Dry-type transformerBecause of its fire prevention, safety, reliability, energy saving, maintenance-free, low loss, low noise, long life, small size, light weight and other advantages, it is widely used in substations, industrial and mining enterprises, hospitals, residential areas and other occasions. It has two main forms: epoxy resin insulation (abbreviated as ORDT) and paint impregnated non-sealed (abbreviated as OVDT). The former has mechanical strength and short circuit resistance, moisture, dust, corrosion resistance. After the end of life, only deep buried. The latter has good insulation pressure resistance, heat resistance and flame retardancy. The insulation class can reach H level. After the end of life, biodegradable recycling. Dry-type transformers are usually equipped with a housing. Its shell material, structure, in and out of the line, sealing heat dissipation, basic form, etc. are important factors that must be considered in the design of dry-type transformer shell.

Materials and structures.

The dry-type transformer shell can effectively close the dry-type transformer, play a role in safety protection, avoid the exposed conductor on the dry-type transformer from causing harm to the human body, prevent small animals such as snakes and rats from approaching or climbing to cause short-circuit accidents, and shield electromagnetic radiation. Reduce the impact of noise on the surrounding environment. Therefore, currently used dry-type transformers are usually equipped with a housing.

Material

Dry-type transformer shell is generally made of stainless steel, aluminum alloy, steel plate and other materials. Commonly used stainless steel brands are 201(17cr-4.5ni-6mn-n) and 304(18cr-9ni). 201 stainless steel has a slightly poor corrosion resistance and is easy to rust in the outdoor environment; 304 stainless steel has good corrosion resistance and can be used outdoors at a relatively high price; 316(17crni-12mo2) stainless steel has good corrosion resistance and high price, and is generally used Especially harsh environments. Aluminum alloy has good thermal conductivity and poor strength. Cold-rolled steel plates are often used for steel plates, which can be consistent with the switch cabinet color, good strength, low price, but long production cycle. In the design process, the appropriate material can be selected according to the user's economic situation and the use environment.

Structure

There are two main types of common structures for dry-type transformer housings: integrated and assembled. The former is mainly used in the early stages. The advantage is that there is no need to assemble on site and the installation is convenient, but the big problem is inconvenient transportation. If it is covered on the dry-type transformer, it is not convenient to fix the dry-type transformer on the transportation vehicle. If it is separately fixed on the vehicle with the dry-type transformer, it will occupy a larger vehicle space and the transportation cost will be higher. In addition, when the door of the distribution room is narrow, the integration will also encounter the problem of not being able to enter the distribution room. Currently, most choose the latter. The assembled dry-type transformer housing consists of left and right frames, front and rear door frames, a top cover and connecting accessories. Can be assembled on site, convenient transportation, convenient access to the power distribution room.

The level of operating and maintenance personnel in individual locations is limited. The housing door of dry-type transformer is electrified and opened, causing personal injury accident that should not occur. Therefore, the designer should clearly require in the technical agreement that the front and rear doors should be equipped with travel switches and electromagnetic locks. The travel switch can be connected to the secondary switch circuit of the high-voltage switch cabinet. Once the door is opened, the travel switch acts to start the secondary switch circuit of the high-voltage switchgear to trip to ensure the safety of the operator. Even if individual users do not connect the travel switch to the high-voltage switch cabinet, this protection is meaningless. The electromagnetic lock (introducing 220V power from the transformer) can also ensure that the door cannot be opened unless it is urgently unlocked. The high-voltage column insulator on the dry-type transformer can also be replaced by a sensor, and a live display is installed on the door to visually see the live state of the transformer.

The dry-type transformer enclosure shall be assembled in stainless steel. The entry and exit method shall be selected according to the project site conditions. IP20 is applied to indoor protection level, IP23 is applied to outdoor. The designer should consider the external dimensions of the dry-type transformer enclosure. In addition to ensuring a safe distance, the heat dissipation performance should also be considered and the foundation should be accurately matched.