Introduction To Oil-Immersed Transformers

Cooling method
(1) Oil-immersed transformers usually use three cooling methods: oil-immersed self-cooling, oil-immersed air-cooling and forced oil circulation.
(2) The oil-immersed self-cooling type relies on the natural convection of oil to remove heat. The oil-immersed air-cooled type is based on the oil-immersed self-cooling type, with an additional fan blowing air to the fuel tank and oil pipes to enhance heat dissipation. Forced oil circulation uses an oil pump to pump the hot oil in the transformer to the outside of the transformer, cool it, and then send it into the transformer.

oil immersed hermetically sealed type transformer

Structural function
In the main substation of the urban rail transit power supply system, the main transformer usually uses a three-phase oil-immersed transformer, as shown in the figure. Oil-immersed transformers are mainly composed of iron core, windings, oil tanks, voltage regulating devices, radiators, oil pillows, gas relays, insulating sleeves, explosion-proof pipes and other parts.

1.Iron core

The iron core is composed of stacked silicon steel sheets with good magnetic permeability, which forms a closed magnetic flux path. The primary and secondary windings of the transformer are wound around the iron core.

The transformer core is divided into two structures: core type and shell type. Currently, the transformers widely used are core type structures. The core type iron core is composed of south iron core pillar and iron yoke. There is an oil passage inside the iron core of the oil-immersed transformer to cool the iron core, which facilitates the circulation of transformer oil and also enhances the heat dissipation effect of the equipment.
 

2. Winding

The winding, also known as the coil, is the conductive circuit of the transformer. It is wound into a multi-layer cylindrical shape using copper or aluminum wire. The primary and secondary windings are concentrically placed on the iron core column. For insulation, generally the low-voltage winding is inside and the high-voltage winding is outside. Insulating material is wrapped around the wires to ensure insulation between wires and between wires and ground.

3. Fuel tank

The oil tank is the shell of the oil-immersed transformer. In addition to containing oil, it is also used to install other components.

4. Pressure regulating device

The voltage regulating device is set up to ensure the stability of the secondary voltage of the transformer. When the power supply voltage changes, the voltage regulating device is used to adjust the transformer tap changer to ensure the stability of the secondary side output voltage. Voltage regulating devices are divided into two types: on-load voltage regulating devices and off-load voltage regulating devices.

5. Radiator

The radiator is installed on the wall of the oil tank, and the upper and lower parts are connected to the oil tank through pipes. When there is a temperature difference between the oil temperature in the upper part of the transformer and the oil temperature in the lower part, convection of the oil is formed through the radiator, and then flows back to the oil tank after being cooled by the radiator, thereby reducing the oil content of the transformer. The effect of temperature. In order to improve the cooling effect, measures such as self-cooling, forced air cooling and forced water cooling can be used.

6. Oil pillow

The oil pillow is also called the oil tank. Transformer oil will undergo thermal expansion and contraction due to temperature changes, and the oil level will also rise or fall with temperature changes. The function of the oil pillow is to provide a buffer for the thermal expansion and contraction of the oil, keeping the oil tank always full of oil; at the same time, due to the oil pillow, the contact area between the oil and the air is reduced, which can slow down the oxidation of the oil.

7.Gas relay

The gas relay, also known as the gas relay, is the main protection device for internal faults of the transformer. It is installed in the middle of the oil pipe connecting the oil tank and the oil pillow. When a serious fault occurs inside the transformer, the gas relay connects the circuit breaker to the same trip circuit; when a minor fault occurs inside the transformer, the gas relay connects the fault signal circuit.

8. Insulating sleeve

High and low insulating bushings are located on the top cover of the transformer oil tank. Oil-immersed transformers generally use porcelain insulating bushings. The function of the insulating sleeve is to maintain good insulation between the high and low voltage winding leads and the fuel tank, and to fix the leads.

9. Explosion-proof pipe

The explosion-proof pipe, also known as the safety airway, is installed on the oil tank of the transformer, and its outlet is sealed with a glass explosion-proof membrane. When a serious fault occurs inside the transformer and the gas relay fails, the gas inside the tank will break through the glass explosion-proof membrane and eject from the safety airway to prevent the transformer from exploding.