Integrated SVC and step-down transformer model for Newton-Raphsonload flow studies

This letter presents an integrated static VAr compensator (SVC) and step-down transformer model suitable for power flow studies using the Newton-Raphson method. The SVC is taken to be a continuous, variable-shunt susceptance that is adjusted automatically to satisfy a specified voltage magnitude. The step-down transformer is represented by an admittance that combines easily with the variable susceptance, representing the SVC plant. The resulting equivalent model allows for a direct SVC voltage regulation at the high-voltage side of the transformer, which does not compromise the quadratic convergence characteristics of the Newton-Raphson method     

葛洲坝换流站换流变分接头档位异常变化原因及整改措施

详细分析了葛洲坝换流站换流变分接头异常变化的原因,介绍了换流变分接头调节基本原理。从硬件和软件两方面提出了解决的方法,对从事高压直流工程换流变的运行维护工作具有较好的参考价值。     

10 kV配电变压器经济运行方式的可行性及经济性分析

针对农村和城市小区的变压器长时间处于空载和轻载状态导致损耗增大的问题,提出了一种变压器组优化经济运行方案。以变压器实时负荷为主要控制参量优化组合变压器组的投切运行,采用电压互感器取能方案解决配电线路停运后变压器高低压侧断路器操作机构的取能问题(冷启动),保证了供电的及时性和变压器的自动投切。并以某小区变电箱内两台变压器组为例,定量分析了优化运行的经济效益,最后通过数字仿真验证了所提方案的可行性。     

Experimental validation of the coupled fluid flow, heat transfer and electromagnetic numerical model of the medium-power dry-type electrical transformer

This paper presents experimental validation of a numerical model of coupled processes within a three-phase medium-power dry-type electrical transformer. The analysis carried out employed a multi-disciplinary approach involving heat, fluid flow and electromagnetics. The thermal and fluid flow analysis was coupled with an electromagnetic model in order to examine the specific power losses within the coils and the core. The thermal boundary conditions, i.e. the local and temperature-dependent heat fluxes, were computed by considering a numerical model of the surrounding internal and external air. Moreover, separate numerical and analytical models were considered in order to obtain the anisotropic thermal conductivities for different types of coils and also for laminated cores. To validate the numerical model, experimental transformer temperature tests in the short-circuit, open-circuit, and under nominal parameters according to the current European Standards for dry-type transformers were performed. During the tests, temperatures were measured at selected points on elements of the transformer using thermocouples and thermometers, while on the external tank walls an infrared thermography was employed. The obtained numerical results showed that the prediction of the temperature distribution within the analyzed transformers and their surroundings was very accurate.     

Thyristor-controlled voltage regulators for critical inductionmotor loads during voltage disturbances

The transient stability of a critical induction machine load group during momentary as well as continuing voltage sags can be enhanced by using a fast-response voltage regulator in the form of a static VAr compensator (SVC) or a thyristor controlled tap changer (CTC). A procedure is presented for determining the minimum SVC rating or CTC off-nominal turn ratio including control of the SVC admittances or CTC taps to meet dynamic and steady-state specifications. The limitations of their effectiveness to preserve operation continuity are also shown     

铸钢用9MVA交流电弧炉炼钢过程电气运行特性研究

大型重型机器制造企业使用交流电弧炉炼钢提供钢液,制造锻造用钢锭和铸钢件。使用电气监测仪表,对鞍钢重型机械有限责任公司1~#交流电弧炉炼钢过程中的电力参数进行了实测,得到72668个有效数据。分析表明,在1挡电压下电弧炉变压器利用率仅为67.79%。研究以二次侧工作电流为自变量,建立该电弧炉炼钢过程电气运行的非线性电抗模型,绘制电气运行特性曲线。研究结果表明,变压器在1,2,5挡电压下运行,工作电流提高至额定电流,输出的有功功率可分别提高35.6%,16.7%,21.3%。     

Single-stage and advanced absorption heat transformers operating with lithium bromide mixtures used to increase solar pond's temperature

Mathematical models of single-stage and advanced absorption heat transformers operating with the water/lithium bromide and water/Carrol™ mixtures were developed to simulate the performance of these systems coupled to a solar pond in order to increase the temperature of the useful heat produced by solar ponds. Plots of coefficients of performance and gross temperature lifts are shown against the temperatures of the heat supplied by the solar pond. The results showed that the single-stage and the double absorption heat transformer are the most promising configuration to be coupled to solar ponds. With single-stage heat transformers it is possible to increase solar pond's temperature until 50°C with coefficients of performance of about 0.48 and with double absorption heat transformers until 100°C with coefficients of performance of 0.33.     

考虑变压器损耗的配电网无功优化研究

针对传统配电网无功优化未考虑变压器损耗的缺陷,提出了考虑变压器损耗的配电网无功优化模型,优化措施包括电容器无功补偿、变压器有载调压等,通过差分进化算法对改进的IEEE 33节点系统进行仿真计算,研究了不同负荷水平情况下配电系统无功优化结果,并与传统无功优化结果进行对比分析。结果表明,系统轻载情况下,考虑变压器损耗对于配电网无功优化尤为必要,可使配电网无功优化方案更加合理全面。     

地区电网变压器经济运行决策系统

基于日时段变压器损耗的变压器经济运行方法,研究开发了变压器经济运行决策系统,分析和设计了系统模型的构架及数据结构,计算了变电所各种运行方式下的变压器损耗,选择了变压器损耗最小的经济运行方式,并考虑变压器负载能力等约束条件,增强了系统的适应性。系统运行结果表明,该系统模型可灵活构建,且具有较高的灵活性、适应性和可扩展性。     

Analysis of self-dual excited synchronous machine. I. Developmentof the general mathematical model and steady-state performanceexperimental verification

The use of the dual excitation system for improving the overall performance of a self-excited synchronous machines is considered, along with the replacement of the compound transformer and rectifier bridge by a potential transformer and thyristor bridge for the self-excitation system. The output DC voltage of the bridge is controlled over a wide range by an automatic feedback control circuit to vary the firing angle of the thyristors in such a way that the terminal voltage is sustained at a constant value. The mathematical models for two distinctive alternatives of the excitation system are derived. The mathematical model thus derived is suitable for transient, dynamic as well as steady-state analysis. However it should be modified to investigate the steady-state and dynamic performance. Exact steady-state operating points are achieved by solving the steady-state equations obtained from the general model. Charts describing the performance of the self-dual excited synchronous machine under steady-state operation for the two alternatives of the excitation system have been calculated at different values of the power factor, i.e., the turns ratio of the transformer and the ratio of field currents. The experimental results obtained on a 7.6 kVA induction machine converted to a d-q synchronous machine confirm the validity and accuracy of the analysis and mathematical models developed     

Environmental cost of distribution transformer losses

Improvements in energy efficiency of electrical equipment reduce the greenhouse gas (GHG) emissions and contribute to the protection of the environment. Moreover, as system investment and energy costs continue to increase, electric utilities are increasingly interested in installing energy-efficient transformers at their distribution networks. This paper analyzes the impact of the environmental cost of transformer losses on the economic evaluation of distribution transformers. This environmental cost is coming form the cost to buy GHG emission credits because of the GHG emissions associated with supplying transformer losses throughout the transformer lifetime. Application results on the Hellenic power system for 21 transformer offers under 9 different scenarios indicate that the environmental cost of transformer losses can reach on average 34% and 8% of transformer purchasing price for high loss and medium loss transformers, respectively. That is why it is important to incorporate the environmental cost of transformer losses into the economic evaluation of distribution transformers.     

330 kV升压变压器中性点保护问题讨论

描述并分析了甘肃电网330kV发电厂升压变压器中性点接地方式及所承受的过电压种类和水平。提出这类变压器中性点保护方法,并给出了具体保护方案：采用合理的保护间隙保护330kV变压器中性点绝缘的方案较可靠,也简便易行。     

AC side harmonic and phenomena accompanying DC-injection of utility-interactive PV system

The experiments investigated phenomena related to direct contact between the DC output of a PV array and the AC power from the utility grid. The results show that the DC power flows through the distribution transformers (DC-injection) saturating their magnetic circuits. The saturation of magnetic circuits makes peak currents, incorporating a large portion of even harmonics, flow through the high-voltage side of the distribution transformer, adding the level of harmonic distortion of its exciting current. With the increase of injecting DC-current to the utility grid, peak currents at the primary side of distribution transformer increases the most, and even among the same effective (rms) values, the increase of primary side current is larger than that of the secondary side current.     

Parametric optimum design of an irreversible heat-transformer based on the thermo-economic approach

The thermo-economic objective function of a heat transformer may include other objective functions such as the coefficient of performance and specific heat pumping load. It is defined as the heat-pumping load divided by the total cost per unit time and its expression is derived from the general cycle model of an irreversible heat-transformer. The general objective function is used to analyze the thermoeconomic and thermodynamic optimum performance of a heat transformer affected by multi-irreversibilities. The bounds of some important parameters are determined. The problem of how to choose optimally these parameters are discussed. The results obtained here can provide some new theoretical guidance for the optimal design and operation of heat transformers and heat engines.     

智能型电力互感器移动计量检定系统设计与应用

鉴于仪器设备笨重、现场接线复杂是造成电力互感器现场检定工作强度大、效率不高的主要影响因素,基于比较法互感器检定接线原理,设计了一套智能型电力互感器移动计量检定系统,该系统采用移动式检定技术,搭载了电流互感器、电压互感器现场试验所需的仪器设备,设计出自动切换变比的试验接线回路及后台管理软件,实现了仪器设备不下车即可开展检定试验及检定回路上位机控制等功能,可满足220kV及以下电力互感器现场试验要求。实例应用结果表明,本文设计的计量检定系统简化了互感器计量检定工作现场操作流程,提高了现场工作效率。     

非晶合金变压器及其节能效果

文章介绍了非晶合金变压器的特点,并与S9系列变压器进行综合效益的对比,指出其节能效益显著,具有广阔的应用前景。     

Single stage and double absorption heat transformers used to recover energy in a distillation column of butane and pentane

This paper presents the theoretical analysis of the use of single stage and double absorption heat transformers operating with the water–lithium bromide mixture coupled to a butane and pentane distillation column in a Mexican refinery. A mathematical model of the heat transformers was developed in FORTRAN and integrated as a user model to the Aspen Plus simulation code. Both components coupled to the column were modelled on steady-state conditions. The results show that it is theoretically possible to reduce the energy consumed in the reboiler between 26 and 43% by the use of single stage heat transformer at specific conditions, and between 28 and 33% with double absorption heat transformers for a wide range of operating conditions. Copyright © 2003 John Wiley & Sons, Ltd.     

多只电压互感器同步校验误差分析

针对目前省市级计量检定部门电压互感器校验量大幅增加,而校验工作人力有限的实际情况,介绍了一种能一次同步校验12只电压互感器的高效方法,分析了电压互感器误差组成,基于高端测差法设计了多只电压互感器同步校验系统接线方案,对12只电压互感器并联给标准电压互感器带来的附加误差进行了理论分析与计算,并通过试验验证了误差理论的正确性及校验方案的可行性。     

我国高效节能配电变压器的生命周期成本分析

本文基于生命周期成本法,分析高效节能配电变压器的投资经济效果。本文首先分析了我国配电变压器能效等级的变化趋势并与欧盟标准进行对比;其次应用生命周期成本法计算各能效等级配电变压器的生命周期成本及动态投资回收期;最后,以S系列630／10型配电变压器为例,进行生命周期成本分析及负载率灵敏度分析。结果显示,在有政府补贴情景下,能效1级、能效2级配电变压器与能效3级配电变压器相比具有明显的投资优势,为推广高效节能配电变压器创造了有利条件。     

Design and analysis of a 35 kVA medium frequency power transformer with the nanocrystalline core material

Medium frequency power transformers embedded into power electronics converters are frequently encountered in many applications such as electrical transportation and renewable energy systems and power supplies. Thus, researchers have been focused on soft magnetic materials such as amorphous and nanocrystalline materials to obtain smaller and more efficient transformer designs with the improvements on manufacturing technologies of the high frequency core materials. In this study, the transformer design methodology is proposed with the finite element analysis method, and a 35 kVA medium frequency transformer with nanocrystalline core material is designed. After the sizing stage, three-dimensional model of the transformer is created with finite element analysis software, and then co-simulations of this electromagnetic transformer model with a power electronics converter circuit are performed for practical operation conditions. Furthermore, thermal behavior of the prototype transformer is determined with the thermal coupling analysis, and temperature distribution of the prototype transformer is visualized with a thermal imaging camera. The transformer efficiency, exact equivalent circuit of the transformer and flux distributions in the transformer core are obtained from these simulation studies. In addition, the prototype of the designed transformer is produced and tested. The design conditions and simulation results are validated with experimental studies.