Proceedings of State Grid Transformer Oil Technology Seminar

New Development of Transformer Oil Filter

Chongqing Optical Submersible Electromechanical Research Co., Ltd

Summary:

This paper describes the new requirements of power equipment for insulating oil, analyzes the causes of acetylene, hydrogen and other gases in transformer oil and the importance of chromatographic analysis for transformer fault diagnosis. The technical characteristics of ZYA double stage vacuum oil filter are introduced. It can ensure that the acetylene in insulating oil is zero, and the hydrogen and total hydrocarbon indexes meet the standards. The vacuum oil filter using electronic oil purification technology has stronger dehydration and degassing capacity than the general oil filter. It is characterized by high oil treatment efficiency, high vacuum pumping speed, high vacuum degree, convenient vacuum distribution, accurate detection, and automatic control of the whole process of vacuum oil injection. It also introduces with examples that the high pumping speed two-stage vacuum oil filter is used to vacuum oil the transformer at the overhaul site, vacuum treat and oil the newly installed transformer, dry the damped transformer at the site, and regenerate the transformer at the site

Application of oil.

Keywords: transformer oil acetylene ZYA oil filter

1 New requirements for insulating oil of power equipment -- zero acetylene

With the continuous expansion of the power grid, large capacity and high-grade transformers are widely used in power production. In order to ensure the safe and reliable operation of the power grid, higher requirements are put forward for the performance of insulating oil treatment equipment.

1.1 Harm of water in oil to equipment

The main function of oil filtering equipment is to remove water, gas and impurities in the oil, and restore and improve the physical and electrical properties of transformer oil. Among them, moisture has great harm to the performance of insulating oil and the service life of oil equipment, which are described as follows:

(1) Reducing the breakdown voltage of oil and the water content in insulating oil are the main reasons affecting the reduction of breakdown voltage.

(2) It increases the dielectric loss factor. Due to the different existing states of water in the oil, the influence on the dielectric loss factor is different. The suspended emulsified water makes the dielectric loss of oil increase most obviously. Corrosion products of water, such as naphthenic acid soaps, are very easy to worsen the dielectric loss, which will sharply increase the dielectric loss, which is an indirect consequence of the influence of water on dielectric loss.

(3) The insulating fiber is easy to age and its dielectric loss is increased.

(4) Water promotes the corrosion ability of organic acids and accelerates the corrosion of metal parts. And metal corrosion products, such as metal soaps, will promote the rapid aging of oil, that is, play a catalytic role in oil aging.

In conclusion, the more water content in the oil, the aging of the oil itself, the faster the aging of equipment insulation and the corrosion rate of metal parts, which will affect the safe operation of the equipment and shorten the service life of the equipment.

1.2 Main means for safety monitoring of transformers

Detect the change of the gas content in the oil through the chromatographic analysis of the gas in the oil, so as to analyze the potential faults and hidden dangers of the transformer, so as to maintain or eliminate the faults in time and prevent them from happening. The change of the content of total hydrocarbon, acetylene and hydrogen dissolved in oil is the main parameter for diagnosing transformer faults. Therefore, using gas chromatography to regularly analyze the gas dissolved in oil can find the latent fault in the equipment as soon as possible, and grasp the development of the fault at any time and take necessary measures.

It is difficult to correctly judge the severity of equipment failure only based on the absolute value of dissolved gas analysis results in oil. The development trend of the fault must be investigated, that is, the gas production rate at the fault point. The gas production rate is directly related to the energy consumption of the fault, the fault location, the temperature of the fault point, etc. Therefore, in order to correctly measure the gas production rate and conduct gas analysis, and improve the safety performance of the transformer, it is required that the content of characteristic gas in the insulating oil of newly installed or overhauled transformers or tracking fault transformers after oil filtering should not exceed the normal specified value, the acetylene content should be zero, and the total gas content should be limited to a certain range.

2. The reason why acetylene still exists in the oil after being treated by some vacuum oil filters

The causes of acetylene in the oil are: first, the acetylene contained in the transformer oil itself; Second, during the treatment of vacuum oil filter, the oil is partially overheated and decomposed due to electric heating or pump pressure system - from high molecular weight to low molecular weight, resulting in hydrogen, acetylene, CH4 (methane) and other gases. Currently used oil filters generally produce acetylene gas during oil treatment. If it is not removed at the end of oil treatment, there is always a small amount of hydrogen and acetylene gas in the treated oil.

(1) The working principle of the oil engine should be to evaporate and separate the water and low distillates in the oil, such as hydrogen, methane, ethane, ethylene, acetylene, total hydrocarbon, carbon monoxide, carbon dioxide and other gases from the oil. However, due to the strong binding force between the extremely small amount of water, gas and oil molecules, the separation capacity of general vacuum oil filters is limited, which cannot ensure that the water and gas in the oil reach a very low level, and that the acetylene and hydrogen in the oil are zero. Therefore, some vacuum oil filters currently used have the problem of acetylene.

(2) Some vacuum oil filters do not match the vacuum pumping rate, vacuum evaporation space and heating power with their production capacity (i.e. flow). The production capacity of such equipment is to pull a cart by a small horse, which is not enough; It can only be solved by repeatedly filtering oil.

(3) The degassing and dehydration capacity of vacuum oil filter is mainly determined by four factors: working vacuum degree, oil temperature, oil film evaporation area in vacuum tank, and evaporation time. The oil film evaporation area and time are determined by its structure and size. If the size is too small, the evaporation area and time of the oil film must be reduced, thus affecting its degassing and dehydration capacity. The essence of vacuum degassing and dehydration is an evaporation process under negative pressure. When the water in the oil evaporates, it takes away a lot of heat. In order to maintain the production capacity of the oil engine, it is necessary to set the matching heating power.

3 Technical features of ZYA two-stage vacuum oil filter.

(1) Improve separation capacity

ZYA double stage vacuum oil filter adopts electronic oil purification technology. It adopts special structure and oil flow mode in the vacuum separation chamber to form an oil foam molecular state with huge oil film surface area, supplemented by an evaporation atmosphere with high vacuum degree and large air extraction rate, so that it can achieve a strong separation ability, remove water and gas in the oil to a very low degree, and ensure zero acetylene, hydrogen and total hydrocarbon content meet the standard; The extreme dehydration reaches 1.12 PPm.

For example, Chongqing Electric Power Bureau, Yunnan Tonghai Transformer Factory, Jiangsu Antai Transformer Factory, Wuxi Special Oil Products Factory, Wuxi Shuanglong Grease Factory and other units have had several vacuum oil filters, but they all have acetylene problems. ZYA double stage vacuum oil filter newly developed by our institute is selected to ensure zero acetylene in oil.

(2) The vacuum oil filter with electronic oil purification technology has stronger dehydration and degassing capacity than the general oil filter

The machine is equipped with oil inlet filter, high-voltage electronic generator with controllable current, electronic separation chamber, high vacuum degassing tower, precision filter and microcomputer automatic control room. Its working principle can be summarized as follows: ① Introduce a high-voltage electric field of controllable current potential into the oil. ② Water and gas dissolved in oil are agglomerated into free state by electronic action, which is easy to be separated in vacuum degassing tower. ③ The particles in the oil, regardless of their size, carry positive and negative charges respectively. Particles with opposite charges attract each other, neutralize and increase their volume, and are easy to be filtered by precision filters. As a result, the fine particles are removed, the carrier surface on which water and gas depend for attachment and combination is eliminated, and the oil system inside the whole body is thoroughly purified.

Application of four large pumping speed two-stage vacuum oil filter

With the development of electric power industry, more and more large capacity and high voltage transformers are put into use. In order to ensure the safe operation of the system, strict requirements are put forward for the installation and maintenance of the transformer. It is to meet this requirement that a two-stage vacuum oil filter with large pumping speed has been developed. The oil filter can be used to complete the treatment of insulating oil, vacuum pumping and vacuum oil injection of the transformer body within the specified time. In case the insulation strength of the transformer body fails to meet the requirements due to moisture, the vacuum hot oil circulation drying of the transformer can also be carried out. Its typical characteristics are: high oil treatment efficiency, large vacuum pumping speed, high vacuum degree, convenient vacuum distribution, accurate detection, and automatic control of the whole process of vacuum oil injection. Therefore, it has become a special equipment for installation or maintenance of large transformers.

4.1 Application of large flow oil filter in lubricating oil factory

(1) Gangrun Company of Tianjin Dagang Oilfield ordered ZYA-500 two-stage vacuum oil filter in 2003 to solve the problem of water content in transformer oil produced in summer. The machine has been running for 8 hours continuously. It has processed 152 tons of transformer oil, averaging 19 tons per hour. After treatment, the Huishui water reaches 7 ppm, and the withstand voltage is 78 KV. Other indicators are qualified. According to the detection of Tianjin Electric Power Test and Research Institute, the dewatering limit of transformer oil treated by this machine is 1.12ppm.

(2) The refinery of Lanzhou Petrochemical Company of PetroChina purchased ZYA-500 oil machine in 2001. The acetylene gas of transformer oil treated by this machine is zero, and the PH value is increased from 4.1 to 6.0. Other indicators are qualified.

(3) Liaohe Oilfield Petrochemical General Plant, in order to solve the problem of water content in transformer oil produced in summer, purchased ZYA-500 two-stage vacuum oil filter in 2000, with a production capacity of 30m ³/ h。 After treatment of transformer oil in 105 # tank, the oil temperature was controlled at 50 ℃, the breakdown voltage of transformer oil was increased from 23.7KV to 53.6KV by primary filtration, and the water content was reduced from 37ppm to 9ppm. The acceptance results of the factory show that "the oil filter can solve the problem of unqualified breakdown voltage of transformer oil in summer production in our factory, and achieve the expected effect".

(4) Beijing Uni President Petrochemical Co., Ltd. ordered ZYA-500 double stage vacuum oil filter in 2003. Dispose of vehicle engine oil, hydraulic oil, etc., and remove water, gas and impurities from the oil to meet the standards.

(5) Guangdong Liyuan Lubricant Co., Ltd. purchased DYJ-1000 multi-function oil processor in 2002. Flow 50m ³/ h. Used for dehydration and degassing of diesel engine oil, machine oil, transformer oil, compressor oil and base oil. The lubricating oil containing water, emulsified and turbid is clear and bright after one treatment by the machine, and the oil contains water: none.

4.2 Application of Chongqing Electric Power Extra High Voltage Engineering Bureau

In 1994, Chongqing Electric Power Ultra High Voltage Project purchased two ZYA-150 double stage vacuum oil filters. The bureau has successfully used them for on-site maintenance of transformers for many times, fully meeting the oil quality requirements of 110KV, 220KV and 500KV transformers. The machine has been used successfully for 10 years, and its operation performance is still excellent.

In April 2004, the 500KV reactor was online processed in Wanzhou substation: the oil content of the reactor was 25t, the acetylene content before the treatment was 23ppm, the acetylene content after 3 days of treatment was zero, the withstand voltage was 68KV, and the gas and total hydrocarbon content were qualified.

In May 2003, an accident occurred to No. 1 main transformer (SFSZQ-50000/110) of 110KV Xiaonanhai substation. The total hydrocarbon increased to 1274ppm. After on-site body maintenance, ZYA-150 oil filter was used for vacuum oil injection. After 48 hours of vacuum degassing treatment, the acetylene in the oil dropped to zero, the total hydrocarbon dropped to 10.1 ppm, and the withstand voltage was 71 KV. Results: The secondary line of the main transformer is qualified for recovery and commissioning; The electrical test and oil quality test of the main transformer are qualified.

4.3 Vacuum oiling of transformer at overhaul site

In May 1998, Zhejiang Taishan Nuclear Power Plant overhauled an on load voltage regulating split transformer with the model of SFF27-50 000/220 and the oil loading capacity of 39.7t. ZYA-100 large pumping speed two-stage vacuum oil filter is used for on-site treatment. Firstly, the oil in the transformer shall be pumped out and then injected into the reserve oil tank after vacuum oil filtration. The breakdown voltage of the extracted oil is 40KV, which is increased to 60KV after vacuum treatment. Afterwards, the transformer shall be overhauled. After maintenance, vacuum diverter valve is used to vacuum the transformer body, and the vacuum degree reaches 133Pa after 2h of pumping. Stop the booster pump, continue to vacuum with the rotary vane vacuum pump only, and conduct vacuum oil injection after maintaining the pressure for 12h. The oil in the oil storage tank shall be pumped out, filtered and heated by vacuum, and then injected into the transformer. 36t oil shall be injected for 6h continuously, the oil injection temperature shall be 50 ℃, and the vacuum degree shall be 133Pa. At the end, nitrogen shall be filled again to break the vacuum. Finally, the oil conservator and radiator shall be filled with 3.3t oil under normal pressure.

4.3 Vacuum treatment and oil filling of newly installed transformer

In September 1999, Xuzhou Power Transmission and Transformation Company installed two 220KV transformers, and only one ZYA-150 large pumping speed two-stage vacuum oil filter was used to vacuum and vacuum fill the transformer body., One OSFPS9-180 000/220 outdoor autotransformer with 41.2t oil capacity has been installed in place. According to the requirements, the transformer shall be vacuumized to less than 133Pa, and vacuum oil injection shall be carried out after pressure maintaining. Field piping connections are shown in Figure 1.

The working process is as follows: connect the vacuum diverter valve of ZYA-150 oil filter with the air extraction valve on the upper part of the transformer with steel wire reinforced transparent hose, connect the oil inlet valve of the oil filter with the oil storage tank, connect the oil outlet valve of the oil filter with the lower part of the transformer, and set the vacuum gauge on the upper part of the transformer. First, start the vacuum system of the oil filter and vacuum the transformer body. After about 3h, the vacuum degree of the transformer body will reach 70Pa. Then shut down the machine and close the valve. The transformer will naturally keep vacuum. After 10h, the vacuum of the transformer did not leak at all, and the vacuum pressure decreased from 70Pa to 45Pa, which shows that the transformer is well sealed. It is estimated that the decrease of vacuum pressure is caused by the movement of gas molecules in the transformer, that is, the decrease of average free energy, when the temperature drops about 10 ℃ at night. At 6:30, the vacuum system of the oil filter was started again. At 8:00, the vacuum degree of the transformer body reached 35Pa. At noon, the temperature was as high as 42 ℃, and the vacuum was maintained at 70Pa. At night, the vacuum degree of the transformer returns to 40~50Pa, and the temperature is about 28 ℃. On September 12, oil injection was started. While vacuuming the transformer body, the oil filter heated the transformer oil and injected it into the transformer. The oil injection temperature is constant at 68 ℃, the oil breakdown voltage is above 60KV, the internal pressure of transformer is 70~80Pa, and the injection time of 41t oil is about 8h.

On September 13, another newly installed autotransformer was vacuum oiled. The transformer model is OSFPS8-120 000/220, and the oil loading capacity is 32.3t. The installation requirements of the transformer are: first preheat the transformer core to 30 ℃ higher than the ambient temperature, then lift the cover for inspection, vacuum the transformer body to less than 300Pa after closing the cover, and vacuum oil injection after pressure maintaining.

The on-site treatment process is as follows: at 7:00 p.m., the oil filter was operated to heat the transformer circularly, and the oil flowed from the lower part of the transformer. After being filtered and heated by the oil filter, the oil was injected into the upper part of the transformer. The heating temperature was constant at 70 ℃. The heating was stopped at 6:00 the next day, and all 32t transformer oil was pumped out and stored in the oil tank.

Then lift the cover to check and install the conduit and component wiring. After the installation is completed, check whether it is true