电力系统谐波成因分析及谐波潮流计算-外文翻译.doc

中文译文：电力系统谐波成因分析及谐波潮流计算首先一个理想的电力系统是由单一恒定频率与规定幅值的稳定电压供电的。但实际上，由于近年来随着科学技术的不断发展，在电力系统中大功率换流设备和调压装置的使用、高压直流输电的应用、大量非线性负荷的出现以及供电系统本身存在的非线性元件等引起系统中的电压波形畸变是越来越严重，对电力系统造成了很大的危害，例如：导致供电系统中的元件损耗增大、降低用电设备的使用寿命、干扰通信系统等。严重时甚至还能使设备损坏，自动控制失灵，继电保护误动作，从而造成停电事故等及其它问题。所知己知彼，百战不殆，因此,要实现对电网谐波的综合治理,就必须明确谐波的来源及电网在各种不同运行方式下谐波潮流的分布情况，以采取相应的措施限制和消除谐波，从而改善供电系统供电质量和确保系统的安全经济运行。其次，电力系统中谐波源是多种多样的。主要有以下几种：1、系统中的各种非线性用电设备如：换流设备、调压装置、电气化铁道、电弧炉、荧光灯、家用电器以及各种电子节能控制设备等是电力系统谐波的主要来源。即使这些设备提供理想的正弦波电压，它取用的电流也是非线性的，即有谐波电流存在。并且这些设备产生的谐波电流也将注入电力系统，导致系统各处电压产生谐波分量。这些设备的谐波含量决定于它本身的特征和工作条件，基本上与电力系统参数无关，可视为谐波恒流源。2、供电系统本身存在的非线性元件是谐波的又一来源。这些非线性元件主要有变压器激磁支路、交直流换流站的可控硅控制元件、可控硅控制的电容器、电抗器组等。3、用户电器设备产生的谐波分量也会对系统产生影响。如荧光灯、家用电器等的单容量不大，但数量很大且散布于各处，电力部门又难以管理的用电设备。如果这些设备的电流谐波含量过大，则会对电力系统造成严重影响，对该类设备的电流谐波含量，在制造时即应限制在一定的数量范围之内。4、发电机发出的谐波电势。发电机发出额定电势的同时也会有谐波电势产生，其谐波电势取决于发电机本身的结构和工作条件，基本上与外接阻抗无关。故可视为谐波恒压源，但其值很小。再次，电力系统谐波潮流计算，所谓电力系统谐波潮流计算，就是通过求解网络方程In=YnUn (n=3,5,7.n：谐波次数。In为谐波源负荷注入电网的n次谐波电流列向量。Yn为电网的n次谐波导纳阵。Un为电网中各节点母线的n次谐波电压列向量)。求得电网中各节点（母线）的谐波电压，进而求得各支路中的谐波电流。当电力系统中存在有谐波源时，此时系统中各接点电压和支路电流均会有高次谐波。为了确定谐波电压和谐波电流在供电系统中的分布，需要对谐波阻抗构成的等效电路进行潮流计算，同时当整流装置供电系统中有容性元件存在时，还要根据各支路谐波阻抗的性质和大小，来检验有无谐振的情况。进行谐波潮流计算，首先必须确定电网元件的谐波阻抗。31 电网各类元件的谐波阻抗：1.同步发电机的谐波阻抗合格的发电机的电势是纯正弦的，不含有高次谐波，其发电机电势只存在于基波网络。在高次谐波网络里，由于发电机谐波电势很小，此时可视发电机谐波电势为零。故其等值电路为连接机端与中性点的谐波电抗。其中 XGn=nXG1-（1）式中 XG1为基波时发电机的零序、正序或负序电抗，有该次谐波的序特性决定如果需要计及网络损耗，对于发电机，可将其阻抗角按85度估计，对于输电线，变压器和负荷等元件的等值发电机，可将其阻抗角按75度估计。2.变压器的谐波阻抗电力系统谐波的幅值常是随着频率的升高而衰减，故在基波潮流计算尤其是高压电网中，常忽略变压器的激磁支路和匝间电容。在计算谐波电流时，只考虑变压器的漏抗，且认为与谐波次数所认定的频率成正比。在一般情况下，变压器的等值电路就简化为一连接原副边节点其中的谐波电抗为变压器基波漏电抗。在高次谐波的作用下，绕组内部的集肤效应和临近效应增大，这时变压器的电阻大致与谐波次数的平方成正比，此时的变压器谐波阻抗为： Zn=sqrt(n)RT1+jnXT1-（3）其中RT1为基波时变压器的电阻。对于三相绕组变压器，可采用星型等值电路，其谐波阻抗的计算方法通上。当谐波源注入的高次谐波电流三相不对称时，则要根据变压器的接线方式和各序阻抗计算出三相谐波阻抗。3.电抗器的谐波阻抗当只计及电抗器感抗时，对n次谐波频率为：XLn=Nxl*UN/sqrt(3)IN4.输电线路的谐波阻抗输电线路是具有均匀分布参数的电路，经过完全换位的输电线路可看作是三相对称的。在潮流计算中，通常以集中参数的PI型等值电路表示。 在计及分布特性的情况下，则：ZLn=Znsh(rnl)Yln/2=(chrnl-1)/(Znshrnl)ZN和RN分别为对于于该次谐波时线路的波阻抗和传播常数。其中 Zn=sqrt(Z0n/Y0n) Rn=sqrt(Z0nYon)Z0N和Y0N 分别为该次谐波时输电线路单位长度的阻抗和导纳5.负荷的谐波阻抗在谐波潮流计算时，基波部分可按节点注入功率看待，而在谐波网络中将它看作是恒定阻抗，近似地可认为综合负荷为一等值电动机。其综合负荷的谐波等值阻抗值为：ZN=SQRT（N）R1+JNX1其中 R1，X1 为基波等值电动机的负序电阻、电抗、其值可由该节点的基波电压、功率值经换算求得。零序电流一般不会进入负荷，因而在零序性的高次谐波网络里，可忽略负荷支路。当确定了电路中各电气元件的谐波阻抗后，可以构成一个谐波作用的等效电路，以便进行计算，绘制谐波作用下的等效电路时应注意以下几个特点：（1）、谐波作用的等效电路，均应以整流装置为中心，按照实际接线构成，于是整流装置视为谐波源，而电力系统的发电机不是以能源出现，而是作为谐波源的负载阻抗的一部分。（2）、电路元件阻抗可以用有名值进行计算，也可以用标幺值进行计算。当采用有名值进行计算时，全部电路应折算到某一基准电压，便于分析和应用。（3）一般计算中，元件的所有电阻均可忽略，但是当系统某一部分发生或接近并联或串联谐振时，此时的电阻影响却不能忽略。（4）、在谐波电流近似计算中，所确定的是整流装置侧的总谐波电流，根据谐波作用等效电路，才能确定各支路谐波电流和电压的分布。3.2 谐波潮流计算3.2.1 无容性元件网络的谐波潮流计算（1）、对称系统的谐波潮流计算对称系统中三相情况相同，因此可以按一相情况来计算。当确定了整流装置任一侧总谐波电流后，结合谐波等效电路，就可以确定系统网络中任一支路的谐波电流分布。然后再根据节点谐波电压和节点注入谐波电流的关系I=YU（其中，Y为谐波导纳阵），就可以确定各处的节点谐波电压了。进而可求出潮流功率。其计算步骤如下：、根据所给运行条件，以通常的潮流计算方法求解基波潮流。、按谐波源工作条件，确定其它有关参数及需要计算的谐波次数。、计算各元件谐波参数，形成各次谐波网络节点导纳矩阵，并计算相应谐波网的注入电流。、由式IN=YNUN确定各节点的谐波电压，并计算各支路谐波功率。其中，应注意有谐波仪测出的谐波注入电流，其相角是相对于基波电流的相角。故求出基波电流后，需将谐波注入电流相角进行修正。同样，系统节点的功率是基波功率与谐波功率之和，故基波注入功率也应进行修正。但线性负荷处的基波注入功率不必修正。（2）、不对称系统谐波潮流计算在不对称系统中，三相情况各不相同，而且相互影响，因此必须同时进行三相系统的计算。不对称网络潮流的计算可将网络分为各次谐波网络，先计算基波网络，求得各节点基波电压后，按它计算各谐波潮流的各次注入电流，再按此谐波注入电流解算各次谐波的网络方程，求出各节点的各次谐波电压。四总结电力系统中谐波的出现，对于电力系统运行是一种污染。它们减少了系统电压正玄波形的质量，不仅严重地影响了电力系统自身，而且也损害了用户和周围的通信系统。因此对电力系统谐波的研究对于改善电能质量，抑制和消除谐波具有十分重要的意义。Power system harmonic analysis and harmonic tidal calculationFirstly, the ideal electrical power system is supplied by a regulated voltage source that has a single and constant frequency and specified amplitude . But in fact, with the development of science and technology in recent years, the use of high - power commutation devices and regulating devices, the applications of HVDC ，the emergence of a large number of non-linear load as well as the power supply system itself and so on that have cause a distortion which is more and more serious to the Voltage waveform, which has caused very great harm to the electrical power system. For example: it can Causes the Component Losses in the power supply system more serious, reduce the life of electrical equipment, disturb the communication system and so on. It can also damage the equipment, result in automatic control malfunction and cause the misoperation of relay protection. Thus cause the power outage accident and other questions. So-called Know me and know thee, lose none and win all , therefore, if you want to Comprehensive manage the power system harmonic, you must make clear the harmonic sources and distribution grid of harmonic power flow in a variety of different operating modes , then you can take appropriate measures to limit and eliminate harmonics to improve power quality of the power supply system and ensure the safety of system with economic operation . Secondly, the source of electrical power system overtone has a varied forms. It mainly has the following several kinds: 1, systems each kind of nonlinear electric equipment. For example: Converter equipment, regulator device, electrified railway, electric-arc furnace, fluorescence the lamp, the domestic electric appliances and kinds of electronic energy conservation control device and so on are the important source of electrical power system overtone. Even if these equipment supplies the ideal sine wave voltage, the electric current it takes is also non-linear, namely the harmonic current exists. And the harmonic current the equipment produces will also pour into the electrical power system, which will cause existence of harmonic component in the system voltage of each place. The overtone that has nothing to do with the electrical power system parameter in these equipment decided its characteristic and working condition, which maybe regarded as source of the overtone with constant flow. 2, the overtone generated by the nonlinear element in the power supply system itself is another origin. There are many kinds of nonlinear element. For example: transformer excitation branch , Ac/dc converter thyristor control element, thyristor controlled capacitor, reactor, etc.3, The harmonic component produced by user electric equipment will also impact on the system. Such as fluorescent lamps, household appliances with a small capacity has a large quantity and spread in everywhere.So the power sector has difficulty in managing such equipment. If harmonic content current of these devices is too large, it will cause serious impact to power system,and the manufacturing number of the current harmonic content of this kind of equipment should be limited in a certain range.4, Harmonic voltage from generator is another source. Generator is sued to produce the rated voltage but at the same time also engender harmonic voltage which is determined by the structure and the working conditions of the generator.And harmonic voltage has nothing to do with external impedance that can be treated as the harmonic constant voltage source, but its value is very small.Thirdly, The calculation of power system harmonic power flow is completed by solve the network equations In = YnUn (n = 3, 5, 7. n: number of harmonics. In: Harmonic currents n times column injected into power grid by load that is considered as the harmonic source . Yn: n times harmonic admittance matrix of power grid. Un: n times harmonic voltage of each bus nodes in the grid column). We can get the power grid harmonic voltage of each node (bus) then the harmonic current of each current branch.When there are harmonic sources exist in the power system, the system of contact voltages and branch currents will have higher harmonic. In order to determine the distribution of harmonic voltage and harmonic current in power supply system , we need do calculation of power flow for equivalent circuit consisted by harmonic impedance.At the same time, when capacitive component exist in rectifying device in the power supply system, also according to the nature and size of each branch of harmonic impedance to verify presence of resonance condition.To do harmonic power flow calculation, we must determine the harmonic impedance of power grid element first.3.1 Power grid harmonic impedance of all kinds of components:1. Harmonic impedance of synchronous generatorQualified potential is pure sine generator, do not contain high order harmonic, the generator voltage is only the base network.In higher harmonic network, due to the harmonic voltage generator is very small, we can regard harmonic voltage generator as zero at this time. Therefore, its equivalent circuit is harmonic reactance that connected to the machine side and neutral.The XGn = nXG1 - - - - - - - - - - - - - (1) Type of XG1 is fundamental wave generator, positive sequence and negative sequence based on the zero sequence reactance decided by the characteristics of harmonic sequence. if needs to take lose of the network into consideration, estimates that the generators impedance angle according to 85 degrees, regarding the transmission line, parts and so on transformer and load equivalent generators, may its impedance angle according to 75 degrees . 2.Harmonic impedance of transformer Power system harmonic with the increase of frequency and amplitude attenuation is often change, so often ignore the excitation transformer branch and turn-to-turn capacitive when calculating the base wave method especially in high voltage grid. When calculating the harmonic current, only consider the transformer leakage reactance, and think that is proportional to the harmonic frequency determined by the frequency. In the general case, the transformer equivalent circuit is simplified as the former vice edge connection node and one of the fundamental harmonic reactance is transformer leakage reactance.Under the action of high order harmonic, the skin effect and the adjacent effect inside the winding increases, then the of the transformers resistance is proportional to the square of the number of times for the harmonic, the harmonic impedance for the transformer:Zn= SQRT (n) + jnXT1 RT1 - - - - - - - - - - - (3)The RT1 is fundamental wave resistance of a transformer.For three-phase winding transformer, the radial equivalent circuit can be used, the calculation method of the harmonic impedance is same above.When the three-phase of higher harmonic current injected in harmonic sources are asymmetric, three-phase harmonic impedance can be calculated according to the connection mode of the transformer and each sequence impedance.3.Harmonic impedance of reactor. When only consider reactor inductance, the NTH harmonic frequency is: XLn = Nxl * UN/SQRT (3) IN4.Harmonic impedance of the transmission lineThe distributed parameter of transmission lines are uniform, the transmission line is considered to be a three-phase symmetrical after complete transposition. In the calculation of power flow, it usually be expressed as PI type equivalent circuit with a lumped parameter.Under the consideration of the meter and the distribution characteristics, then:ZLn=Znsh(rnl)Yln/2=(chrnl-1)/(Znshrnl)Zn and RN: the line impedance and the harmonic propagation constant.The Zn = SQRT (Z0n/Y0n) Rn = SQRT (Z0nYon)Z0N and Y0N: the harmonic impedance and admittance of per unit length of transmission lines5.Harmonic impedance of load In the calculation of harmonic power flow, the fundamental part can be regarded as the power injected by node, but it often be seen as a constant impedance in harmonic network, approximately integrated load can be thought of as an equivalent motor. Equivalent impedance values of the comprehensive load harmonic:ZN=SQRT（N）R1+JNX1R1, the X1 : the fundamental negative sequence resistance of equivalent motor, reactance, its value can be calculated by base waves voltage and power of the node.Not to load in the zero sequence current, so negligible load branch can be ignored in the higher harmonic zero sequence sex network because there is no zero-sequence current in load Under normal circumstances.When the harmonic impedance of each electric component are determined in the circuit, a harmonic equivalent circuit can be formed and calculated, in order to draw equivalent circuit under the action of harmonic , should pay attention to the following features:1.Equivalent circuit under the action of harmonic and shall be centered on rectifying device, according to the actual wiring, so regard the rectifier device as a source of harmonic, and power system energy generator is not to appear, but as part of the harmonic source load impedance.2.Circuit components impedance can be calculated by using a name value and also using the MAO values to calculate. When using a name values to calculate, all should be converted to a voltage reference circuits, in order to facilitate analysis and application.3.The resistance of all component can be ignored in general calculation, but when one part of the system or nearly parallel or series resonance occurs, the influence of the resistance cannot be ignored.4.Harmonic current is determined by total harmonic current of the rectifying device side in the approximate calculation, the selection of harmonic current and voltage distribution can be determined according to equivalent circuit of the harmonic.3.2 The calculation of harmonic power flow 3.2.1 The calculation of harmonic power flow without capacitive element network (1). Calculation of harmonic power flow in the symmetric systemThree-phase system is the same in the Symmetric system, so you can make a calculation according to consideration of one phase.When the total harmonic current of the rectifying device either side is determined, the harmonic current distribution of the system at any branch in the network can be determined according to harmonic equivalent circuit. Then according to the node harmonic voltage and harmonic current injected by the node I = YU (among them, Y : harmonic admittance matrix), the harmonic voltage of various nodes can be determined. And then the power of the tidal current can be worked out. The calculation steps are as follows:. The fundamental wave tide can be calculated by using the usual flow method according to the given operating conditions.According to the working conditions of harmonic source, other relevant parameters and harmonic frequency will be computed.Calculate the component of harmonic parameters, form every harmonic network node admittance matrix, and calculate the current injected in the corresponding harmonic net. Harmonic voltage of each node is determined by the type = YNUN IN and harmonic power of each branch is calculated.Among