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

1. Capacity selection of distribution transformer

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 cart" will appear, the transformer utilization rate will be low, and the no-load loss will increase. If the capacity is too small, the transformer will be overloaded and the loss will increase. In severe cases, the transformer may be overheated or burned. Therefore, the distribution transformer must be reasonably selected according to the normal load and heavy load of the installation area.

2. Selection of distribution transformer model

is mainly to select new models of high-efficiency energy-saving distribution transformers that use new technologies, new materials, and new processes to reduce energy consumption.

(1) Use amorphous alloy transformer. Amorphous alloy iron core transformer is a transformer made of a new type of magnetic material-amorphous alloy with an iron core. Compared with silicon steel sheet as an 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, and is especially suitable for rural power grids and places where the transformer load rate is low.

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

For example: three-phase five-column oil-immersed amorphous alloy power (200kVA) transformer, no-load loss is 0.12kW, load loss is 2.6kW; three-phase five-column oil-immersed S9 distribution (200kVA) transformer, no-load loss is 0.48kW, the load loss is 2.6kW, the load loss value of the two types of distribution transformers is the same, it can be calculated that an amorphous alloy (200kVA) transformer can reduce the power loss each year compared with the same capacity S9 distribution transformer:

△Ws=8760×(0.48-0.12)=3153.6kW·;h

It can be seen from the above calculation that the energy saving effect of the three-phase amorphous alloy core distribution transformer is obvious. Since the oil tank is designed as a fully sealed structure, the oil in the transformer is isolated from the outside air, which prevents oxidation of the oil in the transformer, prolongs the service life of the product, and saves maintenance costs.

(2) Choose a fully enclosed distribution transformer with a wound iron core. The fully enclosed distribution transformer with coiled iron core is a new generation of low-noise, low-loss transformers developed in recent years. The coiled iron core has no joints, and all magnetic flux magnetization directions are the same as the rolling direction of silicon steel sheets, which makes full use of silicon steel. For the orientation performance of the sheet, under the same conditions, compared with the laminated iron core, the no-load loss of the wound core is reduced by 7% to 10%, and the no-load current can be reduced by 50% to 70%. Because the transformer high and low voltage coils are continuously wound on the core column, the windings are tight and the concentricity is good, which further enhances the anti-theft performance of the product, the noise is reduced by more than 10 decibels, and the temperature rise is lower by 16-20K.

Because the no-load current of this type of transformer is small, 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 coiled iron core products have strong resistance to sudden short circuits and good operational reliability.

(3) Select on-load automatic capacity adjustment distribution transformer. The on-load automatic capacity-adjusting transformer is to connect the transformer coils in series and parallel. The low-voltage coil of the transformer is connected with an on-load capacity-adjusting switch, and a current transformer and an automatic controller are connected to the low-voltage side of the transformer. The transformer is provided through the current transformer. In the load state, the automatic controller can automatically adjust gears and run according to the load. The on-load automatic capacity-regulating transformer solves the long-term shortcomings of high voltage transformation loss of the electromagnetic coil and the need for manual operation, and further reduces the no-load loss and no-load current of the transformer. On-load automatic capacity-regulating transformers are especially suitable for users with scattered loads, strong seasonality, and low average load rates.

3, the choice of the installation location of the distribution transformer

In addition to meeting the site and environmental requirements, the transformer installation location should also consider placing the distribution transformer close to the center of the load to shorten the power supply radius as much as possible and control it within 500 meters. For stations with scattered loads, most of the loads should also be controlled within 500 meters as far as possible.

The choice of installation location of distribution transformer

There is no uniform regulation on the installation location of distribution transformers, and the following aspects should usually be considered.

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

2. Avoid flammable and explosive places. It should also avoid polluted areas, which mainly refer to places that are harmful to insulation and wires, such as casting, smelting, and chemical, fertilizer and other production sites. At the same time, it should be considered that the terrain should be high to prevent flooding.

4. High-voltage inlet and low-voltage outlet should be convenient. Mainly should consider the horizontal and vertical safety distances of high and low entry and exit poles and wires to the ground and to the surrounding buildings.

5. Choose the location of the power transformer to be convenient for construction, operation and maintenance. It must also be considered that there is a certain development space and planning.

Distribution transformer installation method

There are many ways to install distribution transformers, such as horizontal-bar transformer stands, parallel-bar transformer stands, ground-type transformer stands, and floor-standing transformer stands.

(1) Horizontal bar transformer station. The transformer, outdoor drop-out fuse, high-voltage down conductor, and lightning rod are all installed on the same pole. It is characterized by small footprint, simple structure, convenient assembly, and material saving. It is suitable for installation of 10/0. 4kV and capacity of 50kVA. The following distribution transformers.

(2) Double pole transformer station. Install on two poles 2.5～3m above the ground. Install a busbar frame 2m above the platform. The high-voltage lead wire is connected to the busbar frame. The pole is also equipped with a cross arm and an outdoor drop-out fuse, lightning arrester and lead wire are installed. This kind of transformer is stronger than the single pole transformer, but uses more materials and higher cost. It is suitable for distribution transformers with a voltage of 10/0.4kV and a consumption of 50-320kVA.

(3) Ground type transformer station. Build a pier with a height of 1.7 to 2m with bricks, and place the transformer on it. This type of transformer station can be divided into two forms: with and without distribution room, and no one can live in the distribution room. Its characteristic is that the terminal rod of the high-voltage line can double as the start-end rod of the low-voltage line.

(4) Floor-standing transformer table. Place the transformer on a low platform on the ground, which is suitable for large-capacity transformers above 500kVA. This type of transformer platform occupies a large area, but it is convenient to disassemble, assemble, and transport. In order to prevent flooding and safety, fences and warning signs must be installed around the transformer platform. The bottom foundation of the transformer must be higher than the height of the flood, but not less than 0.3m.

The indoor power distribution room is to place the transformer indoors for operation, which has the advantages of safety and cleanliness, but the power distribution room must meet the first-class fire resistance standard, have good ventilation conditions, fire doors and windows, and can prevent small animals and rainwater from entering. Indoor passages should be spacious to meet the requirements of installation regulations.