毕业设计外文原文+翻译(电力系统)
电气工程及自动化专业英语考试翻译课文Electric Power Systems 电力系统3.1
Section 1 Introduction 第一节介绍The modern society depends on the electricity supply more heavily than ever before.现代社会比以往任何时候对电力供应的依赖更多。
It can not be imagined what the world should be if the electricity supply were interrupted all over the world. 如果中断了世界各地的电力供应，无法想像世界会变成什么样子Electric power systems (or electric energy systems), providing electricity to the modern society, have become indispensable components of the industrial world. 电力系统（或电力能源系统），提供电力到现代社会，已成为产业界的不可缺少的组成部分。
The first complete electric power system (comprising a generator, cable, fuse, meter, and loads) was built by Thomas Edison –the historic Pearl Street Station in New York City which began operation in September 1882. 托马斯爱迪生建立了世界上第一个完整的电力系统（包括发电机，电缆，熔断器，计量，并加载）它就是位于纽约市具有历史意义的珍珠街的发电厂始于1882年9月运作。
This was a DC system consisting of a steam-engine-driven DC generator supplying power to 59 customers within an area roughly 1.5 km in radius. The load, which consisted entirely of incandescent lamps, was supplied at 110 V through an underground cable system. 这是一个直流系统，由一个蒸汽发动机驱动的直流发电机其供电面积约1.5公里至59范围内的客户。
电气毕业设计外文翻译--电力系统通信蓄电池电源的检测与维护解决方案
英文原文：Power system communication power supply test and maintenance ofthe battery solutionAbstractIn a large number of data experiments and field application, and on the basis of the telecom room in the power the power of common common problems are analyzed and discussed, from, testing and maintenance of real-time monitoring system safety, and put forward a set of complete solutions.Keywords: battery group; Power source; Detection; maintenanceIntroductionThe electric power communication system center room equipped with a large amount of storage battery installation, on the communications department.The operation of the electric power systems and support, spare play an important role. But in the maintenance process, or will often meet many problems, a detailed analysis of the below.1. The battery power supply condition and analyzes the reasonsWe for large communication machine. Room on the actual test, to the battery power supply system for the comprehensive study, found that many rooms, communications equipment have low load capacity battery, system reliability of the poor, in here are two groups of data about battery problems:A. battery service life for the design of the general 8-1 O years, and statistical data show that the battery life ideal circumstances can achieve 4-6 years, generally can not meet the design demand, a large number of telecommunication room used less than 3 years (some two years) appear behind battery, part of the battery even scrapped;B. 2010 years urumqi power bureau telecommunication room data show that because the battery electric power communication power supply fault from accidents accounted for 35%, in recent years the data interface rapidly, the ratio has risen to 7%.Two sets of data to show that the problem is more serious battery, the battery power supply of security and reliability have a serious threat, investigate its reason, mainly in the following nine aspects:1.1 battery design process qualityThe battery design process exists plate technology design, material design, oxygen composite design, the pressure setA comprehensive plan defect, make a battery performance and life have been affected, main performance for battery failure, early leakage water loss, deformation cracks, etc.For simple ascending battery capacity, will the battery plate thin, and increase the number plate, makes the same volume of the casing electrolyte reaction area greatly increased, capacity improve soon, but because thin plate, plate easily corrosion, softening battery, service life and therefore greatly shorten, easy to produce the early failure problems.Because of the low pressure setting, charge once to a certain pressure, control valves will be openRev., gas is through the valve were leaked, cause the battery fluid loss (usually in a hole or a column valve will find a slightly damp near the liquid), this kind of battery also easy to produce the early failure, valve pressure design and material also has a direct relationship between the shell.Due to shell material, oxygen composite efficiency, valve design pressure, and other comprehensive technology lack, some batteries in the process of charging and discharging pool, easy to produce the shell deformation, beat even crack.1.2 the influence of the operation environmentRunning environment is the main room temperature on battery life influence is bigger, in 25 ℃environment conditions, the environmental average temperature increase every 10 ℃, battery life is reduced by half. Northwest temperature changes greatly (a 30 ℃a + 55 ~ C), the substation telecommunication room less equipped with air conditioner, thermal performance is poor, temperature on battery life form directly influence.1.3 operation mode and installation methodBattery packs are generally more battery series into a group, two groups of parallel operation. Site oftenFound in the internal battery, article connection (board) corner of battery performance generally have slightly worse, the main reason is the article connection too long (other connection is the article 5 a l0 times) and the materials of the contact resistance caused too large, lead to the connection of pressure drop article is too big, in the process of charging and discharging, will seriously affect peripheral battery charging and discharging effect, this kind of problem should be avoided.1.4 the quality of power supply and load design problemThe telecom room is located in remote general transformer substation, often without power and the battery in frequent charged, and discharge status, the serious influence battery life. Computer room load relative to the battery capacity are slants small, such as the actual load for 30 A, communications equipment configuration of battery capacity is commonly two groups of 300 Ah, the utility after interrupting, storage battery will to tiny current began to discharge, and small discharge current generation of sulfuric acid lead particles is easy to crystallization into pieces and E telecommunication room are generally rural power supply, the quality of power supply is not stable, power over A long period of time, power outages frequent, sulfuric acid lead particles generated more easily irreversible sulfate.1.5 professional testing methods and lack of equipmentIn the discharge detection, due to lack of monomer detection equipment protection functions, therefore, in discharge only by the group when voltageobservation, combined with manual measuring for inspection. Find a 1.8 v battery, immediately suspend test. This way low efficiency, safety all the sex differences, to the battery can't form an effective protection.The battery characteristic parameters are mainly embodied in the voltage, resistance and capacity, the conventional detection method mainly measuring voltage, observe the shell signs, check the bolt tightness etc. So that only some representations to the parameter, and cannot master's important! Parameters such as resistance, capacity, etc.1.6 charger, discharge management system is not perfectRecharging problems mainly involves to charge cycle, all are charging pressure, flow, all are charging filling time,All filling conversion control, float temperature compensation of detailed regulations.Some maintenance personnel to improve battery charging efficiency, improved charging voltage, and increase the charging current, leading to increased pressure, then combined low efficiency, the battery to dehydrate, are plate bar corrosion. With this several years of battery management know deeply, related problems reduce gradually, but for this problem or must cause enough attention to main pay attention to the following three points: one is the charge can't charge high pressure, even with are charging, voltage must also be restricted in 2.35 V scope (the new battery should be controlled in 2-3 V); 2 it is charging electric current cannot too much, it will speed up plates corrosion, cause plate softening, restrain oxygen composite efficiency; 3 it is charging process must be temperature compensation, compensation coefficients for a 3 mV / ℃2 mV / ~ C one.2. Testing and maintenance program2.1 replacement has serious degradation the battery packs, strengthen the selection of the batteryTo find Bi can have depth degradation and a serious threat to the security of the battery power supply systemGroups should be early change, and strengthen the battery technology selection. Process quality problem is the focus of the selection consider battery, the battery can be based on standard, battery makers to raise specific technical requirements, such as of the materials, valve pressure., plate thickness, quantity, voltage, resistance Sui, balanced equilibrium characteristics, oxygen composite efficiency, water loss rate, for through the acceptance test can detect project, must conduct test on these work can be further ensure the reliability of the battery for long-term use.Vrla batteries for production technology is strict, at present domestic battery lifeManufacturers in the more than 300, all sorts of technology of handicraft is various, the proposal is in before purchase, the battery rigorous screening, as far as possible choice complete production equipment, strong technical force, service facilities, perfect brand enterprise. ,2.2 strengthen early battery test, improve battery support ability of put into operationAt the beginning of the storage battery check is a very important testing link, the battery technology standardsIn early to check the battery has a clear request, the engine room of the electric power communication battery installation, run and maintenance and management is of important significance. For the specific requirements of the early battery check is: batteries before put into operation, the first first check sex discharge, its capacity should be not less than 95%, after the completion of the discharge to the battery charge; Filled, a quiet place 1-2 h, make a second check sex discharge, after the completion of the discharge of battery charge; Filled, a quiet place 1 ~ 2 h, third check Bi discharge, its capacity should be not less than 100%, after the completion of the discharge to charge the battery.2.3 maintenance change ideas, strengthen the battery power supply of professional monitoring managementProfessional centralized monitoring system in the traditional monitoring system based on the function, increase the storage of electricityPool monomer battery voltage, resistance and check test functions, the more the earth played a monitoring management functions, improve the maintenance efficiency.Implementing specialized monitoring, and other installation common monitoring or not pack monitoring communications equipment phaseThan, the power supply rate reduced greatly, found that the problem is timely, ensure the safety and reliability of the telecom room improved.2.4 configuration diesel generators, strengthen intelligent control management, ensure that electric power communication securityThe battery electric power communication communications equipment is necessary short time dc power, and diesel generatorMachine is long time plays the role of communication standby power. Most of the communications are no spare room woodOil generator, can increase the small diesel generator configuration.Considering the maintenance workload is big, shortage of personnel, vehicles and equipment and turnover nervous the actual problem, can not intelligent diesel generator increase intelligent control system, in the utility power lost, the utility is unstable, the phase lack, owe pressure, pressure and so on many kinds of conditions, can be automatically start diesel generator, and to switch into power network operation.For the operation of the diesel generator maintenance and management, should also together with battery, into the professional centralized monitoring system, so that in time control system of power the battery operation parameters and working state.中文翻译：电力系统通信蓄电池电源的检测与维护解决方案摘要在大量的数据实验和现场应用的基础上，针对电力通信机房电源普遍存在的共同性问题进行了分析和探讨，从检测维护、实时监控及系统安全等角度提出了一套完整方案。
电气专业毕业设计外文翻译
附录1：外文资料翻译A1.1外文资料题目26.22 接地故障电路开关我们目前为止报道的接地方法通常是充分的, 但更加进一步的安全措施在某些情况下是必要的。
假设例如, 有人将他的手指伸进灯口（如Fig.26.45示）。
虽然金属封入物安全地接地, 但那人仍将受到痛苦的震动。
或假设1个120V 的电炉掉入游泳池。
发热设备和联络装置将导致电流流入在水池中的危害，即使电路的外壳被安全地接地，现在已经发展为当这样的事件发生时，设备的电源将被切断。
如果接地电流超过5mA ，接地开关将在5 ms 内跳掉，这些装置怎么运行的？如Fig.26.46所示，一台小变流器缠绕上导线 ，第二步是要连接到可能触发开合120 V 线的一台敏感电子探测器。
在正常情况下流过导体的电流W I 与中性点上的电流N I 准切的相等，因此流经核心的净潮流(N W I I -)是零。
结果，在核心没有产生电流，导致的电压F E 为零，并且开关CB 没有动作。
假设如果某人接触了一个终端(图Fig.26.45示)，故障电流F I 将直接地从载电线漏到地面，这是可能发生的。
如果绝缘材料在马达和它的地面封入物之间断开，故障电流也会被产生。
在以下任何情况下，流经CT 的孔的净潮流等于F I 或L I ，不再是零。
电流被产生，并且产生了可以控制CB 开关的电压F E 。
由于5 mA 不平衡状态只必须被检测出，变压器的核心一定是非常有渗透性的在低通量密度。
Supermalloy 是最为常用的，因为它有相对渗透性典型地70000在通量密度仅4mT 。
26.23 t I 2是导体迅速发热的因素它有时发生于导体短期内电流远大于正常值的情况下，R I 2损失非常大并且导体的温度可以在数秒内上升几百度。
例如，当发生严重短路时，在保险丝或开关作用之前，会有很大的电流流过导体和电缆。
此外，热量没有时间被消散到周围，因此导体的温度非常迅速地增加。
在这些情况下什么是温度上升？ 假设导体有大量m ，电阻R 和热量热容量c 。
电力系统毕业论文中英文外文文献翻译精选全文完整版
可编辑修改精选全文完整版电力系统电力系统介绍随着电力工业的增加，与用于生成和处置现今大规模电能消费的电力生产、传输、分派系统相关的经济、工程问题也随之增多。
这些系统组成了一个完整的电力系统。
应该着重提到的是生成电能的工业，它不同凡响的地方在于其产品应按顾客要求即需即用。
生成电的能源以煤、石油，或水库和湖泊中水的形式贮存起来，以备以后所有需。
但这并非会降低用户对发电机容量的需求。
显然，对电力系统而言服务的持续性相当重要。
没有哪一种服务能完全幸免可能显现的失误，而系统的本钱明显依托于其稳固性。
因此，必需在稳固性与本钱之间找到平稳点，而最终的选择应是负载大小、特点、可能显现中断的缘故、用户要求等的综合表现。
但是，网络靠得住性的增加是通过应用必然数量的生成单元和在发电站港湾各分区间和在国内、国际电网传输线路中利用自动断路器得以实现的。
事实上大型系统包括众多的发电站和由高容量传输线路连接的负载。
如此，在不中断整体服务的前提下能够停止单个发电单元或一套输电线路的运作。
现此生成和传输电力最普遍的系统是三相系统。
相关于其他交流系统而言，它具有简便、节能的优势。
尤其是在特定导体间电压、传输功率、传输距离和线耗的情形下，三相系统所需铜或铝仅为单相系统的75%。
三相系统另一个重要优势是三相电机比单相电机效率更高。
大规模电力生产的能源有：1.从常规燃料（煤、石油或天然气）、城市废料燃烧或核燃料应用中取得的蒸汽；2.水；3.石油中的柴油动力。
其他可能的能源有太阳能、风能、潮汐能等，但没有一种超越了试点发电站时期。
在大型蒸汽发电站中，蒸汽中的热能通过涡轮轮转换为功。
涡轮必需包括安装在轴承上并封锁于汽缸中的轴或转子。
转子由汽缸周围喷嘴喷射出的蒸汽流带动而平稳地转动。
蒸汽流撞击轴上的叶片。
中央电站采纳冷凝涡轮，即蒸汽在离开涡轮后会通过一冷凝器。
冷凝器通过其导管中大量冷水的循环来达到冷凝的成效，从而提高蒸汽的膨胀率、后继效率及涡轮的输出功率。
电力系统继电保护毕业论文中英文资料外文翻译文献
电力系统继电保护论文中英文资料Relay protection development present situation[Abstract ]reviewed our country electrical power system relay protection technological devil orpiment process，has outlined the microcomputer relay protection technology achievement, pro posed the future relay protection technological development tendency will be: Computerizes, n networked，protects, the control，the survey，the data communication integration and the artificial I intellectualization.[Key word ］relay protection present situation development，relay protections future development1 relay protection development present situationThe electrical power system rapid development to the relay protection proposed unceasingly t he new request，the electronic technology，computer technology and the communication rapid development unceasingly has poured into the new vigor for the relay protection technology de velopment，therefore，the relay protection technology is advantageous, has completed the deve lopment 4 historical stage in more than 40 years time。
电气毕业设计用外文翻译(中英文对照)
The Transformer on load ﹠Introduction to DC Machine sThe Transformer on loadIt has been shown that a primary input voltage 1V can be transformed to any desired open-circuit secondary voltage 2E by a suitable choice of turns ratio. 2E is available for circulating a load current impedance. For the moment, a lagging power factor will be considered. The secondary current and the resulting ampere-turns 22N I will change the flux, tending to demagnetize the core, reduce m Φ and with it 1E . Because the primary leakage impedance drop is so low, a small alteration to 1E will cause an appreciable increase of primary current from 0I to a new value of 1I equal to ()()i jX R E V ++111/. The extra primary current and ampere-turns nearly cancel the whole of the secondary ampere-turns. This being so , the mutual flux suffers only a slight modification and requires practically the same net ampere-turns 10N I as on no load. The total primary ampere-turns are increased by an amount 22N I necessary to neutralize the same amount of secondary ampere-turns. In the vector equation , 102211N I N I N I =+; alternatively, 221011N I N I N I -=. At full load, the current 0I is only about 5% of the full-load current and so 1I is nearly equal to 122/N N I . Because in mind that 2121/N N E E =, the input kV A which is approximately 11I E is also approximately equal to the output kV A, 22I E .The physical current has increased, and with in the primary leakage flux to which it is proportional. The total flux linking the primary ,111Φ=Φ+Φ=Φm p , is shown unchanged because the total back e.m.f.,（dt d N E /111Φ-）is still equal and opposite to 1V . However, there has been a redistribution of flux and the mutual component has fallen due to the increase of 1Φ with 1I . Although the change is small, the secondary demand could not be met without a mutual flux and e.m.f. alteration to permit primary current to change. The net flux s Φlinking the secondary winding has been further reduced by the establishment of secondary leakage flux due to 2I , and this opposes m Φ. Although m Φ and2Φ are indicated separately , they combine to one resultant in the core which will be downwards at the instant shown. Thus the secondary terminal voltage is reduced to dt d N V S /22Φ-= which can be considered in two components, i.e. dt d N dt d N V m //2222Φ-Φ-=or vectorially 2222I jX E V -=. As for the primary, 2Φ is responsible for a substantially constant secondaryleakage inductance 222222/Λ=ΦN i N . It will be noticed that the primary leakage flux is responsiblefor part of the change in the secondary terminal voltage due to its effects on the mutual flux. The two leakage fluxes are closely related; 2Φ, for example, by its demagnetizing action on m Φ has caused the changes on the primary side which led to the establishment of primary leakage flux.If a low enough leading power factor is considered, the total secondary flux and the mutual flux are increased causing the secondary terminal voltage to rise with load. p Φ is unchanged in magnitude from the no load condition since, neglecting resistance, it still has to provide a total back e.m.f. equal to 1V . It is virtually the same as 11Φ, though now produced by the combined effect of primary and secondary ampere-turns. The mutual flux must still change with load to give a change of 1E and permit more primary current to flow. 1E has increased this time but due to the vector combination with 1V there is still an increase of primary current.Two more points should be made about the figures. Firstly, a unity turns ratio has been assumed for convenience so that '21E E =. Secondly, the physical picture is drawn for a different instant of time from the vector diagrams which show 0=Φm , if the horizontal axis is taken as usual, to be the zero time reference. There are instants in the cycle when primary leakage flux is zero, when the secondary leakage flux is zero, and when primary and secondary leakage flux is zero, and when primary and secondary leakage fluxes are in the same sense.The equivalent circuit already derived for the transformer with the secondary terminals open, can easily be extended to cover the loaded secondary by the addition of the secondary resistance and leakage reactance.Practically all transformers have a turns ratio different from unity although such an arrangement issometimes employed for the purposes of electrically isolating one circuit from another operating at the same voltage. To explain the case where 21N N ≠ the reaction of the secondary will be viewed from the primary winding. The reaction is experienced only in terms of the magnetizing force due to the secondary ampere-turns. There is no way of detecting from the primary side whether 2I is large and 2N small or vice versa, it is the product of current and turns which causes the reaction. Consequently, a secondary winding can be replaced by any number of different equivalent windings and load circuits which will give rise to an identical reaction on the primary .It is clearly convenient to change the secondary winding to an equivalent winding having the same number of turns 1N as the primary.With 2N changes to 1N , since the e.m.f.s are proportional to turns, 2212)/('E N N E = which is the same as 1E .For current, since the reaction ampere turns must be unchanged 1222'''N I N I = must be equal to 22N I .i.e. 2122)/(I N N I =.For impedance , since any secondary voltage V becomes V N N )/(21, and secondary current I becomes I N N )/(12, then any secondary impedance, including load impedance, must become I V N N I V /)/('/'221=. Consequently, 22212)/('R N N R = and 22212)/('X N N X = .If the primary turns are taken as reference turns, the process is called referring to the primary side. There are a few checks which can be made to see if the procedure outlined is valid.For example, the copper loss in the referred secondary winding must be the same as in the original secondary otherwise the primary would have to supply a different loss power. ''222R I must be equal to 222R I . ）222122122/()/(N N R N N I ∙∙ does in fact reduce to 222R I .Similarly the stored magnetic energy in the leakage field )2/1(2LI which is proportional to 22'X I will be found to check as ''22X I . The referred secondary 2212221222)/()/(''I E N N I N N E I E kVA =∙==.The argument is sound, though at first it may have seemed suspect. In fact, if the actual secondarywinding was removed physically from the core and replaced by the equivalent winding and load circuit designed to give the parameters 1N ,'2R ,'2X and '2I , measurements from the primary terminals would be unable to detect any difference in secondary ampere-turns, kVA demand or copper loss, under normal power frequency operation.There is no point in choosing any basis other than equal turns on primary and referred secondary, but it is sometimes convenient to refer the primary to the secondary winding. In this case, if all the subscript 1’s are interchanged for the subscript 2’s, the necessary referring constants are easily found; e.g. 2'1R R ≈,21'X X ≈; similarly 1'2R R ≈ and 12'X X ≈.The equivalent circuit for the general case where 21N N ≠ except that m r has been added to allow for iron loss and an ideal lossless transformation has been included before the secondary terminals to return '2V to 2V .All calculations of internal voltage and power losses are made before this ideal transformation is applied. The behaviour of a transformer as detected at both sets of terminals is the same as the behaviour detected at the corresponding terminals of this circuit when the appropriate parameters are inserted. The slightly different representation showing the coils 1N and 2N side by side with a core in between is only used for convenience. On the transformer itself, the coils are , of course , wound round the same core.Very little error is introduced if the magnetising branch is transferred to the primary terminals, but a few anomalies will arise. For example ,the current shown flowing through the primary impedance is no longer the whole of the primary current. The error is quite small since 0I is usually such a small fraction of 1I . Slightly different answers may be obtained to a particular problem depending on whether or not allowance is made for this error. With this simplified circuit, the primary and referred secondary impedances can be added to give: 221211)/(Re N N R R += and 221211)/(N N X X Xe +=It should be pointed out that the equivalent circuit as derived here is only valid for normal operation at power frequencies; capacitance effects must be taken into account whenever the rate of change of voltage would give rise to appreciable capacitance currents, dt CdV I c /=. They are important at high voltages and at frequencies much beyond 100 cycles/sec. A further point is not theonly possible equivalent circuit even for power frequencies .An alternative , treating the transformer as a three-or four-terminal network, gives rise to a representation which is just as accurate and has some advantages for the circuit engineer who treats all devices as circuit elements with certain transfer properties. The circuit on this basis would have a turns ratio having a phase shift as well as a magnitude change, and the impedances would not be the same as those of the windings. The circuit would not explain the phenomena within the device like the effects of saturation, so for an understanding of internal behaviour .There are two ways of looking at the equivalent circuit:(a) viewed from the primary as a sink but the referred load impedance connected across '2V ,or (b) viewed from the secondary as a source of constant voltage 1V with internal drops due to 1Re and 1Xe . The magnetizing branch is sometimes omitted in this representation and so the circuit reduces to a generator producing a constant voltage 1E (actually equal to 1V ) and having an internal impedance jX R + (actually equal to 11Re jXe +).In either case, the parameters could be referred to the secondary winding and this may save calculation time .The resistances and reactances can be obtained from two simple light load tests.Introduction to DC MachinesDC machines are characterized by their versatility. By means of various combination of shunt, series, and separately excited field windings they can be designed to display a wide variety of volt-ampere or speed-torque characteristics for both dynamic and steadystate operation. Because of the ease with which they can be controlled , systems of DC machines are often used in applications requiring a wide range of motor speeds or precise control of motor output.The essential features of a DC machine are shown schematically. The stator has salient poles and is excited by one or more field coils. The air-gap flux distribution created by the field winding is symmetrical about the centerline of the field poles. This axis is called the field axis or direct axis.As we know , the AC voltage generated in each rotating armature coil is converted to DC in the external armature terminals by means of a rotating commutator and stationary brushes to which the armature leads are connected. The commutator-brush combination forms a mechanical rectifier,resulting in a DC armature voltage as well as an armature m.m.f. wave which is fixed in space. The brushes are located so that commutation occurs when the coil sides are in the neutral zone , midway between the field poles. The axis of the armature m.m.f. wave then in 90 electrical degrees from the axis of the field poles, i.e., in the quadrature axis. In the schematic representation the brushes are shown in quarature axis because this is the position of the coils to which they are connected. The armature m.m.f. wave then is along the brush axis as shown.. (The geometrical position of the brushes in an actual machine is approximately 90 electrical degrees from their position in the schematic diagram because of the shape of the end connections to the commutator.)The magnetic torque and the speed voltage appearing at the brushes are independent of the spatial waveform of the flux distribution; for convenience we shall continue to assume a sinusoidal flux-density wave in the air gap. The torque can then be found from the magnetic field viewpoint.The torque can be expressed in terms of the interaction of the direct-axis air-gap flux per pole d Φ and the space-fundamental component 1a F of the armature m.m.f. wave . With the brushes in the quadrature axis, the angle between these fields is 90 electrical degrees, and its sine equals unity. For a P pole machine 12)2(2a d F P T ϕπ= In which the minus sign has been dropped because the positive direction of the torque can be determined from physical reasoning. The space fundamental 1a F of the sawtooth armature m.m.f. wave is 8/2π times its peak. Substitution in above equation then gives a d a a d a i K i mPC T ϕϕπ==2 Where a i =current in external armature circuit;a C =total number of conductors in armature winding;m =number of parallel paths through winding;And mPC K a a π2=Is a constant fixed by the design of the winding.The rectified voltage generated in the armature has already been discussed before for an elementary single-coil armature. The effect of distributing the winding in several slots is shown in figure ,in which each of the rectified sine waves is the voltage generated in one of the coils, commutation taking place at the moment when the coil sides are in the neutral zone. The generated voltage as observed from the brushes is the sum of the rectified voltages of all the coils in series between brushes and is shown by the rippling line labeled a e in figure. With a dozen or so commutator segments per pole, the ripple becomes very small and the average generated voltage observed from the brushes equals the sum of the average values of the rectified coil voltages. The rectified voltage a e between brushes, known also as the speed voltage, is m d a m d a a W K W mPC e ϕϕπ==2 Where a K is the design constant. The rectified voltage of a distributed winding has the same average value as that of a concentrated coil. The difference is that the ripple is greatly reduced.From the above equations, with all variable expressed in SI units:m a a Tw i e =This equation simply says that the instantaneous electric power associated with the speed voltage equals the instantaneous mechanical power associated with the magnetic torque , the direction of power flow being determined by whether the machine is acting as a motor or generator.The direct-axis air-gap flux is produced by the combined m.m.f. f f i N ∑ of the field windings, the flux-m.m.f. characteristic being the magnetization curve for the particular iron geometry of the machine. In the magnetization curve, it is assumed that the armature m.m.f. wave is perpendicular to the field axis. It will be necessary to reexamine this assumption later in this chapter, where the effects of saturation are investigated more thoroughly. Because the armature e.m.f. is proportional to flux timesspeed, it is usually more convenient to express the magnetization curve in terms of the armature e.m.f. 0a e at a constant speed 0m w . The voltage a e for a given flux at any other speed m w is proportional to the speed,i.e. 00a m m a e w w e Figure shows the magnetization curve with only one field winding excited. This curve can easily be obtained by test methods, no knowledge of any design details being required.Over a fairly wide range of excitation the reluctance of the iron is negligible compared with that of the air gap. In this region the flux is linearly proportional to the total m.m.f. of the field windings, the constant of proportionality being the direct-axis air-gap permeance.The outstanding advantages of DC machines arise from the wide variety of operating characteristics which can be obtained by selection of the method of excitation of the field windings. The field windings may be separately excited from an external DC source, or they may be self-excited; i.e., the machine may supply its own excitation. The method of excitation profoundly influences not only the steady-state characteristics, but also the dynamic behavior of the machine in control systems.The connection diagram of a separately excited generator is given. The required field current is a very small fraction of the rated armature current. A small amount of power in the field circuit may control a relatively large amount of power in the armature circuit; i.e., the generator is a power amplifier. Separately excited generators are often used in feedback control systems when control of the armature voltage over a wide range is required. The field windings of self-excited generators may be supplied in three different ways. The field may be connected in series with the armature, resulting in a shunt generator, or the field may be in two sections, one of which is connected in series and the other in shunt with the armature, resulting in a compound generator. With self-excited generators residual magnetism must be present in the machine iron to get the self-excitation process started.In the typical steady-state volt-ampere characteristics, constant-speed primemovers being assumed. The relation between the steady-state generated e.m.f. a E and the terminal voltage t V isa a a t R I E V -=Where a I is the armature current output and a R is the armature circuit resistance. In a generator, a E is large than t V ; and the electromagnetic torque T is a countertorque opposing rotation.The terminal voltage of a separately excited generator decreases slightly with increase in the load current, principally because of the voltage drop in the armature resistance. The field current of a series generator is the same as the load current, so that the air-gap flux and hence the voltage vary widely with load. As a consequence, series generators are not often used. The voltage of shunt generators drops off somewhat with load. Compound generators are normally connected so that the m.m.f. of the series winding aids that of the shunt winding. The advantage is that through the action of the series winding the flux per pole can increase with load, resulting in a voltage output which is nearly constant. Usually, shunt winding contains many turns of comparatively heavy conductor because it must carry the full armature current of the machine. The voltage of both shunt and compound generators can be controlled over reasonable limits by means of rheostats in the shunt field. Any of the methods of excitation used for generators can also be used for motors. In the typical steady-state speed-torque characteristics, it is assumed that the motor terminals are supplied from a constant-voltage source. In a motor the relation between the e.m.f. a E generated in the armature and the terminal voltage t V isa a a t R I E V +=Where a I is now the armature current input. The generated e.m.f. a E is now smaller than the terminal voltage t V , the armature current is in the opposite direction to that in a motor, and the electromagnetic torque is in the direction to sustain rotation ofthe armature.In shunt and separately excited motors the field flux is nearly constant. Consequently, increased torque must be accompanied by a very nearly proportional increase in armature current and hence by a small decrease in counter e.m.f. to allow this increased current through the small armature resistance. Since counter e.m.f. is determined by flux and speed, the speed must drop slightly. Like the squirrel-cage induction motor ,the shunt motor is substantially a constant-speed motor having about 5 percent drop in speed from no load to full load. Starting torque and maximum torque are limited by the armature current that can be commutated successfully.An outstanding advantage of the shunt motor is ease of speed control. With a rheostat in the shunt-field circuit, the field current and flux per pole can be varied at will, and variation of flux causes the inverse variation of speed to maintain counter e.m.f. approximately equal to the impressed terminal voltage. A maximum speed range of about 4 or 5 to 1 can be obtained by this method, the limitation again being commutating conditions. By variation of the impressed armature voltage, very wide speed ranges can be obtained.In the series motor, increase in load is accompanied by increase in the armature current and m.m.f. and the stator field flux (provided the iron is not completely saturated). Because flux increases with load, speed must drop in order to maintain the balance between impressed voltage and counter e.m.f.; moreover, the increase in armature current caused by increased torque is smaller than in the shunt motor because of the increased flux. The series motor is therefore a varying-speed motor with a markedly drooping speed-load characteristic. For applications requiring heavy torque overloads, this characteristic is particularly advantageous because the corresponding power overloads are held to more reasonable values by the associated speed drops. Very favorable starting characteristics also result from the increase in flux with increased armature current.In the compound motor the series field may be connected either cumulatively, so that its.m.m.f.adds to that of the shunt field, or differentially, so that it opposes. The differential connection is very rarely used. A cumulatively compounded motor hasspeed-load characteristic intermediate between those of a shunt and a series motor, the drop of speed with load depending on the relative number of ampere-turns in the shunt and series fields. It does not have the disadvantage of very high light-load speed associated with a series motor, but it retains to a considerable degree the advantages of series excitation.The application advantages of DC machines lie in the variety of performance characteristics offered by the possibilities of shunt, series, and compound excitation. Some of these characteristics have been touched upon briefly in this article. Still greater possibilities exist if additional sets of brushes are added so that other voltages can be obtained from the commutator. Thus the versatility of DC machine systems and their adaptability to control, both manual and automatic, are their outstanding features.负载运行的变压器及直流电机导论负载运行的变压器通过选择合适的匝数比，一次侧输入电压1V 可任意转换成所希望的二次侧开路电压2E 。
电气专业毕业设计外文翻译---电力系统自动化
外文资料翻译Power System AutomationPower system integration is the act of communication data to, or among IED s in the I&C system and remote users. Substation integration refers to combining data from the IED′s local to a substation so that there is a single point of contact in the substation for all of the I&C data. Poletop devices often communicate to the substation via wireless or fiber connections. Remote and local substation and feeder control is passed through the substation controller acting as a single point of contact. Some systems bypass the substation controller by using direct connections to the poletop devices, such as RTU s, protective relays, and controllers.Power system automation is the act of automatically controlling the power system via I&C devices. Substation automation refers to using IED data, control and automation capabilities within the substation, and control commands from remote users to control power system devices. Since true substation automation relies on substation integration, the terms are often used interchangeably.Power system automation includes processes associated with generation and delivery of power. A subset of the process deal with delivery of power at transmission and distribution levels, which is power delivery automation. Together, monitoring and control of power delivery system in the substation and on the poletop reduce the occurrence of outages and shorten the duration of outages that do occur. The IED′s, communications protocols, and communications methods described in previous sections, work together as a system to perform power system automation.Though each utility is unique, most consider power delivery automation of transmission and distribution substation and feeders to include : Supervisory Control and Data Acquisition(SCADA)-operatorsupervision and control;Distribution Automation-fault location, auto-isolation, auto-sectionalizing, and auto-restoration;Substation Automation-breaker failure, reclosing, battery monitoring, dead substation transfer, and substation load transfer;Energy Management System (EMS)-load flow, VAR and voltage monitoring and control, generation control, transformer and feeder load balancing;Fault analysis and device maintenance.System without automated control still have the advantages of remote monitoring and operator control of power system devices, which includes: Remote monitoring and control of circuit breakers and automated switches;Remote monitoring of non-automated switches and fuses;Remote monitoring and control of capacitor banks;Remote monitoring and voltage control;Remote power quality monitoring and control.IED s described in the overview are used to perform power system integration and automation. Most designs require that the one IED act as the substation controller and perform data acquisition and control of the other IED s. The substation controllers is often called upon to support system automation tasks as well. The communications industry uses the term client/server for a device that acts as a master, or client, retrieving data from some devices and then acts as a slaver, a server, sending this data to other devices. The client/server collecting and concentrating dynamically. A data concentrator creates a substation databases by collecting and concentrating dynamic data from several devices. In this fashion, essential subsets of data from each IED are forwarded to a master through one data transfer. The concentrator databases is used to pass data between IED s that are not directly connected.A substation archive client/server collects and archives data from several devices. The archive data is retrieved when it is convenient for the userto do so.The age of the IED s now in substations varies widely. Many of these IED s are still useful but lack the most recent protocols. A communications processor that can communicate with each IED via a unique baud rate and protocol extends the time that each IED is useful. Using a communications processor for substation integration also easily accommodates future IED s. It is rare for all existing IED s to be discarded during a substation integration upgrade project.The benefits of monitoring, remote control, and automation of power delivery include improved employee and public safety, and deferment of the cost of purchasing new equipment. Also, reduced operation and maintenance costs are realized through improved use of existing facilities and optimized performance of the power system through reduced losses associated with outages and improved voltage profile. Collection of information can result in better planning and system design, and increased customer satisfaction will result from improved responsiveness, service reliability, and power quality.Power system automation includes a variety of equipment. The principal items are listed and briefly described below.Instrument transformers are used to sense power system current and voltage. They are physically connected to power system apparatus and convert the actual power system signals, which includes high voltage and current magnitudes, down to lower signal levels.Transducers convert the analog output of an instrument transformer from one magnitude to another or from one value type to another, such as from an ac current to dc voltage.As the name implies, a remote terminal device, RTU, is an IED that can be installed in a remote location, and acts as a termination point for filed contacts. A dedicated pair of copper conductors are used to sense every contract and transducer value. These conductors originated at the power system device, are installed in trenches or overhead cable trays, and are thenterminated on panels within the RTU. The RTU can transfer collected data to other devices and receive data and control commands from other device through a serial port. User programmable RTUs are referred to as “smart RTUs.”A communication switch is a device that switches between several serial ports when it is told to do so. The remote user initiates communications with the port switch via a connection to the substation , typically a leased line or dial-up telephone connection. Once connected, the user can route their communication through the port switch to one of the connected substation IEDs. The port switch merely “passes through” the IED communication.A meter is an IED that is used to create accurate measurement of power system current, voltage, and power values. Metering values such as demand and peak are saved within the meter to create historical information about the activity of the power system.A digital fault recorder ,is an IED that records information about power system disturbances. It is capable of storing data in digital format when triggered by conditions detected on the power system. Harmonics, frequency, and voltage are examples of data captured by DFRs.Load tap changer are devices used to change the tap position on transformers. These devices work automatically or can be controlled via another local IED or form a remote operator or process.Recloser controllers remotely control the operation of automated reclosers and switches. These devices monitor and store power system conditions and determine when to perform control actions. They also accept commands form a remote operator or process.电力系统自动化电力系统集成是在I&C系统中的IED和远程用户之间进行数据通信的操作。
电动机无级调速毕业设计--外文翻译资料
Ⅰ.system analysis and synthesis1．Analysis（1）In the speed and current dual closed-loop speed control system, in order to change the motor speed, what parameters should be regulating? Change speed regulator Kn magnification work? Power electronic converter to change the magnification factor Ks work? Change the speed of the feedback coefficient of work? To change the motor's stall current system should adjust the parameters of what?A: To change the motor speed, change speed regulator Kn magnification and power electronic converters will not work magnification factor Ks, stable when n = Un = Un *, so the only change in the value of a given coefficient of Un * and feedback before. To change the motor's stall current, only need to change the same value given Uim * and feedback coefficient, because the stability, Uim * = Idm, can be drawn from the type(2) Speed, the current double closed-loop speed control system when the steady-state operation, the two regulator input voltage and output voltage deviation is the number?A: The speed and current dual closed-loop speed control system when the steady-state operation, the two regulators are the input bias voltage is zero, by the formula n = Un = Un *, n = n; Uim * = Idm, Idm = Idl.(3) In the speed and current dual closed-loop speed control system, the two regulators are PI regulator. When the system is running with rated load, the speed feedback line suddenly disconnected, the system re-enter the steady-state, the current regulator is the input bias voltage to zero? Why?A: When the system is running with rated load, the speed feedback line suddenly disconnected, then Un = 0, = Un *- Un = Un *, so that Ui to reach Uim, 0, rate of increase in n, when the system after re-entering the steady-state , that is, Id = Idl, then, = Uim *- Idl 0, are no longer changes, changes in rotational speed n is no longer, but at this time than the rotational speed n at the time of the feedback line speed to break big.(4) Why is the speed with integral control system is not static poor?A: Speed regulator integral system, to achieve non-static error is due to the characteristics of integral control regulator, that is, the accumulation of points and the role of memory.(5) Double-loop speed control system (PI), load changes, Idl> Idm, asked bicyclol speed control system ASR and ACR how-conditioning, the result?A: When the load changes, Idl> Idm, speed decreased rapidly, the current Id soon to Idm, and of limited amplitude, rapid rate of ASR saturation, ACR has been limiting conditions, to form a blocking phenomenon, long-running will damage the system.2. SystemSpeed regulator and current regulator in the Double Loop DC Motor Control System can be summarized as follows:(1). The role of speed regulatorSpeed regulator is a speed control system of the dominant regulator, which allows speed n will soon change with a given voltage Un * changes in steady-state speed error can be reduced, if the PI regulator can achieve the non-static error.1) The effect of load changes in the role of anti-disturbance.2) The output amplitude of the decision limit the maximum allowable motor current.(2) The role of current regulator1) As a regulator of the inner ring, outer ring at the speed of the adjustment process, it makes the current closely followed the given voltage Ui * (that is, the outer ring modulator output) changes.2) Fluctuations in voltage from the role of disturbance rejection in time.3) The speed of the dynamic process of ensuring that the maximum allowable motor current, thereby speeding up the dynamic process.4) When the motor overload or stall when the armature current limit of the maximum, automatic protection from the role of acceleration. Once the faultdisappears, the system automatically return to normal. Yesterday, the role of the reliable operation is very important.Ⅱdouble-loop speed control system common faults analysis1.Introduction of a system(1). Double-loop speed control system components in Figure 1. Current loop: from the current regulator LT, trigger CF (input transformation for the CSR), silicon-controlled rectifier bridge, motor armature and current loop transform LB component. the speed of outer ring: the speed regulator from ST, current loop, such as link inertia, motor and load moment of inertia and the speed of transformation components SB. in the double-loop speed control system, the speed of the decision loop of the running characteristics of the whole system and stability, and play a leading role, and to change the current ring plays the role of the internal structure of the system is dependent, but since it is as a whole to participate in the closed-loop speed to the speed of a direct impact on the work of the closed-loop, it must first good debugging current loop, and then testing the speed of outer ring, so that the whole system has good dynamic performance.(2). Double-loop speed control system of the typical working condition1) Start (or the speed):ST in the start-up process has been saturated, so that the speed of this loop in the equivalent open-loop state. System only in the constant current loop under the regulation to ensure the motor at a constant current of the maximum allowable under the start-up.Figure 1 double-loop speed control system structure2) slow down (or stop):ST at this time to reach the output amplitude of the reverse limit. Main circuit current by the bridge is reduced to zero after the inverter. LT and CSR output will soon reach the maximum reverse. CF pulse output to reach βmin, current loop for open-loop. motor torque under deceleration until the motor speed close to the given new value, current loop and speed loop one after another into the closed-loop work, motor in the new value of a given run .3) Grid voltage fluctuation: This motor because of the larger moment of inertia, which caused the first change in armature current, ST output also did not change the effect of current loop, LT rapidly changing the output so that angle α be adjusted quickly, so the impact on the speed .4）Small changes in load: in the operation, load changes, will cause the motor speed deviation from the given value. speed up the recovery process and the aforementioned speed (or deceleration) is similar to the process.2. Common Fault Analysis and Processing(1) The normal supply voltage, thyristor rectifier output waveform arrhythmia caused by this phenomenon is due to trigger sawtooth slope caused inconsistency. Sawtooth slope adjust potentiometer, the output waveform uniformity could be achieved. in the adjustment process to strike a balance between Qi, this point should be paid attention to the actual debugging.(2) DC Motor Analysis of mechanical properties of soft thyristor DC motor system, when the current intermittent mechanical properties when the first no-load speed is characterized by high ideals, and the second is characterized by mechanical properties of soft . The so-called mechanical features soft, that is, small changes in load will cause great changes in speed. oscilloscope to observe when using the bridge rectifier output waveform, one may find that missing relative. at this time need to check whether the trigger has pulse output, fast whether the fuse melting, whether the breakdown or thyristor circuit,synchronous transformer is damaged, whether the lack of power. to identify the problems, can be resolved.(3) The speed of the speed of instability caused by many factors of instability:1) Electric guns are not firmly fixed or with the host of different axis .2) The parameters of the speed regulator inappropriate. Respond to the dynamic parameters to adjust (change the ratio of integral parameters ) .3) Of a speed control system there are(or bad)4) May be caused as a result of interference. should be found to interfere with the reasons for taking anti-jamming measures.(4) A little to the set rated motor speed is higher than that should first check whether it is normal for the external control system, such as outside the normal control system, it may be given points, speed regulator, current regulator, such as caused by link failure. Should be cut off the main circuit power supply, only the control system to the electricity, not a given in the case, testing each of the key points (such as the current regulator, voltage regulator, etc. of the potential. and then given together with the former to one by one after each of the key points to check the potential changes, you can find out the fault lies.(5) Bridge rectifier output voltage is not high stressed 1) the speed regulator and current regulator limiter too small, should be liberalized in accordance with appropriate amplitude threshold .2) than the speed feedback signal, in that they can reduce the rate of appropriate feedback signals.(6) To the timing system still in the absence of low-speed operation (that is, the phenomenon of emergence of reptiles) This is because the system of "zero drift" caused by. When the input signal is zero, the output voltage by the input amplification stage of the offset potentiometer decisions can be offset by adjusting the potential allows α = 90 °, at this time to zero output voltage rectification system, the electrical will not crawl.(7) With a given system can not runShould first check whether it is normal for the external control system, such as outside the normal control system, it may be given points, speed regulator, currentregulator, such as caused by link failure. Shall be cut off main circuit power supply, only the control system to the electricity, not Add the given circumstances, the key points of each test (such as the current regulator, voltage regulator, etc.) of the potential. and then combined with a given, after the previous one by one to each of the key points to check the potential changes, that is, where to find fault. (8) Lack of control accuracy in the distributor for a given run-time external control often requires precision sufficient parking in order to work properly. If poor precision parking, you can adjust the speed of the appropriate regulator of the PI link, generally by reducing the the ratio of the integral part of efforts to get satisfactory results.(9) Reversible system oscillation 1) open-loop system in the state (the main circuit disconnect) the oscillation can be changed at this time given the previous inspection to the key points of the potential changes. If a given unchanged, but the potential is still a point of change, here is the crux of .2) system in the state when the closed-loop oscillation, in which case in order to ensure the safety of the electrical load should be replaced by the general resistance of the load, if there is no suitable resistance box which can be used in place of the two electric sub-series. inspection methods and similar open-loop, focusing on the link to check is: given points, level detection, operation control, such as the speed regulator. oscillations are often caused as a result of operational amplifiers, such as damage to electronic components , system parameters caused by improper, according to the specific circumstances, properly addressed.一、系统分析与综合1.系统分析（1）在转速、电流双闭环调速系统中，若要改变电动机的转速，应调节什么参数？改变转速调节器的放大倍数Kn行不行？改变电力电子变换器的放大系数Ks行不行？改变转速反馈系数∂行不行？若要改变电动机的堵转电流，应调节系统中的什么参数？答：若要改变电动机的转速，改变转速调节器的放大倍数Kn和电力电子变换器的放大系数Ks都不行，稳定时∂n=Un=Un*,所以只有改变给定值Un*和反馈系数∂才行。
- 1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
- 2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
- 3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。
对称相电压
在图 2-10 中,三相电源的终端呗标记为 a、b、c，电源相电压标记为Ean ， Ebn ，Ecn ，当电源的三相电压有相同的幅度，任意两相之间互差 120 度角时，电 源是对称的。当以Ean 作为参考相量时，相电压的幅值是 10v，对称三相相电压 如下所示：
Ean =100 Ebn 10 120 10 240 （2.5.1） Ecn 10 120 10 240
8
河南理工大学 HENAN POLYTECHNIC UNIVERSITY
480 30 Ean 3 IA= Z L ZY 180 30 40 3 277.1-30 （0.0872+j0.9962）（ + 7.660+j6.428） 277.1-30 277.1-30 = = =25.83-73.78 A （2.5.18） （7.748+j7.424） 10.7343.78 I B 25.83166.22 A I C 25.8346.22 A
Ebn Eab
Ebc
30
Ean
Ecn
Eca
（a）向量图
b
Eab Ebn
a
Ebc Ean Eca
c
Ecn
（b）电压三角形
图 2.12 正序三相 Y 形连接系统相电压和相线电压
3
河南理工大学 HENAN POLYTECHNIC UNIVERSITY
对称线电流
在图 2-10 中，因为从电源到负载的中性线的阻抗忽略不计，所以 n 与 N 之间是 同电位的，即EnN =0。因此每一相都可以列一个单独的 KVL 方程，经观察，线电 流为：
I a Ean ZY I b Ebn ZY （2.5.7） I c Ecn ZY
例如，如果每一相负载阻抗
ZY = 230 ，那么
100 5 30 230 10 120 Ib 5 150 230 10 120 Ib 590 230 Ia
3 倍且滞后于 30
。也就是说：
I a = 3I AB -30 I b = 3I BC -30 I c = 3I CA-30
Ic
（2.5.14）
I CA
I AB
-30
Ib
I BC
Ia
图 2.15
对称 形负载线电流相电流向量图
6
河南理工大学 HENAN POLYTECHNIC UNIVERSITY
（2.5.10）
ib ia ic
图 2-13 对称三相系统线电流向量图
4
河南理工大学 HENAN POLYTECHNIC UNIVERSITY
线电流向量图见图 2.13。 因为这些线电流组成一个闭合三角形， 它们的和， 也就是所谓的中性点电流，为零。一般来说，任意三相对称矢量和为零，因为对 称矢量组成了一个闭合三角形。因此，虽然中性线阻抗设为零，只要系统是对称 的，不论中性线阻抗是为零还是为 ，中性点电流为零。当电源电压，负载阻 抗，或是线路阻抗不对称时，也就是所谓的系统不对称时，此时，在中性点 n 与 N 之间将会有中性点电流 I n 流过，即线电流不对称。
而且，线电流也可由每个 形负载 KCL 方程求得，如下所示：
（2.5.12）
I a =I AB -I CA =3.4640 -3.464-120= 3 3.464-30 I b =I BC -I AB =3.464 120 -3.4640= 3 3.464-150 (2.5.13) I c =I CA -I BC =3.464120 -3.464-120= 3 3.464 90
式（2.5.12）和式（2.5.13）所求出的线电流都是对称的。因此对称 形 负载的线电流和（ I AB + I BC + I CA ）等于零。即使系统是不对称的，由于没有中 性线，线电流和（ I a + I b + Ic ）恒为零。比较式（2.5.12） 和式（2.5.13）得出以下结论： 对于一个对称正序电源带对称 形负载电路，流入负载的相电流是 形负 载线电流的
对称 连接负载
图 2-14 是一个 Y 连接电源带动一个 负载的电路图。对于对称 连接，见 图 2-14，相同的负载阻抗组成了一个三角形，三角形的顶点代表母线，标为 A， B，C。 形连接没有中性线。 因为图 2-14 忽略了导线阻抗，所以电源线电压等于负载线电压，所以 形 连接的负载电流 I AB ， I BC ， I CA 分别为：
对称线电压
电压Eab ，Ebc ，Eca 称为线电压。在图 2-10 中的线路 a、b 之间列一个 KVL 方程如下;
Eab Ean Ebn
对于式 2.5.1 中的相电压：
（ 2.5.2 ）
1 j 3 Eab 100 10120 10 10 2 3 j1 Eab 3 10 3 1030 2
同理可得，线电压Ebc ，Eca 为：
（ 2.5.3 ）
Ebc Ebn Ecn 10 120 10 120 3 10 90 （2.5.4） Eca Ecn Ean 10 120 100 3 10150 （2.5.5）
A
+
IA
E AB
C
Z
Z Z
-
B
（a）对称 形负载
A + C
EAB
- B
ZY
ZY
N
ZY
ZY
Z 3
（b）等效对称 Y 形负载
2.16
对称负载 -Y 变换
对称负载 -Y 变换
图 2.16 显示的是一个对称 向 Y 形负载的变换。 如果电压一定， 从终端 A， B，C 端子看， 形电路和 Y 形电路的电路是相等的。对于 形负载：
Eab 3Ean 30
这是由图 2-12 总结出的一个非常重要的结论。 Ebc 3Ebn 30（2.5.6）
Eca 3Ecn 30
在图 2-12（a）中，每一个相量都起始于向量图的起点。在图 2-12（b）中，线 电压组成了与系统中 a，b，c，相相对应的以 a，b，c 为顶点的等边三角形。相 电压起于三角形的顶点,止于三角形的中心点,三角形的中点被标记为 n。同时， 图 2.12 （b） 中的三角形顶点标为 abc 也就意味着电压为正序电压。 在两个图中， Ean 均为参考电压。然而，这两个图都可以被旋转以适应任何一个电压作为参考 相量。 图 2.12 中的线电压组成了一个闭合三角形，他们的向量和为零。实际上， 线电压和Eab + Ebc +Eca 总为零， 即使系统是不对称的， 因为这些电压围绕线路 a， b， c 组成了一个闭合途径。 而且， 在一个对称系统中， 相电压之和Ean +Ebn +Ecn 为 零。
Ib
B
图 2-14
Y 连接电源带 连接负载电路图
5
河南理工大学 HENAN POLYTECHNIC UNIVERSITY
1030 I AB = 3 =3.4640 A 5 30 10-90 I BC = 3 =3.464-120 A 5 30 10150 I CA = 3 =3.464+120 A 5 30
线电流也是对称的，因为它们幅值相同，都为 5A，且任意两相相差 120 度。图 2-10 中的中性点电流可以通过中性点 N 出列 KCL 求得：
I n =I a +I b +Ic
由式（2.5.8）的线电流可得：
（2.5.9）
I n =5 30 +5 150 +590 3-j1 - 3-j1 I n =5 +5 +j5=0 2 2
2.5
对称三相电路
在这一部分,我们介绍三相对称电路的一下几个话题：Y 连接,相电压，线电
压，线电流，△形连接负荷，△-Ｙ变换，以及等效的相图。
c C
a
AC
A
ZY ZY
Ecn
AC
Ean
n
AC
N
Ebn
ZY
b
B
图 2-10 三相Ｙ连接电源带Ｙ连接对称负荷电路图
对称Ｙ连接
图 2-10 显示的是一个三相Ｙ连接电源带Ｙ连接对称负荷电路图。对于Ｙ连 接电路，每个相的中性点是连接起来的。在图 2-10 中电源中性点标记的是 n， 而负载中性点标记的是Ｎ。 把三相电源假设为理想电源， 即阻抗忽略不计。 同时， 电源和负载之间线路阻抗， 中性点ｎ与Ｎ之间的线路阻抗也可忽略不计。三相负 荷是对称的，意味着三相之中任意两相间的阻抗是相同的。
1
河南理工大学 HENAN POLYTECHNIC UNIVERSITY
E cn
120
Ean
Ebn
图 2-11 以Ean 作为参考的对称正序相电压向量图 当Ean 超前Ebn 120 度，Ebn 超前Ecn 以 120 度角时，此时的相序称为正相序或 者 abc 相序。当Ean 超前Ecn 120 度，Ecn 超前Ebn 以 120 度角时，此时的相序称为 负相序或者 acb 相序。公式 2.5.1 的电压为正相电压，因为Ean 超前Ebn 120 度。 相应的向量图见图 2-11。
A
ZY
n
AC
N
Ebn
b
Z L =185
ZY
IB
B
图 2-17
例 2.4 电路图
解：很容易得出如下解:首先转换 形负载到等效的 Y 形负载电路，然后用一个 零阻抗导线连接电源中性点和负载中性点，因为在对称系统中 I n =0 ，所以中性 线的连接对电路无影响。所得的电路见图 2-17，所以，线电流为：