Recent Researches in Environmental and Geological Sciences

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1 The Influence of Reactive Power on Energy Efficiency in Household Applications MIRCHEVSKI SLOBODAN, ARSOV LJUPCHO, ILJAZI ILJAZ, RAFAJLOVSKI GORAN. Faculty of Electrical Engineering and Information Technologies, Departments of Electric Drives, Electrical Measurements and Electric Machines, University Ss. Cyril and Methodius Karposh bb. PO Box 574, 000 Skopje. Faculty for Contemporary Sciences and Technologies, South East European University, Ilindenska nn, 00 Tetovo MACEDONIA Abstract: - In this paper a look at reactive power on energy efficiency of air conditioning and electric lighting in household applications is taken. Usualy in energy efficiency only efficiency η as sign of active power consumption is treated. Through examples with airconditioner of inverter type and electric energy saving lighting non neglecting consumption of reactive (nonactive) power is presented. The measurements are realized by virtual instrument for power quality monitoring based on NI LabVIEW platform. It generally means that exept benefets of power electronics using for adjustable speed drives and energy saving lighting, new problems are generating in the producing, transfering, distributing and using of electric energy. Key-Words: - Energy Efficiency, Inverter Type Airconditioner, Energy Saving Electric Lighting, Measurement, Reactive Power, Efficiency (η), Power Factor (λ). Introduction Energy efficiency is the basis of technical systems working. It is powerful way for environment protection by reducing energy consumption. It is well known that generating of kwh in fossil thermo plants produce 0,435 kg CO [], [], [3], [4], [5], [6]. The production of green house gases CO, SO, N O is the main reason for environment pollution with cataclysm consequences. Therefore, energy efficiency is in fact conditio sine qua non. Modern life with more and more smart electronic devices is in close relations with greater energy consumption. Today, even in non high development countries using of home electronics, computers, HVAC (Heating, Ventilation, Air Conditioning) systems and other household applications has very fast spread. What energy efficiency practice for? The answer is simple - because of getting high quality and cheaper products, better life, lower production costs and reducing of global pollution. The order of listing could be opposite. How to realize energy efficiency? The right way is by equal treating of efficiency as measure of active power consumption and power factor as measure for reactive power consumption. Power electronics is a powerful tool for realising these goals. However, wide application of power electronics in household applications as inverter type airconditioners and energy saving electric lighting is a great reason for generating new problems. As a nonlinear load, due to commutation process of switches, the current delays behind voltage. So power electronics needs reactive power [], [8], [9]. The compensation of reactive power is not a unique problem. Harmonics produce a disturbance (distortion) power [5], [6], [7] and initiate the power quality problem. As a consequence reactive and disturbance power often is not registered either paid. EMC problems are also evident and need expensive solutions. Power Needs The industry is the greatest electricity user, especially in high development countries [], [], [3], [4], [8], [9]. In the industry electric drives are the greatest consumers of electric energy, more than 60% in high development countries. AC motors, induction and synchronous, transformers and power converters for their supplying need active and ISBN:

2 reactive power in the greatest percentage, as it is presented in Table [8]. It is necessary to mention that reference [8] is from 987 and that data are for the industry of former Soviet Union. Table Consumers of active power P [kw] and reactive power Q [kvar] in industry, [8] Consumer P (%) Q (%) Induction motors Synchronous motors 3 0 Power electronics converters 8 0 Electric heating devices 8 Lighting and other services 7 5 Self needs of the power plant 5 Losses in electric network 5 4 Normally, today in high development countries the percentages for P [kw] and Q [kvar] of AC motors and converters are increased and relatively changed. Second, the losses Q (%) in electric network have to be comment. In fact, the main part of these losses is not paid reactive power. The consumption of electric energy in household applications is estimated approximately 30% of total produced electric energy. It must be commented that smart electronic devices have spread use and are sources for non active energy consumption. It has happened with greater increase than in industry, even in non high development countries. But that consumption is not registered and paid. 3 Measurement of Electric Power The measurement of electric power is based on current and voltage measurement. The active power P [kw] is the arithmetic mean value of the known function P = U I cos ϕ (3) where ϕ is the delay/forward angle between voltage and current. It means that only for ideal sinusoidal supply power factor λ is equal to cos ϕ. λ = P/UI = cos ϕ (4) In the case of nonsinusoidal supply the state is presented in Fig., where P 50, Q 50 and S 50 are active, reactive and apparent power for the basic with network frequency f = 50 Hz, D is disturbance power, Q is total reactive power and S is total apparent power with influence of s. Fig. Power presentation according DIN 400, [5] The disturbance power D [kvar] could be expressed on two ways, with eq. (5) and eq. (6) (5) () The apparent power S [kva] is the peak value of the power function eq. () and presents product of effective voltage and current values S = U I () Assuming ideal sinusoidal form of voltage and current curves (6) It is clear that eq. (6) results from Fig.. Only active power is useful, working power and therefore P=P 50. Now the power factor is (7) where ϕ is the angle between P 50 and S 50 and λ is the angle P 50 and S. ISBN:

3 Concerning the measurement of the power in non-sinusoidal conditions, there are number of different approaches and definitions of reactive power. New definitions of powers have been discussed almost 50 years among the engineering community. Budeanu [] introduced reactive power Q, and a quantity named distortion power, D. The distortion power mainly consists of cross-products of voltage and current s. The reactive power definition proposed by S. Fryze [] is based on a time domain analysis. Different definitions of reactive power were proposed by N. L. Kusters and W. J. M. Moore [3], by W. Shepherd and P. Zakikhani [4], by Sharon [5], by L. S. Czarnecki [6], by IEEE working group on s [7] and IEC [0]. There is not yet available a generalized power theory that can provide a simultaneous common base for energy billing, evaluation of electric energy quality, detection of the major sources of waveform distortion, theoretical calculations for the design of mitigation equipment such as active filters or dynamic compensators. The IEEE working group on nonsinusoidal situations has suggested practical definitions for powers, [7]. The main difference between this definition and other definitions is that it separates the fundamental quantities P and Q from the rest of the apparent power components. Focus is also rather put on revenue metering than on compensation. The new definitions were developed to give guidance with respect to the quantities that should be measured for revenue purposes, engineering economic decisions, and determination of major polluters. The overall deviation of a distorted wave from its fundamental is estimated with the help of the total distortion. The total distortion of the voltage is defined with: V H V THDv = = V V (8) The total distortion of the current is as follows: I H I THDi = = I I (9) τ + kt v dt V = kt and τ τ + kt i dt I = kt and where τ H 0 h h> V = V + V (0) H I = I + I () H V = V + V = V V () I = I + I = I I (3) H 0 h h> are the squares of the rms values of voltage v H and current i H, respectively. Before practical use of the virtual instrument for monitoring of power characteristics, it was calibrated using the multifunctional calibrator Fluke 5500A. The virtual instrument using computer enables accurate, and versatile metering of electrical quantities defined by means of advanced mathematical models. Measurements presented in the paper are according to IEEE Std 459/00, IEEE Standard Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Nonsinusoidal, Balanced, or Unbalanced Conditions [7]. 4 Energy Efficiency in Household Applications Two examples are presented as a proof for non neglecting reactive power in household applications. The measurements are realized by virtual instrument for power quality monitoring based on NI LabVIEW platform. 4. Air Conditioning with Inverter Type The generation of s from an inverter wall split air conditioner with cooling / heating regime, 3,/4,5 kw, energy efficient class A, was measured and studied. The current distortion and the spectrum are shown in the Fig. and Fig. 3. The corresponding rms values squared are as follows: ISBN:

4 Table Power factor and distortion of air conditioner in different operation modes Air conditioner operation mode Cooling Power factor PF (%) distortion of the voltage THD V (%) distortion of the current THD I (%) Irms=.06A Irms=.6A Irms=.003A Fig. Current waveform graph of inverter air conditioner, Operation mode: Cooling, Line voltage RMS: 35.4V, Load current RMS:.87A, THDI: % Heating Irms=.60A Irms=3.487A Irms=4.55A The inverter air conditioner with cooling / heating is an important source of distortion in the households. The power factor and the distortion vary depending of the working point, but they should be considered in the analyses of the energy efficiency and use of energy in the households. The importance of this problem is widely discussed [7], [8], [9], [0], [], [3], [4]. Fig. 3 Current waveform graph of inverter air conditioner, Operation mode: Heating, Line voltage RMS: 33.6V, Load current RMS: 3.487A, THDI: % 4. Electric Lighting The generation of s from a particular light bulb may be illustrated by the distortion of the current sinusoidal form, and by the spectrum. On Figures 4-6 the measured currents of different light bulbs are presented. Power characteristics of the inverter air conditioner with cooling / heating for different working points are shown in the Table. Fig.4 Current waveform graph of Fluorescent light with inductive ballast, THDI=.4% ISBN:

5 Fig. 5 Current waveform graph of ECO Energy saving light, THDI=3.% fluorescent light with inductive ballast and of the ECO Energy saving light is rather low. The energy conversion efficiency should be considered together with the complete power characteristics of the lighting technologies. In [5] an example with power consumption of energy save lamp of W is shown. Power measurements give the following results: P=3 [W], Q=66 [VAr], D=56 [VAr], S=67. 3 [VA]. The price of active electric energy is 5 eurocent/kwh and approximately 30 % of that price for reactive electric energy, or.5 eurocent/kvar [4]. The total sum of paid electric energy should be equivalent to P=49.6 [W], what is comparable with classic heating thread lamp. It means that energy save lamp is in fact money save lamp, due to nonpaid reactive power. Important remark in this case is that the load is nonlinear, but constant, what is different than in HVAC usages. Fig. 6 Current waveform graph of LED light, THDI=5.03% Comparison of the power characteristics of different light technologies is shown in the Table 3. Table 3 Power factor and distortion of different light technologies Light technology Power factor PF (%) distortion of the voltage THD V (%) distortion of the current THD I (%) Fluorescent light with inductive ballast ECO Energy saving light LED light It is obvious that the power factor and the distortion vary very match depending on the light bulb technology. The power factor of the 5 Conclusion Energy efficiency is the powerful way for reducing the global pollution problem. Electric drives dominate in household applications and therefore have great saving potential. It is based on improving efficiency η (with decreasing losses by use of power converters and increasing dimensions of electric machines) and power factor λ (by using compensation and filtering methods). Modern electric lighting is also significant consumer which generates problems as nonlinear load. However, the consumed total (for all s) power must be paid. It is the best way to provide solid conditions for producing, transferring, distributing and using electricity. Reactive power [kvar] including disturbance power [kvar] must be registered and paid. Better tariff models are always possible. It is time to use better measuring apparatus for electric power in industry and domestic applications. Consumption of reactive power is not negligible even for domestic use, due to increased use of smart electronics devices. References: [] Anibal de Almeida, Paolo Bertoldi, Werner Leonhard (Editors), Energy Efficiency Improvements in Electric Motors and Drives, Springer-Verlag Berlin, Heidelberg, 997. [] Energy Efficiency, ABB Review, /007. ISBN:

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