双绕组电流互感器(TA)串并联时对变比和误差的影响分析

经常采用双绕组TA,或者配合电流表、功率表测量电路中的电流和功率;或者配合电能表计量电能等。借助双绕组TA两个二次绕组(绕组I和绕组II)串并联方法,可以改变TA变比和改善误差特性。下面就串并联使用时对TA变比和误差的影响分析如下。     

两元件电能表——相互感器接错时的计算方法

在实际使用中,电压互感器的变比按规格是固定的,不容易接错。而旧式的计量用高压电流互感器可通过改变接头改变其变比,容易接错。如果两相都接错,变比一致,计量结果乘以实际变比即可。倘若只有一相电流互感器的变比接错,使两只互感器变比不一致,那么实际计量结果该怎样计算?本文即是某企业在高压供电计量时,由于一相电流互感器的变比接错而发生的案例。为了便于分析,这里仅画出两元件电能表的一般接线原理(如图1所示)。图1两元件电能表接线原理两元件电能表实质上是两只单相电能表的组合,两元件电能表测量三相有功电能的方法,与用两只单相电…     

一次变压器环流引起智能电能表反向电量的原因分析

结合一次10 kV专变用户两台变压器并联运行，导致智能电能表出现反向电量的现场实例，运用计量参数数据和变压器并联运行条件，分析智能电能表反向电量原因和计量误差，提出了相应防范措施。     

电能表计量失准原因浅析

电能表作为电量结算的强检计量器具,按国家检定规程进行安装前的首次检定,以后还要每3年或5年检定1次。据调查,现在在用的电能表及新建住宅中安装的电能表许多都未经检定或根本没有检定过。正因为如此,由电能表计量失准引起的纠纷已呈逐年上升趋势。因此,寻找电能表计量失准原因并妥善解     

单相电能表错误接线剖析

在萍乡地区 ,为了发现农村计量装置因故障而少计电量 ,较普遍采用三只单相电能表计量三相四线制低压用户的电量。一用户计量装置接线如图１所示 ,装于配电板上 ,其二次线布置在板后。现场校准时 ,用钳形互感器在一次线上取电流信号 ,在同一相的一次线上取电压信号 ,对对应相电能表校准。三只电能表工作误差均较大 ,如Ａ相当电压为２３０Ｖ ,电流为９０Ａ ,ＣＯＳφ＝０．６９５（Ｌ）时 ,相对误差ｒＡ＝ +３８．６%。在电能表接线端子处取电压和电流信号 ,对电能表校准 ,三只电能表工作误差均较小 ,如Ａ相电压为２３０Ｖ ,电流为４．５Ａ,Ｃ…     

浅谈对感性负载消耗电能的两种错误计量

在三相交流电路中,通常采用感应系电能表或交流电子电能表测量其电能。对于三相三线电路,使用三相三线有功电能表或两只单相电能表;对于三相四线制电路,使用三相四线制有功电能表或三只单相电能表都能对电路消耗的电能进行正确计量。可是在日常工作中,我们经常发现一些农村基层供电站,在对单相电焊机(接线电压)等不对称感性负载所消耗的电能进行计量时,有的采用一块单相电能表,有的采用两块单相双向记数电能表进行计量,笔者认为以上这两种计量方法都是错误的。在三相四线制电路中,电路为正相序,作为电焊机这种感性负载,若用三相四线制电能表…     

电能表修校管理分析探讨

电能表是计量电量的重要仪器,电能表的准确度关系到用户所缴纳的电费数量,也关系到企业的发展。本文对电能表的修校管理策略进行探讨,旨在加强电能计量装置的管理,防止电能表的计量显示出现差错。     

远传通信在电能计量中的应用

电能计量的方法主要有两种 :一种是使用电能表计量 ;另一种是使用功率变送器计量。前者性能稳定 ,寿命长 ,适用于电量结算。后者瞬态响应好 ,适用于监视高峰负荷 ,高峰电量。使用远距离计量时 ,采用带输出脉冲信号的电能表 ,根据用电量的多少 ,输出稳定的脉冲数量 ,脉冲信号再与单片机接口进行计量。功率变送器也可以与单片机接口 ,进行计量。目前 ,我厂采用电能表进行结算。十年前投入了大量资金对一级计费电能表进行了全面改造 ,全部使用新型号带脉冲信号输出的电能表。由于近几年地下电缆老化 ,线间绝缘电阻下降 ,导致信号无法传输。为使…     

远传通信在电能计量中的应用

电能计量的方法主要有两种 :一种是使用电能表计量 ;另一种是使用功率变送器计量。前者性能稳定 ,寿命长 ,适用于电量结算。后者瞬态响应好 ,适用于监视高峰负荷、高峰电量。使用远距离计量时 ,采用带输出脉冲信号的电能表 ,根据用电量的多少 ,输出稳定的脉冲数量 ,脉冲信号再输入单片机进行计量。功率变送器的信号也可以输入单片机进行计量。目前 ,我厂电能结算采用电能表数据。 1 989年投入了大量的资金对一级计费电能表进行了全面改造 ,全部使用新型带脉冲信号输出的电能表。由于近几年地下电缆老化 ,线间绝缘电阻下降 ,导致信号无法传输…     

电子式三相三线电能表A相失压后电量的追补

通过一例电子式三相三线电能表A相失压后,电量追补的分析和计算,使我们认识了电子式三相三线无功电能表计量原理的特点;当电子式三相三线电能表不正常工作时,电量的退补不仅与计量的主回路有关,而且还与表内二次回路有关。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

卧式金属罐容量的测量结果不确定度

本文根据多年的实践检定经验 ,参照JJF1 0 59- 1 999《测量不确定度评定与表示》以及《测量不确定度表达 1 0讲》 ,对卧式金属罐容量的测量结果不确定度进行了评定。     

盐酸浓度不确定度的评估

通过对盐酸浓度标定的过程分析，找出影响结果的各个分量，进行不确定度的评定，按照计量技术规范给出标准的表示法。     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.