Decomposing Apparent Power and Losses in Distribution Systems with Nonlinear Loads

The definition of reactive power for non-sinusoidal conditions is a controversial issue.The mathematical treatment of nonlinear loads in power systems is also unsettled.This paper starts with the decomposing of apparent power in the cases of linear and nonlinear loads.When harmonics are present,apparent power is composed of active power,reactive power,and disturbed reactive power.Linear element can be defined as the element without disturbed reactive power.This definition is based on a practical engineering concept which can separate the contribution from the apparent power into utility-duty part and custom-duty part.The field investigation of home-used facilities was conducted.Also the data acquisition in the 0.4 kV distribution systems was completed.Moreover,the loss increase due to the nonlinear loads was estimated.Nonlinear loads can be a dominant effect with respect to reactive power and power factor.Field data from a number of nonlinear load types indicate that the disturbed reactive power can cause significant losses in utility supply systems.

亚克力人造石废粉/ABS复合材料的非等温热分解动力学

采用熔融共混法制备了亚克力人造石废粉/ABS复合材料,利用热重分析法(TGA)研究了不同升温速率下,ABS、亚克力人造石废粉/ABS复合材料的热分解过程,采用Kissinger法和Flynn-Wall-Ozawa法研究了ABS及其复合材料的热分解动力学,计算得到动力学参数。结果表明,亚克力人造石废粉的加入提升了体系的热稳定性;随着升温速率的增加,ABS及其复合材料的TG曲线及DTG曲线逐渐向高温方向偏移,最大热分解速率温度逐渐增大;与纯ABS相比,采用Kissinger法和Flynn-Wall-Ozawa法得到的亚克力人造石废粉/ABS复合材料的表观活化能均较高,并且,随着亚克力人造石废粉含量的增加,复合材料的表观活化能逐渐增大,当亚克力人造石废粉含量为25%时,与纯ABS相比,2种方法计算得到的复合材料表观活化能分别约提高了27.77%、31.39%。

考虑虚拟电阻局限的电网电压跌落VSG暂态稳定性提升

虚拟电阻(virtual resistance,VR)方案能有效抑制虚拟同步发电机(virtual synchronous generator,VSG)并网过程中的同步振荡(synchronous resonance,SR),但会恶化系统暂态稳定性能,尤其是在高压线路中较大的线路电感将使其恶化程度进一步加剧。针对上述矛盾,首先基于功率流模型绘制功率-虚拟功角曲线,进而以最大功角过冲、总减速面积和最小初始功角定量描述VSG暂态稳定性。然后以增大最大功角过冲和总减速面积为目标,提出在电压跌落故障发生时通过减小等效有功指令和增大等效无功指令来提升系统暂态稳定性,并给出调节系数组合稳定域。最终在Matlab/Simulink平台中搭建仿真模型,结果表明,考虑VR和高压线路固有较大线路电感时,改进VSG控制策略可显著提升系统暂态稳定性能,应用良好。

绿电制氢装置并网与离网供电稳定控制方案研究

针对绿电制氢装置并网向离网切换的过程中,有功功率和无功功率不平衡引起的微电网频率、电压振荡以及变流器过载退出运行等问题,以制氢并离网切换稳定运行为目标,提出储能多模式控制策略。首先,建立储能系统功率转换方程,分析储能控制器功率、频率调节关系;其次,研究储能多模式切换策略,分析离网切换稳定关键因素,比较储能容量、控制器参数对系统影响;最后,以典型绿电制氢微电网为例,仿真计算不同储能容量及调差系数下的切换性能。结果表明:储能容量占比越高,储能视在功率超调越少,设备过载风险越小;同样储能容量下,调差系数越小,视在功率峰值越小,过载风险越低,但同时要求变流器电流过载能力强;调差系数取0.20时,可满足并网、离网中多种运行工况。

磷钒矿发电灰渣空白焙烧工艺及动力学研究

以磷钒矿发电灰渣为原料,对其空白焙烧工艺及动力学进行了研究。结果表明:灰渣中钒主要以钒云母形式存在,而且主要呈V^(3+)价态;灰渣空白焙烧适宜的工艺参数为:焙烧前将灰渣磨矿至细度为-0.074 mm占90%,在880~900℃温度下焙烧16 h, V_(2)O_5浸出率可达71%左右;灰渣空白焙烧反应由界面化学反应控制,表观反应活化能为89.75 kJ/mol,动力学方程为1-(1-x)^(1/3 )=114.47exp[-89 750/(RT)]t。

基于线损等效的视在功率和功率因数计算方法研究

分析了三相严重不平衡条件下现有功率因数的计算结果,指出了现有计算方法在反映实际线路利用率情况存在的不足。基于线路功率损耗等效原理,提出了一种能够准确反映实际线路利用率的功率因数和视在功率计算新方法。给出了现有智能电能表实现等效功率因数和视在功率计算的升级方案,同时以高准确度智能电能表作为测试平台,与现有功率因数进行三相非正弦不平衡试验条件下的对比测试。数据分析表明,与现有功率因数和视在功率相比,所提出的功率因数和视在功率新方法能够如实反映实际线路利用率情况,能够为功率因数的改善提供合理依据。

Optimization and Sizing of a Stand-Alone Photovoltaic System and Assessment of Random Load Fluctuation on Power Supply

This study presents an optimization technique and design for a stand-alone photovoltaic (PV) system to provide the required electricity for a single residential household in remote areas. From the basic solar components analysis, the irradiance on tilted surface is derived and compared to that on horizontal surface for Furu-Awa locality to infer the appropriate tilt angle (β) that maximizes the collection of solar energy. Seven optimum values of β applicable to the PV network were then derived depending of the period of the year and this simulation resulted that the panels are to be adjusted seven times a year. The optimization technique for load demand based on total apparent power of the household appliances produces an increase of 18% compared to the simple case of the PV components design using active power but leads to the optimum configuration that meets the real load demand of the household. Following the sizing of the station, reliability tests simulations were conducted for a one year corresponding period to infer the sensitivity of power supply to initial state of charge, to check the system autonomy and to evaluate the effect of random variation of the load on the smooth functioning of the PV system using a pseudo random number generator. This analysis shows that the minimum capacity of the battery for normal run of the Plan is 22.2% and that with random fluctuation of load, there will be periods of the year where the system experiences power failure depending on how important is the variation. The result of the study may imply a small increase in the cost of the entire plant but improves the stability and flexibility of such a station.

Economic Improvement of Power Factor Correction: A Case Study

Power factor (PF) is simply an expression of energy efficiency, which is always expressed in terms of percentage. Technically, PF is a ratio of real power in Kilowatts to the apparent power, which is always expressed in kilovolts amperes. In AC power analysis, power is always expressed in three ways, the real power (P), reactive power (Q), and the apparent power (S). The real power is the work useful power, while the reactive power is the wasted power in the 3-phase AC system, and the apparent power is the vectorial sum of the two powers. The increase of reactive power will reduce the presence of real power, thus making the power to be more expensive. In this paper, we will analyze the importance of improving the power factor by applying a bank of capacitors to a case study in Lebanon. Analysis of the economic improvement in the application of power factor correction is carried out. The result shows a reduction of 12 percent in the total cost.

Different Options Regarding Power Components in Electric Circuits

This paper describes two methods of representation of voltages and currents in electric circuits： in the vector form and in the shape of oscillations, represented as diagrams in the plane. The appropriate power components are discussed depending on the representation of voltages and currents. Special attention is paid to the instantaneous power peculiarities for diverse loads and non-sinusoidal conditions. A case study of power calculations in an electric circuit with a pluggable capacitor is presented. For these types of transient modes, the instantaneous power is represented in the form of active and reactive components. Calculation of active, reactive, and exchange powers for steady-state processes is presented.

非牛顿流体滩涂钢板桩围堰泄漏量分析

以非牛顿流体淤泥为介质,采用ANSYS Fluent软件,对滩涂埋地管道抢修围堰不同位置的泄漏量进行研究,得到稠度系数、幂律指数、缝隙尺寸对围堰泄漏量的影响规律,并对围堰内部淤泥每小时上升高度进行了计算。结果表明:幂律指数小于1时,发生剪切稀化,淤泥表观黏度随剪切应变率的增加而降低;随着幂律指数的增大,泄漏量逐渐增加,淤泥表观黏度随幂律指数的增大而降低,尤其是幂律指数大于1时,泄漏量进一步增加,说明流体流动过程中剪切应变率小于1。稠度系数增大时,围堰的泄漏量逐渐降低;缝隙尺寸增加时,围堰的泄漏量显著增大。当幂律指数为0.3~0.5、稠度系数为3~9 kPa·s、缝隙尺寸为5~10 mm时,围堰内部淤泥上升的总高度对围堰内部施工影响很小。

不同气候环境下接地电阻对农业电网电能质量的影响

春季雨季土壤湿度高,土壤电阻率降低,系统接地电阻变小;夏秋季高温干旱,土壤电阻率升高;冬季温度太低形成冻土层,土壤电阻率急速增加,系统接地电阻变大。建立了配电网终端农场的电网模型,研究不同气候环境下,接地电阻的变化对具体农业用户电能质量的影响。计算表明,当接地电阻变大时,农场电压幅值、有效视在功率变化量超过允许范围,电压总谐波畸变率、HRUh_(vs d,CP99)、THDU_(vs d,CP99)超过限值范围,极端气候时会更严重。当湿度增加、接地电阻变小时,农户电压会发生电压暂降,波形会随湿度变化而波动。

T_(2)WI联合DWI用于直肠癌的诊断、术前分期效能及rADC、ADC值与患者临床特征的相关性

目的探析T2加权成像(T_(2)WI)联合扩散加权成像(DWI)用于直肠诊断及术前分期的效能及其相对表观扩散系数(rADC)、表观扩散系数(ADC)值与患者临床特征的相关性。方法选择疑似直肠癌患者212例,其中男性118例,女性94例;年龄42~83岁,平均年龄60.93岁;病程3个月~10年,平均病程5.64年。均行T_(2)WI联合DWI检查,以患者最终病理诊断结果为标准,计算T_(2)WI联合DWI对直肠癌的诊断效能,进行T、N分期诊断;以最终病理诊断结果为依据,计算其T、N分期诊断效能,并进行一致性检验;观察不同临床特征的患者间rADC、ADC值差异,绘制受试者工作特性(ROC)曲线,计算rADC、ADC值对直肠癌的诊断效能。结果术后病理诊断恶性172例,良性40例。T1期、T2期、T3期、T4期分别为8例、35例、31例、6例,N0期、N1期、N2期分别为37例、22例、21例。T_(2)WI联合DWI诊断直肠癌的准确度为92.45%,灵敏度为93.02%,特异度为90.00%;分期诊断中T1期、T2期、T3期、T4期诊断准确度为95.00%、93.75%、96.26%、95.00%,灵敏度为75.00%、94.12%、93.55%、71.43%,特异度为97.22%、95.65%、95.92%、97.26%。一致性检验显示T_(2)WI联合DWI与病理诊断结果的T分期诊断一致性较好(Kappa=0.863,P=0.000);N分期诊断中N0期、N1期、N2期诊断准确度分别为93.75%、90.00%、96.25%,灵敏度分别为94.59%、77.27%、95.24%,特异度分别为93.02%、94.83%、96.61%,一致性检验提示T_(2)WI联合DWI与病理诊断的N分期诊断一致性较好(Kappa=0.844,P=0.000);病变特征与rADC、ADC分析中,恶性病变rADC、ADC显著低于良性病变(0.84±0.09 vs 1.18±0.12、0.93±0.11 vs 1.39±0.11。P<0.05)。腺癌rADC、ADC显著高于黏液腺癌(0.89±0.11 vs 0.75±0.09、0.97±0.14 vs 0.83±0.11。P<0.05)。不同分化程度患者间rADC、ADC从高至低依次为高分化、中分化、低分化(rADC:0.95±0.16 vs 0.82±0.10 vs 0.72±0.08;ADC:1.05±0.17 vs 0.911±0.14 vs 0.81±0.09。P<0.05)。ADC诊断直肠癌AUC为0.987,灵敏度为92.44%,特异度为97.50%(P<0.001);rADC诊断结直肠癌AUC为0.941,灵敏度为92.44%,特异度为87.50%(P<0.001)。结论T_(2)WI联合DWI诊断直肠癌具有良好的诊断效能,且其术前T、N分期准确度高,与病理诊断一致性较好。rADC、ADC值在不同良恶性肿瘤、不同分化等级肿瘤、不同病理类型肿瘤间存显著差异,可作为良恶性及肿瘤分化程度的诊断依据。

SMOGN,MFO,and XGBoost Based Excitation Current Prediction Model for Synchronous Machine

The power factor is the ratio between the active and apparent power,and it is available to determine the operational capability of the intended circuit or the parts.The excitation current of the synchronous motor is an essential parameter required for adjusting the power factor because it determines whether the motor is under the optimal operating status.Although the excitation current should predict with the experimental devices,such a method is unsuitable for online real-time prediction.The artificial intelligence algorithm can compensate for the defect of conventional measurement methods requiring the measuring devices and the model optimization is compared during the research process.In this article,the load current,power factor,and power factor errors available in the existing dataset are used as the input parameters for training the proposed artificial intelligence algorithms to select the optimal algorithm according to the training result,for this algorithm to have higher accuracy.The SMOGN(Synthetic Minority Over-Sampling Technique for Regression with Gaussian Noise)is selected for the research by which the data and the MFO(Moth-flame optimization algorithm)are created for the model to adjust and optimize the parameters automatically.In addition to enhancing the prediction accuracy for the excitation current,the automatic parameter adjusting method also allows the researchers not specializing in the professional algorithm to apply such application method more efficiently.The final result indicated that the prediction accuracy has reached“Mean Absolute Error(MAE)=0.0057,Root Mean Square Error(RMSE)=0.0093 andR2 score=0.9973”.Applying this method to themotor control would be much easier for the power factor adjustment in the future because it allows the motor to operate under the optimal power status to reduce energy consumption while enhancing working efficiency.

中波三频共塔带通耦合网络的实现

文章介绍了设计全固态中波广播发射机三频共塔网络的关键部分——预调网络和阻塞网络,并结合实际介绍了江门中波台的三频共塔的设计思路,同时分析了采用带通耦合网络作为匹配网络的优越性。

提高烧结余热发电量的生产技术实践

从铁矿烧结工艺参数控制角度研究了影响余热回收的因素,得出大烟道温度、终点温度波动趋势可间接表征烧结矿显热量的变化趋势。针对影响烧结大烟道温度、终点温度稳定性、终点位置控制等因素采取了相应的管控措施,结合当前公司烧结生产现状建立了烧结余热发电管控模型,2022年烧结余热发电量提高至20.51kWh/t,同比增加16.38%。

柴油发电机组容量计算公式差异简析

针对柴油发电机组的容量计算公式在各规范、手册中出处较多,且彼此之间存在一定差异,给工程设计带来诸多困扰,本文分别对按稳定负荷计算发电机容量时各公式的差异、按最大单台电动机启动容量计算发电机容量时各公式的差异等角度,就差异问题做简明分析,以供参考。

非正弦三相非平衡系统视在功率定义的研究

针对非正弦三相不平衡系统下视在功率的定义尚未达成统一的问题,利用MALTAB分别对算术、矢量和有效视在功率3种计量方法建立仿真模型,并分析比较3种不同视在功率平方与线路损耗的线性度关系,得到能正确反映线路损耗的视在功率计量方法。通过实例分析表明在非正弦三相非平衡系统下,现有的算术和矢量视在功率计量方法存在很大的问题,而IEEE STD.1459-2010试行标准中推荐使用的有效视在功率能够准确反映线路损耗大小,可以为电能计量的正确考核提供依据。

基于感应电动机网荷互馈特性的暂态电压失稳机理探析

正确认识电压失稳机理是进一步对电力系统电压稳定问题进行深入研究的关键。分析了网络视在功率传输特性和感应电动机负荷特性,揭示了以感应电动机为核心的暂态电压失稳正反馈动态过程。将与滑差相关的感应电动机负荷及网络视在功率传输的相互作用关系定义为感应电动机网荷互馈特性,并据此进一步分析了含有感应电动机负荷的系统电压崩溃过程,明确了基于感应电动机网荷互馈特性的暂态电压失稳机理,提出了感应电动机负荷电压失稳判据,构建了简单系统算例验证分析结果。分析表明,以感应电动机为核心的电压失稳正反馈动态过程是系统暂态电压失稳的重要环节;将感应电动机故障切除时滑差对应的恢复电压作为判断感应电动机电压稳定的必要条件,能够提高暂态电压失稳判定的准确性与适用性。所述电压稳定判据为预防电压失稳现象的发生和制定电压失稳解决措施提供了有力的理论支撑。

基于当地量的电压稳定指标

利用功率变化量在临界时刻为0的原理,提出并详细推导了一种电压稳定指标。该指标首次明确区分2种引起电压不稳定的因素;有功功率负荷过重与无功功率缺乏。算例的仿真验证表明该指标可以明确地给出电压不稳定的信息,可以为电压稳定监视或者电压稳定控制提供准确的参考依据,具有一定意义。

无功及视在功率物理意义的剖析

研究并分析了视在功率及无功功率的物理意义。虽然在正弦情况下,视在功率、无功功率都得到合理的定义,但指出即使在正弦情况下,其传统的物理意义是令人费解和误导的。所以,应消除错误的物理解释在电工领域所造成的影响。