Summary:The power transformer is the most important equipment in the power system. It uses the principle of ...
The power transformer is the most important equipment in the power system. It uses the principle of electromagnetic induction to convert alternating current energy of one voltage level into alternating current energy of another voltage level. The role of electricity is widely used in various sectors of the national economy.
1. Transformer structure
The transformer is mainly composed of an iron core, winding, lead wire, voltage regulating device, cooling device, bushing and insulating medium (oil, SF6, epoxy resin), and other parts.
2. The role of the main components of the transformer
(1) Iron core. Transformers are manufactured according to the principle of electromagnetic induction, and the magnetic circuit is the medium of electrical energy conversion. The iron core is the magnetic circuit part of the transformer. Its main function is to conduct magnetism. It is made of electrical steel sheets (silicon steel sheets) with high magnetic permeability. It converts the electrical energy of the primary circuit into magnetic energy, and then from its own magnetic energy into the electrical energy of the secondary circuit.
Under the action of the alternating electric field of the coil, the iron core and its metal structural parts generate suspension discharge. Due to the different positions, the induced floating potentials are also different. This kind of suspension discharge is intermittent, and the result of the intermittent discharge damages the solid insulation and decomposes the transformer oil, which leads to the occurrence of transformer failure. In order to avoid damage to the transformer, the iron core and its metal structures must be grounded so that they are at zero potential.
If the iron core is grounded at two or more points, a circulating current will be induced in the ground loop when the magnetic flux in the iron core changes. These circulating currents will increase the no-load loss of the transformer and increase the temperature of the iron core, so the iron core must be grounded, and only one point can be grounded.
(2) Winding. The winding is the circuit part of the transformer. It is made of wire wrapped with insulation on the surface. It is sheathed on the iron core column of the transformer. The wire material can be divided into copper wire and aluminum wire.
Transformer windings should have sufficient dielectric strength, mechanical strength, and heat resistance. The main insulation of the winding mainly includes insulation paper, insulation paper tube, end insulation, pressure plate, stay, pad, angle ring, electrostatic screen, etc.
The insulating paper commonly used in oil-immersed transformers is cable paper. Cable paper has sufficient thermal stability in oil and is generally used as wire turn insulation, layer insulation, or wire covering insulation.
(3) Leads. The lead is to input the external power into the transformer, and then output the transmitted power to the transformer.
Generally divided into three types: the lead wire connecting the winding wire end and the bushing, the connecting lead between the windings of each phase, and the tap lead connecting the winding tap to the tap changer.
(4) Transformer oil. Transformer oil has a much higher dielectric strength than air. The insulating material is immersed in oil, which not only improves the dielectric strength but also protects it from moisture.
Transformer oil has a large specific heat and is often used as a coolant. The heat generated during the operation of the transformer causes the oil near the core and the winding to expand and rise due to heat. Through the upper and lower convection of the oil, the heat is dissipated through the radiator to ensure the normal operation of the transformer.
On the on-load tap changer of the transformer, arcing occurs when the contacts are switched. Because the transformer oil has good thermal conductivity, and a large amount of gas is decomposed under the high temperature of the arc, a large pressure is generated, thereby improving the arc extinguishing performance of the medium and making the arc extinguish quickly.
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