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ISSN 1843-6188 Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17) MONITORING OF ENERGY QUALITY FOR RESIDENTIAL CONSUMERS Oana Florentina MARIN, Marius Robert GHITA, Traian IVANOVICI, Horia ANDREI Department of Electrical Engineering, University Valahia Targoviste, Romania E-mail: [email protected], [email protected], [email protected], [email protected] Abstract. This paper proposes a real measurement analysis of non-sinusoidal regime of the residential consumers in order to identify the equipmenst that pollute and affect the power quality. Power quality issues important to the functioning of energy systems as a whole, have become topical in recent years and of particular importance especially due to explosive development of equipment and power electronics technologies and consumers due to the emergence of increasingly more sensitive to disturbance. sector and residential electrical network causes important disturbances that lead to lower levels of power quality (harmonics, unbalance, flicker, etc.). The presence of harmonics indicates a distorted current or voltage wave. The distortion of the current or voltage wave means that the distribution of electrical energy is disturbed and power quality is not optimum. Harmonic currents are caused by non-linear loads connected to the distribution network. The flow of harmonic currents causes harmonic voltages via distribution network impedances and consequently distortion of the supply voltage. Devices and systems that cause harmonics are present in all sectors, i.e. industrial, commercial and residential. Harmonics are caused by non-linear loads (i.e. loads that draw current with a waveform that is not the same as that of the supply voltage). For example, non-linear loads are: Industrial equipment (welding machines, arc furnaces, induction furnaces, rectifiers) Variable-speed drives for asynchronous or DC motors UPSs Office equipment (computers, photocopy machines, fax machines, etc.) Home appliances (television sets, micro-wave ovens, fluorescent lighting) Certain devices involving magnetic saturation (transformers) The disturbances caused by non-linear loads are harmonic current and voltage. Non-linear loads draw harmonic currents that flow in the distribution network. Harmonic voltages are caused by the flow of harmonic currents through the impedances of the supply circuits Keywords: quality of electric energy, real measurements, LabVIEW application, non-sinusoidal regime. 1. INTRODUCTION In 1985, the Commission determined that electricity is a (EC Directive 85/374), and clearly defining the essential characteristics and test methods to ensure proper functioning electricity consumers. Produced electricity is used by different consumers, from the industrial to household [1]-[4]. Power quality is a concern for energetics, becoming the subject of numerous studies, both internationally and nationally, that led to the introduction of rules, standards and regulations on the parameters of delivery/supply of electricity. Thus, deviations beyond predetermined limits void all receivers to normal operation, damage and / or damage. Thus, based on studies conducted by specialists in accordance with international norms, ANRE introduced performance and quality requirements for both electricity suppliers and industrial consumers and the like connected to public networks. Energy Strategy [4]-[7] is "a complex activity involving initiation, development and correlation of political action, economic, technical and ecological to national energy security, diversification of supply sources both internal and external, to improve and diversify the forms of energy production, increase production efficiency and energy consumption, improving the impact of polluting energy production and consumption ". If so not much attention to ensure proper quality of power given to large industrial consumers are connected to high voltage networks, the impact it has customers connected to the low voltage begins to be questioned. Development of modern industrial technologies, increasing the share of consumption in the services 2. NON-SINUSOIDAL REGIME AND QUALITY OF ELECTRICAL NETWORKS Troubleshooting power quality is a complex process which requires energy supplied quality assessment, monitoring voltages and currents in power points, and by monitoring disturbances introduced by the consumer to determine the source that generates symptoms. Non-sinusoidal regime is only bad consequences on the functioning of the consumer and overall power system, the main effects [8]-[10]: 29 Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17) a) affecting the operation of electronic equipment connected to mains voltage, including the rectifier control equipment; b) Introduction of additional errors of measurement devices, protective relays and distorting ripple control receivers; measurement errors of their wattmeters (up to 3%) and induction meters (up to 14%) are due to decrease power factor deforming under k = P / S < cos ϕ ; c) request beyond established facilities for reactive power compensation capacitors; d) Additional loss of power and active power in electricity networks, because the term apparent power S = P2 + Q2 + D2 corresponding increase PF = ISSN 1843-6188 P S (1) • Crest factor The crest factor is the ratio between the value of the peak current or voltage (Im or Um) and its rms value CF = Um U (2) For a sinusoidal signal, the crest factor is therefore equal to 2 , and for a non-sinusoidal signal, the crest factor can be either greater than or less than 2 . In the latter case, the crest factor signals divergent peak values with respect to the rms value. • Distortion power When harmonics are present, the distortion power D is defined as (3) D2 = S 2 − P 2 − Q 2 where S, P, and Q are respectively the apparent, active and reactive power[11]. - Harmonic spectrum and harmonic distortion Each type of device causing harmonics draws a particular form of harmonic current (amplitude and phase displacement). These values, notably the amplitude for each harmonic order, are essential for analysis. - Individual harmonic distortion The individual harmonic distortion is defined as the percentage of harmonics for order h with respect to the fundamental. power deforming D; e) lower yields due to additional losses of electric motors and couples pests; f) additional loading of power system elements (lines, transformers); g) the emergence of dangerous overvoltage conditions for certain harmonic resonance. Deforming element is a device that produces or increases the harmonic tension. In Budeanu’s acceptance deforming elements separate into two categories [11]: a) distorting elements of class I - powered strictly sinusoidal voltages or currents produce deformed phenomena (eg. arc furnaces, rectifiers, electric charge any pronounced nonlinear character); In other words, supply with sinusoidal voltage currents produce deformed (generate harmonic currents); b) distorting elements of class II - powered by currents deform the deformation increases (such power lines whose own up circuit inductance and capacitance-frequency oscillating harmonic currents close to the network) capacitors of reactive power compensation installation. The quality indicators of electricity should allow measurement / estimate the level of quality at some point in the network and at a time and comparing information obtained with the considered optimal or at least tolerated by most consumers connected to the electrical network. The number of consumers computerized greatly increased, with adverse consequences for installation that are connected. These include consumer electronic circuit components and features that have strong nonlinear effects of deviation in particular, the power curves from the ideal form, that the sinusoid. A number of indicators are used to quantify and evaluate the harmonic distortion in current and voltage waveforms [12]-[19], namely: Power factor Crest factor Distortion power Harmonic spectrum Harmonic-distortion values. These indicators are indispensable in determining any necessary corrective action. • Power factor The power factor PF is the ratio between the active power P and the apparent power S. ( ) I Uh 100 , I h (% ) = h 100 I1 U1 U h (%) = (4) By representing the amplitude of each h-harmonic order with respect to its frequency, it is possible to obtain a graph called the harmonic spectrum. - rms value The rms value of the voltage and current can be calculated as a function of the rms value of the various harmonic orders n I = ∑ I h2 (5) h =1 U = n ∑U h2 (6) h =1 where n is the total number of harmonics. Generally speaking, for a non-linear circuit element the total number of harmonics n can be different for voltage and current. • Total harmonic distortion (THD) The term THD means Total Harmonic Distortion and is a widely used notion in defining the level of harmonic content in alternating signals. For a signal y, the THD is defined a as: n ∑ yh2 THD = h=2 (7) y1 wher y1 is the first (fundamental) harmonic. This complies with the definition given in standard IEC 61000-2-2. Note that the value can exceed 1. 30 ISSN 1843-6188 Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17) According to the standard, the variable h can be limited to 50. The THD is the means to express as a single number the distortion affecting a current or voltage flowing at a given point in the installation. The THD is generally expressed as a percentage. - Current or voltage THD For current harmonics the relation for THD is: and analysis. The measurement data are transferred into computer through a high speed PCI highway. High-performance measurement devices determine very quickly, almost instantly, deformed shapes of the curves of current and voltage harmonics and the number and rank a series of indicators that characterize the intensity of deforming regime. In this paper for waveform analysis, harmonics, diagrams, graphs, we used a three-phase electrical network port analyzer model CA 8352 – CHAUVIN ARNOUX (figure 2), measurements were made in the project PREDEX - POSDRU/CPP107/DMI1.5/S/77497. n ∑ I h2 THDi = h=2 (8) I1 The equation below is equivalent to the above, but easier and more direct when the total rms value is available 2 I THDi = − 1 I1 (9) An analogue relation exists for voltage THD n ∑U h2 THDu = 3. h =2 U1 U = Um 2 −1 (10) LabVIEW APPLICATION FOR MONITORING THE ENERGY QUALITY FOR RESIDENTIAL CONSUMERS Power quality monitoring involves collecting and processing the voltage and current signals in different points of power system. Power quality monitoring using data acquisition systems impose certain requirements on the system and tehnical process used. These include hardware and software structures, the project dedicated to certain types of applications, in accordance with industry standards. Current development of hardware and software technology has made possible the deployment of real-time data acquisition, flexible, with multiple channels [20]-[23]. A monitoring system can generally include three components (Figure 1): 1. Subsystem input signal conditioning and acquisition; 2. Digital processing and storage subsystem; 3. System user interface. Figure 2. Three-phase electrical analyzer model CA 8352 - Chauvin ARNOUX The following are the harmonic spectrum of some equipment used for residential consumers: television, washing machine, refrigerator, lamps with minimum power consumption (economics), computer, air conditioning, microwave oven. All these receivers with less distortion effect or intense, especially the current curves are sources of harmonic currents which pollute and affect power quality, reason why the measurements presented in this article were made to the public network. Among the indicators that characterize the intensity of deforming regime, according to the purpose of this communication, the actual values of the curve is kept current and voltage distorted and harmonic spectrum, which can reach up to rank 50, i.e. 2500 Hz. An indicator that expresses very well the intensity of regime is the distortion factor THD deforming. In figure 3 are shown for a few standard consumers the deformed current curves, the spectrum of current harmonics and distortion factors. According to standard EN 50160 harmonics are allowed to rank 25 and distortion factor ≤ 8%, 95% of the week. It is found that the refrigerator is less distorted (THD = 7.24%), air conditioning (THD = 17.74%), microwave (THD = 36.19%), washing (THD = 53.45 %) TV (THD = 94.42%), computer (THD = 109.69%), maximum deformation effect, is that given the economic lamp operation (THD = 111.07%) Figure 1. The main components of a monitoring system The measurement of the current and voltage harmonics for the non-sinusoidal generator and for each element of the circuit are made it using LabVIEW application [24], [25]. LabView is a software packet for analysis and virtual instrumentation meant to make easier the data acquisition 31 Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17) Non-linear consumer Computer Current waveform Spectrum ISSN 1843-6188 THD 109,69% Fluorescent lamps 111,07% Television 94,42% Microwave ovens 36,19% 32 ISSN 1843-6188 Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17) Air conditioning 17,74% Refrigerator 7,24% Washing machine 53,45% Figure 3. Harmonics characteristics of residential consumers 4. For each problem as there are many and varied ways to solve their specific limits required for each consumer. Obviously, their introduction requires an analysis of a cost - benefit, the investment required to reveal their effects on growth and economic efficiency for consumers. CONCLUSIONS Most modern electronic equipment used in switching power supplies (SMPS). Advantage - for equipment manufacturer - is that the size, cost and weight are significantly reduced and the power unit can be made in almost any required form factor. Disadvantage - in addition to other types - is that instead of DC source, absorbs a current of mains power pulses as containing a large amount of harmonics of rank 3 and higher and higher frequency components harmonic. So consumers in the home computer network low voltage injected harmonic currents, ideal curves greatly distortig the fundamental (50 Hz). 5. REFERENCES [1] [2] [3] 33 Arrillage, J.; Watson, N. & Chen, S. Power System Quality Assessment, John Wiley & Sons, New York, 2001. H. Andrei, C. Cepisca, S.D.Grigorescu, Power Quality and Electrical Arc Furnaces, pp. 55-100, chapter 2 of the book Power Quality, InTech, Wien, 2011. Fuchs, E. F. & Masoum, M.A.S. Power Quality in Power Systems and Electrical Machines, Elsevier Academic Press, Amsterdam, 2008. Scientific Bulletin of the Electrical Engineering Faculty – Year 11 No. 3 (17) [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] ISSN 1843-6188 [18] Andrei, H., Cepisca, C. Calculation method of the relative variation in the electro energetic steady state circuits, Applied Electromagnetics and Mechnical Systems, Proceedings of the 3-rd Japan Romania Seminar on Applied Electromagnetics and Mechnical Systems, pp.16, Oradae, 2001. [19] Andrei, H.; Spinei, F.; Cepisca, C. & Caciula, I. 3 - D mathematical model of the power factor in electro energetical systems, Proceedings of VIth World Energy System Conference, pp. 257-261, Torino, Italy, July 1012, 2006. [20] Andrei, H.; Cepisca, C. & Spinei, F. (2006). 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