Electrical insulation oil basic knowledge, sales staff must see

April 19, 2024

Electrical insulation oil basic knowledge, sales staff must see

1. What kinds of electrical insulation oil are there?

Electrical insulation oils include transformer oil, capacitor oil, cable oil and switch oil (circuit breakers, etc.). Such oils are often called electrical or insulating oils.

2. What are the sources of moisture in insulation oil?

In what form? Insulating oil in the process of packaging, transportation and storage management, such as improper storage may enter the water, in addition, petroleum products have a certain degree of water absorption, from the atmosphere or contact with water, absorb and dissolve part of the water, the water absorption capacity of insulating oil and its composition and the temperature environment are related. Generally speaking, when the insulating oil dissolving water capacity is about 40 ×10-6 at 20 ° C, the water content of the transformer oil can be reduced to about 10×10-6 through the industrial dewatering device, in addition, the moisture absorption of the oil increases linearly with the relative humidity of the air and the oil temperature. For example, when the oil sample is at 60℃ and the relative humidity is 40%, the water content in the oil reaches 80 ×10-6, and when the relative humidity is 80%, the water content in the oil reaches 200 ×10-6. Different chemical composition of the oil, its water absorption can reach dozens of 10-6 difference, the more aromatic hydrocarbon components in the oil, the higher the moisture absorption of the oil, the presence of some polar molecules in the oil can also increase the moisture absorption of the oil.

Water exists in insulating oil in 3 ways:

(1) Suspension: water is suspended in the oil in the form of water droplets.

(2) Floating: refers to the water of very small droplets evenly dispersed in the oil.

(3) Dissolved form: water exists in the form of dissolved in oil.

3. What is the effect of kinematic viscosity on the use of insulating oil?

In the transformer transformer oil as insulation and heat transfer medium, it is required to select the appropriate viscosity to ensure that the oil plays an ideal cooling role in long-term operation, and select a reasonable low temperature viscosity to ensure that the transformer can work safely when it stops running and starts again. Therefore, the United States ASTM D3487 transformer oil standard stipulates the requirements of 0 ℃ and 100 ℃ kinematic viscosity, and the IEC 296 standard issued by the International Electrotechnical Commission also stipulates the requirements of 40 ℃, -15 ℃(or -30 ℃, -40 ℃) kinematic viscosity. Excessive viscosity affects heat transfer, and conversely, the working safety is reduced.

4. What is the significance of determining the acid value for the use of insulating oil?

The acid value of the insulating oil is to indicate that the oil contains acidic substances, that is, the total value of organic acids and inorganic acids, and the potassium hydroxide mg number required for the acidic substances in the general acid and lg insulating oil is expressed. For the unused new transformer oil almost does not contain acidic substances, its acid value is quite small, but the oil in long-term storage, especially after the electrical equipment is put into operation, it will inevitably come into contact with oxygen in the air, and the oil is easy to be aging. At the initial stage of oxidation, low molecular organic acids are mainly generated, and further oxidation produces polymer organic acids and acidic products. After the existence of the above acidic substances in the insulating oil, the electrical conductivity of the oil will be improved, the insulation of the oil will be reduced, and the corrosion of the metal may also be produced. Under the condition of high operating temperature (above 80 ° C), the aging phenomenon of solid fiber paper insulation material is promoted, thus shortening the service life of the equipment. The oil acid value of the unused transformer is generally 0.03mgKOH/g, and the acid value of the operating oil is not more than 0.1mgKOH/g.

5. What is the significance of determining the PH value of insulation oil in operation?

Generally, the unused (new) transformer oil almost does not contain acidic substances, its acid value is low, pH value is in the range of 6-7, pH value is mainly used to represent the index of water-soluble acid of insulation oil, according to China's field investigation, simulation test and laboratory aging test results of oil analysis, the general acid value of transformer oil in operation is greater than 0.1mgKOH/g. When pH value is equal to or less than 4.0, the possibility of oil precipitation from transformer operation increases, on the contrary, transformer oil can basically ensure good and reliable operation of the transformer. When the acid value rises to 0.2mgKOH/g or the pH value is lower than 3.8, the oil quality deteriorates significantly, and more sludge will be generated. Therefore, the pH value of the operating oil should be greater than 4.2.

6, what is the breakdown voltage of insulation oil?

Breakdown voltage is also an indicator to assess the electrical performance of insulation oil, which can be used to judge the degree of water and other suspended matter pollution of insulation oil, as well as the test of the degree of oil drying and filtration before injection into the equipment. When a gradually rising voltage is applied to the clean and dry oil, electrons will be fired at the negative extreme of the voltage, when the electrons have enough energy, the oil molecules can be micro-dissociated, so the whole dissociation process is strengthened with the increase in voltage, when a certain voltage is reached, a large amount of conduction current will be generated and arc will be formed, this phenomenon is called breakdown. The voltage at breakdown is called the breakdown voltage. If there is water or solid in the oil, it will make the breakdown voltage smaller, because the electrical conductivity of water and solid is greater than that of oil. The low breakdown voltage of oil in operation is the signal of transformer danger. For transformer oil domestic and foreign standards stipulate that the breakdown voltage is generally 40-50kV, up to 60kV or more.

7, China's current insulation oil standards? What are the main application areas of this product?

At present, China has developed GB2536-90 electrical insulation oil standard (transformer oil standard), mainly used in 330kV and below transformers and electrical equipment with similar requirements. SH 0351-92 Circuit breaker oil, mainly used in circuit breakers. SH 0040-91 Ultra high voltage transformer oil, mainly used in 500kV transformers and electrical equipment with similar requirements. GB 4624-84(88 confirmed) capacitor oil, of which No. 1 is power capacitor oil, No. 2 is telecommunications capacitor oil, such products can be applied to power capacitors with high power factor in transmission and transformer systems, low-voltage phase-shifting capacitors and medium-frequency electric heater series capacitors, DC pulse capacitors and so on.

8. How to purify the insulation oil containing impurities?

Purification treatment can have the following methods: (1) filtration: can remove fiber, carbon black, metal and other particles, sludge and other solid impurities; (2) heating: can separate dissolved and free water; (3) Vacuum: remove dissolved air and other gases.

9. What does dark oil mean?

Some small factories produce transformer oil color is darker, can it be used? From the color of the oil, you can also roughly understand the degree of refinement of the oil and the deterioration of the oil after use. Transformer oil good quality oil are produced by appropriate refining process, the color is lighter, generally light yellow, according to GB/T 6540 method to measure its chroma are below 1, and some oil color is close to water white. During the use of the oil, due to oxidation, acidic substances or sludge (sediment) will be generated, which can make the oil darker. If the color of transformer oil produced by some small factories is darker, attention should be paid to whether the indicators such as dielectric loss factor, breakdown voltage, moisture, acid value and color meet the new oil standards, and conditional units can also determine whether the oxidation stability indicators meet the standards.

10. What is the impact of water in transformer oil on the use of transformer? How to remove water?

If the transformer oil in the transformer contains supersaturated water, when the equipment is working, there will be a breakdown, affecting the normal operation, and serious strong arc will be generated, causing the porcelain sleeve to explode, and there have been stories of personal injury. Therefore, attention should be paid to avoiding the entry of water in the transportation, transfer and storage of transformer oil. If the oil barrel into a large amount of water, should try to treat and remove the water, you can first use the sedimentation method, the water sinking at the bottom of the barrel, and then try to pull out the upper oil, but it is inevitable that the oil also contains some water, and then use repeated filtration or desiccant adsorption method until the water in the oil is 20×10-6 ~ 50×10-6 below.

11. What are the reasons for the deterioration of the electrical performance of the oil in operation? What remedies are available?

Breakdown voltage and dielectric loss factor are commonly used to indicate the electrical performance or insulation capacity of insulating oil. Even if there is only a small amount of moisture and impurities, the breakdown voltage of the oil will be reduced, in addition to the metal filter debris, fibers, dust and carbon black and other suspended matter will also have an adverse effect on the breakdown voltage. When the insulating oil is aging into acidic substances or sludge, or the oil mixed with water or impurities will increase the loss factor of the medium, in addition, the use of inappropriate oil hose or plastic pipe when loading and unloading the oil, resulting in the oil and these materials are dissolved resulting in the deterioration of the oil, at this time the loss factor of the oil medium suddenly increases, sometimes up to 0.1. When it is found that the oil deteriorates, the electrical performance decreases, and can not meet the requirements of the performance index of the running oil, the used oil can be recycled, and the common way is to use white soil treatment and then add antioxidant to make all aspects of its performance meet the requirements of the new oil.

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