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The selection of distribution transformer includes the selection of distribution transformer capacity, model and transformer installation location.

1. Selection of distribution transformer capacity

The capacity of the distribution transformer should be selected according to the current situation and development trend of the area. If the capacity is selected too large, the phenomenon of "big horse-drawn trolley" will appear, the utilization rate of the transformer is low, and the no-load loss will increase. Select the capacity is too small, will cause the transformer overload, loss also increased, serious when may lead to transformer overheating or burning, therefore, the distribution transformer must be installed according to the area usually load and heavy load for a reasonable choice.

2. Selection of distribution transformer model

The main selection is the application of new technologies, new materials, new technology of new models of high-efficiency energy-saving distribution transformers, reduce energy consumption.

(1) choose amorphous alloy transformer. Amorphous alloy iron core transformer is a transformer made of a new type of magnetic material-amorphous alloy iron core. Compared with silicon steel sheet as iron core transformer, the no-load loss is reduced by about 80% and the no-load current is reduced by about 85%. It is a distribution transformer with ideal energy-saving effect at present, especially suitable for rural power grid and places with low load rate of transformer.

Compared with the S9 type distribution transformer, the three-phase amorphous alloy core distribution transformer has a considerable annual energy saving.

For example, a three-phase five-column oil-immersed amorphous alloy power (200kVA) transformer has a no-load loss of 0.12kW and a load loss of 2.6kW. Three-phase five-column oil-immersed S9 power distribution (200kVA) transformer has no-load loss of 0.48kW and load loss of 2.6kW. The load loss values of the two types of distribution transformers are the same, it can be calculated that an amorphous alloy (200kVA) transformer can reduce the annual power loss compared to the S9 distribution transformer with the same capacity:

　　△Ws=8760×(0.48-0.12)=3153.6kW·;h

Through the above calculation, it can be seen that the energy saving effect of the three-phase amorphous alloy core distribution transformer is obvious. Because the oil tank is designed as a fully sealed structure, the oil in the transformer is isolated from the outside air, the oxidation of the oil in the transformer is prevented, the service life of the product is prolonged, and the maintenance cost is saved.

(2) Selection of coil core fully sealed distribution transformer. The coiled iron core fully sealed distribution transformer is a new generation of low noise and low loss transformer developed in recent years. The coiled iron core has no seams, and the magnetization direction of all magnetic flux is the same as the rolling direction of silicon steel sheet, giving full play to the orientation performance of silicon steel sheet. Under the same conditions, compared with laminated iron core, the no-load loss of coiled iron core is reduced by 7% ~ 10%, and the no-load current can be reduced by 50% ~ 70%. As the transformer high and low voltage coil in the core column continuous winding, winding tight, good concentricity, more enhanced the anti-theft performance of the product, noise drop more than 10 decibels, low temperature rise 16~20K.

Due to the small no-load current of this type of transformer, the loss reduction effect is obvious, which can improve the network power factor, reduce the investment of reactive power compensation equipment, save equipment investment and reduce operating energy consumption. In addition, the coil core product has strong resistance to sudden short circuit and good operation reliability.

(3) Select the on-load automatic capacity adjustment distribution transformer. On-load automatic capacity adjustment transformer adopts series and parallel connection for transformer coils, an on-load capacity adjustment switch is connected to the low-voltage coil of the transformer, a current transformer and an automatic controller are connected to the low-voltage side of the transformer, and the load state of the transformer is provided through the current transformer, and the automatic controller can automatically adjust and operate according to the load. The on-load automatic capacity regulating transformer solves the shortcomings of high transformer voltage loss of electromagnetic coil and manual operation for a long time, and further reduces the no-load loss and no-load current of the transformer. Load automatic capacity transformer is particularly suitable for load dispersion, strong seasonal, low average load rate of users.

3. Selection of installation position of distribution transformer

Transformer installation location in addition to meet the site, environmental requirements, but also consider the distribution transformer close to the load center location, so that the power supply radius as short as possible, controlled within 500 meters. For the relatively scattered load area, most of the load should be controlled within 500 meters as far as possible.

Selection of Installation Position of Distribution Transformer

Distribution transformer installation location does not have a uniform provisions, usually should consider the following aspects of the problem.

1. The distribution transformer should be close to the load center, and the power supply radius should not be greater than 0.5km.

2. Flammable and explosive places should be avoided. Also should avoid filthy areas, mainly refers to the insulation and wire harmful places, such as casting, smelting and chemical, fertilizer and other production sites. At the same time, it should also be considered that the terrain should be high to prevent flooding.

4. High-voltage incoming line and low-voltage outgoing line shall be convenient. The horizontal and vertical safety distances of equipment and wires of high and low incoming and outgoing poles to the ground and surrounding buildings shall be mainly considered.

5, choose the location of the installation of power transformer to facilitate the construction and operation and maintenance. Also consider that there is a certain development space and planning.

Distribution transformer installation method

Distribution transformer installation methods include horizontal bar transformer table, parallel bar transformer table, ground table transformer table, floor type transformer table, etc.

(1) Horizontal bar transformer table. Its transformer, outdoor drop fuse, high-voltage down lead, lightning rod are installed on the same pole, characterized by small footprint, simple structure, convenient assembly, material province, suitable for installation of 10/0. 4kV, capacity 50kVA distribution transformer.

(2) Double pole transformer table. Install on two poles 2.5~3m above the ground, install bus bars 2m above the bench, connect high-voltage leads to bus bars, install cross arms on the poles and install outdoor drop fuses, lightning arresters and leads. This kind of transformer is stronger than single pole transformer, but it uses more materials and has higher cost. It is suitable for distribution transformers with voltage of 10/0. 4kV and dosage of 50 ~ 320kVA.

(3) the ground table transformer table. A 1.7~2m high pier is made of brick, and the transformer is placed on it. This kind of transformer station can be divided into two forms: with and without distribution room. No one can live in the distribution room. Its characteristic is that the terminal rod of the high-voltage line can double as the beginning rod of the low-voltage line.

(4) Floor type transformer table. The transformer is placed on the ground low platform, suitable for large-capacity transformers above 500kVA. This kind of transformer platform covers an area of more, but it is convenient to disassemble and transport. In order to prevent flooding and safety, fences and warning signs must be installed around the transformer station. The bottom foundation of the transformer must be higher than the height of the flood, but not less than 0. 3m.

Indoor distribution room is the transformer placed in the indoor operation, with safety, clean and other advantages, but the distribution room must reach a fire-resistant standard, with good ventilation conditions, fire-resistant doors and windows, and can prevent small animals and rainwater immersion. Indoor access shall be spacious to meet the requirements of the installation regulations.