外文翻譯---發(fā)電機和變壓器-文庫吧資料
2025-01-23 23:07本頁面
【正文】 driven turbinegenerators are usually twopole or fourpole, turning at 3600 rpm or 1800 rmp, espectively, corresponding to high speeds are needed to achieve high steam turbine efficiencies. At these rotation rates, high centrifugal forces limit rotor diameters to about ft for two pole and 7 ft for fourpole machines.The average power ratings of the turbinegenerator units we have been describing have been increasing,scince1960s, from about 300MW to about 600MW，with maximum sizes up to about ratings are acpained by increased rotor and stator size, and with rotor diameters limited by centrifugal forces, the rotor lengths have been increasing. Thus in the larger sizes, the rotor lengths may be five to six times the diameters. These slender rotors resonate at critical speeds below their rated speeds and care is requied in operation to avoid sustained operation at these speeds.A Transformer is a device that changes ac electric energy at one voltage level into ac electric energy at another voltage level through the action of a magnetic field. It consists of two or more coils of wire wrapped around a mon ferro magnetic core. These coils are not directly connected. The only connection between the coils is the mon magnetic flux present within the core.One of the transformer windings is connected to a source of ac electric power, and the second(and perhaps third)transformer winding supplies electric power to load. The transformer winding connected to the power source is called the primary winding or input winding, and the winding connected to the power source is called the primary winding or output winding. If there is a third winding on the transformer, it is called the tertiary winding.Power transformer is constructed on one of two types of cores. One type of construction consists of a simple rectangular laminated piece of steel with the transformer windings wrapped around two sides of the rectangle. This type of construction is known as core form. The other type consists of a threelegged laminated core with the windings wrapped around the center leg. This type of construction is known as shell form. In either case, the core is constructed of thin laminations electrically isolated from each other in order to
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