Dry type Transformer

　　A Comprehensive Analysis of Dry-type Transformers

　　I. Definition and Working Principle

　　Definition: A dry-type transformer is a type of transformer that relies on air convection for cooling. Its iron core and windings are not impregnated with insulating oil but are insulated using solid insulating materials.

　　Working Principle: It operates based on the principle of electromagnetic induction, just like ordinary transformers. When the primary winding is connected to an AC power source, an alternating magnetic flux is generated. This alternating magnetic flux passes through both the primary and secondary windings simultaneously. According to the law of electromagnetic induction, an electromotive force is induced in the secondary winding, thereby achieving voltage transformation. For example, it can transform high-voltage electricity of 10kV into low-voltage electricity of 0.4kV to supply various low-voltage electrical equipment.

　　II. Classification

　　By Insulating Material and Cooling Method

　　Epoxy Resin Cast Dry-type Transformer: The windings are cast into a whole using epoxy resin, providing good insulating properties, mechanical strength, and moisture and dust resistance. Its heat dissipation mainly relies on natural air convection or forced air cooling. This type of transformer is commonly used in places with high requirements for fire and explosion prevention, such as high-rise buildings, shopping malls, and hospitals.

　　Open Ventilated Dry-type Transformer: The windings adopt special insulating materials and structures without being cast and encapsulated. They are directly exposed to the air and rely on natural air convection for heat dissipation. Its advantage is good heat dissipation performance, but its moisture and dust resistance are relatively poor. It is suitable for relatively dry and clean environments, such as some industrial plants.By Iron Core Material

　　Silicon Steel Sheet Iron Core Dry-type Transformer: It uses silicon steel sheets as the iron core material. Silicon steel sheets have high magnetic permeability and low losses, making them the most widely used iron core material for dry-type transformers. According to the manufacturing process of silicon steel sheets, they can be further divided into hot-rolled and cold-rolled silicon steel sheets, with cold-rolled silicon steel sheets having better performance.

　　Amorphous Alloy Iron Core Dry-type Transformer: It uses amorphous alloy material as the iron core. Amorphous alloy has excellent magnetic properties, and its no-load loss can be reduced by 60% - 80% compared to silicon steel sheet iron core transformers, offering significant energy-saving effects. However, the manufacturing process of amorphous alloy iron cores is complex, and the cost is relatively high.III. Characteristics

　　Advantages

　　Safety and Fire Prevention: Since it does not use insulating oil, there is no risk of transformer oil leakage, combustion, or explosion, greatly improving the safety of use. It is particularly suitable for places with strict fire prevention requirements.

　　Simple Maintenance: The daily maintenance workload is small. Unlike oil-immersed transformers, it does not require regular oil sample testing, oil changing, and other maintenance operations. Only regular inspections of the transformer's appearance, connection points, and operating temperature are needed.

　　Environmentally Friendly and Pollution-free: It does not produce oil pollution and is environmentally friendly. Meanwhile, amorphous alloy iron core dry-type transformers also have the characteristic of energy conservation, which complies with national environmental protection and energy conservation policies.

　　Flexible Installation: It has a relatively small volume and light weight, and the installation location is not restricted. It can be installed in various environments, both indoors and outdoors, and can be flexibly arranged according to actual needs.Disadvantages

　　High Cost: Compared to oil-immersed transformers of the same capacity, the manufacturing cost of dry-type transformers is higher, mainly due to the more complex insulating materials and manufacturing processes they adopt.

　　Capacity Limitation: Currently, the manufacturing of large-capacity dry-type transformers is difficult, and they are generally suitable for medium and small-capacity power transformation occasions. With the continuous progress of technology, the manufacturing level of large-capacity dry-type transformers is gradually improving, but oil-immersed transformers still have advantages in some ultra-large power projects.

　　Relatively Weak Overload Capacity: Its ability to withstand short-term overloads is not as good as that of oil-immersed transformers. When operating under overload conditions, the temperature rise is fast, which may affect the service life of the transformer.

　　IV. Application Scenarios

　　High-rise Buildings: High-rise buildings have limited space and extremely high requirements for fire safety. The safety, fire prevention, and simple maintenance characteristics of dry-type transformers make them the preferred transformer type for the power distribution systems in high-rise buildings, providing power for lighting, elevators, air conditioners, and other equipment in the buildings.

　　Commercial Centers: Commercial centers are densely populated with numerous electrical equipment, and have strict requirements for the reliability and safety of power supply. Dry-type transformers can meet their power demand, and their flexible installation methods facilitate arrangement within commercial centers.

　　Industrial Plants: In some industrial plants with high environmental requirements where oil pollution is not allowed, such as the electronics, pharmaceutical, and food industries, dry-type transformers are widely used. At the same time, for industrial places with relatively stable loads and dry environments, open ventilated dry-type transformers are also a cost-effective choice.

　　Subways, Tunnels, and Other Underground Projects: Underground projects have closed spaces and limited ventilation conditions, with strict requirements for fire safety. Dry-type transformers will not cause fires due to oil leakage and are suitable for use in these places, providing power保障 (power guarantee) for subway trains, tunnel lighting, ventilation, and other equipment.V. Key Points for Selection

　　Capacity Selection: Determine the rated capacity of the transformer based on the total capacity of the electrical equipment and the load development situation. Generally, the rated capacity of the transformer should be slightly larger than the total capacity of the electrical equipment, and a certain load development margin should also be considered. For example, if the total capacity of the electrical equipment in a place is 800kVA and it is expected that the load will increase by 20% in the next 5 years, a 1000kVA dry-type transformer can be selected.

　　Voltage Level: Ensure that the rated voltage of the primary winding of the transformer matches the supply grid voltage, and the rated voltage of the secondary winding is consistent with the voltage requirements of the electrical equipment. For example, in China's 10kV power distribution system, the rated voltage of the primary winding of the transformer is usually 10kV or 10.5kV, and the rated voltage of the secondary winding is 0.4kV.

　　Short-circuit Impedance: Select an appropriate short-circuit impedance according to the short-circuit capacity of the system and the overload capacity requirements of the transformer. A larger short-circuit impedance can limit the short-circuit current, but it will increase the voltage regulation ratio and losses of the transformer. Generally, the short-circuit impedance of dry-type transformers is in the range of 4% - 6%.

　　Insulation Level and Protection Level: Choose appropriate insulation levels and protection levels according to the requirements of the use environment. If the operating environment has a high temperature, a transformer with a higher insulation level should be selected; if the transformer is installed in a dusty, humid, or watery place, a housing with a higher protection level should be selected.