Iron Loss Analysis of Permanent Magnet Motors Fed by PWM Inverter

Carrier harmonic losses that consist of iron loss, eddy current loss, and ac copper loss are produced in a permanent magnet machine driven by a PWM inverter. It is already known that a higher motor inductance can lead to lower carrier harmonic losses. This paper investigates the carrier harmonic loss composition of two motors with identical dimensions but different inductances. The results of finite element analysis (FEA) showed that the eddy current loss in the iron core accounts for most of the carrier harmonic loss. It is also shown that the carrier harmonic loss of the iron core is quantifiable using theoretical calculations.     

太原电网线损计算与分析

叙述了太原电网的构成情况及线损理论计算结果 ,并对线损计算结果进行了分析 ,针对太原电网线损存在的问题 ,提出了降损措施     

网损及无功优化计算对降损的指导意义

从开展网损理论计算和系统无功优化计算 ,合理组织电网的运行方式等方面对网损进行了分析 ,得出网损理论计算和无功优化计算对降低网损具有的重要指导意义     

Optimizing the geometrical parameters in a group of high- and intermediate-pressure stages used in large steam turbines

An algorithm for calculating a turbine flow path compartment is considered using which it is possible to minimize the loss of energy in a group of stages while fulfilling strength limitations. The calculations were carried out using information from a database containing the generalized characteristics of flow path elements obtained from tests. Calculation examples are given, the results of which are compared with the data of previous calculations carried out for a compartment in the high-pressure cylinder of a K-800-240 turbine.     

Laminated steel eddy-current loss versus frequency computed usingfinite elements

Eddy-current loss in laminated steel cores is computed with unusual planar eddy finite elements over the wide frequency range produced in AC motor drives. The loss computed by the finite element method at low frequencies is shown to agree within 1% with a common simple formula. A formula used by radio-frequency engineers is shown to agree within 1% with the finite-element results at very high frequencies. The loss calculations are also compared with published curves from a steel manufacturer. At medium frequencies, no simple formula exists and, thus, the core loss computed by finite elements should be useful in the design of chokes and motors of AC variable-frequency drives     

Reduction of second- and third-order harmonic distortion bynonlinear absorption in gain-coupled distributed-feedback laser diodes

We have calculated the characteristics of second- and third-order harmonic distortion in gain-coupled distributed feedback (DFB) lasers using a set of three rate equations. In these calculations, the relaxation oscillation, nonlinear gain compression, and nonlinear loss compression are taken into account. We have found that modulation distortion due to nonlinear gain compression is reduced significantly in the gain-coupled DFB laser of absorptive-grating type. This improvement occurs because gain compression is compensated by loss compression within the grating     

基于图模库一体化的配电网线损管理系统的研制

介绍了一种适应于现代配电网的线损管理系统,该系统基于图模库一体化的平台开发,将线损理论计算和统计计算、报表管理及指标管理、线损分析集成于一体,给出了系统总体设计图。线损管理的数据包括电网的结构数据、运行数据和电量数据。在使用电量数据计算线损时,提出将负荷进行分类,按负荷类型进行计算,以减少平均功率对线损计算的影响。配电网线损管理系统共有7个模块,包括数据库、外部系统接口、图形系统、网络拓扑、线损计算、线损分析及报表,可对高、中、低压配电网中各类设备的电能损耗进行离线/在线计算和分析,能有效提高数据的精确性和工作效率。     

基于体积损失速率的混凝土抗冲磨性能评价

采用风砂枪法并配合图像分析技术,揭示了两组不同混凝土质量损失速率、体积损失速率、被磨损物料的密度、固定纵断面上冲坑轮廓随时间的变化规律,结合各特征时间节点处混凝土的表观形貌,确定了混凝土冲磨破坏稳定阶段的判据,并结合混凝土抗冲磨强度计算结果优选出了可靠的抗冲磨强度评价指标。结果表明：质量损失速率和体积损失速率在某个时间点处同时趋于稳定,此时,被磨损物料的密度与混凝土的表观密度保持一致,且无论从混凝土表面形态还是冲坑轮廓来看,混凝土均表现出稳定且均匀的磨损,由此可以判断该阶段为混凝土冲磨破坏稳定阶段。研究证明,趋于稳定的体积损失速率才是混凝土抗冲磨强度可靠的评价指标。     

脉冲液体射流泵能量平衡的研究

运用能量平衡原理,导出了脉冲液体射流泵内脉冲液体能量损失的时均压力比表达式,分析了影响泵内能量转换与耗损的主要因素,研究了主要流动部件的能量损失变化对射流泵性能的影响,并进行了相应的试验研究。结果表明：理论分析与试验结果基本一致,验证了脉冲射流是提高射流泵效率的有效途径。     

Simplified three-phase lateral and feeder models for fast distribution system calculations

This paper introduces three simplified three-phase lateral models for fast distribution system calculations. The models can also be applied to model a feeder with short laterals, whose impedances are negligible. These models are formulated using three lumped individual phase loads to represent single-phase, three-phase unbalanced, and nonuniformly distributed loads along a lateral or feeder. Proposed voltage-drop and line-loss models are developed to accurately simulate the total series voltage drop at the end and the total copper loss of a given lateral, respectively. A hybrid model is then developed to simulate both voltage drop and line loss accurately. All of the proposed models are used to represent the unbalance features of a physical distribution system in which various transformer connections are presented. The proposed models are applied to a physical feeder of Taiwan Power Company (Taipower). The simulation results show that it is possible to simplify complicated laterals or feeders to simple equivalent models in the calculations of voltage profiles and line losses with negligible error, even if there are various transformer connection schemes in the lateral or feeder.     

地区电网理论线损计算需求数据合成方法研究

在研究分析电网理论线损计算需求数据的类型以及数据之间的内部关联关系的基础上,提出一种以映射数据和计量(量测)数据为数据关联映射中心的电网理论线损数据合成方法。结合地区电网理论线损计算需求数据的来源构成情况,推导出地区电网某一理论线损计算方法需求数据合成的详细过程。该合成方法为理论线损计算全面实现数据自动采集、自动合成、自动计算,实现理论线损在线计算与分析提供理论技术支撑。目前该合成方法已在南方电网广东电网佛山供电局实现并成功运行。     

广州换流站408329号换流变压器的网侧绕组更换

针对利用色谱分析发现的广州站408329号换流变压器的重大缺陷,在检修时采用单一线规绕制两个网侧新线圈并进行整体替换。仿真计算表明,该方案实施后可消除环流损耗,但横向涡流损耗会稍为增加,总体负载损耗基本不变。出厂试验数据显示,各项关键性指标如局放量、温升后的色谱结果、总损耗等均接近甚至优于出厂值,表明修复工作取得了圆满成功。     

电力机车主变压器油箱损耗的三维有限元分析

利用基于边单元的有限元法,对一台200km/h高速电力机车主变压器的油箱损耗进行了三维有限元分析和计算。由于电力机车主变压器是高漏抗,多绕组变压器,经试验(采用放大法)得到该台变压器油箱损耗为31.245kW,使用FEM二维有限元分析法计算结果为45.791kW,而采用三维有限元分析法计算结果为30.478kW。从而表明,采用三维有限元分析能够更加准确地计算主变压器油箱的涡流分布和杂散损耗,为其采取有效的屏蔽措施提供了更加可靠的科学依据。     

两级三电平与两级两电平光伏变流器效率分析与比较

对应用于光伏发电领域的两级两电平和两级三电平变流器的效率进行了分析计算并给出了相应的比较结果。首先分析了两种电路拓扑结构的工作过程以及损耗来源。在相同的设计要求下,分别对两电平以及三电平两种电路拓扑结构进行参数设计、器件选型。并在所选器件和所设计参数的基础上,计算出有损器件的损耗。同时,为了使损耗比较更有说服力,对于两电平和三电平两种拓扑结构,尽最大可能选择恰巧满足设计要求且为同一工艺甚至同一系列的功率器件。通过详尽的损耗计算和比较,结果说明,在相同工况下,三电平变流器的损耗要低于两电平变流器,并且随着开关频率的增高,效率优势越明显。     

Harmonic load losses in HVDC converter transformers

Short-circuit losses were measured on a 213 MVA single-phase converter transformer at a number of frequencies between 60 Hz and 6 kHz. Using the results of these tests the harmonic losses during AC/DC converter operation were calculated. Variations of harmonic losses with transformer reactance, transformer winding stray loss factor and converter firing angle were studied. Using exponents of the components of harmonic losses with frequency derived from the tests, a table has been developed for determined the magnitude of the harmonic loss during converter operation. The data required to use the table are derived from design calculations and normal load loss test results     

Experience Gained from Designing Exhaust Hoods of Large Steam Turbines Using Computational Fluid Dynamics Techniques

Experience gained from designing exhaust hoods for modernized versions of K-175/180-12.8 and K-330-23.5-1 steam turbines is presented. The hood flow path is optimized based on the results of analyzing equilibrium wet steam 3D flow fields calculated using up-to-date computation fluid dynamics techniques. The mathematical model constructed on the basis of Reynolds-averaged Navier–Stokes equations is validated by comparing the calculated kinetic energy loss with the published data on full-scale experiments for the hood used in the K-160-130 turbine produced by the Kharkiv Turbine-Generator Works. Test calculations were carried out for four turbine operation modes. The obtained results from validating the model with the K-160-130 turbine hood taken as an example were found to be equally positive with the results of the previously performed calculations of flow pattern in the K-300-240 turbine hood. It is shown that the calculated coefficients of total losses in the K-160-130 turbine hood differ from the full-scale test data by no more than 5%. As a result of optimizing the K-175/180-12.8 turbine hood flow path, the total loss coefficient has been decreased from 1.50 for the initial design to 1.05 for the best of the modification versions. The optimized hood is almost completely free from supersonic flow areas, and the flow through it has become essentially more uniform both inside the hood and at its outlet. In the modified version of the K-330-23.5-1 turbine hood, the total loss coefficient has been decreased by more than a factor of 2: from 2.3 in the hood initial design to a value of 1.1 calculated for the hood final design version and sizes adopted for developing the detailed design. Cardinally better performance of both the hoods with respect to their initial designs was achieved as a result of multicase calculations, during which the flow path geometrical characteristics were sequentially varied, including options involving its maximally possible expansion and removal of the guiding plates producing an adverse effect.     

基于GMDH算法的配电网线损数据预处理研究

针对当前配电网线损计算的特点及数据存在缺失、异常等情况,基于数据分组处理算法(GMDH)建立了配电网线损缺失数据的预处理模型,实现对线损缺失数据的预处理。模型基于最邻近算法确定因变量和自变量缺失值的上下限,并进行随机插补,建立所有变量的数据分组处理模型,寻找最优复杂度模型,计算缺失值并进行迭代循环。算例结果表明,模型计算结果误差小、运算速度快,对缺失的线损数据能进行有效的动态更新,提升了数据质量,优化线损计算分析结果。     

变压器电容式套管电容量及介损测量接线方式分析

在6支电容式套管电容量及介损角正切值测试数据异常后,通过对两种接线方式定性分析和理论计算找出了电容量偏小和介质损耗角正切值偏大的原因,提出了修正公式,并通过了试验论证,同时提出了防止误判的建议。     

铁合金厂无功全额补偿节能方法

通过现场调研、详细计算及设计,利用微机系统进行控制对铁合金厂设备进行无功补偿,使铁合金厂功率因数提高到0．93,降低了线损,取得了良好的经济效益。     

地区供电网络网损计算

为了准确而简便地计算地区供电网络的网络损耗,以实现电网经济运行,介绍了地区供电网络（包括３５ｋＶ及以上高压供电网和１０ｋＶ及以下中压配电网）的两种网损计算方法——等值功率法和等值电阻法,并用ＦＯＲＴＲＡＮ语言进行编程计算。计算结果表明了该方法的简便,快捷和实用性。