Community > Forums > Other Industries > Transformer overheating
Post a topic Post a survey Forum Guidelines

Transformer overheating 0 replies,1136 views

#1
Overheating overheating transformer power transformer failure is a common fault of multiple failures, the safe operation of transformers pose a serious threat, thus causing widespread concern in the field. Focuses on the causes transformer overheating, diagnostic methods and treatment measures. First, the transformer overheating causes (a) of the system group of overheating the last decade, to reduce the transformer losses, the factory has adopted the transposition with the system insulation transformer winding wire around the system. CTC because early domestic production technology is not yet fully grasp and make use of CTC to run ten years or so the transformer insulation system expansion there. Road Section to ask the oil plug, oil flow impeded, turn insulation are not fully cooled so serious aging, resulting in hair paste, crisp, long-term electromagnetic vibration, the insulation off, local exposed copper, the formation of inter-turn (between segments ) short circuit, causing the transformer burning accident. For example, the Northeast power grid of a step-up co-240MVA transformers, normal operation of the load was 90%, the upper oil temperature generally does not exceed 70 \u2103. Since 1988, the transformer furfural analysis found that there is insulation aging. Chromatographic analysis showed that the oil runs, CO and CO2 higher than the absolute value and growth. June 1992 in normal operation, the main transformer of light and heavy gas protection action, explosion-proof cylinder fuel injection, hanging out the high voltage winding check and found: A phase failure occurred in the number of low-voltage winding 3 to 4 under the outermost section of a group of CTC, several root Shao Rong. After further examination, found that low-voltage winding up and down both ends of paragraphs 1 to 5 scorch marks, and the phenomenon of exposed copper. Wire segments have been burned between the insulating paper, 6 ~ 8 insulation was dark red. The single half-spiral winding at 1.5mm with spiral oil passages have been blocked, 4.5mm 1.4mm oil path it can only be inserted into the board. In addition, poor quality of winding material itself, can lead to overheating. For example, a Bureau of a SF7 \ u00008000/35-type transformers, installed and put into operation in 1994 found that: the transformer to the load and under the same circumstances 5600kVA transformer, the transformer high temperature than 5600kVA about 10 \u2103, in environmental temperature is higher than 5 \u2103, as long as the transformer input, regardless of load size (maximum load 4500kw), fan motor has been activated (start the fan temperature setting is 50 \u2103, then the transformer oil temperature higher than 50 \u2103), which shows that the transformer has been Hidden overheating fault exists. Hanging cover, the disintegration of packet inspection technology that, B-phase low voltage winding section obviously overheating 1,4 cakes, insulation paper has turned into a dark brown, open the inspection, found a small glitch leakage interturn copper point, but turn to turn does not completely short-circuit, so the fault current is not large, slow heat, so temperature rise. (B) tap the dynamic and static contact is bad. In the OLTC transformers, in particular, frequent voltage, load current large transformer, the frequent transfers cause contact between the mechanical wear, corrosion, and contact contamination, thermal effects would make the current spring weak elasticity, so that dynamic and static contact pressure between the decline in contact, the contact resistance according to the formula Rs = K / Fn where n-index, and contact form on contact; K-constant, and the nature of contact material ; F-contact pressure. Can be seen, the contact pressure decreases, will increase the contact resistance between the contacts, resulting in contact between the increase in volume is too hot, because heat and accelerate the corrosion of the contact surface oxidation and mechanical deformation, creating a vicious cycle, such as not in time, often cause an accident damaged the transformer. For example, a chemical plant 8000kVA load transformer, due to negligence of the on-load tap-coarse part of the contact problem, increasing contact resistance, heat, and gradually form a dynamic and static contact between the metal melting, evaporation, Epoxy resin insulation support carbonation, the last in the voltage caused by arcing during phase short circuit, transformer burst into flames, and thus causing damage to the transformer accident. In the no-load regulating transformers, the tap is bad, will make the contact surface corrosion, oxidation, or contact the contact pressure between the decline in the contact resistance increases, and the formation of transformer overheating failures. For example, a Bureau of a 35kV, 18MVA transformer, there had been bad for the tap, fever, leading to the transformer tap-burning flow, transformer gas relay, forcing the transformer outage. (C) lead failures lead failure are: 1. This failure leads many shunt malfunction, the Northeast Power Grid 1989 ~ IR93 years of statistics, 10% of the total failures. These failures have occurred within the casing 66kV, 66kV side of the current is high on the one hand, on the other hand is not straight along most of 66kV lead the direction of the casing into the tube, therefore, not covered with any insulated wire and catheter contact, causing diversion, resulting in heat failure. The following reasons: appearance of a half stack of wire cable with a white cloth bag, after making the pass and lead the assembly process, most have no close and incomplete. Some of the factories, or even not to this level white belt. While the long-lead, in the assembly, such as cable, after pressure causing bare copper strand and the casing wall by then. This creates a closed loop, as shown in Figure l-61. Figure 1-61 by copper cable and the casing then the diagram 1 - cable; 2 - copper pipe when the lead through current, the wire around the magnetic field and there are magnetic flux \u03A6, the mutation leads alternating magnetic currents pass, which will be out in the loop induction electric potential, e = d\u03A6 / dt as large-capacity transformer current per phase I lot, the corresponding magnetic flux around the wire and the induction of the electric potential \u03A6 e is relatively large. Closed loop resistance force R = PI / S, the shorter the path l, and the larger wire cross-section S, R smaller, if the potential for the IV, the loop resistance is 0.01\u03A9, the current flowing through the loop I = e / R = 1/0.01 = 100A. Relatively speaking, the exposed cable and copper loop connected by a local contact resistance is relatively large, when a large current through the circuit will heat. Known by the failed instance, copper melting into four shape environmental phenomenon, indicating the temperature of hot spots has reached above 1000 \u2103. 2. Wire connectors overheating. Pin connector (the cap) is overheating multiple failures. For example, a bureau of the Northeast power grid of a main transformer, the total hydrocarbon 455.9Ppm, acetylene was 4.23ppm. Inspection found that the phase 66kVA hanging wire threading the first heat pipe, solder dripping out of pieces of the clamp and pressure; another example, a main transformer station, B relative to the casing head and fever, upon inspection, will be deducted screw cap with the bad, the Lo burn 5 to 6 buckle buckle, causing overheating. 3. Lead-off shares a platform DFL \ u000060000/220-type single-phase transformer, in May 1990 began to see the results of chromatographic analysis of abnormal hot spot temperature may be higher than 1000 \u2103, until May 1993 for a major overhaul when found that the transformer point of the casing of the lead. Has two blown, three strands burn (a total of 35 shares, section 240mm2), the reason is a May 1989 inspection, the update of the casing when the neutral wire (copper braided) Do not pull up the relatively strong, to lead halfway around the white outer belt off, naked braids. Brass wire and casing wall collide, the occurrence of diversion, discharge, overheating. (D) result in overheating transformer winding leakage flux in flux, including the main flux and leakage flux, both the main flux or leakage flux can be divided into components of the axial and radial component. Axial component distribution is relatively simple, along the winding height smaller. Height distribution along the winding radial component complex eddy current losses caused by its distribution is very uneven, and with the capacity of the transformer changes, not only with the windings of the axial height, radial size also changes with the winding. Especially in the end all changes, and its maximum appears in the end are nearby. Within the transformer winding from the **** near. Higher than the radial magnetic flux leakage outside the winding, the transformer winding for the low, medium, high order, then the low voltage winding of the high radial magnetic flux leakage. In large transformers, due to leakage flux density, so the stray loss generated a great, sometimes up to hundreds of kilowatts, lead; cause local overheating. For example, a transformer station SFPS a 120000/220 overheating appears the side walls of the box is low due to severe leakage flux. In another example, a SZL7 a 6300/35 type transformers, the stray flux in the **** by the upper and lower clamping lever on the formation of the individual parts of a high concentration of magnetic flux density, resulting in local overheating and result in abnormal chromatographic analysis of insulating oil. (E) cooling air duct cooling air duct blockage blockage caused by overheating has been reported from time to time. For example, a co-OSFPSl \ u0000120000/220 transformer, run the 11 annual normal. August 28, 1992 a sudden rise in oil temperature, increased from about 42 \u2103 for about 90 \u2103. Compared with the same temperature rise of transformer capacity varied widely, but the electrical test results were normal. Found by visual inspection, air fin heat pipe cooler gathering dust in question (long-run has never been cleaned), the gap has closed, the wind has not blown fan cooling tube, causing the temperature of the transformer rising. The oil has been washed about 40 \u2103. In another example, a table DSFPSL \ u000090000/220-type transformers, the top oil temperature too high, had been about 80 ~ 90 \u2103, check that the gap is the radiator clogged duct, affecting the normal cooling, washing with high pressure water jets, the oil temperature down to 60 \u2103, back to normal. (Vi) the fan not working fan is not working properly include: 1. Fan of a reversal of a Board and main transformer, the cooling system overhaul, the power reverse, causing the fan reversal, the cooling effect of lower oil with the same load than the other main transformer high 15 \u2103, identify the correct reasons, the temperature returned to normal (two main transformer temperature only a thin l \u2103). 2. Start fan setting is incorrect type of a table SFY7 a 63000/110 Transformer (French patent), running in a traction substation. Found in the operation of CO/CO2 = 0.68, is an exception; combustible gas volume is also an "attention value" of the column, and the increasing trend has been an exception. Clearly, there is an early heat transformer failure. Check that, start the fan temperature 75 \u2103 (drawing on the ASEA is 75 \u2103 CONTROL). It does not meet the Ministry of Railways was awarded the "Traction Substation maintenance of order", a point of order under Article 36: When the upper air-cooled transformer oil temperature over 55 \u2103 fan should start. Main transformers for the oil of the air-cooled, due to start the fan setting is incorrect, leading to the main transformer can not be air-cooled heat. Hence the heat failure. 3. Fans, a loss of power in a power plant main transformers for the three cases of forced oil circulation cooled three-winding load tap transformer, three sides of the capacity ratio 180000/12000/180000kVA, three sides of the charging pressure ratio was 231 \u00B1 8XI. 25% / 121/13.8kV, B class insulation, allowing the maximum temperature of 120 \u2103. Found in the operation of fuel injection pressure release valve is the main transformer body top oil temperature exceed 100 \u2103. Repeated examination found that the main power transformer cooler B, C phase fuse, and their fans, and submersible pump to stop running. However, as the temperature is too high, signaling can not normal fuse circuit signal, leading to overheating of the main transformer Mao You. (G) silicone leakage caused by blockage of a power plant a SFL \ u000063000/110 type transformer, high-temperature heat for two consecutive years. Finally found hanging hood, the chassis fuel **** filled with silicone, about 200kg, in the bottom **** of about 1.2cm gap between the chassis have all been blocked, after examination, because the purifier filters are not tight, there is a large gap After 18 years of operation so that the silicone poured into the ****, blocking the oil circulation path, the oil circulation, causing overheating of transformer temperature. (H) foreign body left inside the transformer caused local overheating may cause foreign body not only asked the windings short circuit, causing localized overheating, and may be formed in circulation in the foreign body, causing localized overheating. For example, a main transformer station DFL-60000/220 A-type phase (single phase transformers) in 1960, put into operation in normal, but in 1982, when the washed oil change and **** winding, the total hydrocarbons discovered a month later by the 100PPm increased 300PPm, year, total hydrocarbons increased 1125ppm. Three-ratio method to determine fault by the nature of medium temperature of 300 ~ 700 \u2103 thermal fault range. However, the experiment will not make exceptions, and finally the disintegration of the overhaul period of 3 months. Since the transformer is the transformer factory in Shenyang in the early product, was limited to the technical level, not only phase transformer, and each **** has since the beginning phase transformer frame, as shown in Figure 1-62. In the overhaul, the first **** on the yoke removed, hanging high and low voltage winding walking, and then separate the inside and outside the box found the bottom of the **** columns inside and outside the oil path between the **** has a diameter of about 15mm spherical carbon black particles, just on the silicon steel sheet. Resistance measurement of carbon particles 5\u03A9, was identified as welding slag, there are three silicon near the local overheating, blue. Figure 1-62 cores per phase diagram 1 - frame; 2 - within the frame; 3 - Analysis of welding slag welding slag is that the manufacturers in the assembly into the oil channel between the inside and outside the box, because of the location of coincidence, 20 exception did not occur over the years. Later, when the welding slag flushing oil change along the oil road was washed into a location; the silicon layers mixed, narrow the location, you will encounter inside and outside the box ****. In operation, the points inside and outside the box, the magnetic potential difference exists between, the formation of circulation, resulting in local overheating. The operating normally after the repair. (Pill) **** overheating caused by failure or ground described in section IV of this chapter. Second, the overheating of the transformer fault diagnosis (a) chromatography gas chromatography analysis is an important diagnostic method for transformer fault overheating. Practice shows that in the case of local overheating, transformer oil contains large amounts of CH4 and C2H4, involving solid insulation fault, the oil also contains a lot of CO and CO2, based on this feature, you can use the graphical method and the ratio of the gas law to determine the nature of the fault. 1. Graphic method with the greatest concentration of gas to 1, draw the relative concentration of gas components, namely gas graphics. A typical fault gases overheating graphics shown in Figure 1 for a 63, that is, a CH4 C2H4-type map. Figure 1-63 Fault gas overheating graphics 2. Gas component ratio method (1) determine the fault nature. Ratio method to determine the nature of fault ratio method and three members of the ratio method. Comparison of the ratio method, we can see, C2H2/C2H4. And the ratio of a fault CH4/H2 the nature of the two is valid. Of the overheating fault, the ratio of coding C2H2/C2H4 three encoding is 0, CH4/H2 coding for the 2; in the ratio of coding C2H2/C2H4 four coding for the 0, CH4/H2 coding is 1 or 2. Accordingly the following criteria: C2H2/C2H4 <0. l and CH4/H2 \u2265 1 satisfy the above criteria is the overheating of the failure. Temperature overheating fault can be divided into low, moderate high temperature in the three areas. Three-ratio method are listed in detail the results of this diagnosis. (2) to determine the thermal fault circuit. Diagnosis, the ratio of three-ratio method and the Combination of four, failure to distinguish between thermal conductivity in the magnetic circuit or loop. In the four-ratio method, when CH4/H2 = 1 ~ 3, C2H6/CH4 3, code can be written as 0,2 D, 2, is the thermal conductivity of circuit failure. Further examination is recognized as tap switch is bad. 3. CO and CO2 concentration curve given in accordance with the results of chromatographic analysis of CO and CO2 content, can determine whether there is overheating transformer winding insulation failure. Northeast Electric Power Research Institute OFTA directly under the Board of the Northeast, the plant about 150 220kV and above diaphragm (including capsule) sealed transformer oil content of CO and CO2 analysis, and the preliminary criteria. Determine the equation for the CO content of YCO = 133 +407 \u221A XCO2 content YCO2 = 1896 +1042 \u221A X where X-running life. Plotted curves of the above regression equation, as shown in Figure 1-64. Figure 1-64 membrane-type transformers to determine CO, CO2 concentration index (a) CO annual average number of years the relationship between content and operation; (b) CO2 run average number of years the relationship between content and the curve shows that when the transformer oil in the CO and CO2 over the corresponding value on the curve or gas production rate when the slope is greater than is generally believed that the transformer may be abnormal. For example, a 260MVA transformer oil content of CO and CO2 curve shown in Figure 1-65. Curve can be seen from the country, in terms of growth rate of CO and C02, or its absolute value judgments are far more than shown in curve. Down the middle is the result of processing the oil, but based upon the higher rate after the fall, but fewer years of operation, its absolute value is not enough accumulation. As a result, combined with the transformer winding structure, will be able to analyze and judge the possible overheating of the transformer failures. Figure 1-65260MVA CO and CO2 content of the transformer compared to determine (a) CO content in comparison (b) CO2 content in comparison (b) measuring the DC resistance DC resistance measurement circuit heat conductivity can further determine fault. The two cases are based on the DC resistance for further judgments. Former tap switch is bad, which is low-voltage short circuit between the windings. Third, the countermeasures according to the overheating fault caused by different treatment of different reasons to take countermeasures. (1) causes the structure of low-voltage winding coil hot, low-voltage transformer winding should be changed to double-helix structure. 2) cooler group of overheating due to failure of tube blocking, should be periodically (1 to 3 years) with compressed air or water cooler group of tubes, cleaning process is as follows. 1) Before cleaning, stop the cooler, remove the fan guard and fan blades, so that can be thoroughly cleaned before and after cooler. 2) the first inlet side with a vacuum cleaner from top to bottom in the siphoning off of dust, debris, and then used in the air side of the compressed air pressure of 0.1MPa group of tubes, while blowing suction side (cooler is running in the vicinity ), would enhance the cleaning efficiency of 2. 3) the dust, the use of tap water, flushing out the wind from the same side of the direction to the inlet side of the dash Do not allow debris to enter the middle management group, to avoid debris falling into the dead zone. (3) properly connected to lead and tap, tighten the nut to prevent loosening of the fever. (4) To avoid lead and copper pipe after the heat by then, you can take the following measures: l) does not change the current way of wire insulation wrap, but only when the trial installation on every product, accurate cut pieces the length of wire cable, lead length and be equipped with casing accurate. This can eliminate the cable is too long to dock with the brass wall of the adverse consequences. But after doing so on the accuracy of spare tube assembly replacement difficult. 2) changing the way lead cable insulation wrap. If the current is only half stack with a white cloth bag with a layer of crepe paper to be both positive and negative directions with 0.1mmX30mm half stack package after each layer, then a layer of white cloth bag with a half stack. In the assembly casing, it is necessary to maintain the integrity of wire cable insulation, loose insulation allowed the phenomenon of exposed copper. Thus, lead-free assembly, even if lead and copper by then, the loop will be closed and difficult to separate the insulation to prevent the current flow and overheating. (5) To prevent overheating caused by fault slip magnetic, cell wall in the transformer oil and winding installation of magnetic shielding steel pallet. The purpose of magnetic shielding is set to magnetic flux leakage better performance by as much as possible the magnetic shielding devices, and not penetrate the **** wall plate, thus avoiding the walls of the **** have a big loss, causing the **** to local overheating. In the large transformer in order to reduce the leakage flux in the mountains has caused the loss of the ****, in a particular area (such as the casing installation parts) and non-magnetic steel is sometimes used instead of ordinary steel. But on the inside wall of a large area of the **** to install magnetic shielding method is more economical and reasonable. For large current transformers, the system groups the more serious end of magnetic leakage. The bottom of the pallet in the winding on the installation of magnetic shielding steel, steel pallets can become very small surface flux density, thus reducing the leakage magnetic windings are losses, windings are insulated to prevent overheating problems. SSPL-260000/220 type of a power plant main transformer in the transformation process, the winding in the **** wall and to install magnetic shielding steel pallets received good results, on several occasions subjected to the impact of the harmonics, and always stable operation. For example, in 1993 due to system harmonic, another transformation of the transformer **** without local overheating, the upper and lower **** connecting screws red-hot, burning sealing gasket, causing a large number of transformer oil, heavy gas protection Tripping forced outage repair, but after this transformation has emerged unscathed transformer. After more than four years of tracking and monitoring of oil chromatography, the analysis results are stable. After transformation, the transformer and the total hydrocarbon CO, CO2 levels have dropped significantly and has been stable. Before and after reconstruction of oil dissolved gas chromatography analysis as shown in Table 1 31. (6) to strengthen management, to avoid mismanagement and other reasons of failures caused by overheating. Strong oil circulation of the cooling system of the three, the countermeasures according to the different causes of failure to take a different reason for the countermeasures. (1) causes the structure of low-voltage winding coil hot, low-voltage transformer winding should be changed to double-helix structure. 2) cooler group of overheating due to failure of tube blocking, should be periodically (1 to 3 years) with compressed air or water cooler group of tubes, cleaning process is as follows. 1) Before cleaning, stop the cooler, remove the fan guard and fan blades, so that can be thoroughly cleaned before and after cooler. 2) the first inlet side with a vacuum cleaner from top to bottom in the siphoning off of dust, debris, and then used in the air side of the compressed air pressure of 0.1MPa group of tubes, while blowing suction side (cooler is running in the vicinity) This can improve the cleaning efficiency of 2. 3) the dust, the use of tap water, flushing out the wind from the same side of the direction to the inlet side of the dash Do not allow debris to enter the middle management group, to avoid debris falling into the dead zone. (3) properly connected to lead and tap, tighten the nut to prevent loosening of the fever. (4) To avoid lead and copper pipe after the heat by then, you can take the following measures: l) does not change the current way of wire insulation wrap, but only when the trial installation on every product, accurate cut pieces the length of wire cable, lead length and be equipped with casing accurate. This can eliminate the cable is too long to dock with the brass wall of the adverse consequences. But after doing so on the accuracy of spare tube assembly replacement difficult. 2) changing the way lead cable insulation wrap. If the current is only half stack with a white cloth bag with a layer to the first crepe paper with a 0.1mm \u00D7 30mm package both positive and negative direction of the layer stack after the half, and then a layer of white cloth bag with a half stack. In the assembly casing, it is necessary to maintain the integrity of wire cable insulation, loose insulation allowed the phenomenon of exposed copper. Thus, lead-free assembly, even if lead and copper by then, the loop will be closed and difficult to separate the insulation to prevent the current flow and overheating. (5) To prevent overheating caused by fault slip magnetic, cell wall in the transformer oil and winding installation of magnetic shielding steel pallet. The purpose of magnetic shielding is set to magnetic flux leakage better performance by as much as possible the magnetic shielding devices, and not penetrate the **** wall plate, thus avoiding the walls of the **** have a big loss, causing the **** to local overheating. In large transformers, in order to reduce the leakage flux in the fuel **** has caused the loss, in a specific area (such as the casing installation parts) is sometimes used instead of ordinary non-magnetic steel plate. But on the inside wall of a large area of the **** to install magnetic shielding method is more economical and reasonable. For large current transformers, the system groups the more serious end of magnetic leakage. The bottom of the pallet in the winding on the installation of magnetic shielding steel, steel pallets can become very small surface flux density, thus reducing the leakage magnetic windings are losses, windings are insulated to prevent overheating problems. SSPL a power plant -260000/220 type transformer, the transformation process, the winding in the **** wall Ji install magnetic shielding steel pallet received good results, the harmonics have been several times subjected to shocks, and always stable operation. For example, in 1993 due to system harmonic, another transformation of the transformer **** without local overheating, the upper and lower **** connecting screws red-hot, burning sealing gasket, causing a large number of transformer oil, heavy gas protection Tripping forced outage repair, but after this transformation has emerged unscathed transformer. After more than four years of tracking and monitoring of oil chromatography, the analysis results are stable. After transformation, the transformer and the total hydrocarbon CO, CO2 levels have dropped significantly and has been stable. Before and after reconstruction of oil dissolved gas chromatography analysis as shown in Table 1 31. (6) to strengthen management, to avoid mismanagement and other reasons of failures caused by overheating. Strong oil circulation of the cooling system must have two reliable power, there should be an automatic switching device, and periodically switch test, the signal device is complete, and reliable. Table 1-31 students in a power plant transformer oil before and after transformation of the results of chromatographic analysis (PPm) total hydrocarbon gas components H2CH4C2H4C2H6C2H2COCO2 transformed before the transformation 526,373,127.99909460156 16.712.618.64.50575.72980.835.7 test after two summer peak load
Share to:



Forum Guidelines

For general Alibaba.com customer inquires, please contact Alibaba Service Center.
To lodge a dispute/complaint, please visit our Complaints Center.
For general AliExpress customer inquiries, please contact AliExpress Customer Support.
If any posts corresponding to the categories above are located in the Forums, they will be deleted without prior notice.
Subject:
Message: