毕业设计变压器外文翻译

I 摘 要 XF 110KV 变电所是地区重要变电所 是电力系统 110KV 电压等级的重要部分 其设计分为电气一次部分和电气二次部分设计 一次部分由说明书 计算书与电气工程图组成 说明书和计算书包括变电所 总体分析 负荷分析与主变选择 电气主接线设计 短路电流计算 电气设备选择 配电装置选择 变电所总平设计及防雷保护设计 二次部分由说明书 计算书与电气工程图组成 说明书和计算书包括整体概 述 线路保护的整定计算 主变压器的保护整定计算 电容器的保护整定计算 母线 保护和所用变保护设计 计算书和电气工程图为附录部分 其中一次部分电气 AutoCAD 制图六张 二次部分为四张手工制图 本变电所设计为毕业设计课题 以巩固大学所学知识 通过本次设计 使我 对电气工程及其自动化专业的主干课程有一个较为全面 系统的掌握 增强了理 论联系实际的能力 提高了工程意识 锻炼了我独立分析和解决电力工程设计问 题的能力 为未来的实际工作奠定了必要的基础 关键词关键词 变电所 变压器 继电保护 II AbstractAbstract XF county 110KV substation is an important station in this distract which is one of the extremely necessary parts of the 110KV network in electric power system The design of the substation can be separated in two parts primary part and secondary part of the electric design The first part consists of specifications computation book and Electrical engineering drawings about the design The specifications has several parts which are General analysis of the station Load analysis The selection of the main transformer Layout of configuration Computation of short circuit Select of electric devices Power distribution devices General design of substation plane and the design of thunderbolt protection The second part also consists of specifications computation book and electrical drawings about the design Specifications and computation book include following section General The evaluation and calculate of line protection Transformer protection capacitor protection Bus protection and Self using transformer protection Computation book Electrical engineering drawings and catalogue of drawings are attached in the end There are nine drawings total in which four are prepared by hand others are prepared by computer in which installed the software electrical AutoCAD From other view it also can be classified as first part and second part This is a design of substation for graduation design test It can strengthen our specified knowledge Key words substation transformer Relay protection 1 附录附录 1 1 外文资料翻译 外文资料翻译 A1 1 译文 变压器 1 介绍 要从远端发电厂送出电能 必须应用高压输电 因为最终的负荷 在一些点 高电压必须降低 变压器能使电力系统各个部分运行在电压不同的等级 本文我 们讨论的原则和电力变压器的应用 2 双绕组变压器 变压器的最简单形式包括两个磁通相互耦合的固定线圈 两个线圈之所以相 互耦合 是因为它们连接着共同的磁通 在电力应用中 使用层式铁芯变压器 本文中提到的 变压器是高效率的 因为它没有旋转损失 因此在电压等级转换的过程中 能量损失比较少 典型的 效率范围在 92 到 99 上限值适用于大功率变压器 从交流电源流入电流的一侧被称为变压器的一次侧绕组或者是原边 它在铁 圈中建立了磁通 它的幅值和方向都会发生周期性的变化 磁通连接的第二个 绕组被称为变压器的二次侧绕组或者是副边 磁通是变化的 因此依据楞次定律 电磁感应在二次侧产生了电压 变压器在原边接收电能的同时也在向副边所带的 负荷输送电能 这就是变压器的作用 3 变压器的工作原理 当二次侧电路开路是 即使原边被施以正弦电压 Vp 也是没有能量转移的 外加电压在一次侧绕组中产生一个小电流 I 这个空载电流有两项功能 1 在 铁芯中产生电磁通 该磁通在零和 m之间做正弦变化 m是铁芯磁通的最大 值 2 它的一个分量说明了铁芯中的涡流和磁滞损耗 这两种相关的损耗被 称为铁芯损耗 变压器空载电流 I 一般大约只有满载电流的 2 5 因为在空载时 原边 绕组中的铁芯相当于一个很大的电抗 空载电流的相位大约将滞后于原边电压相 位 90 显然可见电流分量 Im I0sin 0 被称做励磁电流 它在相位上滞后于原边 电压 VP 90 就是这个分量在铁芯中建立了磁通 因此磁通 与 Im同相 第二个分量 Ie I0sin 0 与原边电压同相 这个电流分量向铁芯提供用于损耗 的电流 两个相量的分量和代表空载电流 即 I0 Im Ie 2 应注意的是空载电流是畸变和非正弦形的 这种情况是非线性铁芯材料造成的 如果假定变压器中没有其他的电能损耗一次侧的感应电动势 Ep和二次侧的感 应电压 Es可以表示出来 因为一次侧绕组中的磁通会通过二次绕组 依据法拉第 电磁感应定律 二次侧绕组中将产生一个电动势 E 即 E N t 相同的磁通会 通过原边自身 产生一个电动势 Ep 正如前文中讨论到的 所产生的电压必定滞 后于磁通 90 因此 它于施加的电压有 180 的相位差 因为没有电流流过二次 侧绕组 Es Vs 一次侧空载电流很小 仅为满载电流的百分之几 因此原边电压 很小 并且 Vp的值近乎等于 Ep 原边的电压和它产生的磁通波形是正弦形的 因此产生电动势 Ep和 Es的值是做正弦变化的 产生电压的平均值如下 Eavg turns 给定时间内磁通变化量 给定时间 即是法拉第定律在瞬时时间里的应用 它遵循 Eavg N 4fN m 2 1 2 m f 其中 N 是指线圈的匝数 从交流电原理可知 有效值是一个正弦波 其值为平均 电压的 1 11 倍 因此 E 4 44fN m 因为一次侧绕组和二次侧绕组的磁通相等 所以绕组中每匝的电压也相同 因此 Ep 4 44fNp m 并且 Es 4 44fNs m 其中 Np和 Es是一次侧绕组和二次侧绕组的匝数 一次侧和二次侧电压增长的比 率称做变比 用字母 a 来表示这个比率 如下式 a p s E E p s N N 假设变压器输出电能等于其输入电能 这个假设适用于高效率的变压器 实际上我们是考虑一台理想状态下的变压器 这意味着它没有任何损耗 因此 Pm Pout 或者 VpIp primary PF VsIs secondary PF 这里 PF 代表功率因素 在上面公式中一次侧和二次侧的功率因素是相等的 因 此 VpIp VsIs 从上式我们可以得知 3 a p s V V p s I I p s E E 它表明端电压比等于匝数比 换句话说 一次侧和二次侧电流比与匝数比成 反比 匝数比可以衡量二次侧电压相对于一次恻电压是升高或者是降低 为了计 算电压 我们需要更多数据 终端电压的比率变化有些根据负载和它的功率因素 实际上 变比从标识牌 数据获得 列出在满载情况下原边和副边电压 当副边电压 Vs相对于原边电压减小时 这个变压器就叫做降压变压器 如果 这个电压是升高的 它就是一个升压变压器 在一个降压变压器中传输变比 a 远 大于 1 a 1 0 同样的 一个升压变压器的变比小于 1 a 1 0 当 a 1 时 变压器 的二次侧电压就等于起一次侧电压 这是一种特殊类型的变压器 可被应用于当 一次侧和二次侧需要相互绝缘以维持相同的电压等级的状况下 因此 我们把这 种类型的变压器称为绝缘型变压器 显然 铁芯中的电磁通形成了连接原边和副边的回路 在第四部分我们会了 解到当变压器带负荷运行时一次侧绕组电流是如何随着二次侧负荷电流变化而变 化的 从电源侧来看变压器 其阻抗可认为等于 Vp Ip 从等式 p s V V p s I I p s E E a 中我们可知 Vp aVs并且 Ip Is a 根据 Vs和 Is 可得 Vp和 Ip的比例是 p p V I s s aV Ia 2 s s a V I 但是 Vs Is 负荷阻抗 ZL 因此我们可以这样表示 Zm primary a2ZL 这个等式表明二次侧连接的阻抗折算到电源侧 其值为原来的 a2倍 我们把这种 折算方式称为负载阻抗向一次侧的折算 这个公式应用于变压器的阻抗匹配 4 有载情况下的变压器 一次侧电压和二次侧电压有着相同的极性 一般习惯上用点记号表示 如果 点号同在线圈的上端 就意味着它们的极性相同 因此当二次侧连接着一个负载 时 在瞬间就有一个负荷电流沿着这个方向产生 换句话说 极性的标注可以表 明当电流流过两侧的线圈时 线圈中的磁动势会增加 因为二次侧电压的大小取决于铁芯磁通大小 0 所以很显然当正常情况下负 载电势 Es没有变化时 二次侧电压也不会有明显的变化 当变压器带负荷运行时 将有电流 Is流过二次侧 因为 Es产生的感应电动势相当于一个电压源 二次侧电 流产生的磁动势 NsIs会产生一个励磁 这个磁通的方向在任何一个时刻都和主磁 4 通反向 当然 这是楞次定律的体现 因此 NsIs所产生的磁动势会使主磁通 0 减小 这意味着一次侧线圈中的磁通减少 因而它的电压 Ep将会增大 感应电压 的减小将使外施电压和感应电动势之间的差值更大 它将使初级线圈中流过更大 的电流 初级线圈中的电流 Ip的增大 意味着前面所说明的两个条件都满足 1 输出功率将随着输出功率的增加而增加 2 初级线圈中的磁动势将增加 以此来抵消二次侧中的磁动势减小磁通的趋势 总的来说 变压器为了保持磁通是常数 对磁通变化的响应是瞬时的 更重 要的是 在空载和满载时 主磁通 0的降落是很少的 一般在 1 至 3 其需 要的条件是 E 降落很多来使电流 Ip增加 在一次侧 电流 Ip 在一次侧流过以平衡 Is产生的影响 它的磁动势 NpIp 只停 留在一次侧 因为铁芯的磁通 0保持不变 变压器空载时空载电流 I0必定会为其 提供能量 故一次侧电流 Ip是电流 Ip 与 I0 的和 因为空载电流相对较小 那么一次侧的安匝数与二次侧的安匝数相等的假设 是成立的 因为在这种状况下铁芯的磁通是恒定的 因此我们仍旧可以认定空载 电流 I0相对于满载电流是极其小的 当一个电流流过二次侧绕组 它的磁动势 NsIs 将产生一个磁通 于空载 电流 I0产生的磁通 0不同 它只停留在二次侧绕组中 因为这个磁通不流过一次 侧绕组 所以它不是一个公共磁通 另外 流过一次侧绕组的负载电流只在一次侧绕组中产生磁通 这个磁通被 称为一次侧的漏磁 二次侧漏磁将使电压增大以保持两侧电压的平衡 一次侧漏 磁也一样 因此 这两个增大的电压具有电压降的性质 总称为漏电抗电压降 另外 两侧绕组同样具有阻抗 这也将产生一个电阻压降 把这些附加的电压降 也考虑在内 这样一个实际的变压器的等值电路图就完成了 由于分支励磁体现 在电流里 为了分析我们可以将它忽略 这就符我们前面计算中可以忽略空载电 流的假设 这证明了它对我们分析变压器时所产生的影响微乎其微 因为电压降 与负载电流成比例关系 这就意味着空载情况下一次侧和二次侧绕组的电压降都 为零 译自 5 A1 2 原文 TRANSFORMER 1 INTRODUCTION The high voltage transmission was need for the case electrical power is to be provided at considerable distance from a generating station At some point this high voltage must be reduced because ultimately is must supply a load The transformer makes it possible for various parts of a power system to operate at different voltage levels In this paper we discuss power transformer principles and applications 2 TOW WINDING TRANSFORMERS A transformer in its simplest form consists of two stationary coils coupled by a mutual magnetic flux The coils are said to be mutually coupled because they link a common flux In power applications laminated steel core transformers to which this paper is restricted are used Transformers are efficient because the rotational losses normally associated with rotating machine are absent so relatively little power is lost when transforming power from one voltage level to another Typical efficiencies are in the range 92 to 99 the higher values applying to the larger power transformers The current flowing in the coil connected to the ac source is called the primary winding or simply the primary It sets up the flux in the core which varies periodically both in magnitude and direction The flux links the second coil called the secondary winding or simply secondary The flux is changing therefore it induces a voltage in the secondary by electromagnetic induction in accordance with Lenz s law Thus the primary receives its power from the source while the secondary supplies this power to the load This action is known as transformer action 3 TRANSFORMER PRINCIPLES When a sinusoidal voltage Vp is applied to the primary with the secondary open circuited there will be no energy transfer The impressed voltage causes a small current I to flow in the primary winding This no load current has two functions 1 it produces the magnetic flux in the core which varies sinusoidally between zero and m where m is the maximum value of the core flux and 2 it provides a component to account for the hysteresis and eddy current losses in the core There combined losses are 6 normally referred to as the core losses The no load current I is usually few percent of the rated full load current of the transformer about 2 to 5 Since at no load the primary winding acts as a large reactance due to the iron core the no load current will lag the primary voltage by nearly 90 It is readily seen that the current component Im I0sin 0 called the magnetizing current is 90 in phase behind the primary voltage VP It is this component that sets up the flux in the core is therefore in phase with Im The second component Ie I0sin 0 is in phase with the primary voltage It is the current component that supplies the core losses The phasor sum of these two components represents the no load current or I0 Im Ie It should be noted that the no load current is distortes and nonsinusoidal This is the result of the nonlinear behavior of the core material If it is assumed that there are no other losses in the transformer the induced voltage In the primary Ep and that in the secondary Es can be shown Since the magnetic flux set up by the primary winding there will be an induced EMF E in the secondary winding in accordance with Faraday s law namely E N t This same flux also links the primary itself inducing in it an EMF Ep As discussed earlier the induced voltage must lag the flux by 90 therefore they are 180 out of phase with the applied voltage Since no current flows in the secondary winding Es Vs The no load primary current I0 is small a few percent of full load current Thus the voltage in the primary is small and Vp is nearly equal to Ep The primary voltage and the resulting flux are sinusoidal thus the induced quantities Ep and Es vary as a sine function The average value of the induced voltage given by Eavg turns change in flux in a given time given time which is Faraday s law applied to a finite time interval It follows that Eavg N 4fN m 2 1 2 m f which N is the number of turns on the winding Form ac circuit theory the effective or root mean square rms voltage for a sine wave is 1 11 times the average voltage thus E 4 44fN m Since the same flux links with the primary and secondary windings the voltage per turn in each winding is the same Hence 7 Ep 4 44fNp m and Es 4 44fNs m where Ep and Es are the number of turn on the primary and secondary windings respectively The ratio of primary to secondary induced voltage is called the transformation ratio Denoting this ratio by a it is seen that a p s E E p s N N Assume that the output power of a transformer equals its input power not a bad sumption in practice considering the high efficiencies What we really are saying is that we are dealing with an ideal transformer that is it has no losses Thus Pm Pout or VpIp primary PF VsIs secondary PF where PF is the power factor For the above stated assumption it means that the power factor on primary and secondary sides are equal therefore VpIp VsIs from which is obtained a p s V V p s I I p s E E It shows that as an approximation the terminal voltage ratio equals the turns ratio The primary and secondary current on the other hand are inversely related to the turns ratio The turns ratio gives a measure of how much the secondary voltage is raised or lowered in relation to the primary voltage To calculate the voltage regulation we need more information The ratio of the terminal voltage varies somewhat depending on the load and its power factor In practice the transformation ratio is obtained from the nameplate data which list the primary and secondary voltage under full load condition When the secondary voltage Vs is reduced compared to the primary voltage the transformation is said to be a step down transformer conversely if this voltage is raised it is called a step up transformer In a step down transformer the transformation ratio a is greater than unity a 1 0 while for a step up transformer it is smaller than unity a 1 0 In the event that a 1 the transformer secondary voltage equals the primary voltage This is a special type of transformer used in instances where electrical isolation is required between the primary and secondary circuit while maintaining the same 8 voltage level Therefore this transformer is generally knows as an isolation transformer As is apparent it is the magnetic flux in the core that forms the connecting link between primary and secondary circuit In section 4 it is shown how the primary winding current adjusts itself to the secondary load current when the transformer supplies a load Looking into the transformer terminals from the source an impedance is seen which by definition equals Vp Ip From a we have Vp aVs and Ip p s V V p s I I p s E E Is a In terms of Vs and Is the ratio of Vp to Ip is p p V I s s aV Ia 2 s s a V I But Vs Is is the load impedance ZL thus we can say that Zm primary a2ZL This equation tells us that when an impedance is connected to the secondary side it appears from the source as an impedance having a magnitude that is a2 times its actual value We say that the load impedance is reflected or referred to the primary It is this property of transformers that is used in impedance matching applications 4 TRANSFORMERS UNDER LOAD The primary and secondary voltages shown have similar polarities as indicated by the dot making convention The dots near the upper ends of the windings have the same meaning as in circuit theory the marked terminals have the same polarity Thus when a load is connected to the secondary the instantaneous load current is in the direction shown In other words the polarity markings signify that when positive current enters both windings at the marked terminals the MMFs of the two windings add Since the secondary voltage depends on the core flux 0 it must be clear that the flux should not change appreciably if Es is to remain essentially constant under normal loading conditions With the load connected a current Is will flow in the secondary circuit because the induced EMF Es will act as a voltage source The secondary current produces an MMF NsIs that creates a flux This flux has such a direction that at any instant in time it opposes the main flux that created it in the first place Of course this is Lenz s law in action Thus the MMF represented by NsIs tends to reduce the core flux 0 This means that the flux linking the primary winding reduces and consequently the 9 primary induced voltage Ep This reduction in induced voltage causes a greater difference between the impressed voltage and the counter induced EMF thereby allowing more current to flow in the primary The fact that primary current Ip increases means that the two conditions stated earlier are fulfilled 1 the power input increases to match the power output and 2 the primary MMF increases to offset the tendency of the secondary MMF to reduce the flux In general it will be found that the transformer reacts almost instantaneously to keep the resultant core flux essentially constant Moreover the core flux 0 drops very slightly between n o load and full load about 1 to 3 a necessary condition if Ep is to fall sufficiently to allow an increase in Ip On the primary side Ip is the current that flows in the primary to balance the demagnetizing effect of Is Its MMF NpIp sets up a flux linking the primary only Since the core flux 0 remains constant I0 must be the same current that energizes the transformer at no load The primary current Ip is therefore the sum of the current Ip and I0 Because the no load current is relatively small it is correct to assume that the primary ampere turns equal the secondary ampere turns since it is under this condition that the core flux is essentially constant Thus we will assume that I0 is negligible as it is only a small component of the full load current When a current flows in the secondary winding the resulting MMF NsIs creates a separate flux apart from the flux 0 produced by I0 which links the secondary winding only This flux does no link with the primary winding and is therefore not a mutual flux In addition the load current that flows through the primary winding creates a flux t