外文翻译---基于LabVIEW的电流互感器校验仪.docx

附录A LabVIEW Based Instrument Current Transformer CalibratorXin Ai Hal Bao Y.H. Song 1) North China Electric Power University, Beijing, China 107206 2) Brunel University. UKABSTRACTThe Virtual Instrument (VI) mainly refers to build all kinds of instruments by software such as LabVIEW, which likes a real instrument build in a computer. Its main characteristics are flexibility, multi-functions, multiple uses for one PC computer, giving high performance, and is less costly. In this paper, the VI technology is applied to the test and measurement of instrument current transformer (TA). By using the LabVIEW, the TA accuracy calibrator was developed. This virtual T.4 calibrator can automatically measure the accuracy of T.4 and can indicate the ratio error and phase error curves. The tests and calibration for the TA show that the virtual TA calibrator can be used in place of the traditional calibrator and is much better than the traditional one.Keywords：Instrument current transformer (TA), TA calibrator, Virtual Instruments, LabVIEW.I. INTRODUCTIONSince 1992 the VXIbus Rev.1.4 standard was established by the United States and LabVIEW was presented by the National Instruments co.(Nl), the Virtual Instrument (VI) have lain the foundation for its commercial use. The main characteristic of Virtual Instrument is that it makes instruments by software. Most of the traditional instrument can be developed by VI. The VI is a real instrument made by the personal computer.The Instrument current transformer (TA) is widely used in all kinds of current measurement and it has the functions of protection, isolation and extending the measuring range. With the rapid development of computer measurement and control technology, and with the sequent emergence of current transformer and transducer, there is an increasing number of current transformers with high accuracy and low secondary current. The standard TA secondary current is usually 1A or 5A: some non-standard TA secondary current may be 0 1A or lower. Although we have the technique to make this kind of calibrator by means of hardware such as single chip computer and electronic circuit, DSP and so on, it will cost too much money for these no-standard calibrator and will take too much time and the calibrator made by these hardware mill not be satisfactory in both function and practicality for designing all kinds of new TA.The calibrator that adopts VI technology not only can meet the requirements of the traditional one but also can satisfy customers with such advantages as multi-functions, convenience, and high ratio between performance and cost. The experiment results indicate that the virtual calibrator can provide excellent condition for TA measurement and design. The VI technology and personal computer must be widely used in the area of calibration on instrument transformer. THE WORKING PRINCIPLE OF TA CALIBRATORThe error of TA includes ratio error and phase error. The measuring of the error of TA or the calibration of the accuracy of TA usually applies differential measuring method. The method needs a standard TA except the measured TA and a TA calibrator. There is the same turn ratio between the standard and measured T4 and the standard TAs accuracy should be 2 levels higher than the measured one. The calibrator function lies in forming comparison circuits, measuring, and showing the error at all range. The comparison circuit, also referred to the difference measuring principle circuit, is showed in Fig. 1. By measuring the voltage on I, and Rd, calculate the corresponding current. Then the calibrator can indicate the error.When a TA has the same turn ratio between the primary and secondary winding, the self-comparison circuit could be used and is shown in Fig.2. In the figures, TA0 and TAX are standard and TA being measured respectively. Np and Ns are primary and secondary winding turns. ip and io, id, i, are primary current secondary standard current, secondary error current, secondary current of TA being measured respectively. Ro and R,R, are secondary windings resistance of standard TA, error current detecting resistance, burden resistance of TA being measured respectively. To and K, Tb. T, are voltage sampling points which can calculate the current In this paper, only voltage between K and T, voltage between Tb and T, are being measured and they represent the voltage on R, and R, respectively.In general, the TA calibrators principle of the sample resistance should be: 1） it can not affect the accuracy of the comparison circuit. In the ideal condition R, and Rd should be 0, but it can not be sampled. So there must be sample resistance, in this paper, R, as shown in Fig, is used; 1） the magnitude of the sample resistance should make the sampled standard current and error current in pro rata and should not have too much difference. The sampled resistance is set by experiment: R, is the secondary standard current sampling resistance and can be 0.1-0.50, R, is the error current sampling resistance and can be, R, is the burden resistance and it depends on the TA being measured. E$ sampling the voltage uo and U, on R, and R, respectively, the ratio error and phase error are showed on the LED through some process and calculations.According to the TA errors phase diagram, when io is maximum, the value of id is the ratio error; when io changes from negative to positive and equals to 0, the value of id is the phase error. For the same principle, the relationship is equal to the voltage signal U, and ud. showed in Fig.3. a and b is represent the ratio error and phase error separately. the TAs real ratio error C and phase error 6 can be found out through proper calculation,Where U, is the amplitude of uo The T.4 calibrator doesnt need very high accuracy. 1% to 3% error for the calibrator is enough. Because of the difference measuring principle, the error is the read error of calibrator, that is, the TAs errors error being measured. But the calibrator needs to have a suitable enlargement factor. The calibrator maximum enlargement factor through all channels should be 1000 times.III. THE PRINCIPLE OF VIRTUAL CA LIBRATORThe Virtual Instrument consists of three parts: the external comparison circuit (showed in Fig.1 or Fig.2), data acquisition card (PCI-6023) installed in the PC and the VI program by LabVIEW Then, after the two channels signal U, and ud come into the PC through the ADC, the rest of the work is done by the software. In this paper we use voltage U, on R, substitute for U, approximatively. The virtual calibrators work flow chart is shown as follow: 1) Set the essential initial values of the virtual calibrator; 2) Press the start button to start to work, adjusting the voltage regulator and changing the primary current, let the ratio between primary current and the rated current change from 10% to 120%; 3) The VI program will group the voltage signal U, and ud , then use the digital filter to eliminate the harmonic:4) Calculate the root-mean-square (RMS) value of tlx and 14, find out the amplitude of 21; 5) Calculate the RMS valve of io (substitute for f, ), i, and the ratio between io and its rated current and show the results. 6) Find out the a and b showed in Fig. 3, calculate the ratio error and phase error and show the results. 7) Set the L times loop, record and show the errors acquired by every time, 8) Show and print all the results of calibration. 9）Stop. The front panel of the virtual calibrator has the Controls, indictor and Switch. The function of Controls is to set the initial value before it works, The function of the Indictor is to show at1 kinds of needed values, including digital, curve and diagram etc. The switch decides the start and stop of the virtual calibrator. Of course, to change the measuring range, the operator needs to adjust the voltage regulator and change the primary current. This operation is necessary like that of the traditional calibration, but the recording for the error in any range is done by the virtual calibration. This confirms the accuracy of recording and relieves the operators work. The use of virtual calibrator is most interesting. The controls of virtual calibrator include:1) Setting the two sampling (analogue input) channels; 2) Setting the magnitude of sampling resistance in the comparison circuit; 3) Setting the secondary rated current of measured TA; 4) Setting the number of sampling of error curve; The Indictor of virtual calibrator has:1) Showing ratio and phase error, ratio between the primary current and the rated ones in digital; 2) Showing ratio and phase error, ratio between the primary) current and the rated ones In curves and diagram, where the curve include the active sampling points and function fitting curves; 3) Showing the error for the ratio between the primary current and the rated current from 10% to 1 20%;4) Showing the waveform of standard and error current, digital value of amplitude; 5) Showing of digita1 RMS value the standard and error current;6) Showing the pole of TA in the comparison circuit;The above shows that the function of virtual calibrator is greatly expended that of the traditional ones. 7111s kind of calibrator is not only convenient to use, but also makes the performance of the calibrator much better. From the function that shows the waveform, we can find out if there are some harmonics in the current, and confirm the accuracy for the calibrator.IV. EXPERIMENTThe virtual calibrator is mainly characterized by the flexibility compared with the traditional ones. Although the front panel has many functions, they can be easily extended by the user. So the virtual calibrator is of important value for the non-standard TA calibration.In the experiment, the primary current produce by a step-up current transformer and its current controlled by a voltage regulator. Through fitting the comparison circuit, the measuring range of the virtual calibrator can be set in any value. This paper gives SA and 0.1A two kinds of TAs calibration experiment. The parameter and method, results are presented below.A. 5A TA experiment The parameter of TA being measured is:Because of the 1:1 ratio of turn, the calibration for it doesnt need standard TA. The calibration circuit show in Fig2 We can apply self calibration method to measure its accuracy. The results are presented in the Ftg.4 and Fig5 and show that this TAs accuracy can be defined as 0.5 degree.B. 0.1A TA experiment The parameter of standard TA: From the Fig4 and 5, the accuracy of the TA being measured can be defined as 0.5 degree. In the experiment, the input signal of virtual calibrator should be properly grounded to avoid the disturbance. The sampling resistance in the comparison circuit should use precise ones and with no induction.V. CONCLUSIONSThe VI technique is one of the new scientific and technique productions. The appearance of VI is called“Revolution of Measuring and Control Technology”. According to the development of the software and hardware for computers, the VI thn01Ogy will have more developing space. The VIS will replace most of the traditional ones in the 21th century. With its flexibility, the virtual calibrator can measure any kind of T.4 including standard and non-standard ones. But the traditional calibrator can not measure most of the non-standard TA. It can record and save, display the data automatically. The method presented in this paper gives a new way to make he TA calibration. The main characteristics of the virtual calibrator are: 1) Flexibility, virtual calibrator is mainly made of LabVIEW software and can be easily modified by rewrite some software; 2.) Multi function, VI is designed on PC. It has waveform indictor, parameter controls and so on. At the time we calibrating a TKs accuracy, these functions can indicate many information such as waveform quality and so on; 3) Convenience to carry and use; 4) High efficiency and accuracy.; 5) High ratio between performance and cost;6) For multiple use in one PC. 7) It can record and save, display the calibration data automatically.基于LabVIEW的电流互感器校验仪Xin Ai Hai Bao T. H. Song-布鲁塞尔大学摘要虚拟仪器（VI），指的是利用软件在计算机上建立各种各样的仪器，比如说LabVIEW，就象是真的建立在计算机上的仪器一样。其主要特点是多功能的，可以集成多种功能于一台PC上，从而使其性能高，成本底。在我所讲的这一章中，LabVIEW虚拟仪器技术应用于测试与测量仪器电流互感器（AT）。利用LabVIEW测量仪器电流互感器精度校准精度是相当高的。这个虚拟的电流互感器校验仪不仅能够自动的进行尺寸计算，而且还能够指出错误的状态曲线。关于基于LabVIEW的电流互感器校验仪的测试表明，它不仅能够用于替代传统的校验仪，而且还能够比传统的检验仪做的更好。关键字：电流互感器（AT） AT校验仪 虚拟仪器 LabVIEW I. 简介 自从1992年美国建立VXIbus Rw.1.1标准以及National Instruments公司出品LabVIEW软件以后，虚拟仪器已经为他们商业上奠定了基础，虚拟仪器扮演的主要角色就是利用软件来构建各种仪器。大多数的传统的仪器都能够通过虚拟仪器来实现，虚拟仪器的通过PC来实现的真实可用的仪器。 虚拟的电流互感器被广泛的应用于各种各样的电流测量，并且它还具有保护功能，能隔离和扩大测量范围。随着业务的快速发展计算机测量与控制技术， 与相继出现的电流互感器和transduczr ，有越来越多的高accuracv和低secondarly 电流的电流变压器。电流变压器的标准电流通常是1A或者5A，而一些不标准的电流变压器有可能是0.1A或者更底。虽然我们有技术，使这种校验方式硬件如单片计算机和电子电路，DSP等集成电路，但是这将耗资太大钱，为这些不符合标准的校准器，并会采取过多的时间来校准所作出的这些硬件，这样不理想，所以无论从功能性和实用性都要求设计各种新的电流变压器（AT）。 该校验仪表示，采用虚拟仪器技术，不仅能符合传统要求的之一，而且还能满足客户要求的多功能，方便等优点，并且还具有很高比例性能和成本。实验结果指出，虚拟的校准仪可以为电流互感器提供比较好的测量和设计条件。虚拟仪器技术和个人计算机将被广泛的应用于电流互感器的校准仪领域。.电流互感器校准仪的工作原理 电流互感器的错误包括比率误差和相位误差。电流互感器的测量误差和校准准确性通常适用于微分测量方法。该测量方法除了实测TA和校验TA之外，还需要一个标准的TA。标准的TA和实测的TA之间必须有一个相同的空白比例，并且标准TA的的准确性应该比实测的TA高两个等级。该校验功能应该是形成比较电路，量度及显示误差在所有范围内。比较电路，提及了不同的测量原理电路，如图（1）所示。通过测量流过R0和Rd的电流,并且计算出其他的相应电流，那么校准仪就可以显示误差了。 当TA的主绕阻和次绕组之间有一个相同的变换比例的时候，自我对比电路将开始工作，如图（2）所示。TA0和Tax是标准的并且TA是分开测量的。Np和Ns分别是主次绕组的匝数。 ip,io,id,ix分别是初级电流，二级标准电流，二次误差电流以及TA的二次被测电流。R0,Rd,Rb分别是TA的标准二次绕组电阻，误差电流检测电阻，被独立测量的工作电阻。T0，K，Tx,Tb 是数据采样点的计算电流。在我将的这一章中，只有K和Tx之间的电压，Tb和Tx之间的测量电压，以及它们分别回馈到Rd和Rb 上的电压。 图（2）TA反馈带电路示意图总体来说，TA的工作原理以及其采样电阻应该是：1）它不能够影响比较电路的准确性，在理想的情况下，R0和Rd应该为0，并且他们都不能够被采样，因此，必须确定采样电阻，在本文中Rd被用于采样电阻；2）规模样本阻力应使采样标准电流与误差电流分配，不应该相差太大，采样电阻是有实验来确定的：R0是次要标准电流采样阻，电阻可0.1-0.5 ，Rd是误差采样电阻，电阻可在10-100，Rb是负载电阻，他由TA来决定的。同理，R0和Rd上的电压u0和ud，就会通过一些计算方法和过程在显示器上显示出比例误差和相位误差。 根据TA的误差相位图9，当i0最大时，相应的id就是比例误差，当i0从负到正变化并逐渐接近0的时候，id的值就是相位误差。同理，U0和Ud的关系是对等的，如图（3）所示，a和b是代表比误差和相位误差分别。则TA的真实的比例误差f和相位误差就可以通过计算得出。其中U0m是U0的振幅。TA校准仪的精度不需要很高，0.1%到3%已经足够了。由于测量原理的不同，误差在于读数的误差，也就是说，TA的误差的误差测量。但是校验需要一个合适的扩张系数，该校准器最多扩张系数必须各个通路应为1000 倍。III.虚拟校准仪的原则 虚拟仪器包括三部分：外围电路比较（如图1图2），数据采集卡（PCI-6023）以及通过LabVIEW安装的个人计算机上的程序。然后，在两个频道的信号u0和ud来进入计算机，通过转换器，其余的工作是由软件.在这篇文章中，我们使用Rb上的电压ux来代替u0。那么虚拟校验仪的工作流程如下：1）设置虚拟校验仪的必要的初始值。2）按下启动按钮，开始工作，调整电压调节和改变初级电流， 让初级电流及额定电流的比率由10 至120 变化。3）虚拟校准仪将连接独立的电压ux和ud然后使用数字滤波器，以消除谐波。4）计算Ux和Ud的均方值，找出U0的振幅。5）计算出i0的均方值，id和i0的额定电流以及比例关系，并显示结果。6）找出如图3中a和b，计算比误差和相位误差，并显示结果。7）设定K倍环路，记录并显示每次错误。8）显示和打印所有的校准结果。9）停止。 虚拟校准的前面板上有管制，指标和开关三个按纽