Transformer life

my country's power transformer products can be divided into large transformers (capacity greater than or equal to 8000kVA) and small and medium-sized transformers (capacity less than or equal to 6300kVA) according to capacity; they can also be divided into 6kV, 10kV, 35kV, 60kV, 110kV, 220kV, 330kV and 500kV according to voltage level. As voltage conversion equipment, transformers are widely used in the fields of power transmission and distribution, especially transformers with voltage levels of 10kV and 35kV, which are widely used in power, industrial and commercial distribution systems, and the number is huge. In 1999, my country produced about 338,000 transformers annually, of which about 313,000 were 10kV and 35kV, accounting for 92.6%.

It is estimated that there are more than 1 billion kVA of 10kV and 35kV transformers in operation on the power grid. Due to the large usage and long operation time, there is a huge energy-saving potential in the selection and use of transformers, especially the 10kV and 35kV transformers, which are in large quantities and widely used. Choosing high-efficiency and energy-saving products is not only of great significance to energy conservation, but also can greatly reduce the operating costs of transformers, which is an important way for enterprises to improve economic benefits. Most of the 10kV and 35kV transformers in my country are of standard design. The product standards have experienced continuous progress from the "64" standard, the "73" standard, the "86" standard to the "95" standard in the mid-1990s. The products have developed from the original high-loss type (SJ, SJL...S7) to the current low-loss type (S9 type, etc.). By the end of 1998, the S7 type transformer and previous products had been announced by the state to be eliminated, and their production and sales had been stopped. With the transition from a planned economy to a market economy and the social demand for energy conservation and environmental protection, the efficiency level of my country's transformers will show a diversified trend. At present, products that are more energy-efficient than the S9 series have appeared on the market, such as the S10 and S11 series.

Among the transformers used in the power grid, old transformers with a service life of more than 20 years still account for more than 10%. These transformers were designed according to the "64" and "73" standards of the 1960s and 1970s, and the losses are very high. Compared with the current S9 series, the average loss is more than 100% higher, and the energy-saving potential is huge. For enterprises, how to determine the appropriate transformer efficiency level from the perspective of long-term economic benefits and whether high-energy-consuming transformers should be replaced with energy-saving transformers is one of the urgent issues to be solved in transformer selection and management.

There are many methods for evaluating transformer energy efficiency in the world, all of which require comparison of transformer prices and their loss costs. In the late 1970s, due to rising energy prices, many power companies in the United States began to require that the designed transformers should have the lowest service life costs, which gave rise to the total ownership cost (TOC) method. The TOC method developed into an industrial standard in the United States in 1981.

The TOC standard for purchasing transformers has been used until now. The TOC method is to sum up the initial cost of the transformer and the loss cost of the equivalent present value to express the comprehensive cost of the purchased transformer. We have used the TOC method to review the economic benefits of distribution transformers S9 and S7. The comparison results show that although the price of S9 transformers is about 20% higher than that of S7, the loss index is about 21% lower than that of S7. The funds of S9 villages can be recovered from the saved loss electricity charges within 2 to 3 years. Similarly, the results of the benefit comparison of using S9 transformers to replace old transformer products from 80 years ago show that under the condition of only paying the equipment fee of S9 and ignoring the recovery value of the old transformer, the funds of S9 can also be repaid from the saved loss electricity charges within 2 to 3 years.