A new approach to calculating parameters of thermohydraulic networks for vapor-gas-liquid flows

A new method referred to as the compressible media solver technique is proposed for calculating parameters in a real thermohydraulic network for two-phase nonhomogeneous and nonequilibrium flows with an arbitrary number of noncondensable gases. This approach is used for simulating heat and mass transfer at the interface, as well as thermal interaction of model elements.     

A new core

This article discusses motors for compressors in domestic air conditioners, an area in which there is a strong demand for high efficiency and also reports the results of the efficiency improvement and productivity of a new core structure. An innovative core structure and manufacturing method boosts efficiency of permanent-magnet motors. This article presents the close relationship between the motor characteristics and the manufacturing method and indicates a way to improve both motor characteristics and the productivity. To pursue further improvement in motor performance by improving the coil space factor further using the joint-lapped core and manufacturing cores with smaller magnetic resistance.     

A new approach combing connection number and fuzzy simulation to calculating power flow of distribution network considering uncertainty

The power flow calculation considering uncertainty is the most basic way for solving the security issue of the system under uncertain conditions. As the renewable energy characterized by randomness and uncertainty, such as wind and solar power, has been applied to the distribution network, it is especially essential to study on power flow of distribution network considering uncertainty. The traditional models of uncertainty have the problem of singleness in expressing uncertainties while the uncertainty objectively shares two or more than two kinds of characteristics. A new model for describing the uncertainties, which combines connection number and fuzzy number and describes the interval quality and fuzziness of uncertain information comprehensively, is presented. Through improving the calculation of sample value and possibility measure, the traditional fuzzy simulation is modified and then applied to the power flow calculation in consideration of wind and solar power output uncertainty and load uncertainty. Two definitions, which are satisfaction index and degree of uncertainty, are introduced to measure the results accuracy with sample number changing and to represent the variation range of uncertain parameters respectively. The proposed model and modified algorithm are verified by case studies based on IEEE 33-bus system. The results are compared with those obtained from Monte Carlo simulation and proved to be correct. In addition, several other numerical examples are presented and discussed in order to achieve the influences of sample number, degree of uncertainty and membership function change on results. Through analysis of the power flow results considering uncertainty, we may find out the weak links of network, which can provide references for making electrical accident premeditation and then adjusting operation scheme.     

一种新型电压稳定计算方法

随着各种新技术的应用,电压稳定问题日益突出,根据现实情况提出一种新型电压稳定的计算方法.首先给出了小干扰电压稳定极限的数学模型,从而提出新型电压稳定的判据,通过常规潮流计算与病态潮流计算的方法,对过渡运行方式进行分析,最后通过模态分析的方法确定了系统初始稳态点和稳定极限点的电压功率灵敏度及其参与因子,从而更有效地确定系统的关键节点和区域.最终通过PSASP的实验,验证了该方法的有效性和可行性.     

A new approach to using simulation software in the electromagneticscurriculum

A possible electromagnetics curriculum using the latest computer-based electromagnetic simulation tools is discussed. The design of the teaching program is justified by the results of earlier course designs based on previous versions of simulation tools. The response from students to the use of simulation techniques in the learning process is deemed positive enough to consider a major reorientation in the way in which the subject of electromagnetic fields is taught     

A new approach to arc resistance calculation

Contents  Arc resistance is an important macroscopic arc parameter, which describes the complex nature of arcs. As it is known, the fault arc resistance can be calculated by the Warrington formula. Authors investigated the results of Warrington's tests. Warrington derived a relation for the arc voltage by using the measured arc voltage gradient and arc current as input data. By analyzing these measurements and by taking into account the conditions under which they are obtained (inaccurate measurement devices), it is unquestionable that the results are highly empirical and not accurate and general enough. Laboratory testing, provided in the high-power test laboratory FGH-Mannheim (Germany), in which long high current arcs are initiated, was the base for the research results presented. In this paper a new approach to arc resistance calculation is given. Two independent approaches delivered the same equation. Both approaches are based on a suitable and a simple arc model assuming the rectangular wave form of the arc voltage, which is in phase with the arc current wave form. The new formula for arc resistance is compared with the Warrington formula. The influences of arc elongation are also investigated. Received: 27 December 2000     

A new approach to adaptive robust control

A new approach is given for the design of adaptive robust control in the frequency domain. Starting with an initial model of a stable plant and a robust stabilizing controller, the new (windsurfer) approach allows the bandwidth of the closed-loop system to be increased progressively through an iterative control-relevant system identification and control design procedure. The method deals with both undermodelling and measurement noise issues. Encouraging results are obtained in the simulations that illustrate the new idea.     

A new approach to distribution arrester design

A new distribution-class surge arrester design concept is introduced. Replacing the conventional gasket-sealed porcelain housing is an epoxy/fiberglass-wrapped metal-oxide varistor disc module, assembled inside a flexible EPM rubber housing. This PDV (polymer distribution varistor) arrester design has the advantage of minimizing the free-gas volume inside the arrester, virtually eliminating concerns of moisture ingress due to seal pumping. In the unlikely event of arrester failure, the rubber-enclosed housing eliminates exploding porcelain fragments normally associated with standard distribution-class arrester designs. Performance questions related to assembling distribution arresters inside housings molded from polymer material are addressed     

A new approach to medical image reconstruction

The authors propose a multiobjective optimization method using the weighted sum problem in order to deal with image reconstruction from projections. In their scheme, after determining the objective functions, a satisfactory solution of the decision maker can be derived by updating the weighted coefficients simultaneously with the tradeoff between the objective functions. Furthermore, the noninferiority of the generated solution in each iteration is guaranteed. As has been shown, the multiobjective optimization-based image reconstruction approach is superior to the least-squares and convolution methods. The authors can say that the multiobjective approach makes traditional image reconstruction from projections flexible and robust to uncertainty and multiplicity of reconstruction objectives. They are convinced that the proposed method and its extension will become an efficient tool for design of new CT scanners     

A new approach for calculating zone-2 setting of distance relays and its use in an adaptive protection system

This paper presents a method for calculating zone-2 setting of distance relays without causing coordination problems. The proposed method is based on the impedance seen by distance relays when faults are simulated on the reach of zone-1 of primary relays for the maximum and minimum generation outputs of the power system. It is shown that the proposed method increases the reach of zone-2 relays without causing coordination problems. The proposed method is modified for use in an adaptive protection system. It is shown that further improvements can be achieved when settings are calculated using the proposed method and the prevailing system conditions. Measures to alleviate the impact of communication failure are discussed. The proposed method and its adaptive version were applied to an existing power system and some results are reported in the paper.     

A Monte Carlo approach for calculating the thermal lifetime of transformer insulation

This paper presents an accurate method for estimating the thermal lifetime of solid insulation in a power transformer. The method estimates the ambient temperature using the monthly average ambient temperature and the monthly solar clearness index. The average daily load curve and the standard deviation for each hour in the daily load curve are used to model the transformer load. The uncertainties associated with the transformer load and the ambient temperature are used to simulate the transformer artificial history using Monte Carlo technique. This artificial history is used to estimate the average lifetime of the transformer solid insulation. The method is tested on a real field transformer data taken from a local utility. The outcome of the test showed that the proposed method provides reliable results.     

A new approach to modeling three-phase transformer connections

The modeling of three-phase transformer connections for power-flow and short-circuit studies can take on many forms, depending upon the assumptions made. Too many times, simplifying assumptions lead to answers that are totally wrong. Exact models of the various connections must be used if correct results are to be achieved. The exact models must satisfy Kirchhoff's voltage and current laws, and the ideal relationship between the voltages and currents on the two sides of the transformer windings and the models must represent any phase shift that is a result of the particular connection. New models for all common three-phase transformer connections have been developed that satisfy all of the requirements stated above. This paper limits the discussion to the ungrounded wye-delta connection and the model developed for use in power-flow and short-circuit studies     

A new approach to underground cable performance assessment

This paper presents a new approach to thermal field sensitivities and ampacity computations of underground power cables using a proposed algorithm of perturbed finite-element analysis. The new approach involves the use of derived sensitivity coefficients associated with various cable parameters of interest, and use these coefficients to achieve optimal cable performance. The proposed model provides a quick methodology, based on the finite-element model, to assess the cable thermal performance subject to variations in the cable thermal circuit parameters. The developed algorithm was applied to various practical cable systems. The effect of multilayered thermal conductivities and boundary parameters variations on the actual cable system ampacity was investigated using the proposed methodology. A comparison was made of the obtained results with the conventional finite-element approach in order to show the applicability and usefulness of the developed methodology. Our objective was to assess the effects of operating parameter variations in a straightforward manner, without repeating the thermal field analysis for each parameter change. The thermal field of an underground power cable sample directly buried in the soil was measured in the laboratory using a developed full-size experimental setup. The investigations involve all parts of the thermal circuit parameters representing cable composition, surrounding soil and boundary phenomena. The experimental setup was used to validate the simulation model by comparing the simulation results with the real laboratory measurements. Such experimental verification confirmed the accuracy of the new introduced finite-element sensitivity methodology.     

电力中性线电流计算新法

低压配电系统三相负载基本上都不平衡,中性线有电流通过,计算该电流的方法有2种:几何法和投影法.2种计算方法比较复杂.笔者不断探索,提出一新的计算方法,即根据负载的性质不同,计算方法也不同,现阐述如下.     

A new approach to model reference adaptive control

A new approach to model reference adaptive control, based on a combination of direct and indirect control methods, is introduced in this paper. The controller structure is identical to that used in the direct method, but the algorithm used to update the controller parameters depends both on the output error as in direct control and on the plant parameter estimates as in indirect control. The global stability of the overall system is assured by the existence of a Lyapunov function. In the ideal case discussed here, the combined approach results in improved transient response with smaller amplitude of the control input as compared to the constituent methods.     

A new approach to secure economic power dispatch

This article presents a new nonlinear convex network flow programming model and algorithm for solving the on-line economic power dispatch with N and N−1 security. Based on the load flow equations, a new nonlinear convex network flow model for secure economic power dispatch is set up and then transformed into a quadratic programming model, in which the search direction in the space of the flow variables is to be solved. The concept of maximum basis in a network flow graph was introduced so that the constrained quadratic programming model was changed into an unconstrained quadratic programming model which was then solved by the reduced gradient method. The proposed model and its algorithm were examined numerically with an IEEE 30-bus test system on an ALPHA 400 Model 610 machine. Satisfactory results were obtained.     

A new approach to evaluate generation capacity bids

Decision making on capacity addition has become highly complex as the power industry worldwide is undergoing regulatory changes. This paper argues the use of mathematical models to aid the decision makers to select generation capacity bids. A three-stage optimization scheme is developed to accurately estimate the benefits from a specific project. A multiobjective framework to capture both quantitative as well as qualitative information (through expert judgement) has been employed. The model can be used to estimate the marginal benefit from a project and calculate a composite index to rank them in order of their desirability. A case study for modified IEEE 30-bus test system illustrates the methodological issues     

A new approach to power supplies for robots

A cableless power supply system for multiaxis robots is proposed. As key components, it contains rotatable transformers placed in the joints of the robot. It consists of two halves of a ferrite pot core containing the primary and secondary windings, respectively. The energy is transferred to the movable parts of the robot through this transformer at a frequency of 25 kHz. This frequency allows a compact design of the transformer. A schematic representation of the new system is offered. Investigations of the steady-state and the transient behavior were carried out. Experimental results were obtained from an experimental setup with a 20 kVA, 650 V IGBT converter     

一种求取静态电压稳定裕度的新方法

通过分析简单交流支路的功率负荷能力,提出了求取静态电压稳定临界点的新算法.在确定临界电压崩溃点的基础上,通过比较不同的计算裕度指标的方式,提出采用复功率差值的模来表示静态电压稳定裕度是比较合理的.本文还给出了IEEE 5 节点系统的算例.