Analysis and Treatment Measures of Insulation Faults in Power Transformers

The most widely used power transformers currently are oil immersed transformers and dry-type resin transformers. The insulation of power transformers is the insulation system composed of transformer insulation materials, which is the basic condition for the normal operation and functioning of transformers. The service life of transformers is determined by the service life of insulation materials (such as oil paper or resin).

Practice has proven that most transformer damages and failures are caused by insulation system damage. According to statistics, accidents caused by various types of insulation faults account for over 85% of all transformer accidents. The insulation material of transformers that operate normally and require maintenance management has a long service life. Therefore, protecting the normal operation of transformers and strengthening the reasonable maintenance of insulation systems can largely ensure that transformers have a relatively long service life, and preventive and predictive maintenance are the key to improving the service life of transformers and enhancing power supply reliability.

In oil immersed transformers, the main insulation materials are insulation oil and solid insulation materials such as insulation paper, cardboard, and wooden blocks. The aging of transformer insulation refers to the decomposition of these materials due to environmental factors, which reduces or loses their insulation strength.

Solid paper insulation failure

Solid paper insulation is one of the main parts of the insulation of oil -soaking transformers, including: insulation paper, insulation plate, insulation pad, insulation roll, insulation band, etc. The main component is cellulose, chemical expression is (C6H10O6) n, format Middle n is the degree of aggregation. Generally, the polymerization of the new paper is about 1300, and the machine has dropped to about 250. Its mechanical strength has dropped by more than half. Extremely aging has caused the aggregation of life to end 150 to 200. After the insulation paper is aging, its aggregation and tension strength will gradually decrease, and water, CO, and CO2 will be generated, followed by branaltalty (bearing formaldehyde). Most of these aging products are harmful to electrical equipment, which will reduce the breakdown voltage and volume resistance of insulating paper, increase the medium loss, and decrease the tensile strength. Solid insulation has irreversible aging characteristics, and the reduction of aging of mechanical and electrical strength cannot be restored. The life of the transformer mainly depends on the life of the insulation material. Therefore, the solid insulation material of the oil -soaking transformer should have good electrical insulation performance and mechanical characteristics. After years of operation, its performance decreases slowly, that is, the aging characteristics are good.

1. Performance of paper fiber materials.

Insulation paper fiber material is the most important insulating component material in the oil -soaked transformer. Paper fiber is the basic solid tissue component of the plant. The atoms that form the material molecules include a positive atomic nucleus and negative electrons with negative electrons around the atomic nucleus, and metal metal Different conductors are almost free electronics in insulating materials. The very small conductivity in the insulator mainly comes from ionic conductors. Cellulose consists of carbon, hydrogen, and oxygen, so that due to the existence of hydroxide roots in the cellulose molecular structure, there is potential possibilities for forming water, which makes paper fiber have the characteristics of water content. In addition, these hydroxide roots can be regarded as the center surrounded by various polar molecules (such as acid and water). They are combined with hydrogen bonds, so that fibers are vulnerable to damage: at the same time The impurities of the left and right) include a certain amount of water in these impurities, because the fiber is collagen, so that these moisture cannot be completely removed. This also affects the performance of paper fiber.

Polarity fiber is not only easy to absorb moisture (moisture to make strong polar media), but when paper fiber absorbs water, the interaction force between hydroxide roots weakened, and the mechanical strength of the mechanical strength has deteriorated sharply under the condition of unstable fiber structure. Therefore, paper insulation parts can generally be used after drying or vacuum -drying treatment and oiling or insulating paint. The purpose of soaking paint is to keep the fiber wet. High mechanical strength. At the same time, after the paper is sealed densely, it can reduce the absorption of water in the paper, prevent the material from oxidation, and fill the gap in the machi to reduce the bubble bubble that may affect the insulation performance, cause local discharge and electricity breakdown. However, some think that if the oil is soaked after soaking, some paint may slowly dissolve human oil, which affects the performance of oil. The application of such paint should be paid attention to.

Of course, the nature of different ingredient fiber materials and the different quality of the same component fiber material, its influence and performance are also different, such as the highest fiber component in cotton, the strongest fiber in marijuana. Performance is obviously better than cardboard with some domestic materials. Most of the insulating materials of transformers are insulated from various types of paper (such as paper belt, cardboard, paper pressure molding parts, etc.). Therefore, it is very important to choose the insulating paper material of the fiber raw material in the transformer manufacturing and maintenance. The special advantages of fiber paper are strong practicality, low price, convenient use of processing, simple and flexible when the temperature is not high, and the weight is light, and the strength is moderate.

2. The mechanical strength of paper insulation materials.

In addition to the fiber component, density, permeability and uniformity of the most important factors of the oil immersion transformer selection of paper insulation materials, it also includes the requirements of mechanical strength, including tension strength, stamping strength, tearing strength, and toughness:

①Thestable strength: When the paper fiber is required to be stretched, it has the maximum stress that can tolerate but not be broken

② Pouring intensity: The amount of paper fiber is required to have the ability to withstand pressure and not be broken.

③ Tear intensity: The force required to tear in paper fiber meets the corresponding standards.

④ toughness: The strength of the paper folding or bending of the paper can meet the corresponding requirements.

Judging the solid insulation performance can try to measure the aggregation of the measuring paper or cardboard, or use high -efficiency liquid chromatography to analyze the metabol content in the oil in order to analyze whether the solid insulation or the existence of coil insulation in the inside of the transformer in the transformer can analyze the local aging of coil insulation. Low temperature overheating, or judging the aging of solid insulation. In the operation and maintenance of paper fiber insulation materials, it should be paid to controlling the rated load of the transformer. It is required to run the environmental air circulation and heat dissipation conditions to prevent the transformer from exceeding the standard and the deficiency of the box. It is also necessary to prevent accelerated aging of fiber pollution and degradation, and the insulation performance, service life and safe operation of the damage transformer.

3. Deficiency of paper fiber materials.

It mainly includes three aspects:

① Fiber crispy.

When excessive heating, the moisture is separated from the fiber material, which will accelerate the brittleness of the fiber material. Due to the crispy and peeling of paper materials, an insulation failure may occur under the impact of mechanical vibration, electric stress, and operating waves to form an electrical accident.

② The mechanical strength of fiber material decreases.

The mechanical strength of the fiber material decreases with the extension of the heating time. When the transformer is heated, the insulation material is discharged again, the value of the insulation resistance may become higher, but its mechanical strength will be greatly reduced. The insulation paper will not resist the short circuit current. Or the impact of mechanical forces such as impact load.

③ The contraction of the fiber material itself.

Fiber material shrinks after crispness, which reduces the clamping force, which may cause contraction and movement, which makes the transformer winding shifting friction under the electromagnetic vibration or impact voltage and damaged insulation.

Liquid oil deductible failure

The liquid insulation referred to here is the insulation of the transformer oil.

Features of oil immersion transformers:

① greatly improved the intensity of electrical insulation, shortened the insulation distance, and reduced the volume of the equipment;

② greatly improves the effective thermal transmission and heat dissipation effect of the transformer, improves the current density allowable allowed in the wires, and reduces the weight of the equipment. Heat the heat dissipation, thereby improving effective cooling and cooling levels;

③ The oxidation level of some components and components inside the transformer is reduced due to the oily sealing, and the service life is prolonged.

1. The performance of transformer oil.

The transformer oil during operation must have stable and excellent insulation and thermal conductivity.

Among them, insulation strength TG8, viscosity, condensation point, and acid prices are the main nature indicators of insulating oil.

The insulating oil refined from oil is a mixture of various hydrocarbons, resins, acids and other impurities. Its nature is not stable, and it will be continuously oxidized under the effects of temperature, electric field and photosynthesis. Under normal circumstances, the oxidation process of insulating oil is slowly carried out. If it is maintained properly or even for 20 years, it can still maintain the due quality without aging, but the metal, impurities, and gas in the mixed oil will accelerate the development of oxidation and make the oil so that the oil will make the oil. The quality is deteriorated, the color becomes darker, and the transparency is turbid.

2. Causes of degradation of transformers.

The hydraulic degeneration of the transformer can be divided into two stages: pollution and degradation according to the degree of severity.

Pollution is mixed with water and impurities in oil. These are not oxidized products. The insulation performance of pollution oil will deteriorate, the intensity of the breakdown of the electric field will be reduced, and the medium loss angle will increase.

Dynamics is the result of oil oxidation. Of course, this oxidation does not only refer to the oxidation of hydrocarbons in pure oil, but that the impurities in the oil will accelerate the oxidation process, especially copper, iron, aluminum metal dandruff.

Oxygen is derived from the air in the transformer. Even if there is still an oxygen existence of about 0.25%inside the full -seal transformer, the solubility of oxygen is high, so the dissolved gas in the oil occupies a high ratio.

When the transformer oil is oxidized, the water and the calories of the acceleration agent as a catalyst make the transformer oil generate oil. The effect is mainly manifested in: under the action of the electric field, the sedimentary particles are large; Insulation to form a "bridge" for conductive electricity; precipitation is not uniform but forms a slender bar that is separated. At the same time, it may be arranged in the direction of the power line. Essence

3. The process of degradation of transformers.

In the process of degradation, the main stages of the oil are peroxide, acid, alcohol, ketone and mud.

Early degradation stage. The oxides generated in the oil and the insulation fiber material react to generate oxide cellulose, which will deteriorate the strength of the insulating fiber mechanical, resulting in brittleness and insulation contraction. The generated acid is a mucus -like fatty acid. Although it is not as strong as mineral acid, its growth rate and impact on organic insulation materials are great.

Late degradation stage. It is to generate mud. When the acid erodes copper, iron, insulating paint and other materials, the reaction generates mud. It is a sticky and like pommellar polymerized conductive substance. It can be moderately dissolved in the oil. Soon, adhere to the edge of the insulating material or transformer box shell, and deposit on the oil pipe and cooler heat sinks to increase the operating temperature of the transformer and decrease the electricity resistance.

The oxidation process of oil is composed of two main reaction conditions. One is that the acid price in the transformer is too high, and the oil is acidic. The second is that the oxides dissolved in the oil transform into an insoluble oil compound, thereby gradually deteriorating the transformer oil.

4. Oily analysis, judgment and maintenance of transformers.

① The insulation oil deteriorates.

Including its physical and chemical properties, they change their electrical properties. Through testing the acid values of insulation oil, interface tension, Shanshan mud analyzed, water -soluble acid values and other items, it can be determined whether it belongs to this type of defect, and regenerate the insulating oil may eliminate the products of oil deterioration. Natural antioxidants may be removed.

② The insulation oil enters the water and is moisture, because the water is a strong polar matter.

Under the role of electric field, the electrical ionization decomposition is increased, and the conductivity of the insulating oil is increased. Therefore, the trace amount of moisture can increase the loss of the insulating oil medium significantly. By testing the micro -water of the insulating oil, it is determined whether it belongs to this type of defect. Pressive vacuum filtration of insulating oil can generally eliminate moisture.

③ Insulation oil infection with microbial bacteria.

For example, when the main transformer is installed or the core, the insects attached to the surface of the insulation and the residue of the installation personnel: stains, etc. can carry bacteria, which infects the insulating oil: or the insulating oil itself has been infected with microorganisms. Main transformers -· · Runy in 40-80 ° C environment, it is very conducive to the growth and reproduction of these microorganisms. Because the insulation properties of minerals and proteins in microorganisms and their excreta are far lower than insulating oil, which increases insulating oil destructive loss. This defect is difficult to deal with on -site cycle processing, because no matter how to deal with it, some microorganisms are always left on the insulation solid. After the processing, the main transformer insulation in the short term will recover, but because the operating environment of the primary variable device is very conducive to the growth and reproduction of microorganisms, these residual microorganisms will grow and reproduce year by year

④ The alcoholic acid resin insulated paint containing polar substances is dissolved in oil.

Under the influence of the electric field, the polar substance will occur polarized, and energy is consumed during the process of AC polarization, so the medium loss of the oil is increased. Although the insulating paint is solidified before the factory, there may still be incomplete treatment. After the main transformer runs for a period of time, incomplete insulation paint gradually dissolves in the oil, making the insulating performance gradually decrease. The time of this type of defect is related to the thoroughness of insulation paint treatment, and a certain effect can be achieved through one or two adsorption treatment.

⑤ Only mixed with water and impurities in the oil.

This pollution does not change the basic nature of oil. The water can be removed by drying the water; the method of filtering the impurities can be removed; the air in the oil can be eliminated by a vacuum.

⑥ Mixed use of insulation and insulation of two or more sources.

The nature of the oil should meet the relevant regulations; the proportion of the oil is the same, the solidification temperature is the same, the viscosity is the same, and the flash point is similar; the stability of the oil after mixing also meets the requirements. For the degraded oil after hybrid oil, due to the changes in the oil, it has produced acidic substances and mud, and the chemical method of recycling oil in Fujian will separate the degradation product in order to restore its nature.

Insulation and characteristics of dry resin transformers

Dry transformer (here a transformer at the insulation of epoxy resin) is mainly used in places with high fire prevention requirements. Such as high -rise buildings, airports, oil depot, etc.

1. The type of resin insulation.

Epoxy trees refer to insulating transformers can be divided into three types: epoxy quartz mixture vacuum -pouring type, epoxy -alkaline glass fiber complement, and the vacuum pressure difference pouring type and alkali glass fiber wrap.

① Epoxy quartz sand mixture vacuum pouring insulation.

This type of transformer is filled with quartz sand as an epoxy resin. It is impregnated with insulating paint to treat the coils that are wrapped in wraps, pour the coils of people, and then use epoxy resin and quartz sand mixed materials under vacuum conditions. pouring. Because the pouring process is difficult to meet the quality requirements, such as the residual air bubbles, the local unevenness of the mixture, and the may cause local thermal stress cracking, etc., such insulating transformers should not be used in areas where the humid heat environment and load change are large.

② Epoxy -alkali -free glass fiber complement the vacuum pressure difference and pour the insulation.

Epoxy -alkaline -free glass fiber reinforcement is an outer wound insulation with an analogical insulation of an alkaline -free glass fiber glass felt. The thickness of the outer layer of insulation is generally a thin insulation of 1 to 3m. Mixing through epoxy resin poured ratio is mixed, and bubbles are removed under high vacuum. Due to the thin thickness of the wound insulation, it should be poorly impregnated with immersion. When it is easy to form a local discharge point, the mixing of the watering is required, the vacuum removal of air bubbles should be thorough, and the low viscosity and pouring speed of the pouring materials should be mastered to ensure the high quality of the line packing during the pouring process.

③ Apine -free glass fiber is impregnated with insulation.

The transformer immersed in an alkaline -free glass fiber wrap is impregnated with a winding transformer coil while completing the insulation treatment and coil impression of the coil layer. The resin should not remain small bubbles during the coil winding and impregnation process.

2. The insulation characteristics and maintenance of the resin transformer.

The void level of the resin transformer is not significantly different from the oil -soaking transformer. The key is the two indicators of resin transformers and local discharge.

① The average temperature rise level of the resin transformer is higher than that of the oil -soaked transformer. Therefore, the corresponding requirements of the insulation material are higher. However, because the average temperature rise of the transformer does not reflect the temperature in the hottest part in the winding, The thermal grade is only selected according to the average temperature rise, or the selection is improper, or the resin transformer is overloaded for a long time, which will affect the service life of the transformer.

Because the temperature rise measured by the transformer often cannot reflect the temperature of the hottest part of the transformer, it is best to check the hottest part of the resin transformer with an infrared temperature tester under the maximum load of the transformer, and adjust it in targeted adjustment. The direction and angle of the fan cooling equipment controls the local temperature rise to ensure the safe operation of the transformer.

② The local discharge of the resin transformer is related to the electric field distribution of the transformer, the uniformity of the resin mixed resin, and whether the residual bubbles or resin cracking. The size of the local discharge affects the performance, quality and service life of the resin transformer. Therefore, the measurement and acceptance of local discharge volume of resin transformers is a comprehensive assessment of its processes and quality. After the transfer and acceptance of the resin transformers should be conducted after the transfer and acceptance of the resin transformers. Its quality and performance stability.

As the dry transformers are becoming more and more widely used, while selecting the transformer, it is clear that its process structure, insulation design, and insulation configuration should be clear. Choose the production process and quality assurance system, strict production management, and reliable technical performance. Ensure the product quality and thermal life of the transformer, so that the safe operation and power supply reliability of the transformer can be improved.

HZ-3320D 20A Three-channel DC Resistance Tester