Power Transformer Introduction

Transformer is used to transform AC voltage, current and transmission of AC electrical energy of a static electrical equipment. It is based on the principle of electromagnetic induction to achieve electric energy transfer. Transformer on its use can be divided into power transformer, test transformer, instrument transformer and special purpose transformer: power transformer is the power transmission and distribution, power user distribution necessary equipment; Test transformer Equipment for voltage withstand (boost) test of electrical equipment; Instrument transformer used for electrical measurement and relay protection of distribution system (PT, CT); Special purpose transformers are smelting furnace transformers, welding transformers, electrolytic rectifier transformers, small voltage regulating transformers.

Power transformer is a static electrical equipment, is used to change a certain value of ac voltage (current) into the same frequency of another or several different values of voltage (current) equipment. When the primary winding with alternating current, it produces alternating flux, alternating flux through the core magnetic action, in the secondary winding induced ac electromotive force. The level of secondary induction electromotive force is related to the number of turns of a secondary winding, that is, the voltage is proportional to the number of turns. Its main function is to transmit electric energy, so its rated capacity is its main parameter. Rated capacity is a conventional value of power performance, it is to characterize the size of the transmission of electric energy, expressed in kVA or MVA, when the transformer is applied to the rated voltage, according to it to determine the rated current does not exceed the temperature rise limit under specified conditions. More energy saving power transformer amorphous alloy core distribution transformer, its biggest advantage is that the no-load loss value is very low. Whether to ensure the no-load loss value is the core problem to be considered in the whole design process. In addition to the fact that the amorphous alloy core itself is not affected by external force, the characteristic parameters of the amorphous alloy must be selected accurately and reasonably in the calculation when the product structure is arranged.

Power transformer is one of the main equipment in power plant and substation. The role of the transformer is multifaceted can not only raise the voltage to send electricity to the area, but also reduce the voltage to all levels of use voltage, in order to meet the needs of electricity. In short, boost and buck must be done by the transformer. In the process of electric energy transmission in the power system, there will be two parts of voltage and power loss, in the transmission of the same power voltage loss is inversely proportional to voltage, power loss is inversely proportional to the square of voltage. The transformer is used to increase the voltage and reduce the transmission loss.

The transformer is composed of two or more coils winding on the same iron core. The windings are connected by alternating magnetic fields and work according to the principle of electromagnetic induction. The installation position of the transformer should be convenient for operation, maintenance and transportation, and the safe and reliable place should be selected. The rated capacity of the transformer must be reasonably selected when using the transformer. When the transformer is running without load, it needs more reactive power. This reactive power is supplied by the power supply system. If the transformer capacity is too large, not only increases the initial investment, but also makes the transformer in no-load or light load operation for a long time, so that the proportion of no-load loss increases, the power factor is reduced, the network loss increases, so that the operation is not economic and unreasonable. If the transformer capacity is too small, the transformer will be overloaded for a long time, which will easily damage the equipment. Therefore, the rated capacity of the transformer should be selected according to the needs of the electricity load, not too large or too small.

Power transformers are classified by use: boost (power plant 6.3kV/10.5kV or 10.5kV/110kV, etc.), connection (inter-substation 220kV/110kV or 110kV/10.5kV), step-down (distribution 35kV/0.4kV or 10.5kV/0.4kV).

Power transformers are classified by phase number: single-phase, three-phase.

Power transformers are classified by windings: double windings (each phase is mounted on the same core, the primary and secondary windings are wound separately and insulated from each other), three windings (each phase has three windings, the primary and secondary windings are wound separately and insulated from each other), autotransformer (a set of windings with a middle tap as a primary or secondary output). A three-winding transformer requires that the capacity of the primary winding be greater than or equal to that of the second or third winding. The percentage of the capacity of the three windings is in the order of high voltage, medium voltage and low voltage: 100/100/100, 100/50/100, 100/100/50. The second and third windings shall not be fully loaded. Generally, the tertiary winding has a low voltage and is mostly used for near area power supply or compensation equipment, which is used to connect three voltage levels. Autotransformer: there are two kinds of boost or buck, because of its small loss, light weight, economic use, so it is widely used in ultra-high voltage power grid. Small autotransformers are commonly used for 400V/36V (24V), used for safety lighting and other equipment power supply.

Power transformers are classified by insulating media: oil-immersed transformers (flame-retardant type, non-flame-retardant type), dry type transformers, 110kVSF6 gas insulated transformers.

The core of power transformer is core structure.

The three-phase power transformer configured in general communication engineering is double winding transformer.