岑华蒙毕业设计外文翻译-SVC与STATCOM在电力系统中应用的效益

广西科技大学毕业设计外文翻译 院 别 电气与信息工程学院 专 业 电气工程与自动化 班 级 电气101班 学 号 7 姓 名 岑华蒙 指导教师 周晓华 2013年12月28日Benefits of SVC and STATCOM for ElectricUtility Application Abstract- Examination of the behavior of SVCs and STATCOMs in electric power systems is presented. The paper is based on analytical and simulation analysis, and conclusions can be used as power industry guidelines. We explain the principle structures of SVCs and STATCOMs, the models for dynamic studies, and the impact of these devices on steady state voltage and transient voltage stability. Sensitivity analysis is provided which shows the impact of SVCs and STATCOMs with regard to network strength. Harmonic issues, space requirements, and price discussions are also briefly addressed. Index Terms Dynamic Compensators, SVC, STATCOM, Short Circuit Capacity, Gain Sensitivity, Short Term Voltage Stability, HarmonicsI. INTRODUCTIONSHUNT-connected static var compensators (SVCs) are used extensively to control the AC voltage in transmission networks. Power electronic equipment, such as the thyristor controlled reactor (TCR) and the thyristor switched capacitor (TSC) have gained a significant market, primarily because of well-proven robustness to supply dynamic reactive power with fast response time and with low maintenance.With the advent of high power gate turn-off thyristors and transistor devices (GTO, IGBT, ) a new generation of power electronic equipment, STATCOM, shows great promise for application in power systems 3,4.This paper aims to explain the benefits of SVCs and STATCOMs for application in utility power systems. Installation of a large number of SVCs and experience gained from recent STATCOM projects throughout the world motivates us to clarify certain aspects of these devices.II. BASIC DESCRIPTIONThis section explains briefly the basic configuration of SVCs and STATCOMs:A. SVCThe compensator normally includes a thyristor-controlled reactor (TCR), thyristor-switched capacitors (TSCs) and harmonic filters. It might also include mechanically switched shunt capacitors (MSCs), and then the term static var system is used. The harmonic filters (for the TCR-produced harmonics) are capacitive at fundamental frequency. The TCR is typically larger than the TSC blocks so that continuous control is realized. Other possibilities are fixed capacitors (FCs), and thyristor switched reactors (TSRs). Usually a dedicated transformer is used, with the compensator equipment at medium voltage. The transmission side voltage is controlled, and the Mvar ratings are referred to the transmission side.The rating of an SVC can be optimized to meet the required demand. The rating can be symmetric or asymmetric with respect to inductive and capacitive reactive power. As an example, the rating can be 200 Mvar inductive and 200 Mvar capacitive, or 100 Mvar inductive and 200 Mvar capacitive.B. STATCOM The voltage-sourced converter (VSC) is the basic electronic part of a STATCOM, which converts the dc voltage into a three-phase set of output voltages with desired amplitude, frequency, and phase. There are different methods to realize a voltage-sourced converter for power utility application. Based on harmonics and loss considerations, pulse width modulation (PWM) or multiple converters are used.Inherently, STATCOMs have a symmetrical rating with respect to inductive and capacitive reactive power. For example, the rating can be 100 Mvar inductive and 100 Mvar capacitive. For asymmetric rating, STATCOMs need a complementary reactive power source. This can be realized for example with MSCs.VII. THE FUNCTIONAL RATING CONCEPTTraditionally, SVCs of a common design have been used to handle different types of network problems. The trend today, however, is to tailor SVCs for their intended use. This is important in order to make SVCs cost efficient.For steady state voltage support, i.e., to follow the daily load pattern, bulk reactive power combined with stepless smooth voltage control is desired. Vernier voltage regulation can be provided by a TCR running in parallel with harmonic filters. The bulk reactive power is provided by mechanically switched capacitor banks (MSCs) or reactors (MSRs) governed by the SVC controller. Thus SVCs serve the purpose of continuously maintaining a smooth voltage, piloting the MSC switching.If the task is to support a system limited by post contingency voltage instability or unacceptable voltage levels, a large amount of quickly controllable reactive power is needed for a short time duration. An SVC with additional TSCs is an excellent choice. Post recovery voltage support may also be necessarythis is then preferably provided by MSCs governed by the SVC.For temporary over voltages, large inductive reactive power is needed for a short period of time. The standard TCR has some short-time over current capability. This capacity can easily be extended by lowering its steady state operating temperature and by “under sizing” the reactors.A. Enhanced SVCsThe SVC characteristic at depressed voltage can be efficiently improved by adding an extra TSC. This branch is intended to operate only during undervoltage conditions. It can be added without introducing additional cost in other parts of the SVC. Most important is that the current rating or the voltage capability of the power transformer does not need to be increased. Power transformers allow large overcurrent during limited time (IEEE C57-115 can be used as a guide for available capacity). In many cases three times overload in current for 10 seconds is available. The additional TSC rating is typically in the range of 50 to 100% of the SVC rating.B. SVC Short Term OverloadThe maximum power from an SVC at a given voltage is determined by its reactance. No overload capacity is available unless the reactance is lowered, e.g., by adding a TSC. For overvoltages, however, the SVC reactance is no longer the limiting factor; instead the current in components defines the limit. In most cases the thyristors set the limit. The design is made so that the thyristors are running at a maximum allowed temperature at maximum steady state system voltage. A margin to destructive temperatures is reserved in order to handle fault cases. The Forbes 500 kV static var system near Duluth Minnestoa USA is an interesting example of an Enhanced SVC 5. VIII. HARMONICSBoth SVCs and STATCOMs generate harmonics. The TCR of an SVC is a harmonic current source. Network harmonic voltages distortion occurs as a result of the currents entering the power system. The STATCOM is a harmonic voltage source. Network voltage harmonic distortion occurs as a result of voltage division between the STATCOM phase impedance and the network impedance.The major harmonic generation in SVCs is at low frequencies; above the 15th harmonic the contribution is normally small. At lower frequencies the generation is large and filters are needed. SVCs normally have at least 5th and 7th harmonic filters. The filter rating is in the range of 2550% of the TCR size.STATCOMs with PWM operation have their major harmonic generation at higher frequencies. The major contributions are at odd multiples of the PWM switch frequency; at even multiples the levels are lower. The harmonic generation decays with increasing frequency. STATCOMs might also generate harmonics in the same spectra as the conventional SVCs. The magnitudes depend on converter topology and the modulation and switching frequency used. In most cases STATCOMs as well as SVCs require harmonic filters.IX. FOOTPRINTMore and more frequently the footprint available for prospective STATCOMs or SVCs is restricted. The trend is, as in many other fields, more capacity on less space. Requirements for extremely tight designs, however, result in higher costs. In general the footprint issue seems not to hinder the utilization of STATCOMs or SVCs, but occasionally, STATCOM has been preferred based on anticipated smaller footprint.When comparing SVCs with STATCOMs, it is tempting to assume that the latter will fit within a much smaller footprint, as the passive reactive elements (air core reactors and high voltage capacitor banks) are “replaced” with semiconductor assemblies. In the authors opinion, this assumption however remains to be practically proved. The main reason for this is that the voltage sourced converter concepts applied in STATCOMs to date have been built with several (even as many as eight) inverter bridges in parallel. This design philosophy implies many current paths, high fault currents and complex magnetic interfaces between the converters and the grid. All in all, not all STATCOMs come out as downsized compared to SVCs. Also the higher losses in the STATCOM will require substantially larger cooling equipment. However, as the STATCOM technology evolves, including the use of very compact inverter assemblies with series connected semiconductor devices, and with pulse width modulation, there is a definite potential for downsizing.In the case of SVCs, the industry has a long product development where, when necessary, measures have been taken to downsize the installation. Such measures include elevated design of apparatuses, stacking of components (reactors and capacitors), vertical orientation of busbars and use of non-magnetic material in nearby structures. In a few extreme cases iron core reactors have been utilized in order to allow installation in very tight premises. In addition the development of much higher power density in high power thyristors and capacitors contributes to physically smaller SVCs.X. LIFE CYCLE OR EVALUATED COSTSIt is the authors experience that the investment cost of SVCs is today substantially lower than of comparable STATCOMs. As STATCOMs provides improved performance, it will be the choice in the cases where this can be justified, such as flicker compensation at large electrical arc furnaces or in combination with active power transfer (back-to-back DC schemes). The two different concepts cannot be compared on a subsystem basis but it is clear that the cost of the turn-off semiconductor devices used in VSC schemes must come down significantly for the overall cost to favor the STATCOM. In other industries using high power semiconductors, like electrical traction and drives, the mainstream transition to VSC technology is since long completed and it is reasonable to believe that transmission applications, benefiting from traction and drive developments, will follow. Although the semiconductor volumes in these fields are relatively small, there is potential for the cost of STATCOMs to come down.Apart from the losses, the life cycle cost for STATCOM and SVCs will be driven by the efforts required for operation and maintenance. Both technologies can be considered maintenance freeonly 12 man-days of maintenance with a minimum of equipment is expected as an annual average. The maintenance is primarily needed for auxiliary systems such as the converter cooling and building systems. In all, the difference in the cost for these efforts, when comparing STATCOM and SVC, will be negligible.XI. LOSSESThe primary losses in SVCs are in the “step-down” transformers, the thyristor controlled air core reactors and the thyristor valves. For STATCOMs the losses in the converter bridges dominate. For both technologies the long-term losses will depend on the specific operation of each installation. The evaluation of investments in transmission has also increasingly included the costs during the entire life cycle, not only the initial investment. Losses will then be increasingly important. With a typical evaluation at $3000/kW (based on 30 years), and additional average evaluated losses of say 300 kW (compared to an SVC), the additional burden on the STATCOM is significant. The evaluated losses at full output will contribute significantly to this, but with less weight on these the difference will be much smaller. Here the evolution does not help the STATCOM as its adequate performance is assumed to be achieved with high frequency PWM, implying that the losses will be quite high even at small reactive power output.We expect most utilities to operate their facilities close to zero Mvar output, in order to have SVCs or STATCOMs available for dynamic voltage support. In these cases both technologies will operate with well below 0.5% losses (based on “step-down” transformer rating). However the losses will typically increase quite rapidly should the operating point be offset from zero. This is valid for both SVCs and STATCOMs. SVCs will frequently operate with both switched capacitors and controlled reactors at the same time, while converter losses of STATCOMs will increase rapidly with output current. The losses of STATCOMs at rated output will be higher than for comparable SVCs.XII. CONCLUSIONSWe have examined the performance of SVCs and STATCOMs in electric power systems. Based on the analytical and simulation studies, the impact of SVCs and STATCOMs on the studied power system is presented. It was shown that both devices significantly improve the transient voltage behavior of power systems. Though SVCs and STATCOMs work on different principles, their impact on increasing power system transmission capacity can be comparable. Specifically, we describe “ enhanced” SVCs with voltage recovery performance similar to STATCOMs. Other issues such as losses, footprint, harmonics, etc., must be examined for each scenario for an optimum investment.SVC与STATCOM在电力系统中应用的效益摘要：提出了对电力系统中SVC和STATCOM的性能检测。本文是基于分析和仿真分析的结论可以作为电力行业指导方针。我们解释了SVC和STATCOM的原理结构，动态研究模型，以及这些设备的稳态电压和暂态电压稳定性的影响。灵敏度分析显示了SVC和STATCOM对网络性能的影响。谐波问题，空间需求和成本的讨论也作了简要介绍。关键词：动态补偿器，SVC，STATCOM，短路容量，增益灵敏度，短期电压稳定，谐波1 引言并联连接的静止无功补偿器（SVC时）被广泛用于控制交流电压的传输网络。电力电子设备，如晶闸管控制电抗器（TCR）与晶闸管投切电容器（TSC）已经获得了很大的市场，主要是因为良好的鲁棒性提供动态无功功率具有快速响应时间和较低的维护。随着大功率门可关断晶闸管和晶体管器件（GTO，IGBT，.）的问世新一代电力电子设备，STATCOM在电力系统中，显示出巨大的应用前景3,4。本文的目的是解释SVC和STATCOM在电力系统中的应用的好处。从近期安装大量SVC和STATCOM的项目在世界各地取得的经验促使我们澄清这些设备的某些方面。2 基本介绍本节简要解释了SVC和STATCOM的基本配置：2.1 SVC补偿器一般包括一个晶闸管控制电抗器（TCR），晶闸管投切电容器（TSC）和谐波滤波器。这还包括机械开关并联电容器（MSC），然后使用长期静态VAR系统。谐波滤波器（用于TCR生产的谐波）是电容的基本频率。该TCR通常比TSC块较大，使得连续的控制得以实现。其他可选择是固定电容器（FCs），与投切电感（TSR）。通常在中压补偿器设备使用一个专用变压器。发送侧的电压被控制，且兆伏评级是指传输方。SVC的评级可以优化,以满足所需的需求。评级可以是对称的或不对称的相对于电感和电容的无功功率，作为一个例子,评级可以是200Mvar电感和200Mvar电容，或100Mvar电感和200Mvar电容。2.2 STATCOM电压源变换器（VSC）是一种静止同步补偿器，其将直流电压转换成输出电压与期望的振幅，频率和相位的三相组的基本电子部件。有不同的方法来实现电压源转换器，省电实用的应用程序。基于谐波和损失的考虑，脉冲宽度调制（PWM）或多个转换器的使用。本质上，STATCOM具有相对于电感和电容的无功功率对称的评级。例如，评级可以是100无功电感和100无功电容。对于不对称的评级，STATCOM需要一个互补的无功功率源。这可以实现，例如用MSC。7 功能等级的概念传统上,SVC的常见的设计已被用于处理不同类型的网络问题。今天的趋势，然而，是定制的SVC作拟定用途。这是很重要的,为了使SVC成本效率更高。对于稳态电压支持，即要遵循日常负载模式，散装无功功率加上无级平滑的电压控制是需要的。游标电压调节可通过TCR的运行与谐波滤波器并联设置。大部分无功功率是通过由SVC控制器管辖机械开关电容器组（MSC）或反应器（MSR）提供的。因此SVC提供持续保持平稳电压的目的，试行MSC切换。如果任务是支持系统故障后的电压不稳或不可接受的电压水平的有限，大量快速可控的无功功率是需要一个短的持续时间。一个SVC附加TSC是个不错的选择。恢复后的电压支持也可能是必要的，这然后优选通过由SVC控制的MSC提供。对于暂时过电压，大型感应所需无功功率是一个很短的时间周期。标准的TCR具有一定的短时过载电流能力。这种能力可以很容易地扩展，通过降低其稳态操作温度和“上浆”反应堆。7.1 增强的SVCSVC的特性在低电压可以通过增加一个额外的TSC有效地改进。这个分支的目的只有在欠压条件下进行操作。它可以在SVC的其他部分没有引入额外的成本增加。最重要的是，目前电源变压器的额定电流或电压能力并不需要增加。电源变压器在有限的时间内允许大过电流(IEEE c57 - 115可以用作有效容量指南)。在许多情况下，3倍过载电流为10秒是可用的。额外的TSC的评级通常被设定在50100的SVC等级的范围内。7.2 SVC短时过载从SVC的给定电压的最大功率是由它的电抗决定的。无过载容量可用，除非电抗降低，例如，通过添加一个TSC。对于过电压，然而，SVC电抗不再是限制因素；相反，由元件的电流极限定义的。在大多数情况下，各晶闸管设置的限制。该设计是由使晶闸管的电压在一个允许的最大温度，最大稳定状态系统运行。一个边缘破坏性的温度以在处理故障情况下被保留。美国福布斯附近的德卢斯的500 kV静态VAR系统是一个有趣的增强型SVC 5 的例子。8 谐波SVC和STATCOM两个产生谐波。SVC的TCR是一个谐波电流源。网络谐波电压失真的发生是由于电流输入电力系统的结果。该STATCOM是一个谐波电压源。电网电压谐波失真的发生是STATCOM相阻抗与网络之间的阻抗分压的结果。谐波主要是SVC在低频产生的，第十五以上的谐波贡献通常是很小的。在较低的频率所需要产生的较大过滤器。SVC通常至少有5次和7次的谐波滤波器。该过滤器的评级是在的TCR大小的25-50的范围内。STATCOM的PWM操作其主要的谐波产生在更高的频率。主要贡献是在PWM开关频率的奇数倍;在偶数倍的水平较低。该谐波随频率的增加产生衰减。STATCOM还可能在相同的光谱与常规的SVC产生谐波。幅值依赖于转换器的拓扑结构和所使用的调制和开关频率。在大多数情况下STATCOM以及SVC需要谐波滤波器。9 安装越来越频繁地用于准