Indices for comparative assessment of the harmonic effect of different home appliances

Transcription

1 EUROPEAN TRANSACTIONS ON ELECTRICAL POWER Euro. Trans. Electr. Power () Published online in Wiley Online Library (wileyonlinelibrary.com). DOI:./etep.6 Indices for comparative assessment of the harmonic effect of different home appliances Alexandre B. Nassif *,, Jing Yong, Wilsun Xu 3 and C.Y. Chung Hydro One Networks Inc., Toronto, ON, Canada MG C9 State Key Laboratory of Power Transmission Equipment, Chongqing University, Chongqing, China 3 Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB, Canada T6G V Hong Kong Polytechnic University, Kowloon, Hong Kong SUMMARY Most of the modern home appliances use power electronic circuits as a power supply to interface with the distribution grid. They have become a major source of harmonic distortions in power distribution systems. This article presents a study of the harmonic current characteristics of such appliance through a measurement-based comparative approach. Magnitude-related indices are introduced to compare the harmonic effects of the various appliances and to quantify their relative severity. Phase angle related indices are introduced to study the diversity of the current harmonics phase angle among the devices and to understand its effect on harmonic cancellation. The proposed approach can be used to establish a database of harmonic characteristics for home appliances and other small, distributed harmonic-producing loads. Copyright John Wiley & Sons, Ltd. key words: power system harmonics; energy-saving home appliances; waveform distortions; harmonic cancellation. INTRODUCTION Power electronic-based home appliances have proliferated in distribution feeders supplying modern houses. For example, in the past, lighting loads were predominantly resistive, and heating, ventilation, and air-conditioning were mostly a combination of resistive and motor loads; today, the former are being gradually replaced by compact fluorescent lamps (CFLs), and the latter are being gradually replaced by variable speed air-conditioning []. The main reason behind this fact is the awareness for energy conservation. Although being power electronic based and being energy efficient are not synonymous, most of the energy-efficient loads are based on power electronics. In general, these appliances consume considerably less power than their older counterparts [,]. Newly introduced appliances are adjustable speed drive (ASD) based fridges, heat pump furnaces, fans, laundry dryers, and washers []; computers, monitors, laptops, and TV sets using switch-mode power supplies [3]; microwave ovens, home entertainment systems, and CFLs; and many other electronic loads. These devices are harmonic polluters and inject a relatively large amount of harmonics into the power grid relative to their power demand. When large amounts of such appliances operate in power distribution systems, the collective effect on the feeder power quality has become a large concern to utilities. For example, there is a need to understand the harmonic effect of mass deployment of CFLs [ 8]. Besides the CFL, the literature has documented the measurement of TVs, PCs, and variable speed air-conditioning as well as their measured or estimated harmonic effects on medium-voltage distribution feeders [,6 ]. In addition, extensive measurements of other common appliances such *Correspondence to: Alexandre B. Nassif, Hydro One Networks Inc., Toronto, ON, Canada MG C9. nassif@ieee.org Copyright John Wiley & Sons, Ltd.

2 A. B. NASSIF ET AL. as TVs of different technologies, heat pumps, stereos, CFLs, and refrigerators have been presented by Hardie and Watson [,]. However, the question Which are the most significant home appliances from the perspective of harmonics currents? is still difficult to answer, as no comparative study of home appliances harmonics has provided quantitative results that can be used in a practical way. Hence, it is difficult for industry to judge the power quality implication of various appliances. The objective of this article is to present a comparative study on the harmonic-producing characteristics of common home appliances. Measurements on the harmonic currents of many appliances were taken for this purpose. The results are then analyzed and compared from both the magnitude and phase angle perspectives. Indices are introduced to ensure a consistent comparison can be made.. CHARACTERISTICS OF COMMON HOME APPLIANCES The measured appliances are listed in Table I. Codes are assigned to them for easy identification in the figures and tables shown later. Table I also identifies the number of measured appliances of each type. Detailed results for all measured appliances are presented in Appendix A along with the data-processing methods. As shown in Table I, more than one piece of equipment of the same type was measured for most of the appliances. The appliances were measured under close-to-ideal voltage conditions. All portable appliances such as TVs and PCs were supplied by a signal generator (California Instruments Lx-Hv) with voltage total harmonic distortion (THD V ) <.%, whereas large appliances such as furnace and laundry loads were measured when installed in residential houses supplied with voltage distortion THD V < 3%. Close to ideal (low-voltage distortion) conditions were adopted because taking into consideration all possible voltage supply conditions would deem such an analysis impossible because of the large combinatorial nature of supply voltage magnitudes and phase angles to carry out the analysis presented in this article. Table II shows the main electric results obtained for the various measured appliances. Those results include the displacement power factor (DPF) and total power factor (PF), which were calculated by using the IEEE definition [3,]. Some appliances have different operating cycles that exhibit different power consumption and harmonic current characteristics. For example, a washing machine can have washing, rinsing, and spinning cycles. Other appliances, such as the CFLs, exhibit practically constant power consumption. To provide representative results, various operating cycles were measured. Table II presents the characteristics for the full load under normal operating conditions, and the column of operating power shows the power consumption under this condition. Therefore, for some appliances, the operating power is less than the rated power and is generally the condition in which the device draws the most distorted current. Table I. Measured home appliances. Appliance type Code No. tested Compact fluorescent lamp CFL Electronic-ballast fluorescent lamp EBL 3 Magnetic-ballast fluorescent lamp MBL Incandescent Lamp INC Desktop PC PC LCD computer monitor LCD Laptop LAP LCD high-definition television LCD TV CRT television CRT TV Microwave oven MW 3 ASD-based fridge ASD FR 3 Regular fridge R FR ASD-based washer WSH ASD-based dryer ASD DRY Regular dryer DRY Furnace FUR Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

3 CURRENT HARMONICS OF HOME APPLIANCES Table II. Harmonic characteristics of the main home appliances. Appliance THD I (%) DPF PF Operating power (W) I rms (A) I (A) CFL.9*.6.. EBL.96*.6.. MBL INC PC LCD.96* LAP 3.96* LCD TV.99* CRT TV MW.99* ASD FR R FR WSH ASD DRY DRY FUR The measured appliances are available in a variety of ratings. The tested CFLs are rated to 3 W, and the tested LCD TVs are rated 7 to 3 W. The shape of the current waveforms and the spectra are, however, similar. A representative rating for each appliance was obtained from survey studies. The most common rating of CFLs was identified as W [], and therefore this amount of power was adopted as the operating power for this device. Although the operating power of the ASD-based fridge is higher than that of the regular fridge, it is important to point out that the measured ASD-based fridges were of a volume much larger than that of the measured regular fridges. In addition, these ASD-based fridges seem to feature harmonic distortion compensation. More details on how to use the operating power to determine the appliances current models are presented in Appendix A. Table II confirms that almost all the electronic home appliances are harmonic producers. Many of the electronic appliances such as CFLs, desktop PCs, and computer monitors have a THD I higher than %. Table II also shows that most of the appliances have reasonably high DPFs, and some of them have a leading PF (indicated by * in Table II). The appliances current phasors at the 3rd to 3th harmonic orders are displayed in Figure. The phasors use the supply voltage angle as a reference, setting the phase angle of the fundamental frequency voltage to zero. The currents are normalized to emphasize the current harmonic angles and to improve visualization. Figure reveals the potential harmonic cancellation that might occur when two or more appliances are operated together. For example, the 3rd harmonic current of the LCD monitor is approximately 8 out of phase with that of the furnace. Conversely, the 3rd harmonic of the desktop PC is almost in phase ( ) with that of the CRT TV. 3. RATE OF HARMONIC DECLINE One way to characterize the harmonic currents from home appliances is by analyzing the decline rate of the current spectrum for these devices. Engineering mathematics books indicate that a square waveform has the spectrum characterized by I h =I /h, where h =,3,,7... Conversely, triangle and trapezoidal waveforms have the spectrum characterized by I h =I /h. Many studies have found that a first approximation to the harmonic characteristics of an ideal single-phase ASD is I h =I /h at all odd harmonics because the waveform is approximated as a square wave []. For the home appliances, however, this type of characterization has not been established. The characterization of the harmonic current magnitudes for home appliances is proposed as I h ¼ I =h a () where a is a parameter that determines the decline rate of the current spectrum and is estimated by performing curve fitting on the normalized (by the fundamental frequency current) spectra of the home Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

4 A. B. NASSIF ET AL. 3 rd harmonic 9 6 th harmonic th harmonic th harmonic th harmonic th harmonic MW ASD FR WSH LCD TV PC LAP LCD CFL FUR EBL MBL ASD DRY R FR CRT TV Figure. Normalized harmonic currents of all appliances using the fundamental voltage phase angle as the angular reference. appliances. Such a relationship is proposed because the electronic home appliances, even those based on the single-phase rectifier topology, do not draw a square current waveform and therefore cannot be approximated to the known relationship I h =I /h. The characterization serves two purposes: (i) it can define patterns for the appliances current spectra for each type of appliance, and (ii) it can be used to compare the relative distortion of the home appliances harmonic currents. The estimated values for a for all appliances are shown in Table III. The appliances are sorted according to the a values, which increase from left to right. Table III reveals that many of the appliances have a <, which means that the currents drawn by those appliances contain an amount of harmonics that are higher than those contained in the ideal square-wave case. This can also be confirmed by comparing the THD of the square wave, which is.7%, to those of the appliances, which were presented in Table II. The appliances current data are displayed in Figure, which reveals that most power electronicbased appliances have a spectrum with harmonics higher than those obtained from the I /h relationship. Figure shows that the LCD TV, ASD-based fridge, furnace, magnetic-ballasted fluorescent lamp, and regular fridge are the appliances that have harmonics below the I /h curve. The appliances that have a values close to are the regular fridge and the furnace. By investigating those appliances current waveforms, it was observed that they have triangular-like shapes. For those two appliances, the approximation to the ratio I /h agrees well. By using these results, the harmonic magnitude characteristics of home appliances can be obtained using as a first approximation by using the frequency-dependent relationship I h =I /h a. Using the Table III. Comparing a for all home appliances. LAP CRT TV EBL CFL PC LCD WSH a ASD DRY MW R FR FUR ASD FR MBL LCD TV a Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

5 CURRENT HARMONICS OF HOME APPLIANCES Harmonic currents [normalized] /h CRT TV LAP PC LCD CFL EBL WSH ASD DRY MW LCD TV ASD FR FUR MBL R FR Harmonic order Figure. Current spectra of the home appliances and curve fitting to obtain a. estimated values for the parameter a is one way to estimate the magnitudes of the current spectra of all appliances if the rated fundamental frequency current is known. This information is useful as a first approximation to perform harmonic studies, as the harmonic current spectra of the appliances are not provided by the manufacturer. To further illustrate the accuracy of this approximation, Figure 3 displays the appliance current spectra along with the respective approximation and shows that an acceptable fitting can be obtained for most of the appliances. To deal with the diversity of the magnitudes and phase angles of the various appliances, two studies are proposed. The severities of the harmonic currents are studied by using the equivalent CFL index, as introduced in Section. The harmonic compatibility index is proposed to study the harmonic currents cancellation due to phase angles disparity and is introduced in Section.. THE HARMONIC MAGNITUDE STUDY This section introduces the equivalent CFL index to assess the relative severity of the current harmonic magnitudes of the home appliances. To provide a consistent comparison, the index is calculated by MW LCD TV ASD FR PC LAP WSH LCD. CFL. FUR. R FR EBL CRT TV MBL ASD DRY Normalized spectrum Fitted spectrum Figure 3. Current spectra and fitted /h a. Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

6 A. B. NASSIF ET AL. calculating the harmonic emissions of an appliance as compared with the emissions of another appliance used as a template to facilitate harmonic emission benchmarking. Of all the power electronic-based home appliances, the CFLs have been most often studied to characterize them and determine their harmonic current effects [6 8]. Because CFLs have been extensively studied and characterized, it is reasonable to use their current harmonics as a relative harmonic injection benchmark for comparing the harmonic injections from the other home appliances. The equivalent CFL index is introduced to provide a quantitative comparison of the harmonic effects of the appliances. This index quantifies each appliance in terms of its harmonic effect expressed as the number of CFLs it is equivalent to. This index is defined as follows:. For each type of appliance measured, a representative harmonic current is established. This representative current magnitude is obtained from a weight average of the measurements of several types of each of the various appliances. This procedure is explained in Appendix A. Two examples are displayed in Figure a: the representative desktop PC and the representative CFL. The operating power of the representative appliances is shown in Table II.. For each harmonic order h, the ratio of the appliance s current to that of the representative CFL current is determined by using the following equation: Ratio h Appliance ¼ I h appliance () I h CFL where I h_appliance is the appliance s harmonic current at order h, and I h_cfl is the representative CFL harmonic current at order h (all in amperes). For example, a Ratio h value of implies that the appliance generates twice as much harmonic current at order h as the representative CFL. Figure b shows the ratios for the desktop PC.. To obtain a single index and compare the appliance with a representative CFL, the ratios of different harmonic orders are aggregated into one value by using a weighted average as follows:.8 I PC I CFL Current [A] Harmonic order a. Equivalent-CFL PC Ratio-h PC Total Harmonic order b. Figure. Harmonic emissions from a desktop PC and a CFL: (a) harmonic current magnitudes (A) and (b) harmonic current ratios. Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

7 CURRENT HARMONICS OF HOME APPLIANCES vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi vffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi X H u X Equivalent-CFL Appliance ¼ t H Ih Appliance w h Ratio h Appliance ¼ u P H C t A h¼3 h¼3 Ih CFL h¼3 rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi PH The weighting factor w h ¼ I h CFL = I h CFL is the individual harmonic distortion of the CFL h¼3 current. This weighting factor is used because if a CFL produces more harmonic at h, the harmonics from other appliances will also be treated with more significance at the same order. The last bar of Figure b (labeled as Total) represents the aggregated ratio (i.e. equivalent CFL) of the desktop PC. (3).. Basic results provided by the equivalent CFL index The results obtained from the calculated individual equivalent CFL index of all appliances are presented in Table IV. The results are arranged in the ascending order of the index. Table IV shows that a desktop PC is equivalent to seven CFLs in terms of harmonic current injection. A microwave oven has a harmonic effect equivalent to 6. CFLs, and a laundry washer has a harmonic effect equivalent to 6 CFLs. Table IV also lists the power ratios with respect to the CFL and the harmonic current ratios from the 3rd to the 3th harmonics... Comparison of all appliance types The equivalent CFL index compares the harmonic effect of the appliances on the basis of individual units. The fact that each household may have multiple appliances of the same type is recognized in this study. The implication is that the total harmonic currents generated by each type of appliance (that can be or more units) in a typical house must also be compared. For this purpose, the number of appliances that could be installed in a household is estimated from statistical surveys [,6]. The average number of TVs is indicated to be, and the average number of refrigerators, laundry washers, and dryers is indicated to be approximately. As mentioned earlier for the lighting loads, an average house has a total number of between and 3 installed lamps. At present, approximately % to % of all lamps are CFLs [], so it is assumed that six CFLs are installed in a typical house. The average number of magnetic-ballasted fluorescent lamps is estimated to be []. On the basis of these data, the total harmonic effect of each appliance type in a household is determined and quantified as the total equivalent CFL index, which compares the harmonic effect of each type of appliance installed in a typical household. Appliance type Table IV. Comparing the harmonic effect of one unit of home appliances. Operating power (W) Power ratio Equivalent CFL Ratio 3 Ratio Ratio 7 Ratio 9 Ratio Ratio 3 MBL CFL ASD FR EBL LCD TV R FR LCD FUR CRT TV LAP PC ASD DRY WSH MW Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

8 A. B. NASSIF ET AL. The values of the total equivalent CFL index and the associated assumptions are shown in Table V, which can be used for several comparisons. For example, the harmonic effect of CFLs is comparable with that of the home-office equipment such as desktop PCs. The washer (ASD-based) and the microwave oven are identified as more significant harmonic sources. The LCD TV injects little harmonic content, whereas the CRT TV injects an amount comparable with that of the CFLs. The collective load of CFLs in a typical household is a harmonic contributor comparable with the other harmonic sources.. THE HARMONIC PHASE ANGLE STUDY The equivalent CFL index is useful for comparing the harmonic current magnitudes of the home appliances, but it does not provide information on the harmonic phase angle diversification. The harmonic current phase angles are important because they indicate how the harmonics from various home appliances will either add to or cancel out each other. Although this effect has been studied by analyzing the diversity effect of single-phase diode bridge rectifiers [7,8], in this article we expanded the concept by defining compatibility indices among all appliance types. The harmonic compatibility index (CI h ) is introduced in this section to account for the current harmonic phase angles of the appliances as these are operated together. The adopted definition for the compatibility index is as follows:. Like the method used for the equivalent CFL index, for each type of appliance measured, the representative harmonic current of each appliance is used for the harmonic compatibility index. The representative harmonic currents are presented in Appendix A.. For each harmonic order h, the phasor relationship of the appliance s current to that of the representative CFL current is determined by using the following equation: I CI h Appliance ¼ _ pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi h Appliance þ _I h CFL eq _I h Appliance þ _I h CFL eq ¼ I þ I þ I cosðθþ ¼ cos θ h I () where _I h CFL eq ¼ _I h CFL Ratio h Appliance () and θ h ¼ ang _I h Appliance ang _I h CFL (6) The meaning of this equation is that because the magnitude of the CFL current phasor is scaled to be of the same magnitude as the magnitude of that of the appliance, only the phase angles of the appliance Appliance type Table V. Comparing the harmonic effect of collective home appliances. Operating power (W/unit) No. units Total power (W) Power ratio Total equivalent CFL MBL LCD TV ASD FR R FR.67.8 FUR.6.8 LCD CFL CRT TV LAP PC..8 ASD DRY..76 WSH MW Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

9 CURRENT HARMONICS OF HOME APPLIANCES and the CFL are taken into consideration in the phasor operation. As θ h varies between and p radians, CI h_appliance varies between and. Figure shows representative values for the index as it is used to explain the index at each harmonic order h. Assume the CFL is being compared with Appliance, Appliance, Appliance 3, and Appliance ; Figure a reveals that the index calculated for Appliance means solely harmonic addition, resulting in CI h_appliance = because both components are in phase; that is, θ =. Conversely, the index calculated for Appliance (Figure b) is CI h_appliance = / because θ = 9. The index calculated for Appliance 3 (Figure c) is found to be CI h_appliance 3 = / because the value of CI h is the same of that of the magnitudes of the individual phasors; that is, θ =. Finally, the index calculated for Appliance (Figure d) is CI h_appliance = because both components are in opposite phase angles; that is, θ = An aggregation similar to that proposed for the magnitude-based equivalent CFL index is introduced for the harmonic compatibility indices, also by using the same weighting factor, which results in the following aggregated index: qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi X CI Appliance ¼ wh CI h Appliance (7) The resulting aggregation of the individual CI h_appliance carries the information about the combined harmonic compatibility into a single index. The calculation of the compatibility between the PC and the CFL is used as an example. The individual current phasors are displayed in Figure 6. The indices CI h_pc and CI PC are shown in Figure 6, where they have all been normalized by the CFL s third harmonic, to show the relative effect of each individual CI h_pc on the total CI PC. The phase angle based harmonic compatibility index can reflect the measure of the harmonic cancellation between two appliances should there be no difference in magnitude, that is, the compatibility index clearly represents potential cancellation should the magnitudes be of comparable sizes. In other words, if both appliances current harmonics were of the same magnitude, the index CI h_appliance would reflect the amount of harmonic cancellation. Suppose case, θ h =, resulting in CI h_appliance = %, which means zero harmonic cancellation, and case, θ h = p/ and CI h_appliance = 7%, which means 9% harmonic cancellation as compared with the first case... Basic results for the harmonic compatibility index The results for the compatibility index for all appliances are calculated and presented in Table VI, in the ascending order of CI Appliance I h _ Appliance 3 3 o I h _ Appliance 9 o 8 8 I h _ CFL _ eq I h _ CFL _ eq 7 a 3 3 CI 7 h b CI h I h _ Appliance I h _ Appliance 8 o 8 o I h _ CFL _ eq 33 I h _ CFL _ eq 33 7 c CIh d CI h Figure. Phasor diagram to illustrate the compatibility index. Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

10 A. B. NASSIF ET AL CI =.8 6 CI =.39 6 CI = CI PC = CI = CI = CI 3 = Figure 6. Normalized current phasors along with CI h for PC and CFL. Table VI. Harmonic compatibility index results using CFL as a template. CI Appliance CI 3 CI CI 7 CI 9 CI CI 3 ASD FR ASD DRY R FR CRT TV WSH PC FUR MW LCD LCD TV MBL EBL LAP CFL To further illustrate the general behavior of the appliances, Figure 7 shows the distribution of the CI h_appliance indices by using histograms. The following conclusions can be drawn from the results presented Table VI and Figure 7:. More appliances show higher compatibility (have higher CI h_appliance ) at the 3rd harmonic than at other orders. This finding agrees with expected harmonic cancellation that can occur in distribution systems [9,] and indicates that the harmonic cancellation at such an order is smaller than that observed at higher orders. The appliances that show notably low compatibility at the 3rd harmonic are the fridges and the ASD-based dryer.. The harmonic compatibility is generally low for harmonics at the th and higher orders. This finding implies that the harmonic cancellation at these orders is higher than that observed for the 3rd harmonic. For the magnitude-based index, the equivalent CFL gives absolute results by using the CFL as a benchmark. These results are straightforward for assessing the relative harmonic severity among the appliances. For the phase angle assessment, the harmonic compatibility index using the CFL as a template does not provide directly the relative harmonic current angle difference between any two Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

11 CURRENT HARMONICS OF HOME APPLIANCES Frequency of CI Frequency of CI Frequency of CI Frequency of CI Frequency of CI Frequency of CI Figure 7. Distribution of the CI h_appliance indices. given appliances. To obtain such a relationship, the indices between any two appliances can be obtained by using the CFL-calculated CI h_appliance as follows: I CI h Appliances - ¼ _ h Appliance þ _I h Appliance _I h Appliance þ _I h Appliance ¼ cos θ h Appliance θ h Appliance (8) where the appliances currents are normalized to have the same magnitude. The results for the harmonic compatibility indices CI h_appliances for each appliance in relation to all the other appliances at the 3rd th harmonic orders are shown in Table VII. Higher-order indices are omitted because of space limitations. Table VII provides a direct measure of the harmonic compatibility between any two given appliances... Results for the aggregated harmonic compatibility index The indices CI h_appliances such as those presented in Table VII can be combined as a weight average. The aggregated indices can be obtained by using a weight average similar to that of Equations (3) and 3rd MW ASD th FR Table VII. Harmonic compatibility index results for 3rd and th harmonic. WSH LCD TV PC LAP LCD CFL FUR EBL MBL ASD DR MW ASD FR WSH LCD TV PC LAP LCD CFL FUR EBL MBL ASD DR R FR CRT TV R FR CRT TV Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

12 A. B. NASSIF ET AL. (7) and by using the same weighting factor. The aggregated index is obtained as qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi X CI Appliances - ¼ wh CI h Appliances - (9) Table VIII shows the aggregate compatibility indices for each appliance in relation to all the other appliances. Table VIII also shows that the lowest compatibility levels are obtained when comparing the pulsed loads (PCs, laptops, and LCD monitors) with the load from the fridge. As a further illustration, Figure 8 shows the distribution of the aggregated index for all appliances by using histograms. Figure 8 is useful to identify the general compatibility trends of each individual appliance. For example, Figure 8 shows that generally, the microwave oven is more compatible than the ASD-based fridge with all other appliances..3. Effect of the phase angle on the harmonic current cancellation A case study is presented to illustrate the importance of the phase angles of the appliances current harmonics. The harmonic currents of selected groups of appliances are analyzed. The combinations of appliances were determined by using survey results, as presented in Table IX. The harmonic injections of these groups are compared by both considering and ignoring the phase angle disparity. This study is useful to show the harmonic current cancellations that occur when appliances of different types are connected together. The indices proposed in this article are used to explain the results. The main results from these studies are presented in Figure 9, which shows the total power of the combination of appliances in the x-axis and the current harmonics in the y-axis. A linear data fitting is also provided to show the rate of harmonic current increase as the total power increases. The upper line is the arithmetic sum, and the lower one is the phasor sum. Figure 9 reveals the following: As the total power of each set of appliances increases, the trends of harmonic currents increase accordingly, for both cases (arithmetic and phasor sum). Although the trends increase, increasing the power does not necessarily increase the net current harmonics. As explained earlier, this result is expected because of a large amount of harmonic cancellation, especially at levels higher than the 3rd harmonic order. The slopes of the linear data fitting show larger difference as the harmonic orders increase. For the case presented in Figure 9, the angles of the slopes for 3rd, th, 7th, and 9th harmonics are 69,, 38, and 7, respectively, for the case of the arithmetic sum. For the case of the phasor sum, the angles of the slopes for 3rd, th, 7th, and 9th harmonics are 6,,, and, respectively. The results confirm that (i) the rate of increase of the harmonic currents is more prominent at lower order harmonics and that (ii) the differences of the slope angle increases for higher-order harmonics. Total MW ASD FR Table VIII. Harmonic compatibility index results for aggregated harmonics. WSH LCD TV PC LAP LCD CFL FUR EBL MBL ASD DRY MW ASD FR WSH LCD TV PC LAP LCD CFL FUR EBL MBL ASD DRY R FR CRT TV R FR CRT TV Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

13 CURRENT HARMONICS OF HOME APPLIANCES CI-MW. CI-ASD FRD. CI-WSH. CI-LCD TV. CI-PC. CI-LAP. CI-LCD. CI-CFL. CI-FUR. CI-EBL. CI-MBL. CI-ASD DRY. CI-R FR. CI-CRT TV. Figure 8. Distribution of the CI Appliance_ indices for all appliances. The observed behavior can be explained by using both indices. The equivalent CFL index is well suited for explaining the arithmetic sum. Between 9 and W, for example, as the microwave oven is connected, an increase occurs in the 3rd harmonic current that is equivalent to Ratio 3 = 33 CFLs, whereas the increase in the 9th harmonic is equivalent to that of only Ratio 9 = 7 CFLs. On the other hand, the compatibility index is useful for explaining the phasor sum. For the same case, the microwave oven has high compatibility at the 3rd harmonic with the computing loads and CFL but low compatibility with the furnace and fridge. For this reason, the increase in the 3rd harmonic current is not as high as that shown for the arithmetic sum but is still high because of the relatively high harmonic compatibility. At the 9th harmonic, however, the microwave has low compatibility with all loads, except those from the PC and furnace, resulting in significant harmonic cancellation. Therefore, there is barely any increase for that power demand step. 6. CONCLUSIONS A comparison of the harmonic levels among home appliances was carried out. The issues relating to the harmonic current magnitudes and phase angles were studied by using developed indices. The equivalent CFL index was introduced to quantify the relative severity of the magnitudes of the harmonic currents from home appliances. The harmonic compatibility index is an indication of how much current cancellation can occur between the harmonic currents of any two given appliances and therefore deals with the phase angle cancellation issue. Both indices provide results that can be used as a benchmark for harmonic studies at a residential customer level. The key conclusions are as follows:. The current spectrum decline rate study was performed to characterize the magnitudes of the current spectra of all appliances. The estimated parameter a is unique for each appliance or set of electrically similar appliances. Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

14 A. B. NASSIF ET AL. Table IX. Appliance usage patterns. Appliances combinations Case Power: 663 W Case Power: 93 W FUR FUR R FR PC + LCD R FR CRT TV CFLs Case 3 Power: W Case Power: 9 W FUR FUR R FR PC + LCD R FR PC + LCD CFLs LAP 6 CFLs LAP CRT TV MW CRT TV Case Power: 63 W Case 6 Power: 9 W FUR R FR FUR PCs + LCD 8 CFLs PC + LCD R FR LAP TVs LAP 8 CFLs MW WSH + ASD DRY MW CRT TVs MBLs 3 rd harmonic [A] 7 th harmonic [A] 3 3 Arithmetic sum Arithmetic sum Phasor sum Phasor sum 3 Power demand [KW] th harmonic [A] 9 th harmonic [A] 6 Phasor sum 3 3 Arithmetic sum Arithmetic sum Phasor sum 3 Power demand [KW] Figure 9. Effect of the harmonic current phase angles.. The equivalent CFL index compares the harmonic effect of appliances on the basis of individual units. On the basis of the index, the appliances can be ranked in the following ascending order on an individual unit basis by taking into consideration their harmonic severities: MBL, CFL, ASD FR, EBL, LCD TV, R FR, LCD, FUR, CRT TV, LAP, PC, ASD DRY, WSH, and MW. 3. The total equivalent CFL index compares the harmonic effect of each type of appliances installed in a typical household. The appliances can be ranked in the following ascending order on the basis of the total number of units by taking into consideration their harmonic severities: MBL, ASD FR, LCD TV, R FR, FUR, LCD, CFL, CRT TV, LAP, PC, ASD DRY, WSH, and MW. As the number of CFLs increases in a house, their harmonic-producing role may become more prominent (if the use of other appliances does not increase).. The phase angle-based harmonic compatibility index is a direct measure of the harmonic cancellation between two appliances should there be no difference in magnitude. It can be used to evaluate whether the appliances harmonic currents will mainly add to or cancel out each other. It was found that the compatibility was highest at the 3rd harmonic order and low at the higher-order Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

15 CURRENT HARMONICS OF HOME APPLIANCES harmonics. Usually, the appliances had high compatibility to those of similar construction. For example, diode-bridge rectifier-based appliances had harmonic currents of high compatibility. Although the results are based on a relatively small sample of appliances, the findings have been quite useful. For example, the CFL is not as harmonically harmful as one may expect even if one house adds to of them. Another value of this work is the establishment of a framework for comparing the harmonic effect of various appliances consistently. The next effort is to increase the population of the appliances measured so a useful database can be established. 7. LIST OF SYMBOLS AND ABBREVIATIONS ASD ASD FR a CFL CI h CRT DRY DPF EBL FUR h I I h I h_appliance I h_appliance INC LAP LCD MBL MW PC PF R FR THD I THD V θh TV VSAC w h WSH Adjustable Speed Drive Fridge Using Adjustable Speed Drive Technology Decline Rate of the Current Spectrum Compact Fluorescent Lamp Compatibility Index at Harmonic Order h Cathode Ray Tube Laundry Dryer Displacement Power Factor Electronic Ballast Fluorescent Lamp Furnace Harmonic Order Current at Fundamental Frequency Current at harmonic h Appliance s Harmonic Current at Order h Representative CFL Harmonic Current at Order h Incandescent Lamp Laptop Liquid Crystal Display Magnetic Ballast Fluorescent Lamp Microwave Oven Desktop Personal Computer Total Power Factor Conventional Fridge Current Total Harmonic Distortion Voltage Total Harmonic Distortion Angle Between Voltage and Current at Harmonic Order h Television Variable Speed Air Conditioning Weighting Factor at Harmonic Order h Laundry Washer REFERENCES. Sulfstede LE. Applying Power Electronics to Residential HVAC-The Issues. IEEE Transactions on Industry Applications 993; 9(): Emanuel AE, Janczak J, Pileggi DJ, et al. Voltage Distortion in Distribution Feeders with Nonlinear Loads. IEEE Transactions on Power Delivery 99; 9(): Gruzs TM. A Survey of Neutral Currents in Three-Phase Computer Power Systems. IEEE Transactions on Industry Applications 99; 6(): IEA International Energy Agency. Cool Appliances Policy Strategies for Energy Efficient Homes. IEA - International Energy Agency: Paris, France, 3.. NEMA. CFL Share of Household Lamps Reaches New High, Nov., 8, available online on January 3, 9 at: Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

16 A. B. NASSIF ET AL. 6. Verberder RR, Morse OC, Alling WR. Harmonics from Compact Fluorescent Lamps. IEEE Transactions on Industry Applications 993; 9(3): Pileggi DJ, Gulachenski EM, Root CE, Gentile TJ, Emanuel AE. The Effect of Modern Compact Fluorescent Lights on Voltage Distortion. IEEE Transactions on Power Delivery 993; 8(3): Dwyer R, Khan AK, McGranaghan M, et al. Evaluation of Harmonic Impacts from Compact Fluorescent Lights on Distribution Systems. IEEE Transactions on Power Delivery 99; (): Browne N, Perera S, Ribeiro PF. Harmonic Levels and Television Events. Proceedings of the IEEE PES General Meeting 7, June 8, 7.. Katic V, Dumnic B, Mujovic S, Radovic J. Effects of Low Power Electronics & Computer Equipment on Power Quality at Distribution Grid-Measurements and Forecast, Proceedings of the IEEE International Conference on Industrial Technology,, pp Hardie S, Watson N. The effect of new residential appliances on Power Quality. Australasian Universities Power Engineering Conference (AUPEC), Christchurch, 8 December.. Hardie S, Watson N. Power Quality implications of new residential appliances. Electricity Engineers Association (EEA) Conference, Christchurch, 7 8 June. 3. IEEE Trial-Use Standard Definitions for the Measurement of Electric Power Quantities under Sinusoidal, Nonsinusoidal, Balanced or Unbalanced Conditions, IEEE STD 9.. IEEE Working Group on Nonsinusoidal Situations: Effects on Meter Performance and Definitions of Power. Practical Definitions for Powers in Systems with Nonsinusoidal Waveforms and Unbalanced Loads: a Discussion. IEEE Transactions on Power Delivery 996; (): 79.. Yacamini R. Power System Harmonics. Part. Harmonic Sources. Power Engineering Journal 99; 8(): Statistics Canada, Selected dwelling characteristics and household equipment, available online at: statcan.gc.ca/l/cst/famil9b-eng.htm 7. Mansoor A, Grady WM, Chowdhury AH, Samotyj MJ. An Investigation of Harmonic Attenuation and Diversity among Distributed Single-Phase Electronic Loads. IEEE Transactions on Power Delivery 99; (): Mansoor A, Grady WM, Staats PT, Thallam RS, Doyle MT, Samotyj MJ. Predicting the Net Harmonic Currents Produced by Large Numbers of Distributed Single-Phase Computer Loads. IEEE Transactions on Power Delivery 99; (): Emanuel AE, Orr JA, Cyganski D, Gulachenski EM. A Survey of Harmonic Voltages and Currents at the Customer s Bus. IEEE Transactions on Power Delivery 993; 8():.. Hegazy YG, Salama MMA. Calculations of Diversified Harmonic Currents in Electric Distribution Systems. IEE Proceedings Generation and Distribution 3; (6): APPENDIX A Measurements were conducted for more than one device within the same appliance type. Each device will yield a set of harmonic spectra data. From these data, representative harmonic characteristics of the devices were derived by using a weighted average of the individual device data according to the following steps:. Compute the per-watt (pw) waveform data for each device i of the same appliance type: I pw i ðþ¼i t i ðþ=p t i rms where P i_rms is the measured operating power of the device. (A). Average the previously mentioned pw waveform data over the number of devices measured within the same brand: I pw-brand bðþ¼ t XN brand where N brand is the number of devices of the same brand i¼ I pw i ðþ=n t brand (A) 3. Average the previously mentioned pw waveform data over the numbers of brands measured: I pw ðþ¼ t XB I pw-brand bðþ=b t b¼ (A3). Select a representative operating power level for the type of applications whose data is being processed, P typical. Some of the representative operating power levels are determined from the survey data and others are based on common sense estimates. Different operating conditions Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep

17 CURRENT HARMONICS OF HOME APPLIANCES for each type of appliance were also considered. Although devices such as the CFL have an approximately constant behavior over all operating conditions, other devices such as the washing machine will operate under several different conditions. We did measure them under different conditions but only considered for this analysis the conditions where the largest harmonic injections (which coincided with largest load demand) were present; those were also conditions that lasted longer (such as the washing machine washing cycle ). If all conditions were to be taken into consideration, the large combinatorial nature of the problem would likely prohibit this analysis.. The representative waveform for the type of appliances under study is finally determined as I Appliance ðþ¼i t pw ðþp t typical (A) The previously mentioned data have two applications. One is to establish the harmonic current source model, which is obtained by calculating the spectra of the obtained waveforms, for the appliance type. The other application is to compute the equivalent CFL and harmonic compatibility indices. The reason for using steps and 3 is because it has been observed that appliances manufactured by the same brand usually have very similar current waveforms. Consequently, if the number of measured devices of brand X is much higher than that of brand Y, the final model will be biased by the devices of brand X. Therefore, a model for each brand is obtained and finally a universal model that fits many brands is proposed. This model can be scaled by the appliance rated power and this can be used for harmonic analyses. The pw models for the home appliances are presented in Figure. pw mag. [A/W] Harmonic order PC LCD LAP LCD TV MW ASD FR WSH FUR CRT TV ASD DRY EBL MBL pw angle [degrees] Harmonic order PC LCD LAP LCD TV MW ASD FR WSH FUR CRT TV ASD DRY EBL MBL Figure. General pw current source model for all appliances. Copyright John Wiley & Sons, Ltd. Euro. Trans. Electr. Power () DOI:./etep