一 Composition of oil-immersed transformer

The main structure of the oil-immersed transformer is composed of the body, the oil tank, the cooling device, the protection device and the outlet device, as shown in the following figure.

1,The body comprises an iron core, a winding, an insulated lead and a tap-changer.

2, the oil tank includes the oil tank body and the oil tank accessories (oil discharge valve, floor, car, nameplate, etc.).

3, the cooling device includes a radiator and a cooler.

4, the protection device includes oil storage tank, oil level gauge, safety airway, moisture absorber, thermometer and gas relay.

5,The outlet device includes high and low pressure bushing.

二The structure of the oil-immersed transformer components

1.Iron core

The iron core of the transformer is the magnetic circuit part and the skeleton of the body, which is composed of an iron core column, an iron yoke and a clamping device. The part of the jacket winding is an iron core post. The part that connects the core pillars to form a closed magnetic circuit is called the yoke. The clamping device is used to clamp the core, clamp the winding and fix the lead. The coil is fitted on an iron post, and the yoke is used to close the entire magnetic circuit. The core is made of silicon steel sheet, which has good magnetic permeability and small hysteresis loss. There are A, B, C three-phase winding on the iron core, each phase winding is divided into high voltage winding and low voltage winding, generally the inner layer around the low voltage winding, the outer layer around the high voltage winding. In order to reduce the hysteresis and eddy current loss in the iron core, the iron core is commonly made of silicon steel sheet with a high silicon content and a thickness of 0.35~0.5mm, and the sheet is coated with insulating paint.

2.Winding

The winding is the circuit part of the transformer, which is generally made of insulated enameled, paper-wrapped aluminum or copper wire. According to the different arrangement of high and low voltage windings, the windings are divided into concentric and overlapping types. For concentric winding, in order to facilitate the winding and core insulation, the low-voltage winding is usually placed near the core column; For overlapping windings, the low voltage winding is usually placed close to the yoke in order to reduce the insulation distance.

3.Insulation sleeve

The wire outlet device is the insulation sleeve, which is composed of a central conductive rod and a porcelain sleeve. The insulation bushing is the connecting part of the high and low voltage coils of the power transformer and the external line. The leads of the high and low voltage coils of the transformer are drawn from the tank to the outside of the tank, and the leads are insulated from the grounded tank. The bushing not only acts as the lead insulation to the ground, but also acts as the fixed lead. Therefore, the bushing of the power transformer must have the specified voltage strength and sufficient mechanical strength and good thermal stability. There are many forms of bushing, which can be divided into pure porcelain, porcelain oil-filled type and capacitor type according to different structures. In order to reduce the leakage caused by dust and rain, the porcelain insulation sleeve has a multi-stage umbrella shape.

4. Oil storage tank

The oil storage tank, also known as the oil pillow, is used when the transformer is in operation, the oil expands due to heat, the transformer stops running or the temperature decreases so that the oil shrinks, and the oil inside the transformer is always full. At the same time, the contact surface between the transformer and the air is also reduced to reduce the impact of oxidation and moisture on the transformer oil.

5. Heat dissipation pipe

For small capacity transformers, the heat generated by the winding and the iron core is cooled naturally through the contact between the transformer oil and the inner wall of the tank, and the contact between the outer wall of the tank and the cold air outside, without any additional cooling device. If the transformer capacity is slightly larger, the heat dissipation tube can be welded on the outer wall of the fuel tank to increase the heat dissipation area. The heat energy generated by the iron core and winding in operation makes the oil temperature rise, the volume expands and the density becomes smaller, the oil rises into the heat dissipation tube, and then the oil temperature into the heat dissipation tube decreases, the volume shrinks and the density increases, and the heat from the iron core and the winding is dissipated through the natural circulation of the oil.

6. Moisture absorber

There is a moisture absorber on the oil storage cabinet, which is equipped with a glass, and contains a desiccant to absorb the moisture in the air entering the oil storage cabinet.

7. Safe airway

The safety airway, also known as the explosion-proof tube, is a trumpet shaped tube installed on the top of the transformer, and the tube mouth is sealed with a diaphragm. Its function is that when a short circuit fault occurs inside the transformer, the transformer oil decomposing into a large number of gases causes the oil pipe pressure to be large, the safety port diaphragm is broken first, and the oil gas is ejected from it, reducing the pressure in the tank and preventing the tank from deforming or exploding due to the sudden increase in pressure.

 

An oil-immersed transformer is a (static) electrical device that changes the voltage and current of an AC supply without changing the frequency. At the same frequency, the AC voltage and current of one system are converted into the AC voltage and current of at least another system by electromagnetic induction, thus transmitting electrical energy. Therefore, oil-immersed transformers should generally have at least two windings of different turns (i.e. rated voltage) and be connected to at least two systems with different AC voltage values.

 

Oil-immersed transformer is a kind of AC electrical equipment that works by electromagnetic induction. Therefore, it must have an iron core as a magnetic circuit; It must have at least two windings with different common turns (i.e. rated voltage); Due to the potential difference between the winding and the ground, there must be a corresponding insulation system. In other words, the three basic parts of the core, winding and insulation system are indispensable components of any oil-immersed transformer.

 

In addition, oil-immersed transformer bushings of the corresponding insulation class are required in order to lead the windings from the circuit to the outside; In order to change the number of turns of the oil-immersed transformer winding as needed, a tap-changer is needed; In order to monitor the temperature of the oil-immersed transformer during operation and change the cooling state of the oil-immersed transformer in time according to the temperature, a temperature measuring element is needed to measure the temperature (even measure the winding temperature), and the measured temperature is used to control the different operating modes of the cooling system (if any) or alarm; For the safe operation of the oil-immersed transformer, other necessary measurement and protection devices are also required.

 

The oil-immersed transformer requires the transformer oil as the cooling medium, the oil tank as the oil tank, and the required accessories and cooling system are installed on the oil tank. In order to adjust the transformer oil volume change caused by the temperature change during operation, it is necessary to set the oil storage tank. Some on-load regulating transformers are also equipped with on-line on-load switching oil filter device; Some oil-immersed transformers are also equipped with on-line fire extinguishing device, oil gas analysis device, partial discharge monitoring device, etc.

 

In oil-immersed transformers, transformer oil is not only a cooling medium, but also a good insulating material. It is no exaggeration to say that the wide application of alternating current benefits from transformers. Therefore, transformers have been widely used in modern human society.

 

三Introduction to oil-immersed transformers

 

1. What is oil-immersed transformer

An oil-immersed transformer is a type of transformer that is insulated and cooled by introducing a special insulating oil inside the transformer. It consists of several coils (main coil and secondary coil) and an iron core designed to meet a variety of voltage, current and power requirements.

This special oil not only has excellent insulation properties, but also can effectively cool the transformer. At the same time, the oil-immersed transformer can improve the mechanical strength and prolong the transformer life.

2. Working principle of oil-immersed transformer

The working principle of the oil-immersed transformer is very simple. The transformer center contains an iron core in which two coils are wound. When the AC voltage passes through the main coil, the magnetic flux builds up in the core and then switches to the secondary coil, which generates the desired voltage.

Oil-immersed transformers operate by continuously storing energy in a magnetic field and passing it through an interconnected loop, eventually converting it into voltage and current outputs.

3. Oil-immersed transformer function

Oil-immersed transformers play a vital role in power systems. It is commonly used to convert high and low voltages to transmit power over long distances, regulate voltage, isolate and coupling.

In addition, oil-immersed transformers can also be used in power plants, substations, and various large-scale industrial and civil facilities. These devices require stable voltage and current to ensure normal operation, and oil-immersed transformers provide them with the necessary power.