Application of on-line oil purification technology

2022-08-08
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Application of transformer on load tap changer oil purification technology

Xinhui City power has 2 220 kV transformers and 49 110 kV transformers, with a total capacity of 1678.5 MVA. Among them, there are 38 on load voltage regulating transformers with a capacity of 1467.0 MVA, accounting for 88% of the total transformer capacity in the city. It can be seen that whether the on load voltage regulating transformer operates safely, efficiently and reliably has a decisive impact on electricity. On load tap changer is an important component in on load tap changer transformer, and the oil quality level in the switching oil chamber of on load tap changer is directly related to the safe operation of on load tap changer transformer. We know that the on load tap changer needs frequent on load switching due to voltage regulation, and a large amount of free carbon is the main factor affecting the oil quality in the oil chamber of the on load tap changer, which limits the switching times and service life of the on load tap changer. Therefore, it is necessary to replace and repair the oil regularly. In the past, the replacement of insulating oil in the oil chamber of on load tap changer and the maintenance of on load tap changer cost a lot of manpower, material resources and funds, and the power failure time is very long, as shown in Figure 1. In order to ensure the quality of oil in the oil chamber of on load tap changer, it is necessary to study the oil purification of insulating oil in the oil chamber of on load tap changer and the application of oil purification device, which is also a powerful measure to implement the industry standard DL/t574-1995 "guidelines for operation and maintenance of on load tap changer"

1 effect of particulate impurities in oil on the insulation level of the switch

when the on load tap changer is switched quickly with load, the insulating oil will decompose under the action of electric arc to produce free carbon, hydrogen and combustible hydrocarbon gases, and will also produce trace metal particles. Some of the impurities such as free carbon and metal particles are deposited on the surface of the insulating parts of the tap changer, especially near the live contacts where the electric field is concentrated. Some of them are suspended in oil, and the rest are deposited at the bottom of the switching oil chamber. The particle impurities distributed on the surface of the insulator will reduce the insulation strength of the insulator, and the particle impurities suspended in the oil. Have you known about its loading? Well, it will affect the breakdown voltage of the oil, especially when the micro water content in the oil increases, which will accelerate the reduction of the breakdown voltage of the oil and affect the insulation level of the on load tap changer. The on load tap changers of transformers under the jurisdiction of Jiangmen Xinhui branch are all composite tap changers, and the influence of particle impurities on the composite tap changers whose plasticizing time itself fluctuates is particularly obvious, because the switching and tapping selection of such switches are integrated, located in the same oil chamber, and the selected insulating parts are directly affected by dirty oil. The amount of particulate impurities increases with the increase of switching times, which will more and more seriously affect the overall insulation level of the tap changer. The "guidelines for operation and maintenance of on load tap changer" stipulates that during operation, the cover shall be opened for cleaning and oil change or oil filtration once every 5000 ~ 10000 times of switching or 1 ~ 2 years or when the breakdown voltage in the oil is lower than 25 kV, and samples shall be taken at least once every 6 months to 1 year or 2000 ~ 4000 times of tap changing. If the oil is not filtered and the insulating parts are not cleaned within the time limit, the insulation level will continue to decline, endangering the safe operation. The breakdown voltage of the oil in the switching oil chamber of the on load tap changer is mainly related to the suspended particles in the oil and the micro water content in the oil. Moisture can be controlled by strengthening the structural sealing of the oil chamber and adding oil, and the generation of particulate impurities is inevitable. The research shows that under the condition of a certain amount of water, the relationship between particle size and its number and breakdown voltage is shown in Figure 2. When the number of particles in the oil is filtered from 10000/ml to 10/ml, the particle diameter is greater than 5 μ The breakdown voltage of M can rise from 24 kV to 38 kV, and the particle diameter is greater than 2 μ The breakdown voltage of M can rise from 21 kV to 49 kV

therefore, we believe that the key to oil purification is to apply high-precision and high-efficiency particulate removal filter to the on load tap changer switching oil chamber in operation to filter oil automatically with electricity. At the same time, considering that reducing the micro water content in the oil found by Professor Guo's team is conducive to improving the breakdown voltage of the oil, the combination of particle removal filter element and water removal filter element should also be adopted in the implementation, which should achieve better oil purification effect. 2 structure, technical indicators and functions of oil purification device

2.1 structure of oil purification device

after investigation and research, we selected an American brand of oil purification device and installed it on the No. 1 main transformer of 110 kV East substation as a pilot. The device has two parts: filtration and control. Its structure mainly includes oil pump, motor, particle removal high efficiency filter, water removal filter, connecting oil pipe, pressure gauge, differential pressure relay, control components, etc. The normal protection of the instrument can prolong the service life. The oil inlet and outlet pipes of the device are connected with the oil outlet pipe and oil inlet pipe of the oil chamber of the tap changer respectively. During operation, the oil circuit is full of oil, without residual air, and is in a closed-circuit circulation state

2.2 main technical indicators

filtration accuracy ≤ 1 μ m;

filtration ratio β 1000 (filtration efficiency 99.99%)

filtration capacity 250 L/h

cleanliness level 7 (NASL 683 standard)

micro water volume fraction ≤ 20 × 10-6;

breakdown voltage ≥ 40 kV

2.3 characteristics of oil purifier

the oil purifier has the following characteristics:

a) the filtering accuracy of combined use is less than or equal to 1 μ M filter element and water removal filter element, remove particle impurities in oil and reduce micro water

b) there are three startup modes: on-site manual startup, automatic startup of tap changer transformation, and remote control tap changer transformation startup of centralized control center. We adopt the way of changing the automatic starting device by the tap changer, that is, the way of automatically starting the oil purification device immediately after each action of the tap changer, which can filter and remove the free carbon and other impurities produced by the switching in time and thoroughly purify

c) it has the cumulative counting function, which can correctly accumulate the switching of on load tap changer

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