1. Temperature control system of dry-type transformer The safe operation and service life of dry-type transformers largely depend on the safety and reliability of transformer winding insulation. The winding temperature exceeding the insulation withstand temperature causes insulation failure, which is one of the main reasons why the transformer cannot work normally. Therefore, monitoring the operating temperature of the transformer and its alarm control are very important. Here is a brief introduction to the TTC-300 series temperature control system. (1) Automatic fan control: The temperature signal is measured by the Pt100 thermistor embedded in the hottest part of the low-voltage winding. When the transformer load increases and the operating temperature rises, the system automatically starts the fan to cool when the winding temperature reaches 110℃; when the winding temperature drops to 90℃, the system automatically stops the fan. (2) Over-temperature alarm and trip: The winding or core temperature signal is collected by the PTC nonlinear thermistor embedded in the low-voltage winding. When the temperature of the transformer winding continues to rise, if it reaches 155℃, the system outputs an over-temperature alarm signal; if the temperature continues to rise to 170℃, the transformer can no longer continue to operate and must send an over-temperature trip signal to the secondary protection circuit to make the transformer trip quickly. (3) Temperature display system: The temperature change value is measured by the Pt100 thermistor embedded in the low voltage winding, and the temperature of each phase winding is directly displayed (three-phase inspection and maximum value display, and the historical highest temperature can be recorded). The highest temperature can be output as a 4-20mA analog quantity. If it is necessary to transmit to a computer at a distance (up to 1200m), a computer interface can be added. One transmitter can monitor up to 31 transformers at the same time. The over-temperature alarm and trip of the system can also be activated by the Pt100 thermistor signal, further improving the reliability of the temperature control protection system. 2. Protection method of dry-type transformer According to the characteristics of the use environment and protection requirements, different shells can be selected for dry-type transformers. IP20 protective enclosures are typically selected to prevent solid foreign objects larger than 12mm in diameter and small animals such as rats, snakes, cats, and birds from entering, causing short circuits and power outages, thus providing a safety barrier for live parts. If the transformer must be installed outdoors, an IP23 protective enclosure can be selected. In addition to the above IP20 protection functions, it can also prevent water droplets from entering at an angle of up to 60° to the vertical. However, IP23 enclosures will reduce the transformer's cooling capacity, so attention should be paid to the reduction in its operating capacity when selecting one. 3. Cooling methods for dry-type transformers Dry-type transformers are cooled by natural air cooling (AN) and forced air cooling (AF). With natural air cooling, the transformer can operate continuously at its rated capacity for a long time. With forced air cooling, the transformer's output capacity can be increased by 50%. It is suitable for intermittent overload operation or emergency overload operation; however, because the load loss and impedance voltage increase significantly during overload, it is in an uneconomical operating state and should not be subjected to long-term continuous overload operation. 4. Overload capacity of dry-type transformers The overload capacity of dry-type transformers is related to the ambient temperature, the load condition before overload (initial load), the insulation and heat dissipation of the transformer, and the heating time constant. If necessary, the overload curve of the dry-type transformer can be obtained from the manufacturer. How to utilize its overload capacity? The author proposes two points for reference: (1) When selecting and calculating the transformer capacity, it can be appropriately reduced: fully consider the possibility of short-term impact overload of certain steel rolling, welding and other equipment - try to utilize the strong overload capacity of the dry-type transformer to reduce the transformer capacity; for some uneven load places, such as residential areas mainly for night lighting, cultural and entertainment facilities, and shopping malls mainly for air conditioning and daytime lighting, its overload capacity can be fully utilized to appropriately reduce the transformer capacity so that its main operating time is at full load or short-term overload. (2) The reserve capacity or number of units can be reduced: in some places, the reserve coefficient of the transformer is required to be high, which makes the transformer capacity and number of units selected for the project large. However, by utilizing the overload capacity of the dry-type transformer, its reserve capacity can be compressed when considering it; the number of units can also be reduced when determining the number of units. When a transformer is operating under overload, it is crucial to monitor its operating temperature. If the temperature rises to 155℃ (an alarm will sound), load reduction measures (reducing some secondary loads) should be implemented to ensure safe power supply to the main load. 5. Low-voltage outgoing line methods and interface coordination of dry-type transformers: Because dry-type transformers do not contain oil, they eliminate the risks of fire, explosion, and pollution. Therefore, electrical codes and regulations do not require dry-type transformers to be placed in a separate room. Especially with the new SC(B)9 series, losses and noise have been reduced to new levels, creating conditions for placing transformers and low-voltage panels in the same distribution room. To adapt to this, in 1996, Shunde Special Transformer Factory, while launching the new SC(B)8 series, first introduced various low-voltage outgoing line methods to customers in its "Dry-type Transformer Technical Manual," including standard enclosed busbars, standard horizontal side-outgoing lines, and standard vertical side-outgoing lines. The "SC(B)9 Series Dry-type Transformer Technical Manual," published in 1998, affirmed and further improved these low-voltage outgoing line methods, which were widely welcomed by customers and design units. In recent years, design units have gradually become familiar with and selected this method. Here is a brief introduction. (1) Low-voltage standard enclosed busbar: If the engineering wiring uses an enclosed busbar (also known as a plug-in busbar or a compact busbar trunking), the corresponding transformer can provide standard enclosed busbar terminals to facilitate connection with external busbars. For products with an outer shell (IP20), an enclosed busbar flange is provided on the top cover of the outer shell; for products without an outer shell (IP00), only enclosed busbar terminals are provided. (2) Low-voltage standard horizontal side-out: When the transformer and the low-voltage distribution panel are placed side by side, in order to facilitate the connection between their terminals, the transformer can provide low-voltage horizontal side-out, which is usually matched with low-voltage panels such as GGD, GCK, and MNS. The transformer manufacturer and the switch manufacturer should sign an interface coordination memorandum to confirm the detailed dimensions of the interface and ensure smooth on-site installation. (3) Low-voltage standard vertical side-out: Similar to the horizontal side-out, when a low-voltage distribution panel with vertically arranged busbars such as domino panels is selected, the transformer can provide low-voltage vertical side-out. Currently, my country's annual production of resin-insulated dry-type transformers has reached 10,000 MVA, making it one of the world's largest producers and sellers of dry-type transformers. With the widespread application of the low-noise (noise levels of distribution transformers below 2500kVA are controlled below 50dB) and energy-saving (no-load loss reduced by up to 25%) SC(B)9 series, the performance indicators and manufacturing technology of my country's dry-type transformers have reached world-class levels. The national architectural standard design atlas "Installation of Dry-Type Transformers," organized by the China Academy of Building Research, edited by the China Textile Industry Design Institute, and co-edited by Shunde Special Transformer Factory, has been completed and published. Approved by the Ministry of Construction, the atlas number is "99D268." It is publicly distributed nationwide by provincial and municipal architectural design standard stations. The atlas provides layout and installation methods for dry-type transformers suitable for various locations and lists multiple schemes for the interface cooperation between transformers and low-voltage PC panels for design and construction selection. With the widespread application of dry-type transformers, their manufacturing technology has also made significant progress. It can be predicted that future dry-type transformers will further develop in the following aspects. (1) Energy saving and low noise: With the introduction of new low-consumption silicon steel sheets, foil winding structure, stepped core joints, environmental protection requirements, in-depth noise research, and computer optimization design, the future dry-type transformers will be more energy-efficient and quieter. (2) High reliability: Improving product quality and reliability will be a relentless pursuit. A large amount of basic research will be conducted on electromagnetic field calculation, wave process, casting process, hot spot temperature rise, partial discharge mechanism, quality assurance system and reliability engineering, and reliability certification will be actively carried out to further improve the reliability and service life of dry-type transformers. (3) Environmental protection characteristic certification: Based on the European standard HD464, research and certification of the weather resistance (C0, C1, C2), environmental resistance (E0, E1, E2) and fire resistance (F0, F1, F2) characteristics of dry-type transformers will be carried out. (4) Large capacity: From dry-type transformers, mainly 50-2500kVA distribution transformers, to 10000-20000kVA/35kV power transformers. With the continuous increase in urban electricity load, urban power grid substations are increasingly penetrating into urban centers, residential areas, large factories and mines, and other load centers. 35kV large-capacity community center power supply transformers will be widely used. (5) Multifunctional combination: From single transformers to multifunctional combined transformers with air cooling, protective shell, temperature computer interface, zero-sequence current transformer, power metering, enclosed busbar and side outgoing lines. (6) Multi-field development: From distribution transformers as the main focus, to special transformers and multi-purpose fields such as power plant auxiliary transformers, excitation transformers, subway traction rectifier transformers, high current electric furnace transformers, nuclear power plants, marine and oil platform transformers. Among them, the dry-type traction transformers used in urban subways and rail transit have three voltage levels of 10, 20 and 35kV, and capacities of 800, 2500 and 3300kVA. To reduce harmonic pollution, the rectifier has been upgraded from 12 pulses to 24 pulses. The excitation transformer for the world's largest 840,000kW generator in the Three Gorges Dam project has been successfully developed by Shunte Factory and has passed national acceptance.