外文翻译变压器的类型及结构

1、types and construction of transformera transformer is a device that changes ac electric energy at one voltage level into ac e1ectric energy at another vo1tage level through the action of a ma8netic fieldit consists of two or more coil of wire wrapped around a common ferromagnetic corethese coils are

2、 (usually) not directly connectedthe 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 loadsthe transfor

3、mer winding connected to the power source is called the primary winding or input winding，and the winding connected to the loads is called the secondary winding or output winding. if there is a third winding on the transformer，it is called the tertiary windingpower transformer are constructed on one

4、of two types of coresone type of construction consists of a simple rectagu1arlaminated piece of steel with the transformer windings wrapped around two sides of the rectangle. this type of construction is known as core formthe other type consists of a three-legged laminated core with the windings wra

5、pped around the center legthis 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 minimumthe primary and secondary windings in a physical transformer are wrapped one on to

6、p of the other with the low-voltage winding innermostsuch an arrangement serves two purposes：1.it simplifies the problem of insulating the high-voltage winding from the core2.it results in much less leakage flux than would be the two windings were separated by a distance on the corepower transformer

7、s 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 vo1tage up to transmission levels is sometimes called a unit transformerthe transformer at the other end of the transmission line，which steps t

8、he voltage down from transmission levels to distribution levels is called a substation transformer. finally，the transformer that takes the distribution voltage and steps it down to the final vo1tage at which the power is actually used is called a distribution transformera11 these devices are essenti

9、ally the same the only difference among them is their intended usein addition to the various power transformers，two special-purpose transformers are used with electric machinery and power systemsthe first of these special transformers is a device specially designed to sample a high vo1tage and produ

10、ce a low secondary vo1tage directly proportional to it. such a transformer is called a potential transformera power transformer also produces a secondary vo1tage directly proportional to its primary voltage; the difference between a potential transformer and a power transformer is that the potential

11、 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 currentthis device is called a current transformer.the directional protection basisearly

12、 attempts to improve power-service reliability to loads remote from generation led to the dual-1ine conceptof course，it is possible to build two 1ines to a load，and switch the load to whichever line remains energized after a di51urbancebut better service continuity will be available if both lines no

13、rmally feed the load and only the faulted line is tripped when disturbances occurfig.1-l shows a sing1e-generator，two-1ine,single-load system with breakers properly arranged to supply the load when one line is faultedfor the arrangement to be effective it is necessary to have the proper relay applic

14、ationotherwise，the expensive power equipment will not be able to perform as p1annedconsider the application of instantaneous and/or time delay relays on the four breakers.obvious1y the type of the relay cannot coordinate for a11 1ine faultsfor example, a fault on the line terminals of breaker d.d tr

15、ipping should be faster than b, however , the condition reverses and b should be faster than d. it is evident that the relay protection engineer must find some characteristic other than time delay if relay coordination is to be achievedthe magnitude of the fault current through breakers b and d is t

16、he same，regardless of the location of the fault on the line terminal of breaker b or dtherefore relay coordination must be based on characteristics other than a time delay that starts from the time of the fault. observe that the direction of current flowing through either breaker b or d is a functio

17、n of which line the fault is on. thus for a fault on the line between a and b, the current flows out of the load bus through breaker b toward the faultat breaker d the current flows toward the load bus through breaker din this case breaker b should trip, but breaker d should not tripthis can be acco

18、mplished by installing directional relays on breakers b and d that are connected in such a way that they will trip only when current flows through them in a direction away from the load bus.relay coordination for the system shown in fig1-l can now be achieved by the installation of directional over

19、current time delay relays on breakers b and dbreakers a and c can have non directional over current time delay relaysthey may also now have instantaneous relays appliedthe relays would be set as follows：the directional relays could be set with no intentional time delay. they will have inherent time

20、delaythe time delay over current relays on breakers a and c would have current settings that would permit them to supply backup protection for faults on the load bus and load equipment faultsthe instantaneous elements on breakers a and c would have current settings that would not permit them to dete

21、ct faults on the load busthus the lines between the generator and the load would have high-speed protection over a considerable portion of their lengthit should be observed that faults on the line terminals of breakers a and c can co11apse the generator vo1tagethe instantaneous relays on breakers a

22、or c cannot clear the circuit instantaneously，because it takes time for power equipment to operateduring this period there will be little or no current flow through breakers b and dtherefore，b or d cannot operate for this fault condition until the appropriate breaker at the generating station has op

23、eratedthis is known as sequential tripping. usually, it is acceptable under such conditionsabg loadcd fig.1-1direction of current flow on an a. c. system is determined by comparing the current vector with some other reference vector，such as a voltage vectorin the systems of fig.1-1 the reference vo1

24、tage vector would be derived from the voltages on the load busdirection of current or power flow cannot be determined instantaneously on acsystems whose lines and equipment contain reactancethis is apparent from the fact that when vo1tage exists, the lagging current can be plus or minus or zero，depe

25、nding on the instant sampled in the voltage cycleaccording1y，the vector quantities must be sampled over a time periodthe time period for reasonably accurate sampling may be from one-half to one cyclework is proceeding on shorter sampling periods where predicting circuits are added to the relay to at

26、tempt to establish what the vectors will be at some future timethe process is complex，because it must make predictions during the time when electrical transients exist on the systemusually， the shorter the time a11owed for determining direction，the less reliable will be the determination.变压器的类型及结构 变

27、压器是通过磁场作用将交流电从某一电压等级转换至另一电压等级的设备。它由两个或多个绕在铁氧体上的绕组构成通常，绕组之间不直接相连，它们是通过铁芯内部的主磁通相连接的。 变压器的一个绕组与交流电源连接，第二个绕组(也许第三个绕组)为负载提供电功率。与电源连接的绕组称为一次绕组或输入绕组。与负载连接的绕组称为二次绕组或输出绕组。如有第三个绕组，称之为第三绕组。 变压器的铁芯分为两类。一类是由绕组缠绕在一个简单的矩形钢片叠成的铁芯两边而构成。此类结构的绕组称为铁芯式结构。另一类是由三个分支的钢片叠成，绕组绕在中间的一个分支上。此类结构称为框式结构。铁芯不论是芯式还是框式，都是由薄薄的铁芯片做成的。铁芯

28、片之间相互绝缘，以最大限度地降低涡流。 在实际的变压器中，一次绕组和二次绕组一个在另一个的外面，低压绕组在最里面。此类结构安排有二个目的：使高压绕组与铁芯之间相互绝缘；使漏磁通较二个绕组相互隔开时少得多。 在电力系统中，根据不同的用途，电力变压器有许多种不同的名称。与发电机连接并将其电压提高到电网电压的变压器被称为升压变压。在输电线另一端，将电网电压降至配电电压的变压器称为降压变压器。最后，把电压降低到能实际应用量级的变压器称为配电变压器。以上变压器的结构基本相同，唯一的区别在于各自的实际用途不同。除了上述多种变压器之外，在电机与电力系统中还使用两种特殊用途的变压器。第一种专门设计的变压器是用

29、来采样电压，并产生一个低的二次电压，该电压与所采样的电压成正比。此类变压器称为电压互感器。功率变压器中产生的二次侧的电压也与一次侧的电压成正比。但电压互感器与电力变压器的不同在于电压互感器设计为仅处理较小的电流。第二种专门设计的变压器设计成为用来提供比一次侧的电流要小的多的二次侧电流，且使二次侧的电流与一次侧的电流成比例。此类装置称为电流互感器。方向保护基础早期，对于远离发电站的用户，为改善其供电可靠性提出了双回线供电的设想。当然，也可以架设不同的两回线给用户供电。在系统发生故障后，把用户切换至任一条正常的线路。但更好的连续供电方式是正常以双回线同时供电。当发生故障时，只断开故障线。图11所示为一个单电源、单负载、双回输电线系统。对该系统配置合适的断路器后，当一回线发生故随时，仍可对负载供电。为使这种供电方式更为有效，还需配置合适的继电保护系统，否则，昂贵的电力设备不能发挥其预期的作用。可以考虑在四个断路器上装设瞬时和延时起动继电器。显然，这种类型的继电器无法对所有线路故障进行协调配合。例如，故障点在靠近断路器d的线路端，d跳闸应比b快，反之，b应比d快。显然，如果要想使继