Dry type transformer: relying on air convection for cooling, it is generally used for small capacity transformers such as local lighting and electronic circuits. In power systems, dry type transformers are commonly used for steam turbine transformers, boiler transformers, ash removal transformers, dust removal transformers, desulfurization transformers, etc., with a transformation ratio of 6000V/400V, used for loads with a rated voltage of 380V. The cross flow cooling fan used in dry-type transformers is a type of fan with no guide vanes at both the inlet and outlet, specifically designed for cooling dry-type transformers Flow fan. Its main components include: dedicated single-phase or three-phase low-power induction asynchronous motor, cross flow impeller, casing, and air guide device.         

Temperature control system for dry-type transformer

The safe operation and service life of dry-type transformers largely depend on the safety and reliability of the transformer winding insulation. The winding temperature exceeding the insulation withstand temperature causes insulation damage, which is one of the main reasons why transformers cannot work normally. Monitoring and alarm control of transformer operating temperature are very important. This article will briefly introduce the GTB series temperature control system.         

(1) Automatic control of fan: Temperature signals are measured by a Pt100 thermistor embedded at the hottest point of the low-voltage winding. The transformer load increases and the operating temperature rises. When the winding temperature reaches 110 ℃, the system automatically starts the fan for cooling; When the winding temperature drops to 90 ℃, the system automatically stops the fan.         

(2) Overtemperature alarm and tripping: The winding or iron core temperature signal is collected through the PTC nonlinear thermistor embedded in the low-voltage winding. When the temperature of the transformer winding continues to rise and reaches 155 ℃, the system outputs an over temperature alarm signal; If the temperature continues to rise to 170 ℃, the transformer cannot continue to operate and an over temperature trip signal must be sent to the secondary protection circuit to quickly trip the transformer.         

(3) Temperature display system: By using Pt100 thermistor embedded in the low-voltage winding to measure temperature changes, the temperature of each phase winding can be directly displayed (three-phase inspection and maximum value display, and historical highest temperature can be recorded). The highest temperature can be output as an analog signal of 4-20mA. If it needs to be transmitted to a remote computer (up to 1200m away), a computer interface can be added, and one transmitter can be used to monitor up to 31 transformers simultaneously. The system's over temperature alarm and tripping can also be triggered by Pt100 thermistor signals, further improving the reliability of the temperature control protection system.

Protection methods for dry-type transformers

According to the characteristics of the usage environment and protection requirements, dry-type transformers can choose different casings. Usually, IP20 protective casing is used to prevent solid foreign objects with a diameter greater than 12mm and small animals such as mice, snakes, cats, and sparrows from entering, causing malignant faults such as short circuits and power outages, and providing a safety barrier for live parts. 

Cooling method of dry-type transformer

The cooling methods for dry-type transformers are divided into natural air cooling (AN) and forced air cooling (AF). During natural air cooling, the transformer can operate continuously for a long time at its rated capacity. When forced air cooling is used, the output capacity of the transformer can be increased by 50%. Suitable for intermittent overload operation or emergency overload operation; Due to the significant increase in load loss and impedance voltage during overload, it is in a non economic operating state and should not be subjected to long-term continuous overload operation.  

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?  

(1) When choosing to calculate transformer capacity, it is advisable to reduce it appropriately: fully consider the possibility of short-term impact overload of certain equipment such as steel rolling and welding - try to use the strong overload capacity of dry-type transformers to reduce transformer capacity; For places with uneven loads, such as residential areas with nighttime lighting, cultural and entertainment facilities, and shopping malls with air conditioning and daytime lighting, their overload capacity can be fully utilized by appropriately reducing the transformer capacity to keep their main operating time at full load or short-term overload.  

(2) Can reduce backup capacity or quantity: In some places, the requirement for the backup coefficient of transformers is high, resulting in the selection of transformers with large capacity and multiple quantities for engineering. By utilizing the overload capacity of the transformer, it can be compressed when considering its reserve capacity; When determining the number of backup units, it can also be reduced. When the transformer is operating under overload, it is important to monitor its operating temperature: if the temperature rises to 155 ℃ (with an alarm), measures should be taken to reduce the load (by subtracting some secondary loads) to ensure safe power supply to the main load.

Low voltage outgoing line method and interface coordination of dry-type transformer

Dry type transformers do not require them to be placed in separate rooms due to the lack of oil, which means there are no issues such as fire, explosion, or pollution. Therefore, electrical codes and regulations do not require dry-type transformers to be placed in separate rooms. Especially with the new SC (B) 9 series, losses and noise have been reduced to new levels, creating conditions for transformers and low-voltage panels to be placed in the same distribution room.  

(1) Low voltage standard enclosed busbar: If enclosed busbar (also known as plug-in busbar or dense busbar trunking) is selected for engineering wiring, the corresponding transformer can provide standard enclosed busbar terminals for easy connection with external busbars. Products with shell (IP20), with enclosed busbar flange provided on the top cover of the shell; Products without casing (IP00), only provide enclosed busbar terminal blocks.  

(2) Low voltage standard horizontal busbar side outlet: When the transformer is placed side by side with the low-voltage distribution panel, in order to facilitate the connection between its terminals, the transformer can provide low-voltage horizontal busbar side outlet, which is usually matched with low-voltage panels such as GGD, GCK, MNS, etc. The transformer factory and the switch factory should sign an interface coordination memorandum to confirm the detailed dimensions of the coordination interface and ensure smooth on-site installation.  

(3) Low voltage standard vertical busbar side outlet: Similar to horizontal busbar side outlet, when using domino screens or other busbars as vertically arranged low-voltage distribution panels, transformers can provide low-voltage vertical busbar side outlet.  

At present, the annual output of resin insulated dry-type transformers in China has reached 10000MVA, making it one of the countries with the largest production and sales volume of dry-type transformers in the world.

With the promotion and application of the SC (B) 9 series with low noise (below 2500kVA distribution transformer noise has been controlled within 50dB) and energy-saving (no-load loss reduced by 25%), the performance indicators and manufacturing technology of dry-type transformers in China have reached the world's advanced level. With the promotion and application of dry-type transformers, their production and manufacturing technology has also made significant progress. It can be predicted that future dry-type transformers will further develop in the following areas.

(1) Energy saving and low noise: With the introduction of new low consumption silicon steel sheets, foil winding structures, stepped iron core joints, environmental protection requirements, in-depth noise research, as well as new materials, processes, and technologies such as computer optimization design, future dry-type transformers will be more energy-efficient and quieter.  

(2) High reliability: Improving product quality and reliability will be people's unremitting pursuit. A large amount of basic research has been conducted on electromagnetic field calculation, wave process, casting process, hot spot temperature rise, partial discharge mechanism, quality assurance system, and reliability engineering, actively conducting reliability certification to further improve the reliability and service life of dry-type transformers.  

(3) Environmental characteristic certification: Based on the European standard HD464, research and certification will be conducted on the weather resistance (C0, C1, C2), environmental resistance (E0, E1, E2), and fire resistance (F0, F1, F2) characteristics of dry-type transformers.  

(4) with the continuous increase of urban electricity load, urban power grid regional substations are becoming more and more deeply integrated into load centers such as urban centers, residential areas, and large factories and mines. 35kV high-capacity central power transformers for residential areas will be widely used.