1、文献翻译 英文 原文： Issues for reactive power and voltage control pricing in a deregulated environment Abstract Issues 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 moto
2、r 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
3、 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 al
4、so be used to justify long-term pricing agreements between suppliers and customers. Keywords: Reactive power； Induction motor loads； Voltage support； Reactive power pricing 1. Introduction Voltage control in an electric power system is important for many reasons: _a. all end-use equipment need near-
5、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 wi
6、th 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. T
7、his 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 inducti
8、on 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 loa
9、ds 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 transmissio
10、n 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 introdu
11、ced 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 discus
12、sed. A pricing approach for voltage support and reactive power requirements is presented. 4. Example results The 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-d
13、own transformer and 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 frequenc
14、y 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 denoted with the variable y in Table 1. Also note that the model requires the mech
15、anical 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 output as the total induction motor load increases. Note that, when the induction motor load increases beyond the value of 0.
16、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,
17、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
18、 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
19、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
20、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 inc
21、rease 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 beco
22、mes 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 illustr
23、ate 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 on syste
24、m 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 i
25、s 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 fo
26、r loads that are predominantly induction motors. 5. Tariff structure The 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 vol
27、tage magnitude and reactive power requirements. These limits are system dependent and should be decided upon extensive studies of the system. The same studies will provide the range of sensitivities of voltage magnitude, reactive power requirements and transmission losses. A direct cost can be assoc
28、iated with the transmission losses. An investment cost can also be associated with 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 elec
29、tric 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 throughout the study period. The cost C provides the basis for establishing the actual tariffs. It is also important to note that, today, tech
30、nology 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 conclusions This paper has addressed the impact of predominantly induction motor loads on
