equipment Co. Ltd. , https://www.intimecnc.com