Research on Transformer Power Pollution

Since the beginning of the 21st century, my country has accelerated its development in all aspects, especially the continuous improvement of industrial technology, and has made great progress in cooperation with developed countries and independent research and development. Some domestic enterprises with high technological content and foreign-owned enterprises have adopted new electrical control methods, which has gradually exposed the shortcomings of my country's power supply system, which has been gradually expanding since the 1950s and 1960s.

Looking at the power supply mode in my country, although there have been some improvements with the development of technology, the problem of power pollution has been ignored. In more developed industrial countries, such as Japan and the United States, they have adopted a large number of new technologies and paid attention to this problem earlier. Some companies have also seen potential business opportunities and have set up offices in my country. For example, the famous American Infor company has established outlets in most provinces in my country and its performance has been developed.

At present, in addition to the new equipment developed and imitated by my country, a large number of new equipment from developed countries have been introduced, such as Germany's Siemens and Japan's Omron. The common feature of these equipment is that they focus on energy conservation and efficiency improvement. Therefore, high-frequency frequency conversion technology and PID-triggered linear load drive are widely used. The use of these equipment seriously interferes with the power grid and poses a serious threat to substation equipment.

In response to the above problems and in combination with the specific situation of our company, this article attempts to discuss from one aspect the process from occurrence, discovery to resolution of our company, hoping to provide some reference for relevant units.

Our company was established in the 1990s as a Sino-Japanese joint venture. The production equipment used is mainly imported from Japan, including heat treatment lines using Omron electrical appliances, induction furnaces from Jingdong High Frequency Production Club, and a large number of frequency conversion equipment to drive and adjust various loads. All of these generate a large number of harmonics during work, among which the working frequency of the induction furnace reaches 500KHZ. After eight years of development, our company's equipment has been continuously increasing, and production capacity and total output value have increased year by year. Before moving into the Science and Technology Park, the company used a 315KVA transformer, which could basically cope with production. However, the site and energy could no longer meet the needs of production development, and it moved to the Science and Technology Park in 2002. When it started operating, it was found that the newly installed 800KVA transformer had a high noise and severe heating. At that time, we invited the engineering and technical personnel of the transformer manufacturer to inspect and study solutions. With the support of the company's leaders, at the request of the user, the manufacturer agreed to replace a transformer to eliminate the quality problem of the transformer. Since the existing problems were not fundamentally found, the same problem still existed after the transformer was replaced. After careful research and analysis, I believe that there is a possibility of feedback and interference in the specific load of our company. General Manager Wang of the company is very supportive and agrees to ask the relevant functional departments of the Municipal Electric Power Bureau to test. After the tests of the two units, it is proved that there is indeed serious pollution in the power supply of our company. The harmonic content of the national standard should be between 1-5%, but our actual measurement is the maximum value of 20% (two test reports are available).

Because it was the hottest time of the summer, our company was about to add a new set of high-power heating furnaces. To cope with production, we used a high-power fan to blow heat, and the working capacity was less than half of the transformer, and the oil temperature of the transformer had reached 83°C. In order to fundamentally solve the harmonic problem, I consulted a lot of information and combined my decades of work experience. I learned about the relevant situation from all aspects: I learned from the transformer manufacturer that the newly added foreign-funded enterprises have special requirements for transformers; the Baotou Strong Magnetic Company of our company once blew up the compensation capacitor of the distribution room due to power pollution, which almost caused a personal accident; there are special institutions abroad that deal with power pollution.

We invited relevant units to rectify the problems that have been found. There are many solutions proposed by various parties, including increasing the volume of the oil tank; adding reactors and capacitors to offset harmonics; and installing filters on each load. The total price is more than 100,000 yuan (our Baotou company asked a scientific research institution in Beijing to install a set of equipment, which cost 120,000 yuan, and it was manually switched). The relevant departments of the headquarters believed that as long as the problem can be solved, it is okay to spend some money. However, these units in Ningbo were not 100% sure. Our requirement at the time was that the temperature of the oil tank should not be too high under the rated load to ensure the safety of the transformer. From a realistic point of view, the premise for solving the above problems is to eliminate the harmonic content in the load.

I analyzed that the harmonics of the company's equipment exist objectively. The blocking method cannot achieve the goal, so it is better to use the dredging method. Analyzing the internal structure of the transformer currently used, the three-phase connection method is closed, and the harmonics of the load (especially the even harmonics) are always circulating inside. The radiated electromagnetic waves hit the outer shielding layer of the transformer and reflect back, causing noise and heating. After finding the cause, I personally visited the Tianyuan Transformer Factory and had technical exchanges with Chief Engineer Wang (General Manager Wang is a senior member of the Chinese Society of Electrical Engineering and the Chinese Electrotechnical Society, and an honorary editor of the "Transformer" magazine). We reached a consensus and accepted my suggestion to replace a transformer with another structure. The new transformer internal structure adopts a winding method that combines closed and open loops. From a theoretical analysis, most of the odd harmonics can be offset. Since the transformer was put into operation on August 25, the load has reached more than 90%, and it has been working normally, with only a slight temperature (<50℃).

The solution to the power supply problem has always been strongly supported by our general manager and relevant departments of the headquarters. Its significance lies in that it has achieved great success with little or no money (the replaced transformer can still be used). It not only saves a lot of money for the company, but also grasps the essence of objective things through practice, and proposes a new solution to the problems in the new scientific and technological fields of our city and even our country.