外文翻译---发电机和变压器

附录一

英文原文

Generator And Transformer

The turbine turns the rotor of the electric generator in whose stator are embedded three windings. In the process mechanical power from the turbine drive is converted to three phase alternating current at voltages in the range of 11kV to 30kV line to line at a frequency of 60 Hz in the United States. The voltage is usually stepped up by transmission to remote load centers.

A generator (also called an alternator or synchronous generator)is shown in longitudinal cross section; the transverse across section is approximately round. The roctoe is called round or cylindrical or smooth. We note that steam-driven turbine-generators are usually two-pole or four-pole, turning at 3600 rpm or 1800 rmp, espectively, corresponding to 60Hz.The high speeds are needed to achieve high steam turbine efficiencies. At these rotation rates, high centrifugal forces limit rotor diameters to about 3.5 ft for two pole and 7 ft for four-pole machines.

The average power ratings of the turbine-generator units we have been describing have been increasing,scince1960s, from

about 300MW to about 600MW

，with maximum sizes up to about 1300MW.Inceased ratings are accompained 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 common ferro magnetic core. These coils are not directly connected. The only connection between the coils is the common 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 three-legged 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 reduce eddy currents to a minimn.

The primary and secondary windings in a physical transformer are wrapped one on top of the other with low-voltage winding innermost. Such an arrangement serves two purpose: (1)It simplifies the problem of insulating the high-voltage winding from the core. (2)It results in much less leakAge flux than would be the two windings were separated by a distance on the core.

Power transformers are given a variety of different names, depending on there use in power systems. A transformer connected to the output of a generator and used to step its voltage to transmission levels is sometimes called a unit transformer. The transformer at the other end of the