Fault Analysis and Prevention of Stator Core of Large Turbogenerator

Hebei Institute of Electric Power Test, Shijiazhuang 050021, China; 2. Hebei Electric Power Company, Shijiazhuang 050021, China; 3. Hengfeng Power Generation Co., Ltd., Hengshui, Hebei, 53000; 4. Shijiazhuang Thermal Power Plant, Shijiazhuang 050041, Hebei Province, frequent occurrences of iron core fault noise in recent years, analyzed the causes of faults, introduced the handling methods and preventive measures of core faults.

In recent years, the southern power grid of Hebei Province, hereinafter referred to as the Hebei South Network generator set, has continuously broken the Generator Stator Core and the vibration and noise caused by the loosening of the Stator Core during operation. The generator core fault vibration and noise generation is more complicated. It involves various factors such as generator design and manufacturing operation and electromagnetic force mechanical force, which brings hidden dangers to the safe operation of the generator. One caused the unit to be forced to stop. Flashing this, it is necessary to pay this question to be sufficient. 1 In recent years, the iron core accident and noise increase phenomenon occurred in the operation of the generator of Hebei South Network. Example 1 Evaluation of the generator system Dongfang Motor Factory production in May 1988, cooling method For water hydrogen, the rated power factor is 0.85, the stator rated voltage is 15.751. The running machine noise is sudden and large. At that time, Gong Gongyu. 200 reactive power. For 53 people, the electrical parameters and the temperature of each component of the generator are normal. The reactive power of the lift has no effect on the noise cluster. Adjusting the noise of the generator card to report the noise does not reduce the load 乍1601; after that, it returns to normal. When the generator is under no-load boost, the generator vibration and noise are measured. When the stator voltage is 13 1 , the frequency doubling vibration is sudden and large, and the frequency doubling vibration occurs at 161. After the pressure reduction, the vibration of each measuring point decreases, and the noise is not obvious. Variety. The shutdown check found. The locating nut at both ends of the generator loosened the steam side of the steamer at the 0 o'clock position. The nut has a loose sound, the nut at the 3 o'clock position is completely loose, and the nut at the 1st position of the excitation side has an empty sound; the back of the iron core is loose.

1.2 cases of a factory hair dryer for the Harbin motor plant in a few years of production, cooling method for water ceremony, rated capacity of 3 called river in the long-distance sound abnormalities, shutdown inspection found the stator excitation side slots 34 and 35 slots Between the 35th slot of the 64th core and the 36th slot between the 1st section of the iron core 1 slot and 2 slots, the first section of the core is severely overheated and the teeth are burned. The 35th slot and 36 slot end core teeth can be shaken by hand. The 23536 slot bar slot insulation of the upper coil is worn due to the iron core shaking, and the 36-slot bar is particularly worn. The movable core will insulate the 5.5 wire to a depth of 5, and the wedge is pressed by a special month instrument. In case, it is found that the wedge is generally loose. According to the manufacturer's regulations, the value should be between 0.20.5mm. The actual measured value is up to 1J. The unit with the eyebrow model of the manufacturer and the machine is in normal operation with a load of 300. And when the internal cold water temperature rises from 25 to 36, the noise and vibration become larger, the noise characteristics are low frequency noise, the vibration amplitude of the base is from 0.008 to 00, when the water temperature is controlled at 3 left and the load is below 30 1 Jia. The noise and vibration of the generator basically tend to be normal.

After the unit was overhauled, it was found in the iron loss test that there were 4 hot spots on the core and 8 pieces on the stator excitation side lead plate were loose.

1.3 cases of a factory machine are Harbin Electric Machinery Factory production rated capacity 300. The cooling method is hydroquinone hydrogen. During the operation, the stator grounding signal was issued twice, and after being forced to stop, it was found that the silicon wire sawing of the stator wire insulation broken at the first core was sawn. Iron core step in the edge; there are many places where the steel can be shaken and shaken, and the iron core overheating in 2 runs. The stator core of the modern large generator is usually cold rolled with low magnetic permeability and low loss ratio of 0.35, 0.5 fan-shaped silicon steel. The sheets are laminated and the silicon steel sheets are coated with insulating varnish. The iron core segment which is composed of 20 pieces of fan-shaped silicon steel sheets is 12 cubits, and the fan-shaped pieces of one machine are stacked on the positioning ribs on the side, so that all the fan shapes are electrically connected to each other through the positioning ribs themselves. If the insulation of the iron chip is damaged or becomes low. The hair dryer forms a closed loop of current during operation. The loss caused by this eddy current is related to the loop resistance. When the insulation of the galvanized steel sheet is seriously damaged, the current may reach a large value, causing the temperature of the iron core to rise or even melt, resulting in Serious accident. The reason for the short circuit caused by the insulation damage between the iron chips is that the manufacturer does not tightly cause the vibration of the splicing and the insulation between the sheets before the winding of the stator windings. The pressure used during press-fitting is too large. 2 River, 3 makes the insulation between the pieces broken; the operating voltage is higher than 1.1 times of rated voltage for a long time; in the operation of the generator, for some reason, there is a sudden occurrence of hard foreign matter inside the stern, and the iron core is struck under the action of wind pressure and rotor rotation. .

3 Generator core failure vibration and loosening reasons 3.1 Manufacturing quality of the core The core of the generator will be subjected to various forces during operation, and the alternating magnetic force generated by the radial force wave between the rotor and the stator The self-twisting of the iron core is greatly avoided. If the iron core is pressed and the old force wave will cause the iron core and the individual, the vibration of the sector is broken and the teeth are broken.

The interaction of the stator and rotor magnetic field causes the stator core coil to be subjected to the rotating force wave, which constantly changes position with the rotation of the magnetic field. For the 2-pole hidden generator, when the rotating magnetic field rotates, the magnetic pull and electromagnetic The vibration changes twice, which is 2 times the power frequency. Therefore, when the generator is in normal operation, the core rod and the like will be subjected to a rotating force wave twice the generator frequency.

Under the influence of this force, the iron core rod may generate vibration, and the iron core generated by the electromagnetic force casts the pharynx and the pharynx. Therefore, when the hairpin machine is designed and manufactured, the self-vibration frequency of the iron core rod should be kept away from 100, and the resonance effect should be avoided when the electromagnetic excitation frequency of 10 is close, and severe vibration and noise are generated.

When the tightness of the iron core is loosened, the action of the force wave will generate vibration friction, which will reduce the insulation between the sheets, and it is easy to form a closed-loop vortex. In the rust caused by it, the surface may be completely dry. The rust spots on the vibrating laminations are often very stable. After the rusting parts are coated with insulating varnish, the rust will not stop because the insulating varnish applied at this part is quickly damaged by the broken core or its individual areas. The main reason is that the thickness of the fan-shaped piece is particularly uneven. The stator positioning rib is not accurately installed. The ventilation groove is not installed correctly. The iron core is assembled at the factory. The test is poor. The stator case is vibrated and the nut lock is unreliable. The nut screw of the tightening screw can be seen from the previous failure phenomenon.

The most common outfits appear loose in the teeth of the fixed edge, which causes damage to individual fan-shaped frying. And keep the core loose.

3.2 Influence of temperature change during operation The load of the day and night is not uniform, the active load changes more, and the reactive load also changes greatly. These will cause the core temperature to change. According to statistics, the active load change of 200,130 cubits and the load change of 020 will cause the core temperature to change to 2535. Some generators have peaks and peaks. It is necessary to start and stop frequently, so that the temperature of the generator stator core can reach 50 70. During the operation of the generator, the temperature of the stator core is drastically changed to make the clamping force between the silicon steel sheets elastically change. The long-term repeated will cause the iron core to be periodically hot-cold and contracted, and it is easy to loosen the core teeth of the four cores. Vibration and noise are generated by the force.

The generator runs at a low load phase in the middle of the holiday, or when the power factor is close to 1, the axial leakage flux of the core at the end of the stator is large, which causes the temperature of the core of the edge to rise. There is only one ventilation channel steel support between the iron cores at the end of the hair twister. The width of the toothed finger is much narrower than the width of the core tooth. The edge core has several trapezoidal grooves. The bottom core cannot guarantee the core tooth. The uniform distribution of the armoring pressure, in the case of electromagnetic force and the temperature change of the core of the edge, easily cause the lamination to vibrate, causing the edge of the gingival steel sheet to be broken and the upper and lower sides of the core segment to be swayed, resulting in a fixed winding insulation mill. Broken grounding, 4 iron core loosening and noise treatment method to deal with the overall or partial looseness of the generator core is more complicated, need to be specifically addressed by the manufacturer according to the specific situation. It should be noted that it is not allowed to press the core with a compacted ceramic, because this method may damage the insulation of the household and this method can only compress a short segment of the iron chip.

When the generator core is designed and manufactured, the scheme and process of avoiding the 7 electromagnetic excitation frequency are generally considered. The modal frequency of the iron core is less than 100 angstroms with elliptical cores. At this time, the locating ribs have a great influence on the vibration and noise of the generator. It is more common and effective to change the self-vibration frequency of the iron core. Adjust the stiffness structure of the positioning rib between the stator core and the casing. Turn down on page 28 to make it have two groups of end networks. The impedance characteristics of the end network are matched with the impedance of the local functional end of the ground adjustment terminal. It avoids the impedance mismatch caused by the local function and the ground adjustment sharing this interface, and the remote device crash caused by the level reduction. The modem remote signal is sent to the key control, corresponding to a sine wave voltage of 0 or 1 milk rate. The equal-amplitude FM signal that changes with the digital has a fixed transmission level after being amplified by the amplifier, and then filters the high-order harmonics and noises through the band-pass filter, and then sends it to the attenuator to adjust the output signal to The size of the transmission level is most closely matched by the line matching transformer for impedance transformation and various transmission channels. The 18th page and the number are connected, which requires the operating unit and the manufacturer to make a plan to complete.

Looseness of the end core and large vibrations are more common.

In order to enhance the insulation between the sheets and to reduce the eddy current, a method of inserting a 0.2 mm thick epoxy glass cloth sheet between the sheets is used in the treatment. The epoxy glass cloth board and the iron chip spacer or two pieces of careful insertion determine the number of inserted pieces and the depth of each piece insertion according to the degree of looseness of the iron core.

According to experience, the maximum insertion depth is about 100 when the bar is not taken out. 1. After inserting the insulation sheet. To do the iron loss test, pay the iron core with the teeth still overheated, and insert the epoxy glass cloth board deeper. If it is more difficult to continue inserting into the deeper part, the wire rod should be taken out to facilitate the insertion of the insert. For the iron chip with small gap and difficult to insert the epoxy glass cloth board, the teeth can be opened by a narrow and thin special tool, and the same grade of insulating paint is poured into the slit.

5 Precautionary measures 5.1 Monitoring and operation during operation and overhaul The operating personnel should pay attention to the change of noise when patrolling the generator. The loose iron core will increase the noise of the generator. If noise is found abnormally, people should find out the cause. At the time, the machine is scheduled to stop. In the repair operation, the noise of the generator can be temporarily reduced by adjusting the generator parameters such as the reactive hydrogen pressure hydrogen temperature and the internal cooling water temperature. Check the tightness of the stator core in detail. The loose iron core can be treated by wedge insulation wedges, and the wedges are wedged and coated with epoxy glue to fix the wedges. The signal is transmitted to the receiving end. The filter attenuator and the line transformer in the modulation circuit are both end networks, and the output of the end network is directly connected to the input of the other end network. In order to achieve matching cascading, the characteristic impedances at both ends of the connection point must be equal, 1 B 4 Inspection and consolidation of the implementation effect of the measures In October and December 2000, the effect of the modified Xuying Zhaotong station was checked. It was found that the utilization rate of the telecontrol equipment after the transformation was significantly improved, reaching 100, effectively ensuring that the dispatcher correctly grasped the station port. , to mention the efficiency of the dispatcher. The expected value was achieved and the transformation was successful. In addition, corresponding consolidation measures have been formulated, and the transformation results have been formally incorporated into the daily maintenance of automation to ensure the reliability of its operation; in the operation and maintenance, various failures of telecontrol equipment have been verified. Find + foot and where to improve. The measures should be improved to improve the generators with large and high-rate or phase-in operation. Pay special attention to check whether the positioning nut is loose or not. Previously, there were such problems in the 200 rounds of the Hebei South Net. This type of loose locating nut was tightened with a special wrench and the locking piece was re-locked.

5.2300倨婪5.缁,笮奘笮奘,疚律,匝,Hebei South Net 300hejia generator stator core in operation many times broke out overheating and noise boundary often, so each generator overhaul The core temperature rise test should be done to determine the state of insulation between the sheets. In order to ensure the magnetic density value of the iron loss test, according to experience, it is best to choose 61 屯 taste grade in the inspection field. The magnetic flux density is 1.4 butyl. The duration is 45. 1. After the test, the thermal imager should be used to check the stator. To find the higher temperature rise, then use the infrared thermometer for special monitoring. The maximum temperature rise of the tooth should not exceed 25, and the most common temperature difference between the teeth should exceed 5.

For excessive toothing, the necessary treatment should be carried out in conjunction with overhaul.

5.3 The operation hall of the generator should be as reasonable as possible. The change of the temperature of the large steam turbine generator hall will have an impact on the tightness of the iron core, in addition to the influence on the life of the fixed coil insulation rotor parts. Therefore, it is necessary to keep the generator load continuous and stable as much as possible in the operation of the generator. The peaking of the grid load should be arranged as much as possible for the small unit. In addition, due to the high leakage force of the high-speed force or the phase-inflow turbine generator due to the leakage at the end, the poorer generator of the end core should be arranged to enter the phase as little as possible. Pay attention to the change of generator noise for generators with more load changes and phase-in operation during operation. Pay attention to the condition of the iron core during maintenance.