The treatment methods and suggestions adopted by this station provide reference for the safe operation management, maintenance and repair of power stations that introduce the same type of units abroad. The generator set of Nanjindu Hydropower Station in Hunan Province is an Austrian bulb tubular unit with a total installed capacity of 3X20MW, the unit type is SV420/40-180, the rated current is 1221A, the rated voltage is 10.5kV, and the stator and rotor winding insulation grade is F grade. The number of stator core slots is 288 slots. In November 1991, Unit 1 was put into operation, and Units 2 and 3 were successively operated in April and June 1992. Since 1999, Unit 1 has experienced the main insulation breakdown of stator bars twice; in September 2000, the stator bars of Unit 2 showed obvious corona and electrical corrosion. 1 Generator structure design and cooling method 1.1 stator core 3m, which is made up of 0.5mm thick high-grade silicon steel sheets stacked in half. Each side of the silicon steel sheet is coated with insulating varnish, and the iron core and the stator are all fully wedged. Three resistance thermometers (GB*B1B3) were designed in the middle of the back of the stator core to monitor the core temperature, and two resistance thermometers were actually installed in the field. 1.2 stator winding 1.2.1 stator bar structure and insulated stator windings use strip coil (ie wire rod) double-layer wave winding, pitch is designed according to 1-8-15 winding resistance. The linear part of the bar in the groove is made of 2×13 solid flat copper wires for 360*Robel transposition. The main insulation of the bar is made of F grade epoxy powder mica material, and the whole bar is vacuum impregnated and baked. Bake hardening treatment, anti-corona treatment of the straight line and end of the rod. 1.2.2 Stator bar anti-corrosion measures and end-fixed epoxy powder mica insulation is solid insulation, hot state does not expand. Due to the electromagnetic vibration, the anti-halation layer on the surface of the wire rod is in poor contact with the groove wall during the weaving, thereby causing the inside of the groove. Gap spark discharge causes electrical corrosion of the insulating surface. In order to prevent the occurrence of electric corrosion, the wire rod is filled with semiconductor silicon rubber between the interlayer dielectric separator, the wedge plate, the wire rod and the air gap of the groove wall at the bottom of the core groove (semiconductor pads are usually used in China) In order to ensure a stable and good contact between the anti-halation layer of the wire rod and the iron core, reduce the potential of the wire rod groove (see). The semiconductor silicone rubber is characterized by elasticity after curing, and can maintain the characteristic for a long time under the rated working condition, and can effectively prevent the vibration of the wire rod. 1 baby rubber 2 lower layer bar 3 layer spacer plate 4 upper layer bar 5 stator core stator bar end fixing: using neoprene tube tape (tube filled epoxy curing glue) respectively upper and lower layer bar end The department is tied to the support ring. The most important feature of the wire rod welt and the end fixing method is that it facilitates the installation and maintenance of the wire rod. A buried resistance thermometer (GB-B4B12) is designed and installed in the middle of the upper and lower bars of the stator, evenly distributed on the three-phase windings to monitor the temperature of the trunking, and only six GB-B4B9 resistors are installed in the field. Thermometer. 1.2.3 Unit cooling mode The unit cooling system is a separate system that is isolated from the slip ring chamber. The ventilation cooling of the generator is to install four 4kW axial flow fans on the upstream side of the generator. The fan sends cold air to the 10 vent holes on the upper and lower discs of the rotor support, and then flows through the downstream stator line. The end of the rod and the ventilating hole between the poles enter the air gap between the stator and the rotor. After the end of the upstream stator bar is merged, the air cooler is returned to the axial fan through eight air coolers to form a closed loop ventilation system. 2 genset fault defect situation 2.1 No.1 unit stator bar insulation breakdown breakdown 195 slot of the stator upper layer bar respectively appeared in the upstream side slot section notch breakdown of the main insulation breakdown. Obvious puncture point can be observed from the faulty bar under replacement. The anti-halation layer in the upstream section of the wire rod groove area is completely damaged and severe electrical corrosion of the main insulation surface occurs, and the anti-halation layer in the middle section of the wire rod groove area and The corrosion of the main insulation surface is slightly lighter than that of the upstream section, while the downstream section of the groove section of the wire rod has 30-40 cm antihalation layer from the notch and is not damaged and no electrical corrosion occurs. 2.2 Unit 2 produced severe corona and electric corrosion Since September 2000, Unit 2 was in operation and there was a strong ozone odor in the generator bulb head. According to this situation, in March 2001, the station inspected the end of the stator bar of Unit 2 and found that the slot and the slot at the upstream end of the stator bar are severely discharged and corroded, and the bar and core There is a gap of 0.3 1.0mm in the groove wall; about 1/3 of the bar groove has white powder; about 1/5 of the bar slot has black spots, burrs, caries and The wedge is loose, the silicone rubber is aging, and the bar is loose. In addition, the toner at the end of the upstream stator bar is heavily polluted. Checking the downstream end of the stator bar, although the above phenomenon was not found, the insulating paint on the surface of the stator bar was contaminated by the oil mist generated by the heat of the combined bearing lubricant. 3 Analysis of the cause of the failure For the case of No. 1 generator stator bar insulation breakdown failure, No. 2 generator stator bar slot corona and electric corrosion phenomenon, the power station has done a lot of experiments, and several expert seminars have been held. After many arguments, it is believed that the cause of insulation breakdown, corona and electric corrosion of the wire rods of this station is firstly caused by the aging of silicone rubber caused by thermal effects. The following will analyze the causes of stator bar insulation breakdown, corona and electric corrosion from the aspects of unit design and manufacture, operation and maintenance, external influence factors, etc. 3.1 Unit design and manufacturing aspects 3.1.1 Generator geometry is not ideal The ratio of the stator core length of the generator to the inner diameter of the stator is 1.3/4.3=0.302. Compared with the tubular bulb unit of the same type, the geometry of the unit is a typical slender body structure. (See Table 1.) From the perspective of ventilation cooling, the biggest problem with slender body motors is that the stator temperature is unevenly distributed along the axial direction, causing the highest temperature to be excessive. According to the unit ventilation and cooling mode of the station, the highest temperature of the line slot is shown in Table 1. The geometry of the unit is compared with the length of the motor. The capacity of the horse power station of the Majitang Power Station of the Nanjindu Power Station is now the core slot section on the upstream side of the stator bar. The semiconductor silicone rubber in the vicinity of the notch is susceptible to heat aging; and in the core slot section on the downstream side of the stator bar, the wire bath temperature is correspondingly low. 3.1.2 Magnetic pole pole shape problem The unit of this station is a salient pole motor, and the air gap between the rotor and the stator is uneven. The width of the pole piece is bp=225mm, the pole pitch is r=337.7mm, and the pole arc coefficient is ctp=bp/T=0*755, which is just in the range of 0680.76. The minimum air gap Smin=9mm, the maximum air gap Smax=413 is much larger than the 1.5 specified. The shape of the pole piece is not good, which may cause the magnetic circuit imbalance of the motor, resulting in the increase of harmonic magnetic potential and strong higher harmonics. The magnetic potential causes the additional loss of the stator bar to increase significantly, which causes the temperature of the unit to rise, which easily causes the semiconductor silicone rubber in the vicinity of the slot at the upstream end of the stator bar to be aged by heat. 3.1.3 Wire rod end fixing Because the elastic semiconductor silicone rubber is used between the iron core groove and the wire rod, the material can prevent electric corrosion, and can also fix the wire rod and prevent vibration, so only in the The end of the bar of the stator is tied with the end hoop, and the beveled pad is not padded between the adjacent upper bar or the lower edge of the lower bar, and the notched bar is also not fixed with the notch pad. The disadvantage of this type of fixing is that when the semiconductor silicone rubber is aged by the heat effect, the wire rod is easily vibrated in the groove, resulting in electrical corrosion of the wire rod at a high potential during operation. 3.2 Operation and maintenance As the station is a run-of-river power station, and in addition to the peaking task in the power grid, the number of units to start and stop is more frequent. When the semiconductor silicone rubber in the vicinity of the slot at the upstream end of the stator bar is subjected to heat aging, the large electric power generated by the inrush current will cause the wire rod to vibrate in the groove when the mesh is frequently turned on or subjected to system impact, and the wear bar is protected against fog. Layer, main insulation, causing the stator bar to stun. Corona produces thermal effects and ozone, which exacerbates the aging of the semiconductor silicone rubber, damages the organic matter in the main insulation, and gradually develops, causing damage and breakdown of the wire rod insulation. The number of resistance thermometers for monitoring the stator bar temperature and stator core temperature is small and the distribution is not reasonable. The operator cannot measure the true groove of the upstream end of the stator core and the upstream end of the slot between the upper and lower stator bars. temperature. According to statistics, when the No. 1 unit is rated at 20MW, the temperature rise of the stator trunking is 55K in June 1991 and 65K in June 1999. The temperature of the three-phase trunking is not much different, and the maximum operating temperature in the middle of the trunking reaches 108.5C. The temperature on the upstream side of the stator bar should be higher. If the long-term temperature is too high, the insulation of the upstream groove of the wire rod and the aging of the semiconductor silicone rubber will be accelerated. When overhauling the insulation breakdown of the stator bar of Unit 1 and checking the corona and electric corrosion of the stator bar of Unit 2, it was found that the windshield of the generator ventilation system was not tightly sealed, and the slip ring chamber and the closed circulation ventilation system colluded and Combined bearing oil, causing loss of air volume, affecting the cooling effect of the unit; Second, when the fan is working, the carbon brush dust of the slip ring chamber is sucked into the generator and attached to the surface of the stator and rotor, especially the upstream stator bar The end pollution is more serious, affecting the insulation resistance and heat dissipation at the end of the wire rod, which easily causes the end insulation surface to flash; and third, the dust particles and oil mist pollute the heat exchange surface on the ventilating side of the air cooler, reducing the cooling efficiency. Fourth, due to the presence of carbon brush dust particles in the air and the tight sealing of the windshield, condensation of the air cooler will be caused. The carbon brush metal dust adsorbed on the surface of the stator bar insulation paint forms a semiconductor film with oil mist and water. The film and the wire sandwich the insulation, just like many capacitors are connected in parallel under the action of voltage. The end of the wire rod forms a capacitor current loop, and the capacitor current flows along the insulating surface to the iron core through a conductive path composed of metal dust, etc., so that the semiconductor silicone rubber at the high-potential wire rod notch portion in operation is subject to heat aging. 3.3 External influence factors Since March 1998, the power station has been supplied by the main transformer 35kV side for the introduction of non-sinusoidal loads such as potassium chlorate plant, smelter, and milk steel plant. The non-sinusoidal load capacity has now reached 16MW. In June 1999, In the No. 1 unit, the main insulation breakdown of the stator bar occurred. In September of the second year, the stator bar of the No. 2 unit showed obvious corona and electric corrosion. In March 2001, the Hunan Electric Power Test Institute conducted a harmonic test for this station. The test report showed that the 5th, 7th, and 11th harmonic currents from the main transformer 35kV harmonic source loader to the generator end reached 17 respectively. 0A, in which the 5th and 7th harmonic currents are severely exceeded by the capacity ratio B. The higher harmonic current has a skin effect in the stator of the generator. In the double-layer winding of the stator, the higher harmonic current mainly causes additional loss in the upper layer bar along the groove height, and is 67 times larger than the corresponding additional loss in the lower layer bar. The harmonic magnetic field is still in the stator core. Additional losses are generated on the teeth. The additional loss generated by the higher harmonics in the upper layer bar of the stator is also one of the main factors causing the aging of the semiconductor silicone rubber in the vicinity of the slot at the upstream end of the upper bar of the stator. In addition, the wire rods are often subjected to large harmonics, which may increase the number of times the insulation gap is discharged, thereby shortening the insulation life faster. Based on the above analysis and test, it is believed that the main insulation breakdown, corona and electric corrosion of the upper layer bar of the station are caused by the thermal factors of the semiconductor silicone rubber in the vicinity of the upstream end of the stator upper bar. Aging. When the semiconductor silicone rubber ages, the wire rod loosens in the groove, and an air gap is formed between the wire rod and the groove wall, causing electric corrosion of the wire rod at a high potential during operation; the wire rod is loosened in the groove, and is frequently turned on or connected to the net or When subjected to system impact, the large electric power generated by the inrush current will cause the wire rod to vibrate in the groove, and the anti-halation layer and the main insulation at the upstream end of the wear bar will cause the stator bar to stun at the notch. Corona, electro-corrosion and higher harmonics will further accelerate the aging of the semiconductor silicone rubber and the main insulation of the wire rod and gradually erode the middle and downstream parts of the wire rod groove, and finally make the upper layer rod groove which is at a high potential during operation. Main insulation breakdown at the upstream end slot. 4 treatment methods and recommendations 4.1 treatment methods 4.1.1 wire rod, wedge loosening treatment to cut the wedge, clean the wire rod and the gap in the gap in the semiconductor silicone rubber. The dry wedge is pushed in, and the new semiconductor silicone rubber is injected from the four injection holes on the wedge at a pressure of 2.5 kg/cm 2 to fill the side gap of the upper rod, the line bar and the wedge gap to prevent the line. The rod vibrates in the groove. The method of loosening the wedge is the same as the method of loosening the bar. 4.1.2 Repair of insulation damage between the core teeth of the iron core Use a non-quenched small chisel to gently open the damaged part, taking care not to injure the insulation of the wire rod. Thoroughly clean with dry, clean compressed air, if necessary, clean with carbon tetrachloride, then brush the insulation varnish between the sheets. After the paint is dry, shape the core teeth. 4.1.3 Generator oil pollution, dust cleaning Use special pressure spray gun, use GX-25 electrical equipment cleaning agent to spray oil and dust on the upper and lower ends of the stator bar and the stator and rotor, and then wipe it with white cloth. And clean the heat exchange surface on the ventilating side of the air cooler. 4.1.4 After the stator painting is cleaned and treated, the stator shall be sprayed with all or part of the 8037 iron red polyester insulating cover paint as appropriate. Small 2 proposes to strengthen the supervision of the unit and shorten the cycle of large and minor repairs. This station is a run-of-river power station. According to the foreign party, the minor repair cycle is 24 years and the overhaul period is 1014 years. According to the site situation of the station, the maintenance rules of the power station unit stipulate that the minor repair cycle of the unit is half a year and the overhaul period is three years. According to the existence of corona and electric corrosion in the power station unit, the current situation of safe operation of the main engine has been jeopardized. The large and small repair cycle of the unit should be shortened, and the problems of wire rods, loose wedges and combined bearing oil in the unit should be dealt with in time to ensure the safe operation of the unit. . Implement the harmonic control plan as soon as possible and implement it to eliminate the damage caused by the 5th, 7th, and 11th harmonics of the 35kV side harmonic source of the main transformer. Coordinate with the local power grid to develop the relationship between power generation and power, and strengthen the optimal scheduling of the unit. Reduce the number of starts of the unit, especially the No. 2 unit with corona and electric corrosion is serious, and should not stop the machine as much as possible, and strengthen the inspection and inspection of the unit. Improve the sealing of the windshield and the slip ring chamber to ensure that the unit is clean and clean during operation and avoid carbon brush dust entering the stator and rotor. Shorten the regular maintenance cycle of the unit air cooler, dehumidifier, and shutdown heater to keep the equipment in optimal working condition. C6) Improve the ventilation inside the generator bulb head and reduce its ambient temperature. 5 Conclusion At present, there are more than ten power stations in the domestic introduction of the Austrian ELIN bulb tubular unit, and the power station with the main insulation breakdown of the unit in the past ten years has only the Nanjindu power station. This paper hopes that by analyzing the cause of the main insulation breakdown of stator bars, it can cause the same type of power station in China to pay attention to the problems of ventilation cooling, combined bearing oil, stator and rotor working environment, non-sinusoidal load, etc. Work on safe operation and routine maintenance of the machine to extend the insulation life of the unit.
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