Zero Acetylene -- New Requirements for Insulating Oil in Power Equipment

Chongqing Optical Submersible Electromechanical Research Co., Ltd

Abstract: The new requirements for insulating oil of power equipment are described. The causes of acetylene, hydrogen and other gases in transformer oil are analyzed, and the chromatographic analysis is carried out

The importance of transformer fault diagnosis. The application example of removing acetylene from oil filter.

Keywords: transformer oil acetylene oil filter

1、 Acetylene gas commonly found in insulating oil

New requirements for insulating oil of power equipment

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.

The main means for safety monitoring of transformers in operation is to detect the change of gas content in oil through chromatographic analysis of gas in oil, so as to analyze potential faults and hidden dangers of transformers, so as to maintain or eliminate faults in time and prevent problems before they occur. The change of the content of total hydrocarbon, acetylene and hydrogen dissolved in oil is the main parameter for diagnosing transformer faults. Therefore, it is required that the acetylene content in the insulating oil of newly installed or overhauled transformers or tracking fault transformers after oil filtering should be zero, and the total gas content should be limited to a certain range.

Reasons for acetylene and hydrogen generation in transformer oil

During normal operation, transformer oil and solid organic insulating materials decompose a small amount of hydrogen, low molecular hydrogen carbide (hydrocarbon), carbon monoxide and carbon dioxide under the action of heat, and most of these gases are dissolved in oil.

When the transformer has defects or faults, the type and quantity of gas in the oil will change. When local overheating occurs, various components of hydrocarbons increase significantly with the increase of temperature. If the solid insulation is damaged, carbon monoxide and carbon dioxide will increase. In case of high energy discharge due to insulation breakdown, the nearby oil is almost completely thermally decomposed and the gas production increases dramatically. Except that carbon particles are evenly distributed in the oil, the main gases are hydrogen (H2) and acetylene (C2H2). When low energy spark discharge occurs, the main gases are still H2 and C2H2, but the quantity is much less than that of high energy discharge. When partial discharge occurs, the free molecules of oil will be free, and the main gas generated is H2, with a small amount of C2H2 and CH4 (methane). No matter what kind of discharge, as long as solid insulation intervenes, CO and CO2 will always be generated.

Why does acetylene still exist in the oil after being treated by vacuum oil filter?

1. Reasons for acetylene in oil: First, acetylene contained in transformer oil itself; The second is that the vacuum oil filter will overheat the oil locally during processing, which will cause the oil to decompose from high molecular weight to low molecular weight, thus generating hydrogen, acetylene and CH4 (methane) gas. The various oil filters currently used generally produce acetylene and other gases during oil treatment. If they are not removed at the end of oil treatment, there is always a small amount of hydrogen and acetylene gas in the treated oil.

2. The working principle of the vacuum oil filter 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, the vacuum oil filter widely used at present has the problem of acetylene.

For example, some transformer plants have several domestic and imported vacuum oil filters. In the past, the requirements for acetylene gas were not high, and the problem was not prominent; Now, the oil treated by these oil filters contains acetylene and hydrogen according to the precise gas chromatographic analysis instrument.

2、 ZYA double stage vacuum oil filter solves the technical characteristics of acetylene and hydrogen.

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 very strong separation ability, remove water and gas in the oil to a very low degree, and ensure zero acetylene and hydrogen.

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 none of them can solve the acetylene problem. ZYA double stage vacuum oil filter newly developed by our institute is selected to ensure zero hydrogen and acetylene in the oil, so that their transformer or transformer oil can be smoothly handed over to users.

2. Why does the vacuum oil filter with electronic oil purification technology have stronger dehydration and degassing capacity than the general oil filter?

This is because the machine is equipped with an oil inlet filter, a high-voltage electronic generator with controllable current, an electronic separation chamber, a high vacuum degassing tower, a precision filter and a microcomputer automatic control room. Its working principle can be summarized as follows:

Introduce a high-voltage electric field of controllable current potential into the oil.

Water and gas dissolved in oil are agglomerated into free state by electronic action, which is easy to be separated in vacuum degassing tower.

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.

3、 Application example of ZYA two-stage vacuum oil filter

1. Chongqing Electric Power Ultra High Voltage Engineering Bureau

In 1994, two ZYA-150 double stage vacuum oil filters were purchased. 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."

2. Nantong Youbang Transformer Co., Ltd

In September 2003, ZYA-100 double stage vacuum oil filter was ordered to treat high voltage transformer oil. The oil sample was sent to Nanjing Electric Power Test and Research Institute for testing. The results showed that water content was 2ppm, breakdown voltage was 73KV, acetylene=0, hydrogen=0. This machine is used to treat a transformer that has been broken down during the high-voltage test. The oil containing acetylene is 46, and the acetylene is zero after being treated by this machine.

3. Vacuum oil injection for transformer

Last May, Zhejiang Taishan Nuclear Power Company overhauled a 40t on load voltage regulating split transformer. Use ZYA-100 oil filter to draw out the oil in the transformer and inject it into the oil storage tank after vacuum treatment. The breakdown voltage of the oil is increased from 40KV to 60KV. After the maintenance, vacuum the transformer body with a vacuum diverter valve for 2h to 133Pa, vacuum oil injection for 6h after 12h pressure holding, and oil temperature of 50 ℃. At the end of the operation, fill ammonia twice to break the vacuum, and vacuum oil injection is successfully completed.

4、 The latest achievements of ZYA-200 two-stage electronic vacuum oil filter:

An aluminum company in Henan Province has many large transformers. Due to continuous operation of high voltage and heavy load, the hydrogen and total hydrocarbon values of transformer oil have seriously exceeded the standard. In order to ensure the normal operation of the transformer, it is urgent to treat these transformer oils to make the water, acetylene, hydrogen, total hydrocarbon, etc. in the oil meet the requirements.

There are four vacuum oil filters in the plant, but none of them can completely remove acetylene, hydrogen and total hydrocarbon from transformer oil. In August this year, the factory purchased ZYA-200 double stage vacuum oil filter with electronic oil purification technology from our institute.

After the oil filter was sent to the plant, the insulating oil of the two large transformers was treated day and night, completely solving the problems of acetylene, hydrogen and total hydrocarbon in the oil.

Comparison of some indicators of oil quality test before and after treatment of 5 # main transformer is as follows (content unit: μ L/L）：

Before and after treatment

Acetylene C2H2: 0.17 0

Hydrogen H2: 5345.9 7.59

Total hydrocarbon: 400.38 2.78

To sum up, ZYA two-stage vacuum oil filter has its own characteristics and unique functions, which can ensure that the acetylene in insulating oil is zero, and the hydrogen and total hydrocarbon indicators meet the standards. It has broad application prospects in many industries such as electric power metallurgy.

Author introduction: Luo Gushi, the director of the institute, has made great contributions to the improvement, promotion and application of oil filters, and has obtained 5 national patents. He has published several papers such as Current Situation and Development of Insulating Oil Treatment Equipment, and was rated as "Excellent Entrepreneur" by Chongqing Hi tech Development Zone.