A transformer is an electrical device that exchanges alternating voltage or current between two or more windings at the same frequency by means of electromagnetic induction. Power from the power plant, to go through a long transmission line transmission to the terminal users, in order to reduce transmission line power consumption, must be used high pressure or high pressure transmission. The current general power plant voltage, due to the level of insulation, the voltage can not be too high, which will go through the transformer power plant will be sent to the power grid voltage increased. This transformer collectively referred to as step-up transformer.
      For end users, the voltage required by a variety of electrical equipment is not too high, but also through the transformer, the power system into a high-voltage electrical equipment in line with user requirements of the rated voltage. Transformers used for this purpose are collectively referred to as step-down transformers. Power transformer is iron core column or iron yoke formed a complete closed magnetic circuit, made of insulated copper wire or aluminum wire coil, forming the original transformer, secondary coil. In addition to small-capacity dry-type transformers, the majority of transformers are oil-immersed natural cooling, insulating oil from the coil insulation and cooling effect.
      From the above we can see, power transformers are the power system, to change the voltage of the main electrical equipment. From the power system point of view, a power grid will be many, power plants and users together, divided into the main system and a number of sub-systems. The voltage of each subsystem is not necessarily the same, and the main system must be a unified voltage level, which also requires a variety of specifications and capacity of the transformer to connect the various systems. Therefore, the power transformer is an indispensable power system electrical equipment.

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