Research and Development of a Virtual Instrument for Measurement, Analysis and Monitoring of the Power Quality

Because of these and other problems, the issue of the power quality delivered to the end consumers is, more than ever, an object of great concern. International standards concerning electrical power quality (EN 50160, IEEE Standard 1459-2010 among others) impose that electrical equipments and facilities should not produce harmonic contents greater than specified values, and also specify distortion limits to the supply voltage [1-4].


Introduction
Due to the intensive use of power converters and other nonlinear loads in industry and by consumers in general, it can be observed an increasing deterioration of the power systems voltage and current waveforms, the presence of harmonics in lines, interference problems in communication systems and, sometimes, in operation failures of electronic equipments.
Because of these and other problems, the issue of the power quality delivered to the end consumers is, more than ever, an object of great concern. International standards concerning electrical power quality (EN 50160, IEEE Standard 1459-2010 among others) impose that electrical equipments and facilities should not produce harmonic contents greater than specified values, and also specify distortion limits to the supply voltage [1][2][3][4].
The paper is organized as follows. Section 2: describes the two International standards concerning electrical power quality related to this work. Section 3: gives the description of the hardware used Section 4: describes briefly the programming environment used for creating the measurement system: data acquisition method, the effective values of the voltage and current, fundamental wave of the three-phase voltage and current, etc. In Section 5: results of experiments. Conclusions are given in Section 6.

Standard EN 50160
In standard EN 50160 several voltage parameters are defined [3,4]. The most important are Harmonic voltage a sinusoidal voltage with a frequency equal to an integer multiple of the fundamental frequency of the supply voltage. Harmonic voltages can be evaluated: individually, globally.

IEEE standard definitions 1459-2010
The standard defines the power measurement when the voltage and current are not sinusoidal, when the load is unbalanced or voltage *Corresponding author: Oleagordia IJ, Department of Electronic Technology, EUITI of Bilbao, University of the Basque, Spain, Tel: +0034 94 601 43 04; E-mail: ij.oleagordia@ehu.es is asymmetric and when the energy dissipated. The key concept of standard for power resolution is the separation fundamental component of voltage and current from all of harmonics component [1,2]. This improves the quality of measurement of instrument and traditional power monitor system. In this paper, we focus on three phase sinusoidal and non sinusoidal system. The most important definitions are summarized in Table 1.
The basic power component definitions [1] for three phase system we use are:  Page 2 of 6 applicable for the data acquisition card through voltage and current transformers, then, through the signal conditioner, these signals are conditioned to be sent to the data acquisition card by were subsequently analyzed.

Software
This section describes briefly the programming environment used for creating the measurement system. LabVIEW is a platform and development environment for a visual programming language from National Instruments. It is a graphical language designed for engineers and scientists and quite unique in the method by which code is constructed and saved [8].
The LabView environment contains pre-installed drivers for a variety of measurement devices. The configuration of devices is in most cases done without user help.
In this software user is able to choose and synchronize used hardware and create measurement tasks. A task is a predefined configuration setting for a specific device. The settings can also be passed to the device directly from a VI. In our case we preferred to set up a task Figures 2 and 3 illustrates a basic LabVIEW structure used to implement continuous acquisition [9]. The current distortion power, voltage distortion power, and harmonic apparent power are as follows: The load unbalance can be evaluated using the following fundamental unbalanced power: The fundamental active power A standard desktop personal computer (PC), running the Windows 7 operating system, was used as the system processing unity. Figure 1 shows a block diagram of the developed power quality monitoring system.
The signals of voltage and current are converted to the signals     Ve1), the nonfundamental VeH, the rms effective current (Ie), the fundamental current (Ie1) and the nonfundamental (IeH). The current distortion power (DeI), voltage distortion power (DeV), the total harmonic distortions (THDeV, THDeI). The phasors diagrams for voltage and current, the fundamental frequency. The phase angle between the phasors, and the cosine and sine. The Figure 9 shows the result of the test with unbalanced resistiveinductive load. The Figure 10 shows the result of the test with distorted and balanced resistive load. Where we noted that the harmonic factor was very high due to the great value of THDeI in the load current and the presence of 0 representing the harmonic current DC (Figures 13  and 14).     FFT spectra VI: Computes the FFT spectra of input waveforms. This VI returns FFT spectra as complex spectra of voltage and/or current, up to a specified maximum harmonic order with a frequency resolution around 5 Hz, which is the fundamental frequency divided by 10 or 12. Power VI: Calculates power values from voltage and current spectra. This VI returns apparent power, active power, reactive power, and the power factor. Storage of measurement data, the data can be stored in different ways, as for example in a database or in a dedicated file. Creation of a dedicated database would be time consuming and was not a part of specifications for the thesis. It was therefore decided to store data in a set of files, according to the aggregation times. Write To Measurement File Express VI.

Summary of findings
This paper describes a developed system that can be very useful for power management and power quality monitoring, suitable for industrial or commercial facilities, or even for research purposes. To accomplish that, transformers de voltage and hall effect sensors current, the National Instruments USB-6211 is a bus-powered USB M Series multifunction data acquisition (DAQ), a LabView environment, as it provides a programming language with possibilities of easy control of external hardware and of being used in many hardware and software platforms, as FPGA, PDA (personal digital assistant) and PC (personal computers) with a variety of operating systems. The system has been used to perform measurements at tension, current, frequency, to      The developed monitoring system is flexible, presents a userfriendly interface and a large data storage capacity, since it uses the PC hard disk for that purpose. It generates HTML reports that can be accessed through Internet, and can also generate data for other applications running in the Windows environment.

Implications for the future
The further development of the created system, by: Addition of modules responsible for control of current or voltage overload.