How many windings are there in distribution transformer?

Changing the performance of distribution transformers and reducing voltage loss indicators are of great significance to improving system reliability and power system energy saving.

Low-loss distribution transformers can greatly reduce losses, greatly reduce the power loss of the grid, and have relatively low cost, small size and light weight. Therefore, there will be a very wide range of applications in the process of power grid transformation. The operation, structure and selection of S11 series distribution transformer windings are comprehensively discussed.

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distribution transformer
distribution transformer

What is distribution transformer winding?

The transformer circuit in the power system is mainly divided into windings, high-voltage leads and low-voltage leads.

Among them, the winding is the main component of the transformer’s electricity, which plays an important role in transformer conversion and power transmission and distribution.

The wire must meet the following requirements: good electrical conductivity, sufficient heat resistance of the insulating paint layer, and a certain degree of corrosion resistance.

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Precautions for transformer winding

  • Electric strength. After long-term operation of the transformer, the insulation effect of the winding must withstand lightning impulse voltage, operating overvoltage and transient overvoltage. The internal overvoltage is mainly composed of operating overvoltage and transient overvoltage.
  • Heat resistance degree. Whether the winding can be heat-resistant can be seen from the following two aspects. The first is that when the transformer is in operation, if a short circuit problem occurs in any circuit, the winding can withstand the heat generated by this part of the short-circuit current. The function will not be damaged; on the other hand, under the long-term working current state, the service life of the winding insulation is higher than 35 years.
  • Mechanical strength. In the case of sudden short circuit or normal operation of the electricity, the winding damage caused by the electromotive force will happen from time to time, mainly divided into the following situations:
    1) Damage caused by electric power under normal operating conditions.
    2) When a sudden short circuit occurs, the damage is mainly caused by lateral force.

Types and selection of transformer windings

The composition of layer winding

The layered winding is shaped like a cylinder and is made by continuous firing. The following mainly introduces the basic composition and application range of several common cylinder sets:

  • Single-layer cylindrical type. The reason why single-layer cylindrical group machinery is less used is due to the disadvantage of poor stability. The single-layer cylindrical type with high filling system that is often used in the market is an on-load tapping transformer. With the increase in the output of on-load tap-changing transformers, the windings of on-load tap-changing transformers have increased.
  • Double-layer and multi-layer cylindrical type. Double-layer and four-layer cylindrical type are generally used for 400V low-voltage windings, double-layer cylindrical windings, simple structure and high production efficiency, often used for small and medium-sized immersion types of 35KV and below Transformers, multilayer windings are generally used for low-voltage or high-voltage windings of 3KV and above.
  • “Aluminum foil cylinder type” is similar to the multilayer type. The layered insulation of each layer in the middle is mainly inter-turn insulation. The winding can be automatically wound. The production efficiency is higher than that of small and medium-sized transformers and dry-type transformers, and the space utilization is good.

Structural characteristics of layer winding

The advantages of layered windings are simple winding and good process performance, but they have the characteristics of poor stability of the end support. Due to the large inter-layer capacitance, the low capacitance to ground, and the uniform voltage distribution, the multilayer winding has slight vibration. Therefore, it has good impact performance against lightning impact.” But considering the problem of poor axial stability, the use of this equipment is greatly restricted.

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The basic structure of the pie winding

The structures of several commonly used parallel windings are as follows:

The structure of parallel winding is mainly divided into continuous type, inner shielded type, spiral type, interleaved type and S-shaped type:

  • Continuous. The line segments of continuous windings are mostly even or multiples of 4, and the number of segments is more than 30 or more than 100. The number of turns of each line segment, the outer winding is an integer, and the inner winding is a fraction. By using this kind of winding, the end of the winding can be changed. Colleagues He Weitou are exposed on the outside of the winding, making it easier to use.
  • Inner shield type. The inner shielded winding is formed by inserting a screen wire that increases the longitudinal capacitance inside the continuous line segment, so it is also called the plug-in capacitive type. Its appearance is very tangled. The number of turns of each free line segment inserted can be freely changed as needed.
  • Spiral. The spiral winding is mainly used in low voltage and high current transformers. The spiral winding is mainly a single-layer cylindrical winding formed by winding multiple wires, and the line formed by the inter-turn oil passage, so it is also a parallel winding.

Structural characteristics of pie winding

In the market, a parallel winding machine is widely used and widely used. This machine has the characteristics of good heat dissipation performance. It is mainly composed of tangled windings and inner shielded windings. It can increase the longitudinal capacitance of the windings at the same time. Changing and distributing the impulse voltage of the winding, good impulse performance.

Winding material

The conductive materials used in oil-immersed transformer windings are mainly copper and aluminum. Because aluminum winding transformers have poor mechanical strength, large load loss, and high welding quality requirements, the current market mainly uses copper as the conductor material of the transformer.

Winding insulation

Winding insulation is mainly insulation between turns, layers, parallels, end rings, and insulated downlights. The front sound constitutes the longitudinal insulation of the winding, and the rear sound constitutes the main insulation of the winding. Insulating materials have the problem of aging when the working temperature is high. In order to prevent similar situations, high heat-resistant paper-clad copper-style wires are used to wind. “In order to meet the requirements of S11 series oil-immersed transformers, aromatic polyamides are used. Insulating paper, polyamide insulating paper has good electrical and mechanical properties, moisture resistance and high temperature resistance, which can fully meet the requirements of the S11 series.

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