First, the oil quality testing project
For oil quality testing, the equipment that first takes the oil sample must be clean and dry. The cleaning method should be carried out in strict accordance with the sampling method standards and the relevant sampling requirements in the various test method standards. The sampling port of the oil storage container should be carefully scrubbed before sampling. The sampling device should be flushed with the initial oil sample when starting sampling. When sampling from the transformer , the oil in the dead zone of the sampling area should be discharged. The sampling operation should prevent the oil sample from being polluted by the outside, prevent the intrusion of air and moisture, and keep the oil sample away from light. The residual air in the sampling device should be drained during sampling, and air bubbles should be prevented from entering the sampler.
The oil sample should be tested in time after collection. If it is not possible to test in time or to test in a different place, the oil sample should be sealed and protected from light; even if this is the case, the oil sample in the oil should not be analyzed for more than 4 days, and the oil sample should not exceed 10 days. There should be enough space above the oil level in the container to accommodate the expansion of the oil sample due to the temperature increase. For the oil-like syringe, the plug and the sleeve should be well sealed, and can slide freely with the expansion and contraction of the oil sample to ensure the balance of internal and external pressure to avoid the situation of positive pressure crushing and negative pressure suction and moisture absorption. At the same time, it is necessary to prevent oscillation during transportation.
1. Appearance test standard
Visual inspection of the appearance inspection of oil is carried out. GB 2536-2011 "Unused mineral insulating oil for electrical fluid transformers and switches" requires that the oil sample taken is placed in a 100 mL measuring cylinder and observed at 20 ° C ± 5 ° C. Transparent, no suspension and mechanical impurities qualified; pure transformer oil should be light yellow and slightly blue, clear, transparent, no visible suspended matter and mechanical impurities and any foreign matter. If there is a diffused state of water in the oil, it will lose its transparency and the color will turn from yellow to white. When the aged material is produced in the oil, the color gradually darkens and darkens with the degree of aging, and gradually loses transparency, so that flocs and sludge appear.
2. Acid value and water-soluble acid standard
Generally, the new oil contains almost no acid, and its acid value is usually 0, and the pH is in the range of 6-7. The acid value of the transformer oil in operation is not more than 0.1; the pH value of the water-soluble acid is not less than 4.2. Long-term storage or long-term operation of transformer oil, due to the absorption of oxygen in the air, combined with it to produce a variety of organic acids and phenols and colloidal sludge, these acidic substances will improve the conductivity of the oil, reduce the insulation properties of the oil Under high temperature operating conditions, it will also promote the aging of fiber insulation materials and shorten the service life of transformers.
3. Flash point standard
A decrease in flash point indicates the presence of volatile combustible materials in the oil. These low molecular hydrocarbons are generally caused by failures such as partial discharges, which cause the oil to be cracked at high temperatures. The flash point of the oil is determined, and it is also found whether or not the oil of the light fraction is mixed. The flash point specified in the pre-test procedure is not less than 135 °C. However, the flash point of the oil in operation is no longer a routine inspection item.
4. Moisture
Transformer oil has a certain hydrophilicity, which will absorb moisture from the air, and the moisture content of the oil is an important factor affecting the insulation performance. When sampling from transformer oil, the specified oil temperature is 40^-600C. DL/T 596-1996 "Procedure Test Procedure for Power Equipment" stipulates that for the transformer oil in operation, "a 110kV water is not more than 35mg/L, and 220kV. The moisture content is not less than 5mg/L.
The water content measurement is generally used in GB 7600-1987 "Determination of moisture content of transformer oil in operation (Coulomb method)" and NB/SH/T 0207-2010 "Determination of water content in insulating liquid Karl Wechat electricity titration method" .
5. Oil breakdown voltage standard
The detection of the oil breakdown voltage value is a measure for judging the degree of purification of the oil. For operating transformers, different voltage levels have different requirements for oil breakdown voltage.
The breakdown voltage below 15kV is greater than or equal to 25kV, the breakdown voltage of 15-35kV is greater than or equal to 30kV, and the breakdown voltage of 60~220kV is greater than or equal to 35kV. When performing the breakdown voltage test, the electrode form of the oil pressure resistant device has the highest breakdown voltage value of the spherical electrode regardless of the breakdown voltage of the oil sample, the spherical cover shape is second, and the flat plate shape is relatively low.
6. Interface tension standard
The interfacial tension between oil and water is an indirect and effective method for checking the presence of soluble polar impurities in the oil due to aging. The interfacial tension between pure oil and water can reach 40-50mN/m or more. However, when the oil is produced by oxidation to produce polar impurities such as organic acids and alcohols, since these impurity molecules contain polar groups of COOH and OH type, they are hydrophilic, and the poles of these molecules at the oil and water interface The base is transferred to the polar phase (water). The hydrophobic hydrocarbon chain turns to the non-polar phase (oil). Since the active materials are aligned at the two-phase interface, the state of the molecular arrangement on the original interface is changed, and the interfacial tension is significantly reduced.
DL/T 596-1996 "Procedure Test Procedures for Electrical Equipment" generally specifies that the interfacial tension of the operating transformer oil is not less than 19 mN/m at 25 °C.
7. Oil dielectric loss tanb standard
The magnitude of tan θ can be sensitive to the extent of oil degradation and contamination.
The new oil has less polar impurities, so the tanb value is very small, generally between 0.01% and 0.1%. However, when the oil is oxidized, the superheat is deteriorated, or other impurities are contaminated, the generated polar impurities and charged colloidal substances are generated. Gradually increasing, tan θ will increase. Since the tanb increases with increasing temperature, the DL/T 596-996 "Procedure Test Procedure for Power Equipment" specifies a measurement temperature of 90 °C. At the same time, the demand for tanb for different voltage levels is: 300kV and below is less than or equal to 4%, and 500kV is less than or equal to 2%.
    8. Volume resistivity
    Its function is similar to oil dielectric loss detection, and has a good correlation with oil dielectric loss at higher temperatures: tan θ increases and volume resistivity decreases.
    9. Oil gas content standard
    When the oil comes into contact with the air, the air gradually dissolves in the oil and eventually reaches saturation.
    The soluble gas in the oil was 10.8% (volume fraction) at 25 ° C and one atmosphere. Therefore, the gas in the oil will precipitate beyond the saturation amount under certain conditions. Generally, when the gas content of the equipment with low voltage is high, the influence on the insulation strength is not great, but the transformer with a higher voltage level has a greater influence on the degree of gas content, because the gas may aggregate to form bubbles, when the temperature When the pressure drops suddenly, the bubbles formed will accumulate in the insulating paper layer or on the surface, and are easily pulled into chains to cause breakdown.
    DL/T 596-1996 "Procedure Test Procedures for Electrical Equipment" stipulates that the gas content (volume fraction %) in the operating transformer oil is less than 3.
    10. Sludge and sediment standards
    When the transformer oil ages, the color becomes darker, but the aged product is still in a dissolved state. Therefore, the determination of the sludge content can avoid further aging of the oil, prevent the sludge from being deposited, deposit on the surface of the transformer body core and the winding, affecting heat dissipation and accelerating the aging of the solid insulation material. When replenishing the transformer, the compatibility of the oil should also be considered. The sludge precipitation test or aging test should be performed. After the aging test, the oil dielectric loss value tanb is determined. DL/T 596-1996 "Procedures for Preventive Tests for Electrical Equipment" stipulates that the mass fraction of transformer sludge and sediment during operation is less than 2%.
Second, the cause of oil quality deterioration or deterioration
    1. Impact of operating conditions
    If the power transformer is operated under normal conditions, the general oil should have a certain oxidation stability, but when the equipment is overloaded or local overheating occurs and the oil temperature increases, the aging of the oil is accelerated accordingly. When the summer ambient temperature is relatively high, if the ventilation and cooling conditions are not adjusted in time, the transformer will accelerate its oxidation process and deteriorate the oil quality. At the same time, the maintenance of running oil is very important. For example, most of the current transformers are not fully sealed. If the desiccant in the respirator fails to be processed in time, the adsorbent in the oil purifier (therm syphon) fails to be replaced in time. Will cause the oxidation of oil to deteriorate. Therefore, the maintenance of the operating oil will not only prolong the service life of the oil, but also extend the service life of the equipment.
    2. Influence of equipment conditions
    The poor sealing performance of the transformer, water leakage and air leakage will accelerate the oxidation and aging of the oil. Improper use of solid insulation materials, poor compatibility with oil, will also promote oil aging. The transformer is designed and manufactured with small spacing, which is prone to hot spots during operation, which not only promotes the aging of solid insulating materials, but also accelerates the aging of oil. Generally, the temperature is from 60-70 ° C, and the oxidation rate of the oil is approximately doubled for every 10 ° C increase. Therefore, the design of the equipment and the selection of insulating materials have an impact on the service life of the oil.
    3. The impact of oil pollution
    Oil pollution mainly refers to improper pollution of mixed oil, pollution of metal particles, pollution of polar impurities such as organic acids and alcohols, and contamination of water molecules, and often leads to sludge precipitation and sedimentation after pollution.
    See Table 2-14 for the reasons and countermeasures for the deterioration of oil quality.
Table 2-14 Reasons and Countermeasures for Excessive Oil Quality Deterioration in Operation
project | Excess | Possible reason for exceeding the standard | Take countermeasures | |
Exterior | (1) opaque and visible impurities (2) The oil color is too deep | (1) Oil contains water or fiber, carbon black and other solid substances (2) may deteriorate or pollute | (1) Check the water content, investigate the cause, and determine the measures in conjunction with other tests. (2) Check the acid value, flash point, sludge determination measures | |
Acid value (mgKOH/g) With water soluble acid | (1)>0.1 (2) pH<4.2 | (1) Overload operation (2) Antioxidant consumption (3) made up the wrong oil (4) Oil is contaminated (5) Oil aging | (1) Investigate the cause, increase the number of tests, put in the oil purifier or replace the adsorbent, measure the antioxidant content and appropriately add the antioxidant (2) Compare with the acid value to find out the cause and put in the oil purifier | |
Flash point | (1) 5 °C lower than the new oil standard (2) 5 ° C lower than the previous test | (1) The device has local overheat or discharge failure (2) Mistaken oil | Identify the cause to eliminate the fault, perform vacuum degassing or oil change | |
Moisture (μg/g) | 220~300kV equipment | ≤30 | 1) The seal is not tight, moisture intrusion 2) Over temperature operation, resulting in solid insulation aging or oil quality deterioration | (1) Replace the desiccant in the respirator (2) Reduce operating temperature (3) Vacuum filtration treatment |
66~110kV equipment | ≤40 | |||
Breakdown voltage (kV) | 66~220kV equipment | ≤35 | (1) The moisture content in the oil is too large (2) contamination of impurities in oil | Identify the cause, vacuum filter or replace with new oil |
20~35kV equipment | ≤30 | |||
Interfacial tension (mN/m) | <19 | (1) Oil aging is severe, and soluble acid or precipitated sludge is precipitated in the oil. (2) Oil pollution | Take measures against the determination of acid value and sludge, carry out regeneration treatment or replace with new oil. | |
Volume resistivity | (1) Oil quality aging is deep (2) oil is contaminated (3) Oil contains polar impurities | The cause should be identified and oil can be exchanged for a small number of equipment. | ||
Sludge and sediment | There are sludge and sediment (the weight is negligible below 0.02%) | (1) Oil aging (2) Impurity pollution | (1) Oil treatment (2) If the economy is economically changeable | |
Third, transformer oil dielectric loss factor abnormal cause and detection and treatment methods
    (1) Anomalies
    (1) Transformer oil dielectric loss factor tan θ increases.
    (2) Transformer oil dielectric loss factor tan θ value is highly dispersive.
    (3) The transformer oil dielectric loss factor tan θ value exceeds the standard and stratifies.
    (2) Reasons for the abnormality
    1. Oil immersed in sol impurities
    The transformer has sol impurities in the residual oil or solid insulating material before leaving the factory. After oiling, the oil is polluted. During the hot oil circulation drying process, the circulation circuit, the oil storage tank is not clean or the oil storage tank is The polluted residual oil can contaminate the circulating oil, causing the oil to re-invade the sol impurities.
    2. Microbial bacterial infection
    Microbial bacterial infections in transformer oil are mainly caused by invasiveness of flies, mosquitoes and bacteria during installation and overhaul. Some mosquitoes were found to adhere to the surface of the winding during the inspection of the hood. It can be roughly classified into micro-insects, bacteria and molds, and most of them live in the lower sediment layer of oil. Due to pollution, the oil contains water, air, carbide organic matter, various minerals and fine elements, which constitute the basic conditions for the growth, metabolism and reproduction of fungi. The temperature of the transformer oil during operation is also an important condition for the growth of microorganisms. Therefore, the temperature has a certain influence on the growth of microorganisms in the oil and the performance of the oil. The test found that the value of tan θ in winter is relatively stable. In addition, temperature has a significant effect on the presence of microorganisms in the oil. The test showed that the average number of bacteria in an oil sample was 0.3/mL, and after heating to 70 ° C for 30 min, the number of bacteria in the oil sample was determined to be zero.
    Environmental conditions have a direct relationship to the growth of microorganisms in the oil, and the amount of microorganisms in the oil determines the electrical properties of the oil. Since microorganisms are rich in protein, microbial contamination of oil is actually a microbial colloid. The effect is to increase the conductance of the oil, so the conductance loss also increases, causing tan θ to increase.
    3. The low degree of oil drilling leads to an increase in electrophoretic conductance leading to an increase in tan
    Compared with No. 25 oil, the No. 45 oil produced in Xinjiang has a narrower cut fraction (the difference between the dry point and the initial boiling point temperature), which is 72-82 ° C, while the No. 7 oil produced by the No. 7 Oil Plant and the Lanzhou Refinery, respectively. It is 108 ° C and 127 - 167 ° C, so the average molecular weight of the oil is low, although the brilliance, specific gravity and flash point are within the acceptable range, but it is relatively low. Therefore, in the case of the same contamination, it is more susceptible to contamination, because the low liberation is easy to migrate the dust in the contacted solid material, and the number of sol particles per unit volume of the oil is increased.
    4. The hot oil circulation increases the charging tendency of the oil and leads to an increase in the value of tan.
    After the installation of the large transformer, hot oil circulation drying is required. Under normal circumstances, the new oil supplied by the manufacturer has a small tendency to electrify, but when injected into the transformer, some still have a low electrification tendency of new oil, and some electrification tendencies increase. After the hot oil cycle, heating will increase the charging tendency of all oils to varying degrees. The charging tendency of the oil is related to the insulating materials used in the transformer, the flow rate and temperature of the oil and oil, etc., so in the process of treating the oil, special consideration should be given to factors affecting the increase in the charging tendency.
    5. High content of copper, aluminum and iron metal elements
    Since oil-immersed appliances are mostly metal combinations, certain metal elements are inevitably contained in the oil. According to the test results, it is suggested that the higher content of metal elements such as copper, aluminum and iron is the main reason for the increase of the oil dielectric loss factor. This is because these metal elements catalyze the oxidation of the transformer oil, causing the oil to produce acidic oxides and sludge. Acidic oxides corrode metals, which in turn increase the metal content of the oil and accelerate the oxidation of the oil, resulting in an increase in dielectric loss factor.
    6. Replenishing oil has a high dielectric loss factor
    A transformer, after adding 2.5t (about 10% of the total oil) oil, measured its dielectric loss factor, which was 5.29% at 70 °C, exceeding the requirements of the relevant regulations. To find out the cause, test the dielectric loss factor of the replenishing oil. The result is 5.75% at 32 °C. At 70 °C, the meter indicates that the range cannot be read. The relevant regulations stipulate that the dielectric loss factor of the supplementary oil is not greater than the dielectric loss factor of the oil in the original equipment, otherwise the dielectric loss factor of the oil in the original equipment will increase. This is because the mixing of the two oils causes a rapid deposition of sludge in the oil, which causes the insulation resistance of the oil to decrease and the dielectric loss factor to increase.
    (3) Treatment method for increasing oil medium loss
    Through the analysis of the reasons for the increase of the dielectric loss factor of the oil and the processing experience of the site, under the circumstance of no power failure, the new material and the new process can be used for the electrification treatment by the vacuum oil filtering method.
    When dealing with oil, the following issues need to be noted:
    (1) The amount of adsorbent used is 1% of the amount of treated oil.
    (2) The adsorbent treatment should be carried out continuously, and it is preferable to change the adsorbent 24 to 48 hours.
    (3) Take the oil sample while changing the adsorbent, measure tan θ, spark discharge voltage value and water content. If it is within the acceptable range, the work of adsorbing and processing the transformer oil can be completed.
    (4) The oil sample taken must be stored away from light, preferably with a brown bottle. The oil sample to be taken out should be tested in time. When the same oil sample is to be repeatedly tested, the oil sample must be replaced to reflect the real situation.
    (5) The oil pipe connection of the oil treatment system cannot use rubber hose. Because the rubber can decompose the particle colloid under the action of high temperature and affect the tan θ of the oil, nylon pipe should be used.
Fourth, the fault finding example
    (1) Example of insulation resistance reduction detection of transformer oil
    1. Transformer fault condition
    Since the transformer was put into operation, it has been 10kv side load and 35kV side idle. The oil conservator is a diaphragm capsule seal with a thermosiphon cleaner. No antioxidants were added before running. The transformer has no oil leakage and the operating temperature is maintained between 30 and 60 °C. In order to monitor the aging of the insulation during the operation of the transformer, four tests were carried out. The insulation resistance of the main body of the transformer is decreasing year by year, and the leakage current is increasing year by year. In particular, the value of the spring inspection pre-test after three years is far from the similar qualified products, and is close to the prescribed lower limit. Therefore, the transformer must be repaired, otherwise it will not be used.
    2. Fault check
    In order to find the fault, the transformer was tested without oil, semi-oil and oil, and the transformer oil was tested for three indexes of pressure resistance, dielectric loss rate and water content.
    It can be seen from the test data that the insulating oil has a normal water content and a good breakdown voltage. Only the dielectric loss rate is slightly larger, but it does not exceed the standard. The insulation resistance and leakage current between the high voltage, low voltage and the outer casing are within the normal range, which is insufficient to explain the local defects of the insulation structure.
    In order to make a clear judgment, the transformer was inspected by a hood. The transformer body and other components were clean and no foreign matter was found. At the same time, the insulation resistance of the insulating members that may have hidden insulation problems is normal. In this way, focus on the transformer oil.
    The water content, breakdown voltage and dielectric loss test of transformer oil indicate that some charged impurities do exist in the transformer oil. The electrophoretic conductance of the colloidal particles or the impurity conductance of the impurities become the main reason for the reduction of the insulation resistance of the main body of the transformer and the increase of the leakage current. This is a distribution defect, which may cause an increase in the dielectric loss rate of the transformer oil under certain conditions, resulting in a decrease in the insulation of the transformer or even an inoperability.
    3. Purification of transformer oil
    The oil filter is repeatedly filtered by an oil filter and the transformer oil is purified by an activated alumina high-efficiency adsorbent. The pressure oil filter oil was sprayed once every 24 hours for a total of 4 times. Before the use of activated alumina, a small-scale test of the adsorption effect was carried out to determine the amount of adsorbent, and a comprehensive evaluation of various indicators of the oil was carried out, and the test showed that the effect was obvious.
    The presence of colloidal particles of impurity particles is a major factor in the deterioration of the insulation performance of the transformer and cannot be ignored. When the water content is normal, it can be evaluated by measuring the volume resistivity of the oil. When a similar phenomenon occurs, the oil is filtered by an oil filter and the oil is purified by an activated alumina high-efficiency adsorbent to improve the quality of the oil. This is because the filtration can filter out the impurity particles and colloidal particles with larger radius, and the activated alumina has a strong adsorption function on the acidic components and oxidation products in the oil, and the combination of the two acts to purify the oil. The effect is remarkable.
    (II) The cause of multiple actions of the main transformer light gas caused by the failure of the submersible pump
    Fault phenomenon
    In a normal operation of a 110kv main transformer (SFPS-6300/110), the light gas protection suddenly operates and sends a signal. After the exhaust gas treatment, the body oil is taken for chromatographic analysis without abnormality. The main transformer continues to operate with load, but the day is light gas. Protect multiple actions, the time interval is about 0.5h. After the shutdown, the insulation test was carried out to eliminate the possibility of insulation damp. After further investigation, it was found that the temperature of the pump body of No. 2 submersible pump was obviously high, which was judged to be caused by the negative pressure of the submersible pump. After stopping the submersible pump No. 2 , light gas protection action problem solving.
    2. Analysis of the cause of the failure
    The transformer adopts forced oil circulation internal cooling method, and the submersible pump matched with the radiator has a flow of 19m and a flow rate of 20m2/h. The submersible pump body structure of the transformer has a shunting circulating cooling oil circuit, the cooling oil path is a high pressure oil chamber of the oil pump, a deep hole of the bottom of the motor housing, a bottom filter, a bearing, a motor, a stator and a rotor, a bearing, a pump, a low pressure oil chamber. . The dismantled inspection of the replaced submersible pump revealed that the pump body was blocked by foreign matter from the circulating cooling oil circuit, and more fiber impurities were attached around the filter screen at the bottom of the submersible pump, thereby affecting the smooth flow of the motor cooling oil circuit and causing the motor to run. The heat is generated, and at the same time, the deep hole of the pump body is blocked, and a negative pressure zone is generated in the rear part thereof. Once the area is not well sealed, a negative pressure air intake is formed.
    To determine whether the submersible pump body is positive or negative during operation, loosen the lowest venting screw of the motor when the pump is running. If there is oil overflow, it is positive pressure, otherwise it is negative pressure.
    Large transformers have a large amount of oil, and all of them overflow into the gas relay after the intake, but it takes a long time to make the signal. Therefore, it is often time to find the pump-by-stage pump stop method. To this end, maintenance and supervision should be strengthened from the aspects of improving the quality of inspection and inspection.
    Pay attention to improve the quality of submersible pump maintenance. When dismantling and repairing, pay attention to ensure the smooth flow of the pump cooling oil circuit: Strengthen the monitoring of the sealing point of the submersible pump negative pressure zone. Once there is leakage oil, it must be treated as soon as possible; sealing rubber parts Should be flexible, smooth surface and no scars, otherwise it should be updated; machine seat, volute, outlet box, rear end cover and other sealing seals, should be free from bumps, scratches, rust and other quality defects, smoothing and smoothing to prevent leakage When the impeller and the bearing are seriously worn, they should be replaced in time. Before the submersible pump is operated, the inner cavity should be filled with the transformer oil, and the venting plug should be opened to remove the air and sealed. Always test the submersible pump motor housing by hand. The surface temperature, once the temperature of the casing rises, may be blocked by the pump motor from the circulating cooling oil circuit. Pay particular attention to observing whether the oil flow relay has an indication.
    (III) Examples of fault finding of the influent hydrogen in the transformer oil
    1. Fault status
    When a 3200kVA, 35kv main transformer was subjected to periodic chromatographic analysis, it was found that the hydrogen content increased by more than ten times compared with the previous one, while the remaining gas components did not change significantly. After careful inspection, it is found that there is a problem in the installation of the explosion-proof glass of the transformer, and there is a large amount of water rust inside, and it becomes a water inlet channel for the transformer oil. The chromatographic analysis data are shown in Table 2-15.
Table 2-15 Chromatographic data (μL/L)
project | hydrogen | Methane | Ethane | Ethylene | Acetylene | Total hydrocarbon |
Cycle test | 130.36 | 2.39 | 7.22 | 1.8 | 4.38 | 15.79 |
Last data | 11.17 | - | - | - | - | - |
    2. Analysis of the cause of the failure
    The hydrogen content in the chromatographic analysis increased significantly, indicating that there is moisture in the transformer oil under the action of the electric field.
    The chemical reaction between water and iron is 3H 2 0+Fe=Fe 2 0+3H 2 ↑, and hydrogen is evolved. Therefore, the reason for the large increase in hydrogen is due to the presence of moisture.
    The oil pressure test has been reduced from the last 48kv to 29kV; the micro water is measured at 75ppm, indicating the presence of moisture in the oil. Therefore, the main transformer is shut down for oil filtration, and the withstand voltage is restored to 45 kV.
    According to the analysis, since the transformer is a qualified new oil that has just been replaced a year ago, after careful inspection, it is found that the glass of the explosion-proof tube is not tightly installed, and there is a large amount of water rust inside. After the treatment, it has been operating normally and the hydrogen content has returned to normal.
    (IV) Example of fault finding of transformer insulation quality deterioration
    1. Fault status
    The main insulation of a main transformer body is seriously degraded. The test conditions since commissioning are shown in Table 2-16.
Table 2-16 Tan θ value of transformer oil at 90 °C
testing time | Test reason | Dielectric loss test value | testing time | Test reason | Dielectric loss test value |
March of the first year | Pretest | 4 .634 | Second year of June | Before the second treatment | 1.733 |
First year of June | track | 5.542 | October of the following year | Before the second treatment | 0.713 |
February of the following year | track | 4.839 | Third year of March | Pretest | 2.127 |
March of the following year | After the first treatment | 1.732 |
    After the oil medium loss becomes larger, first check the appearance of the main transformer, such as the casing and the oil conservator, to see if there is any sign of external water ingress. Test results showed that a good seal of the main transformer, water moisture may not be present. The insulating oil was analyzed and its chemical and physical properties were good, indicating that the insulating oil was not aged. However, the dielectric loss factor of the insulating oil is 4.839%, which exceeds the standard, indicating that the insulation performance of the insulating oil has deteriorated.
    According to the above situation, the following measures were taken: firstly, the oil was filtered, and then the insulation performance of the insulating oil was measured, and it was found that it was still not improved. Finally, the FY-6000 molecular oil filter was used for oil filtration. After the oil filtration was completed, it was found that the 988 adsorbent of the oil machine turned black. Then measure the insulation performance of the insulating oil. The dielectric loss becomes 1.732% at 90 °C. It can be seen that the main transformer body insulation has returned to normal. This year's annual insulation test also reflects that the main transformer insulation has gradually become better, and the dielectric loss factor of the insulating oil (at 90 ° C) tends to be stable.
    2. Analysis of the cause of the failure
    The main transformer is due to the incomplete treatment of the insulating paint containing the polar material alkyd resin in the insulating oil, so that the oil contains the polar material alkyd resin, which causes the insulation oil insulation to decrease, resulting in a decrease in the insulation performance of the main transformer body. Because when the insulating varnish containing the polar material alkyd resin is dissolved in the oil, the polar material will undergo dipole relaxation polarization under the action of the electric field, and consumes a large amount of energy during the polarization process, so that the oil The dielectric loss increases. Although the varnish is cured before it leaves the factory, there may still be an incomplete varnish. After the main transformer is running for a period of time, the insulating paint that is not completely processed is gradually dissolved in the oil, and the insulation performance of the main transformer is gradually decreased.
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