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Issues related to reliability design of power transformers

Power transformers are very critical power equipment in the power grid. Once quality problems occur, they may not only cause significant economic and property losses but also endanger lives and cause immeasurable negative social impacts.

Generally speaking, the reliability of a power transformer is mainly related to its design, technology, materials, and manufacturing level. Among these factors, design, as the source of product quality, greatly affects the overall reliability of power transformers.

Statistics show that "design defects" in products are the main reason for major power transformer quality accidents that have historically occurred in the industry, accounting for more than 80%. The reliability of power transformer design is the prerequisite and fundamental guarantee for achieving overall product reliability. This article discusses some important issues in transformer reliability design.

Short circuit endurance design idea

Short-circuit withstand capability is a key indicator of the reliability of power transformers. It is not uncommon for power transformers to be damaged due to insufficient short-circuit endurance in the power grid. It is also common for power transformers to fail to pass the random short-circuit test.

As a special test project, the proportion of power transformers undergoing short-circuit testing is very small, less than 1% of the total. Therefore, design and verification are the most realistic ways to ensure that power transformers have sufficient short-circuit withstand capability.

The basic idea of short-circuit design of power transformers should be to reduce the occurrence value of short-circuit stress as much as possible, rather than blindly increasing the allowable value of short-circuit stress, because the latter is overly dependent on materials and processes and is an uncontrollable design behavior.

Design concerns for hot spot temperature rise level

The hot spot temperature rise value of each component of the power transformer is closely related to the life of the transformer and also affects the long-term operation reliability of the power transformer. As a type test project, not every power transformer will undergo a temperature rise test. Therefore, design and verification are still important ways to ensure that the temperature rise of hot spots in each component of a power transformer is within safe values.

The design of power transformer hot spot temperature rise should focus on three main aspects: winding hot spot, core hot spot, and metal structural parts hot spot temperature rise. According to the structure and parameters of the product, accurate calculation of the leakage magnetic field distribution and loss density distribution is an important basis for rationally selecting the materials of each component, rationally setting up magnetic flux leakage control measures, and rationally designing the cooling oil circuit, thereby ensuring that the temperature rise of hot spots in each component of the product is within Within the safe value.

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