MÁY BIẾN ÁP PHÂN PHỐI LOẠI KHÔ

1. What is a dry distribution transformer?

A dry distribution transformer is a static electromagnetic device; it is used to convert AC power from one voltage level to another without changing the frequency; the windings are insulated with solid materials such as insulating paper, or epoxy casting, ... cooled by natural or forced air.

The working principle of dry transformers is based on the phenomenon of electromagnetic induction to convert the alternating current system at one voltage to another voltage.

Dry transformers have some advantages compared to oil transformers, including:

• Safer: No cooling oil is used to reduce the risk of fire and explosion; often used in urban works, mines. Works requiring high explosion protection.
• Environmentally friendly: No oil is used to minimize the risk of environmental pollution due to oil leakage as well as end-of-life waste treatment.
• Simple installation: Because there is no oil, the conditions for transporting and installing equipment belonging to the group of monolithic structures without liquids are simple.
• Simple operation and exploitation: Dry transformers do not need to check and maintain the oil tank and change the oil periodically like oil transformers, thereby reducing maintenance costs and time.

However, dry transformers also have some disadvantages such as:

• High investment cost: With the same capacity and voltage, the product price is always higher than that of oil transformers;
• The wire cannot be repaired when there is a problem;
• The epoxy material cannot be reused for the next life cycle.

2. Common types of dry transformers

With dry type distribution transformers, the magnetic circuit structure and the coils are not immersed in insulating liquid. Currently, there are 4 most popular types of dry transformers:

• Dry resin transformer – Cast Coil resin transformer (CRT): The transformer coil is covered with Epoxy resin and vacuumed. The structure of the machine meets the requirements for use in high humidity environments.
• Vacuum pressure impregnation transformer (VPI): The coil is tied in a vacuum protection box and uses polyester resin as the coil insulation material.
• Vacuum Pressure Encapsulated (VPE) transformer: High-class dry transformer with the coil placed in a vacuum box and using VPE silicon as the coil insulation material.
• Open transformer – Open Loud Transformer: Dry transformer is manufactured by heating the coil and dipping it in varnish at high temperature.

3. Structure of dry distribution transformer type: Cast Coil resin transformer (CRT)

A dry type distribution transformer has a general structure consisting of three main parts: Steel core, windings and transformer housing and other electrical equipment:

1. Steel core (Magnetic circuit)

The steel core is made from a material that conducts magnetically well and has high oxidation resistance, usually electrical steel sheets such as silicon steel with a thickness of 0.2 - 0.5mm, joined together to form a closed loop. The steel core consists of two main components: the column and the yoke. The column is where the winding wire is placed. The yoke is where the columns are connected to each other to form a closed magnetic circuit.

2. Winding Wire (Coil)

Winding of dry transformer:

+ Low voltage coils are usually made of copper or aluminum sheets wound into many layers with insulation.

+ High voltage coils are usually made of pure copper or aluminum wire, with a circular or rectangular cross-section wound into many turns and divided into layers, with cooling vents, and the insulation material is Epoxy resin.

3. Transformer and other electrical equipment enclosures

+ The casing of a dry-type transformer is usually made of steel and the design depends on the IP level of the project.

+ Temperature sensor: transformers are often equipped with temperature probes in the coil or steel core to monitor the temperature and control the cooling fan.

+ Cooling fan: Most of these transformers are equipped with a cooling fan to increase the efficiency of the machine. The fan is controlled through the load level of the machine.