本科生毕业设计（论文）
附录Ⅰ
英文资料及其翻译
Transformer
Types and Construction of Transformer
A transformer is a device that alternating current electric energy at one voltage level into alternating current electric energy at another voltage level through the action of a magnetic field.It consists of two or more coils wire wrapped around a common ferromagnetic core.These coils are (usually)not directly connected. The only connection between the coils is the common magnectic flux presen 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 loads. the transformer winding connected to the power souce is called the primary winding or input winding.and the winding connected to the loads is called the secondary winding or input winding.If there is a third winding on the transformer,it is called the tertiary winding.
Power transformer are 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 know as coreform .The other type consists of three-legged laminated core with the windings wrapped around the center leg .This type of construction is know as shell form.In either case,the core is constructed of thin laminations electrically isolated form each other in order in order to reduce eddy currents to a minimum.
The primary and secondary windings in a physical transformer are wrapped one on top of the other with the low-voltage winding innermost.Such an arrangement severs two purposes: 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 transformer are given a variety of different names, depending on their use in power systems.A transformer connected to the output of a generator and used to step its voltage up to transformer levels is sometimes called unit transformer. The transformer ai the other end of the transformer line,which steps the voltage down from
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本科生毕业设计（论文）
transmission levels to distribution levels,is called a substation transformer.Finally,the transformer that takes the distribution voltage and steps is down to the final voltage ai which the power is actually used is called a distribution transformer.All these devices are essentially the same-the only difference among them is their intended use.
In addition to the various power transformer, two special-purpose transformers are used with electric machinery and power systems.The first of these special transformers is a device specially designed to sample a high voltage and produce a low secondary voltage directly proportional to it.Such a transformer is called a potential transformer.A power transformer also produces a secondary voltage directly proportional to its primary voltage;the difference between a potential transformer and a power transformer is that the potential transformer is designed to handle only a very small current.The second type of special transformer is a device designed to provide a secondary current.much smaller than but directly proportional to its primary current.This device is called a current transformer.
Cirtcuit Breakers
A circuit breaker is mechanical switching device capable of making,and breaking currents under normal circuit conditions and also making.carring for a specified time ,and mediujm in which circuit interruption is performed may be designated by a suitable prefix, for example,air-blastcircuit breaker,oil circuit breaker.The circuit breakers currently in use can be dlassified into the following categories according to the arc-quenching principles:air swetches oel ciryit breakers,minmum-oil circuit breakers,air-blast circuit breakers,the magenetic air circuit breakers,minimum-oilcircuit breakers,aer-blast circuit breakers,the by voltage,insulation levelcurrent,interrupting capabilities,transient recovery coltage,interrupting tiome,and trip delay.The nameplate on a circuit breaker usually indicates:１.The maximum steady-state current it can carry, 2. The maximum interrupting current,3. The maximum line voltage,4.The interrupting time in cycles, The interrupting time in may last form 3 to 8 cycles on a 60 Hz system. To interrubt large currents quickly, we have to ensure rapid cooling. High-speed interruption lunits the damage transmission lines and equipment and, equally important,it helps to mainmain the stability of the system whenever a contingency occurs. The main parts of a circuit breaker are usually:arc-quenching chamber (or interrupter with moving and fixed contacts) operating mechanism and supporting structures.
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