When the transformer operates in the power system, it is difficult to avoid some short-circuit events. Depending on the severity of the short-circuit event and the strength of the transformer's anti short-circuit ability, sometimes it is safe and sometimes it is damaged. The damage of a distribution transformer will affect a factory in a short time, while the short-circuit accident of a distribution transformer will affect an urban area, and the replacement is more difficult, and the repair takes 2 ~ 3 months. Therefore, improving the short-circuit resistance of power transformer has always been a matter of great concern to the power department, and it is also the main goal of the manufacturing department.
Before the 1990s, there were only four high current laboratories (stations) in Xi'an, Shenyang, Shanghai and Beijing in China. Their facilities are mainly for switching capacity test in the switching industry, but they can also test distribution transformers. Therefore, in the early and mid-1980s, Shenyang
Transformer Research Institute was responsible for the unified design of sl7 and old s9-30 ~ 1600KVA / 10kV distribution transformers. The prototypes trial produced by each factory had conducted short-circuit tests in the above laboratories (stations). 14 sl7 and 12 old S9 passed the tests. After the success of the test, the new S9 type was trial produced. The first batch of 37 units passed the test, and the qualification rate of the new S9 type reached more than 90% (Kema in the Netherlands tested foreign distribution transformers, with a one-time qualification rate of 50%). By 1996, about 300 distribution transformers had been tested in various laboratories (stations), including S7 type.
For more than ten years, China has done a lot of short-circuit tests on distribution transformers, and improved each damage condition, so that the qualified rate reaches more than 90%, much higher than the foreign qualified rate of 50%, which has been confirmed in the actual operation of power grid and achieved gratifying results. It can be said that the basic solution to the short-circuit strength of distribution transformer depends on "practical test", which is a very important experience.
There is no base for testing power transformers in China, so the short-circuit resistance of power transformers is difficult to solve. In 1986, the State Planning Commission approved the construction of Shenyang Hushitai high current test station, which was loaned by the state and approved to be consulted by EDF company of France. After many years of work, the first phase of the project was completed at the end of 1993, 220kV network was built and two 1200mva / 0 ~ 224kv were installed. After acceptance by the state expert committee, it was put into operation in January 1994 and a large number of distribution transformer tests were carried out in 1994 and 1995, After gaining experience, the short-circuit test of 110kV power transformer was carried out in 1996.
Short circuit test of 110kV power transformer
110kV power transformer is the main transformer in China's transmission and distribution system, and its output accounts for about 1 / 5 of the total output of transformer. According to the statistical data from 1995 to 1996, the short-circuit accident of 110kV transformer accounts for 5O% of the total accident of this level, and shows an upward trend. Therefore, how to improve the short-circuit resistance of this level of power transformer has become the main topic at the Zengcheng conference in Guangdong. It is recognized that the best way is to verify it with short-circuit test.
From 1996 to the first half of 2005, due to the attention of power departments and manufacturing enterprises, More than 60 factories have successively conducted short-circuit tests on 80 110kV power transformers (including 4 from Shenyang Transformer Co., Ltd., 3 from Xinjiang TBEA Co., Ltd., 2 from Nantong AIA Transformer Co., Ltd., 2 from Changzhou transformer factory, 3 from Yunnan Transformer Factory, 2 from Baoding, 3 from Huapeng, etc.) with a pass rate of > 96%. Distribution transformers with qualification rate higher than 10kV.
In order to pass the first test, these factories have invested a lot of human and material resources. In the process of product development, they have made certain efforts in design, process, production and management, which is undoubtedly a great improvement to the comprehensive quality of enterprises. 28 of the 45 products tested in the first half of 2001 have been running on the power grid, and the one with the shortest running time has been running for several months. Among them, a new product of Shenyang substation, 50000kVA / 110kV transformer, has been running for more than five years and is welcomed by users. On the basis of obtaining the test data, these factories have improved the product design structure. Taking this as the standard, they have been put into mass production and put into the power grid, so there are no short-circuit accidents in the future.
The statistical data of Wuhan High Voltage Research Institute of State Power Corporation and China Electric Power Research Institute from 1995 to 1999 show that the short-circuit accident of transformer has decreased from 50% in the past to 40%, which is mainly due to the improvement of system operation reliability due to the operation of the above batch of highly reliable transformers. It should be said that the short-circuit accident of 110V transformer has been initially curbed.
The short-circuit test of 110kV transformer should be further expanded
At present, there are 60 factories that normally supply 110V power transformers in China, and only more than 100 factories have done 110kV transformer short-circuit test, accounting for about 55%. A few factories are preparing conditions for short-circuit test, which requires strong support from users and actively adopt the tested products to play a role in the system. In terms of manufacturing plants, we should carry out work in terms of design and technology, make sufficient material preparations, raise funds and put them into practice. It should also be pointed out that factories that have not done transformer short-circuit test should seize the time, so as not to affect the ordering and even lose the qualification of production.