The load loss of a transformer increases with its operating temperature. Under the same load conditions, for every 10°C increase in operating temperature, the load loss increases by approximately 3.93% (for copper windings) or 4.23% (for aluminum windings). This is because the load loss is directly proportional to the winding resistance, and the winding resistance increases with temperature. For example, the temperature coefficient of resistance for copper is 0.00393°C, and for aluminum it is 0.00423°C. The enclosures of prefabricated substations (also known as European-style substations) are classified into 10, 20, and 30 classes. This is defined as follows: the temperature rise inside the transformer enclosure exceeding the difference in temperature rise measured outside the enclosure for the same transformer should not exceed the value specified for the enclosure class, such as 10K, 20K, or 30K (from GB/T 17467—1998 "High Voltage and Low Voltage Prefabricated Substations"). Physically, this means that under the same load conditions, when a transformer operates inside a European-style substation enclosure, its operating temperature will be raised by 10°C, 20°C, or 30°C. The load losses will increase by approximately 3.93%, 7.86%, or 11.79% respectively (for copper windings). This is an astonishing figure! It is worth noting that tens of thousands of European-style prefabricated transformers with 10, 20, and 30-level enclosures are currently operating in my country's power grid. These transformers not only cause a significant waste of electrical energy but also pose a potential risk of reduced transformer lifespan. As operating temperatures rise, the transformer's insulation materials age rapidly, reducing its lifespan. Especially when the temperature exceeds the maximum permissible hot spot temperature and maximum oil surface temperature, the transformer's lifespan will decrease dramatically, doubling for every 6°C increase in temperature. How can we avoid these drawbacks of European-style prefabricated transformers? For dry-type transformers, the heat dissipation performance of the enclosure should be improved as much as possible, and fans should be installed when necessary to minimize the internal temperature of the enclosure. For oil-immersed transformers, the optimal solution is to use a "zero-level enclosure," as shown in the attached diagram. The "zero-level enclosure" directly exposes the transformer's heat sink to the atmosphere, similar to a pole-mounted transformer. This allows the transformer to operate under optimal heat dissipation conditions, restoring the original design load factor, load loss, and service life, which is essential for economical transformer operation. Prefabricated substations were introduced to my country from EU countries in the 1980s, hence the name "European-style prefabricated substation," or simply "European substation." So, how did EU countries solve the above problems? Any imported technology undergoes a process of consumption and absorption based on national conditions. Several issues remain unresolved: First, EU countries vigorously promote "oil-free" operations, encouraging the use of dry-type transformers as much as possible, minimizing or eliminating the use of oil-immersed transformers. Dry-type transformers must operate within an enclosure, requiring only a sufficiently high heat dissipation level. For the few prefabricated substations equipped with oil-immersed transformers, measures such as increasing the enclosure's heat dissipation level and "reduced load operation" are used to control the transformer's operating temperature. However, my country still largely uses oil-immersed transformers. Second, there is the issue of enclosure heat dissipation level. Large foreign companies producing transformer prefabricated units (such as Schneider Electric and Siemens) have transformer prefabricated enclosures with excellent heat dissipation performance, reaching level 10. They scientifically design the materials and structure of the enclosures based on the thermodynamic principles of conduction, radiation, and convection to achieve optimal heat dissipation. After the introduction of transformer prefabricated units to my country, some manufacturers mistakenly believed that the enclosures were "simple," simply a "house" for the transformer, and that this "house" needed "heat insulation"! They unilaterally pursued "aesthetic appeal" and "landscape design," mistakenly choosing sandwich-faced color steel plates, asbestos-coated steel (aluminum) plates, and so-called "non-metallic materials" as materials for the enclosures and doors, which contradicts the principles of radiation and conduction heat dissipation. They also lacked scientific structural design for gas convection heat dissipation. Most of the prefabricated units produced by these manufacturers are level 20, and many are even level 30. During the hottest season in southern China, many prefabricated units have to open double doors due to excessively high transformer interior temperatures, requiring the use of high-powered fans outdoors for cooling. Thirdly, EU countries use "transformer de-loading operation" to compensate for the temperature rise caused by the transformer enclosure, while my country has not fully implemented this measure in actual operation. Appendix D of the national standard GB/T 7467-1998 "High Voltage and Low Voltage Prefabricated Substations" stipulates that transformers corresponding to the maximum rated capacity of a prefabricated substation can carry different loads for different enclosure classes and ambient temperatures. In other words, if a transformer is configured to operate within an enclosure, it should be de-loaded. The load factor for oil-immersed transformers in enclosures is shown in the attached table. In practical applications, EU transformer enclosures do not implement "de-loading operation." This is because each increase in transformer capacity significantly increases the cost of the substation equipment. Not only does the price of the transformer itself increase, but other system costs also increase. With increased transformer capacity, the short-circuit current increases, the performance parameters of related electrical components in the circuit increase accordingly, and engineering costs increase. Furthermore, excessively large transformer capacity leads to a decrease in load factor, causing the transformer to operate outside the economic operating range (the most economical operating range is 60%–70% load factor), and increasing no-load losses (iron losses). Thus, in actual engineering design, if the capacity cannot be increased by one level after consulting the table, the transformer capacity is not selected according to the "increase by one level" rule. Furthermore, China is currently in a period of rapid economic development. With the rapid increase in load demand, the actual load on transformers quickly exceeds the initial design load in a short period. This results in the objective fact of transformers operating without load reduction, leading to operating temperatures 20-30°C higher than normal, causing significant and unnecessary power grid losses and a reduction in transformer lifespan. Once oil-immersed transformers are enclosed in their enclosures, their operating conditions (ambient temperature) become extremely harsh. Currently, tens of thousands of oil-immersed transformers are working under heavy loads on the grid, enduring the torment of high temperatures. They should be "liberated" as soon as possible, and "returned to nature" from 20- and 30-level enclosures, making their due contribution to a conservation-oriented society! [ALIGN=CENTER] Attached: Zero-level enclosure outline Attached: Load factor of oil-immersed transformers in enclosures [/ALIGN] Article source: "Energy Saving Innovation 2006 - Proceedings of the First National Electrical Energy Saving Competition"