无功补偿毕业设计外文翻译.doc

文献翻译英文原文：Issues for reactive power and voltage control pricing in aderegulated environmentAbstractIssues related to reactive power, voltage support and transmission losses as dictated from a certain class of electric loads are addressed. Specifically, the impact of predominantly induction motor loads on voltage support, reactive power requirements, and transmission losses is examined. These issues are examined with a model, which explicitly models the induction motor mechanical load. Simulation results on a simplified electric power system are presented. Based on these results, a pricing structure for voltage and reactive power support is proposed. The basic assumption of the paper is that, in a deregulated environment, the expense of the incremental requirements for voltage control should be charged to the member causing the additional requirements. The results of this work can also be used to justify long-term pricing agreements between suppliers and customers. Keywords: Reactive power; Induction motor loads; Voltage support; Reactive power pricing1. IntroductionVoltage control in an electric power system is important for many reasons: _a. all end-use equipmentneed near-nominal voltage for their proper operation, _b. near-nominal voltage results in near-minimum transmission losses, and _c. near-nominal voltages increase the ability of the system to with-stand disturbances _security. A reasonable voltage profile throughout an electric power system is associated with the ability of the system to transfer power from one location to another. When the voltage sags to low values, this ability of the system is compromised. The onset of power transfer inability can be detected with sensitivity analysis of reactive power requirements vs. real power load increases. This sensitivity is dependent on the characteristics of the electric load. Such sensitivity analyses have been performed using various electric load models, i.e. constant power load, constant impedance load, or combination of the two _voltage-dependent load. The majority of electric loads are induction motors. These loads do not fit into any of the load model categories mentioned. Yet, they drastically affect the stability of the electric power system. In this paper, we assert the need to model induction motor loads within the power flow formulation and directly evaluate the effects of such loads on reactive power requirements. It is shown that the power flow formulation can be augmented to include the specific induction motor loads. Interesting nonlinear phenomena occur when the voltage at induction motor loads sags to low values. These phenomena affect the performance of the transmission system. In a deregulated environment, it makes sense to examine these phenomena and design a pricing model based on the economic impact of these phenomena. The paper is organized as follows: first, a formulation is proposed, which explicitly models the induction motors. This formulation is introduced as an extension to the usual power flow problem. Then, a sensitivity analysis procedure is introduced. This sensitivity is based on an extension of the co-state method. The proposed methods are applied to a simplified system comprising induction motor loads. The results of this system are discussed. A pricing approach for voltage support and reactive power requirements is presented.4. Example resultsThe application of the model presented in this paper is demonstrated on a simple electric power system, consisting of a generating substation, step-up transformer, a transmission line, step-down transformerand several induction motors. The system is illustrated in Fig. 2. The parameters of the system have been selected to represent typical systems and they are shown in Table 1. It is important to realize that the motors may or may not be controlled by variable voltage-variable frequency drives. For this system, we performed parametric studies of the voltage level, the reactive power requirement, and the transmission losses. The variable parameter is the total induction motor load. This parameter is denotedwith the variable y in Table 1. Also note that the model requires the mechanical load torque, T m . The assumed mechanical torque is listed in Table 1.Fig. 3 illustrates the variation of the voltage magnitude and the generating unit reactive power outputas the total induction motor load increases. Note that, when the induction motor load increases beyond the value of 0.90 p.u., the reactive power requirement increase and the voltage magnitude decreases below 0.9 p.u. When the load increases beyond the value of 1.2 p.u., the voltage collapses. What happens in this case is that the induction motor moves to an operating point of very high slip, in this case, ss0.27, absorbs higher reactive power and causes the termi-nal voltage to dip _voltage collapse. Note that the voltage collapse is abrupt and unexpected. It is important to observe that this behavior of the proposed Fig. 4. model is realistic and quite different from simplified models such as constant power or constant impedance load models. The performance of the system in the presence of induction motor loads can be better understood by studying the sensitivity of voltage magnitude, reactive power requirements and transmission losses vs. induction motor load. Figs. 46 illustrate these sensitivities as functions of total induction motor rated load. In Fig. 4, it is apparent that the sensitivity of the voltage magnitude becomes very high as the electric motor load approaches 1.2 p.u. It would be expedient to impose operating limits using the sensitivity of voltage magnitude. For example, if one is to apply limits to this sensitivity, i.e. 20%, then it is apparent that for this system, the induction motor load should not be more than 0.8 p.u. of the system rated power. Similarly, one can observe in Figs. 5 and 6 that the sensitivity of reactive power requirements and transmission losses increase drastically as the induction motor load increases. It is important to note that when the induction motor load is 0.8 p.u., the sensitivity of reactive power to rated load is 1.0, i.e. any additional 1 MW of load will require 1 MVA of generated reactive power. When the induction motor load becomes 1.0 p.u., the sensitivity becomes 1.58 MVA /MW. Similarly, the transmission loss sensitivity with respect to load increases drastically as the induction motor load reaches 1.0 p.u. For example, when the load is 1.0 p.u., the incremental losses become 4%, a relatively high value.Figs. 46 illustrate that at the point before the voltage collapse, the sensitivities become very high. Specifically, the voltage sensitivity is y1.0, the reactive power sensitivity is 3.8 MVA rMW and the transmission loss sensitivity is 0.094. This data can be used in two ways. First, application of limits onsystem sensitivities will ensure that the system never operates near the point of voltage collapse. Second, the sensitivities can provide the basis for setting tariffs for voltage support and reactive power of predominantly induction motor loads. The basis of the tariff structure and its implementation is discussed in Section 5. One can argue that these tariffs may be applied to all loads for simplicity.The results in Figs. 36 were obtained for a specific system. The same information can be obtained for any system using the proposed model. Then this information can be utilized to impose tariffs for loads that are predominantly induction motors. 5. Tariff structureThe basis of the tariff structure is the cost of providing voltage and reactive power support subject to acceptable system performance. Acceptable system performance can be established by imposing limits to the sensitivities of voltage magnitude and reactive power requirements. These limits are system dependent and should be decided upon extensive studies of the system. The same studies will providethe range of sensitivities of voltage magnitude, reactive power requirements and transmission losses. Adirect cost can be associated with the transmission losses. An investment cost can also be associatedwith reactive power requirements. Let x be the average transmission loss sensitivity and z be the maximum reactive power sensitivity. Then the cost of providing these services is:C=p1 x+p2 z，where p1 is the price of electric energy, and p2 is the investment cost of reactive power sources.Note that the investment cost must be computed on the basis of the maximum requirements throughoutthe study period. The cost C provides the basis for establishing the actual tariffs. It is also important to note that, today, technology exists to monitor the impact of a specific load on the system resources. Using this technology, one can monitor the voltage magnitude, reactive power and most importantly the sensitivities of voltage magnitude, reactive power requirements, and transmission losses. It is conceivable that pricing can be performed in real time on a use-of-resources basis.6. Summary and conclusionsThis paper has addressed the impact of predominantly induction motor loads on voltage magnitudes, reactive power requirements, and transmission losses. A model has been proposed to evaluate this impact on large-scale power systems. The proposed model incorporates the physical model of induction motors into the power flow formulation. As such, it is a realistic model and captures the true behavior of these loads. Example calculations were carried out on a simplified power system. For this system, the voltage level, the active and reactive power requirements, and the transmission losses were computed vs. the total induction motor load. The model provides sensitivities of these quantities with respect to the inductionmotor loads and can be used to predict the total amount of load, which can be supported by the system _voltage stability limit.It was shown that there is a critical value of the load and when the load increased beyond this value,the reactive power requirements and the transmission losses increase in a highly nonlinear fashion. Theonset of this condition is system dependent and can be determined with a series of simulations. A practical approach will be to use probabilistic simulation techniques, similar to those described in Ref., to obtain a statistical distribution of the critical induction motor loads.The results provide the basis for deriving aggregate electric load models and the designing of a pricing schedule for voltage support and reactive power requirements. Specifically, the pricing is based on the cost function of the actual incremental losses and the cost of reactive power source requirements. Incremental loss cost is computed from the price of electric energy. The cost of reactive power sources is computed from the maximum required reactive power over a specified period of operation.译文：在解除管制的环境下功率和电压控制的定价问题摘要对由于处理某一类电负载而引起的功率、电压、传输损耗的相关问题的研究。具体来说，主要是感应电机负载上的电压影响，功率要求和传输损耗的研究。这些问题的研究都与明确模型的感应电动机机械负荷有关。进而提出了一个简化的电力系统的仿真结果。基于这些结果，提出了一种电压和功率价格结构。本文的基本假设是，在解除管制的市场环境下，对电压控制增量要求的费用应计入引起的附加要求。这项工作的结果可以用来证明供应商和客户之间的长期定价协议。关键词：功率；感应电动机负荷；电压；无功功率价格1. 引言电压控制在电力系统中很重要的原因有许多：a.所有的终端设备都需要在额定电压下正常工作。b.额定电压下传输损耗最小。c.额定电压能够提高系统在站的干扰下的安全能力。系统将功率从一处传到另一处的能力使电压在系统中合理分配。当电压降到一个较低值时，系统的这种能力会受到损害。分析功率要求的灵敏度和实际电力负荷的增加可以检测电力不能传递的问题。这种敏感性依赖于电力负荷的特点。这种敏感性分析使用了不同的电力负荷模型，即恒功率负载，恒阻抗负载，或两者的结合压敏负载。主要的负载大部分是感应电动机。这些负载不符合以上提到的任何一种。但是，他们严重影响电力系统的稳定性。在本文中，我们认为在潮流制定和直接评估这种负载对功率的影响需要感应电动机负载模型。结果表明，潮流的制定可以增强包括特定的感应电动机负荷。在出现有趣的非线性现象时，感应电动机的电压值较低。在解除管制的市场环境中，这些现象时很有意义的研究，我们设计了一个基于这些现象的经济影响定价模型。本文结构安排如下：首先，提出一种解决方案，并明确模型的感应电动机。这一提法引入到通常的功率流问题的一个推广。然后，介绍一种灵敏度分析程序。这种敏感性是基于对有限状态的扩展方法。所提出的方法应用于一个简化的系统包括感应电动机负荷。对该系统的结果进行了讨论，并提出了一种电压和功率定价方法。4. 算例结果 本文提出的模型应用在一个简单的电力系统显示，由发电站，输电线路，升压变压器，降压变压器和几个异步电动机。该系统如图2所示。系统的参数已被选定为代表的典型系统，如表1所示。重要的是要认识到，汽车可能会或可能不会由变频控制驱动器。对于这个系统，我们进行的电压水平的参数研究，功率要求，和传输损耗。可变参数是总的感应电动机负荷。此参数表示表1中的变量y。还注意到，该模型需要机械的负载转矩，TM。的假设机械转矩是表1中列出的。图3说明了电压的大小和发电机组功outputas总感应电动机负荷增加的变化。注意，当感应电动机负荷超过0.90标幺值，功需求增加，电压下降到低于0.9 p.u.当负荷超过1.2标幺值，电压崩溃。在这种情况下，所发生的是，感应电机移动到很高的滑动操作点，在这种情况下，ss0.27，吸收高功，使终端电压下降_voltage崩溃请注意，电压崩溃是突然和意外。它是观察所提出的图4这一行为的重要。模型是现实的简化模型如恒功率和恒阻抗负荷模型完全不同。在异步电动机的负载下系统的性能可以通过研究电压幅值的灵敏度更好的理解，功率要求和传输损耗与感应电动机负荷。图46说明这些敏感的总的感应电动机的额定负载的功能。在图4中，这是明显的电压幅值的灵敏度很高的电机负载的方法1.2 p.u