Principle of oil - immersed transformer - brief introduction

Distribution transformer is an important equipment in power supply and distribution system of industrial and mining enterprises and civil buildings. It reduces the 10(6)kV or 35kV network voltage to the 230/400V busbar voltage used by the user.

This product is suitable for ac 50(60)Hz, three-phase maximum rated capacity of 2,500kva (single-phase maximum rated capacity of 833kVA, single-phase transformer is not recommended), can be used indoors (outdoors), the capacity of 315kVA and below can be installed on the pole.

Principles of oil-immersed transformers - classification

According to the structure, it can be divided into iron-core transformer and iron-shell transformer. If the winding is wrapped around the core, it is a core type transformer. For example, the iron core wrapped in the periphery of the winding is the iron shell type transformer. However, the two are slightly different in structure and no essential difference in principle. Power transformers are of iron core type.

It can be divided into three-phase transformer and single-phase transformer according to the number of phases. In three-phase power system, three-phase transformer is generally used. When the capacity is too large and restricted by transportation conditions, three single-phase transformers can also be used to form a transformer group in three-phase power system.

According to the winding can be divided into two winding transformer and three winding transformer. The usual transformer is a double-winding transformer, that is, there are two windings on the iron core, one is the primary winding and one is the secondary winding. A three-winding transformer is a transformer with a larger capacity (above 5,600 kva) for connecting three different voltage transmission lines. Under special circumstances, there are Satons transformers with more windings.

Principle of oil-immersed transformer -- principle

The components of oil-immersed transformer include the body (iron core, winding, insulation and lead), oil-immersed transformer oil, oil tank and cooling device, voltage regulating device, protective device (hygroscope, safety airway, gas relay, oil storage tank and temperature measuring device, etc.) and outlet bushing.

Oil-immersed transformer is an important equipment used to change voltage and transfer electric energy in power system. The oil-immersed transformer works mainly on the principle of electromagnetic induction. On the closed core, there are two windings insulated from each other. The side that is connected to the power supply is called the primary winding, and the side that produces electric energy is called the secondary winding.

When the ac power supply voltage is applied to the primary side winding, an ac current passes through the winding and an alternating flux is generated in the core. The alternating flux passes not only through the primary side winding, but also through the secondary side winding, in which the induced potential E1 and E2 are generated respectively. At this time, if the secondary side winding is connected with the load of the external circuit, there will be current flowing into the load, that is, the secondary side winding has power output.

Principle of oil - immersed transformer - structure

The transformer is mainly composed of iron core, winding, oil tank, oil pillow, insulating sleeve, tap switch and gas relay.

Ⅰ - core

The core is the magnetic circuit part of the transformer. Hysteresis loss and eddy current loss are generated during operation. In order to reduce the heat loss and reduce the volume and weight, the core is made of cold rolled grain oriented silicon steel with a magnetic conductivity of less than 0.35mm. According to the arrangement of windings in iron core, there are iron core type and iron shell type.

In large capacity transformers, in order to make the heat from the loss of iron core can be fully removed by the insulating oil in the circulation, in order to achieve good cooling effect, the cooling oil channel is often set in the iron core.

Ⅱ - winding

Winding and core are the core components of transformer. Since the winding itself has resistance or contact resistance at the junction, I2Rt knows to generate heat. Therefore, the winding cannot pass the current higher than the rated current for a long time. In addition, through the short-circuit current will produce a lot of electromagnetic force on the windings and damage the transformer. Its basic winding has concentric type and overlap type two kinds.

The main faults of transformer windings are inter-turn short circuit and short-circuit to the shell. Turn-to-turn short circuit is mainly due to aging insulation, or due to the transformer overload and through the short circuit when the insulation mechanical damage. When the oil level in the transformer drops and the oil level of the windings is exposed, inter-turn short circuit can also occur. In addition, when passing through the short circuit, the over-current will deform the winding and make the insulation suffer mechanical damage, which will also produce inter-turn short circuit. In case of inter-turn short circuit, the current in the short-circuit winding may exceed the rating, but the current in the whole winding may not exceed the rating. In this case, the gas protection action, serious case, the differential protection will also move. The cause of short circuit to the shell is also due to aging insulation or oil dampness, oil level drop, or due to lightning and operating overvoltage. In addition, when passing through the short circuit occurs, the over-current will deform the winding and cause the phenomenon of short circuit to the shell. In case of short circuit, gas protection device and grounding protection are usually used.

Ⅲ - The fuel tank

The body of the oil-immersed transformer (windings and iron core) is installed in the oil tank filled with transformer oil. The oil tank is welded with steel plate. The oil tank of medium and small transformers is composed of a box shell and a box cover. The transformer body is placed in the box shell, and the box cover can be opened to lift the body out for maintenance.

Principle of oil-immersed transformer -- characteristics

The oil-immersed transformer adopts a fully sealed structure. The oil-immersed transformer oil is isolated from the air, which slows down the change of oil. Surface electrostatic spray, beautiful and corrosion resistant.

Under severe overload, the coil insulation of oil-immersed transformer will not be damaged by aging and thermal breakdown, and excellent electrical and mechanical properties will be maintained during use. Redesigned coil oil duct reduces hot spot humidity. The redesigned oil tank increases the heat dissipation surface to ensure that the oil will not age in case of severe overload.