There are two methods for the life assessment of transformers. The first one is the statistical method. It analyzes the transformers in operation and then evaluates the lifetime. This method is less expensive, but it is difficult to develop new transformers. The life data is obtained before leaving the factory; the second is the accelerated life test method of the whole machine. It uses the transformer test sample or mock sample to carry out the accelerated life test, and then evaluates the life. This method is mature but the cost is high and it is difficult to describe the element. Intrinsic Mechanism of Device Damage This paper presents a new method based on the determination of the degree of polymerization of transformer insulation paper to evaluate the life of the transformer, deduces a new calculation formula, designs and implements a paper aging test, and establishes a new set of life assessments. system. It can provide lifetime evaluation of newly developed transformers before leaving the factory. The cost of evaluation is only equivalent to % of the second method. 1 Transformer aging mechanism From the perspective of reliability, the transformer is a system consisting of cores, high-voltage windings, low-voltage windings, main insulation oil, fuel tanks, casing, and auxiliary equipment. The weaker main components are insulating paper and Insulation oil. According to the paper, insulating paper is the weakest component. Therefore, by studying the aging mechanism of insulating paper, it can be equivalent to the study of the aging mechanism of the transformer. Then the life assessment of the transformer is performed. The main component of insulating paper is cellulose. If the units are connected in series, see the average number of the above units contained in a chain is called the degree of polymerization of insulating paper (Dp is used in the text). The aging process of insulating paper is the process of aging the molecular chain from long chain to short chain. The process, which is the process of decreasing the Dp value, is mainly caused by water and oxidation temperature. The more water there is in a water paper, the faster the Dp value is decreased. The paper's aging rate is directly proportional to the initial water content in the paper. The water content and the water content of the insulating paper are basically proportional to each other when the balance is reached, and the ratio is related to the temperature. Because the moisture content in the paper is difficult to measure, and the moisture content in the oil is easy to measure, we will calculate the moisture content in the paper through the moisture content in the oil. The reaction process of oxygenated oxide with insulating paper is a very complicated process, not only with the oxidation flow speed Relevant, but also depends on the reaction with the oil to seal the transformer oxygen content is very small, the paper oxidation process can be ignored. temperature. Dakin found that in the case of the same chemical reaction mechanism, any change in chemical quantity or even some physical quantity obeys the law of chemical reaction, and the relationship between any chemical reaction and heat is subject to the following formula: K0 is the chemical reaction rate; Absolute temperature; A, B is a constant, B is a constant constant in the aging process of the transformer insulation material, according to the experimental determination, B is about 15. 2 Mathematical model of aging of insulating paper In order to establish the quantitative relationship between Dp value and life, the process of aging such as insulating paper is used in this paper. It is the process of chain breaking between the basic unit and the basic unit in the fiber chain of insulating paper. The key inside the basic unit is not During the aging process of the broken insulation paper, the total length of the fiber chains remains unchanged, and the number of chains continues to increase. The bond breaking of long-chain molecules has the same degree of difficulty at the same temperature as the bond-breaking of short-chain molecules, ie, having the same possible property is the most critical assumption, which ensures that the Dp value decreases exponentially with time. The aging rate of insulation paper at any moment is proportional to the initial moisture content in the paper. This is an experimental rule. Based on the above basic assumptions, we derive the formula. When t is set, the total length of the chain is L, and the number of chains is No. In a very short time At The number of chains generated in the decomposition corresponding to the decomposition is KtNAt, so there are: The calculation formula of the life of the transformer (see formula (8)) c. The aging process of the insulating paper is the degradation process of the polymerization degree. The aging of the insulation paper and the temperature, oxygen and Moisture is closely related. Under low oxygen and moisture conditions, the degree of polymerization decreases exponentially. At the same time at the same temperature, the Dp value is dispersive, and the Dp value is normally distributed. The solution viscosity of the insulation paper after the quick-life can calculate the DP value of the insulation paper. The estimated life of the SBS9 transformer at 2C ambient temperature and full load is 22.28 years. The probability that the estimated life expectancy exceeds 19.15 years is 90%. The new life assessment method proposed in this paper can provide the manufacturer with the expected life of the transformer before leaving the factory. The test cost is only equivalent to 1% of the accelerated life method of the whole machine. Applied to the power supply bureau to estimate the remaining life of the transformer in operation, in order to achieve regular replacement of the transformer and improve the reliability of power supply.
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A New Method for Life Evaluation of Medium and Small Capacity Power Transformers