Harmonic Levels and Television Events

Transcription

1 1 Harmonic Levels and Television Events N. Browne, Member, IEEE, S. Perera, Member, IEEE, P.F Ribeiro, Fellow, IEEE. Abstract This paper investigates the impact on the harmonic levels of changes in television viewing patterns in Australia. Harmonic levels during special sporting events which attracted large television viewing audiences were recorded at several sites and compared to levels at other times. The enormous increase in television audience levels (compared to typical levels at that time of the night) during the World Cup soccer match resulted in a modest increase in harmonic voltage levels. The surprisingly low impact may be attributable to the number of television receivers which are continually in operation or standby mode. No conclusive trends were observed in harmonic voltages during the 00, and Melbourne cup races. There was a reduction in harmonic voltages at one site during 00 and races. However this trend was not repeated in. The influence of network capacitors on harmonic levels was considered. Lessons learned from these observations could potentially improve our understanding of the impact of customer equipment and customer behaviour on harmonic levels and assist in managing waveform distortion now and in the future. Index Terms power quality, harmonic distortion, tv receivers. T I. INTRODUCTION He presence of harmonics in electricity networks can lead to increased losses, heating of components and loss of equipment life. In some cases they can cause multiple-zero crossings of the waveform, fuse blowing, communication system interference, acoustic noise (eg in ceiling fans) and energy meter inaccuracy. They also have an impact on power factor. Television receivers have power supplies which create current harmonics. Whilst the harmonic current levels are small in magnitude, the cumulative effect of large numbers of receivers can be significant. One way to examine the effect of television receivers on network harmonic levels is to monitor harmonic levels during periods of increased television viewing. This paper records the results of monitoring harmonic levels during two sporting events which had very high television ratings. Harmonic levels at several sites during the World Cup Soccer matches and during the This work is supported by Integral Energy. N. Browne (neil.browne@integral.com.au) is with System Development Branch, Integral Energy, Huntingwood, NSW 18, Australia. S. Perera (sarath@uow.edu.au) is with the School of Electrical, Computer and Telecommunication Engineering, University of Wollongong, NSW, 5, Australia. P. F. Ribeiro (pribeiro@calvin.edu) is with the Department of Engineering, Calvin College, Grand Rapids, II 956 USA. Melbourne Cup horse race were examined. The Melbourne Cup is an annual event so harmonic levels at one site for the last years were compared. II. TELEVISION RECEIVERS A. Power Supply Description In contrast to the linear power supplies used in older electrical equipment, more recently switch mode power supplies have become the standard interface between the power system and many electrical appliances including TV receivers. These switch mode power supplies use a capacitor after the bridge rectifier to smooth the 100 Hz ripple on the dc link. The coincidence (or near coincidence) current pulses drawn by these devices has led to significant peak flattening of supply voltage waveforms [1]. There are a number of design solutions for switch-mode power supplies which address this problem. One solution is a pre-converter switchmode supply. A pre-converter can operate from the unsmoothed rectified mains supply and produces a dc voltage with only a very small 100 Hz ripple. By proper modulation of the pre-converter, the input current can be made sinusoidal and in phase with the voltage and hence the harmonic distortion is reduced to very low levels and the power factor is close to unity []. It is probable that the network load includes television receivers containing a variety of power supply design types. Other harmonic loads also may have changed over the years as product standards have developed to control harmonic levels. B. Viewing Patterns The World Cup soccer match between Australia and Japan occurred at 00 AEST (Australian Eastern Standard ) on Monday 1 June. The match between Australia and Brazil took place at 000 on Monday 19 June. In Australia, the television audience peaked at 1.7 million at 06 hours. Soccer matches last 5 minute for each half, with a break of approximately ten minutes. The Melbourne Cup race is held on the first Tuesday in November each year at 1500 hrs. It lasts approximately minutes, however viewing time is typically 15 to 0 minutes. C. Method of Measurement of Harmonics Power quality monitors were connected to measure the phase to phase voltages on the 11kV busbars at 7 zone substations. They also measured each phase of the summated currents of the zone substation transformers. Voltage at two /07/$ IEEE.

2 1kV transmission substations were also monitored. 10- minute average harmonic voltages and currents were recorded up to the 8th harmonic. D. Site Details The characteristics of a typical zone substation site are shown in Figure 1. previous years. At another site the 5 th harmonic voltage increased, slightly more than in previous years, as shown in Figure. Between 1/06/ and 1/06/ 1:00:00 PM HU1_5 -Parramatt a ZS 11kV HU1_5 -St Marys ZS 11kV Z S 1kV Source Impedance= 0.11+j. % on 100 MVA Transmission Substation 1kV Bus x 10MVA transformers A Transmission Substation kv Bus Load 17 MVAr 17 MVAr 17 MVAr 1 MVAr Z line1 6.7+j16. % on 100 MVA 1 Mon Jun 1 Tue 1 W ed Between 1/06/ and 1/06/ 1:00:00 PM Zone Substation kv Bus Industry load Z line x 5MVA transformers 5 MVAr 5 MVAr Residential Customers 5+j1 % on 100 MVA km B kv Source Impedance=.1+j1.7 % on 100 MVA 11kV Source Impedance=.+j7.8 % on 100 MVA HU1_5 -Parramatta ZS 11kV HU1_5 -St Marys ZS 11kV 1 Mon AM 6AM 9AM 1PM PM 6PM 9PM 1 Tue AM 6AM 9AM 1PM Jun Between 1/06/00 and 15/06/00 1:00:00 PM Fig. 1. Layout of a typical zone substation HU1_5 -Parramatt a ZS 11kV 00 HU1_5 -St Marys ZS 11kV III. SURVEY RESULTS A. World Cup Results Australia versus Japan, 1 June This match was held during a public holiday weekend in June. It started at 00 hrs. The 5 th harmonic voltage levels for 9 sites during the Australia versus Japan match are shown in Figure. The THD was observed to be very similar to the 5 th harmonic levels. [% ] 1 Between 11/06/06 and 1/06/06 HU1_5 -Blacktown T S 1kV Fdr 9 HU1_5 -Bonnyrigg Z S 11kV HU1_5 -Bossley Park ZS 11kV HU1_5 -Macquarie Fields ZS 11kV HU1_5 -Parramatta ZS 11kV HU1_5 -Riverstone ZS 11kV HU1_5 -Springhill TS 1kV HU1_5 -St Marys ZS 11kV HU1_5 -West Wollongong ZS 11kV 1 Mon Jun 00 AM 6AM 9AM 1PM PM 6PM 9PM 15 Tue AM 6AM 9AM 1PM Fig.. Comparison of 5 th harmonic voltage levels with previous years for public holiday weekend, at two sites B. World Cup Results Australia versus Brazil, 19 June This match started at 000 hrs. 5 th harmonic results for 9 sites during the Australia versus Brazil match are shown in Figure. The THD level was observed to be very similar to the 5 th harmonic levels. Harmonic levels are seen to have increased during the match. Between 18/06/06 0:00:00 and 19/06/06 10:00:00 HU1_5 -Blacktown TS 1kV Fdr 9 HU1_5 -Bonnyrigg ZS 11kV HU1_5 -Bossley Park ZS 11kV 0 Sun 11 Jun Mon 1 Tue 1 Wed 1 HU1_5 -Macquarie Fields ZS 11kV HU1_5 -Parramatta ZS 11kV HU1_5 -Riverstone ZS 11kV HU1_5 -Springhill TS 1kV HU1_5 -St Marys ZS 11kV HU1_5 -West Wollongong ZS 11kV Fig.. 5 th harmonic voltage levels at 9 sites during Australia versus Japan match 5 th Harmonic voltage levels decreased at one site during the match to a level less than the level during a similar time in the 1:00 Sun 18 Jun Fig. 5 th Mon 19 :00 6:00 9:00 Unipo wer PQSecure (C) harmonic voltage at 9 sites during Australia

3 versus Brazil match voltages for all three years are shown in figure 7. The currents are depicted below the voltages. No patterns of interaction between harmonic current and harmonic voltage were observed during the event. The increase in harmonic voltage levels at the same time in previous years was generally less. This comparison is shown for one of the monitored sites in Figure 5.. [V] Between /11/00 and /11/00 HU1_5[V] -Bonnyrigg ZS 11kV Bonnyrigg ZS 11kV STot [VA] THDF_U1 -Macquarie Fields ZS 11kV Between 18/06/06 0:00:00 and 19/06/06 9:00:00 HU1_5 -Macquarie Fields ZS 11kV [VA] HU1_7 -Macquarie Fields ZS 11kV HU1_11 -Macquarie Fields ZS 11kV :00 Sun 18 Jun.0 1:00 Sun 19 Jun HU1_1 -Macquarie Fields ZS 11kV THDF_U1 -Macquarie Fields ZS 11kV HU1_7 -Macquarie Fields ZS 11kV HU1_1 -Macquarie Fields ZS 11kV Mon 19 :00 6:00 9:00 Between 19/06/05 0:00:00 and 0/06/05 9:00:00 HU1_5 -Macquarie Fields ZS 11kV HU1_11 -Macquarie Fields ZS 11kV Mon 0 :00 6:00 9:00 Fig. 5 THD, 5 th, 7 th, 11 th and 1 th harmonic at one site during Australia versus Brazil match compared to same time in C. Melbourne Cup Results Harmonic voltage levels during Melbourne Cup were examined for a single site. The results are from the zone substation depicted in Figure 1. During the Melbourne Cup there was a reduction in harmonic voltages at one site during 00 and races, but not during race. The 5 th harmonic results together with total apparent power for the three years are depicted in Figure 6. No significant change in apparent power was observed during the event. Capacitor operation at the zone substation was examined to see if it explained the reduction in harmonic voltages in 00 and. Capacitor operation is discussed in section V. In addition to harmonic voltages, harmonic current was also monitored at zone substations. The harmonic components of the summated currents in the transformers were recorded. At the same site there was a drop in 5 th harmonic current before the race then increase in 5 th harmonic current during the race. This was consistent in all three years, 00, and. The harmonic currents compared to harmonic [V] [VA] [V] [VA] Tue Nov 00 1 Tue Nov 7 Tue Nov AM 6AM 9AM 1PM PM 6PM 9PM Wed Between 7/11/ and 8/11/ HU1_5[V] -Bonnyrigg ZS 11kV AM 6AM 9AM 1PM PM 6PM 9PM Wed Between 1/11/ and /11/ HU1_5[V] -Bonnyrigg ZS 11kV Bonnyrigg ZS 11kV STot [VA] Bonnyrigg ZS 11kV STot [VA] AM 6AM 9AM 1PM PM 6PM 9PM 8 Wed Fig. 6 Melbourne Cup 5 th harmonic voltage and apparent power Tue Nov 00 1 Tue Nov 7 Tue Nov HU1_5 -Bonnyrigg ZS 11kV 00 Between /11/00 and /11/00 HI1_5 -Bonnyrigg ZS 11kV AM 6AM 9AM 1PM PM 6PM 9PM Wed Between 1/11/ and /11/ HU1_5 -Bonnyrigg ZS 11kV HI1_5 -Bonnyrigg ZS 11kV AM 6AM 9AM 1PM PM 6PM 9PM Wed HU1_5 -Bonnyrigg ZS 11kV Between 7/11/ and 8/11/ HI1_5 -Bonnyrigg ZS 11kV AM 6AM 9AM 1PM PM 6PM 9PM 8 Wed

4 Fig th harmonic voltage and 5 th harmonic current during Melbourne Cup Total TABLE I Capacitor Status IV. STANDBY MODE It is believed that many television receivers are left in standby mode when not in use. Standby power was recognized in the mid 1990s and with the proliferation of household electronic appliances it has become a significant proportion of household energy consumption. In Australia standby power is currently around 10% of total household energy consumption. Televisions contribute 7% of total standby power. There are on the average 1.9 TV receivers per household, consuming.6 watts per item in standby mode []. This compares with the average power consumption of 79 watts per item in use []. The authors are not aware of any studies on the harmonic levels generated in standby mode. Nevertheless, the harmonics generated by TVs in standby mode may explain why the increase in harmonic voltage levels during special events is not very apparent. V. IMPACT OF CAPACITORS ON HARMONICS Capacitor banks are switched in and out of service to meet reactive power requirements. In relation to the system shown in Figure 1, the switching of the kv banks immediately upstream from the monitored site and switching of the 11kV banks at the monitored site are known operations. No data was available for the kv capacitors for year 00. However during the and Melbourne Cups the installed capacitor banks at the kv level was 6 MVAr. The kv capacitors are generally switched out at night and this was the case during both World Cup matches considered above. During the 00 and Melbourne Cup races, 7.5 MVAr of 11kV capacitors were in service. On both occasions the capacitance increased from 5 to 7.5 MVAr about 5 minutes before the commencement of the race. This may have affected 5 th harmonic voltage levels observed during the 00 and races. In there was 5 MVAr of 11kV capacitors during both the Melbourne and World Cups. Capacitor bank status is summarized in Table I. Melbourne Cup World Cup Cap bank MVAr Nov 0 1 Nov 05 7 Nov 06 6 Jun 06 kv capacitor banks at transmission substation 1 17 No data On On Off 1 No data On On Off 17 No data On On Off 17 No data On On Off Total 6 No data kV capacitor banks (detuned) at zone substation 1: stage 1 On On On On 1: stage Off Off On On : stage1 On On Off On : stage On On Off Off VI. RESONANT FREQUENCIES The resonant frequency N res for each capacitor bank is given by: N res = where X c / X s X c = 1 / Q = 1 / 5 = 0 pu on 100 MVA for a MVAr capacitor bank. X s is the 11kV source impedance in pu on 100 MVA. Capacitors can create harmonic resonance on distribution systems. At each site, the resonant frequency changes depending on the number of MVAr banks which are switched in. Consider an n th harmonic equivalent circuit as shown in Figure 8. Fig. 8. n th harmonic equivalent circuit Where the fundamental equivalent circuit is shown in Figure 9. V 1 jnx s jx s Fig. 9. Fundamental frequency equivalent circuit The impedance seen by the n th harmonic current source is: Z h = (jnx s )//(-jx c /n) i.e. Z h = nx c X s /(n X s -X c ) Parallel resonance can occur when the harmonic order n is such that: n= (X c /X s ) = (FL/Q c ) -jx c /n -jx c PCC PCC FL is the fault level in MVAr at the PCC and Q c is the capacitor MVAr rating. For example, at the kv transmission substation bus, resonance would occur at harmonic order n = (19/6) =.5, based on the 6 MVAr kv capacitor bank only. At the 11kV zone substation bus, resonance would occur at harmonic order n = (08/10) =.6, I n I 1

5 5 based on the 10 MVAr 11kV capacitor bank. With 7.5 MVAr, resonance would occur at the harmonic order n = (08/7.5) = 5.. Note that system loads in practice will usually damp resonances considerably. The 11kV capacitor banks are equipped with detuning reactors and hence the harmonic equivalent circuit will be as shown in Figure 10. Fig. 10. Detuned capacitor banks - n th harmonic equivalent circuit The detuning effectively decreases the resonant frequency. For 7.5 MVAr of capacitance, ( x MVAr) the plot of impedance versus frequency for the system in Figure 1 is shown in Figure 11. For banks in service ( x MVAr), (as was the case during the Melbourne Cup), the impedance plot is as shown in Figure 1. Impedance (Ohms) Parallel and Series Resonance, x MVAr Cap Bank Harm onic Orde r Fig MVAr banks harmonic impedance Impedance (Ohms) Rs+ jnxs jnxd -jxc Parallel and Series Resonance, x MVAr Cap Bank Harmonic Order Fig MVAr banks harmonic impedance n Cap bank jnxd Zn Ohms Zn Ohms As well as reducing the resonant frequency, increasing the capacitance from 5 to 7.5 MVAr actually reduces the -jxc n In harmonic impedance at the 5 th harmonic, by 17.6% from 1.7 to 1. ohms. Thus a decrease in 5 th harmonic voltage would be expected assuming a constant current source model of Figure 10. The observed decrease in 5 th harmonic voltages in 00 and could be due to capacitor bank operation. It is intended to check voltages further away from the resonant frequency to determine if harmonic impedance is sensitive to the proximity to resonant frequency. VII. CONCLUSIONS During the World Cup soccer match of Australia versus Japan at 00 on Monday 1 June, a smaller reduction in harmonic voltages compared to previous years was observed. During the World Cup soccer match of Australia versus Brazil at 000 on Monday 19 June, an increase in harmonic voltages was observed across all sites. The increase was greater than that experienced in the previous year at the same time. During the Melbourne Cup viewing period there was a drop in harmonic voltages at one site during 00 and races, but not during race. By contrast, the harmonic voltage levels at the same site increased during the World Cup match in June. At the same site there was a drop in 5 th harmonic current before the race then increase in 5 th harmonic current during the race. This was consistent in all three years, 00, and. There was also a 50Hz load increase after the race in each year at this site. At all sites there was a small drop in load during race. Across the sites, no general trends in harmonics during the Melbourne Cup viewing period were observed. The large increase in television audience levels during the World Cup soccer match resulted in a modest increase in harmonic voltage levels. The surprisingly low impact may be attributable to the number of television receivers which are in operation or standby mode for hours each day. The effect of capacitors was investigated at the site where harmonic voltages fell during the 00 and Melbourne Cup Races. The observed decrease in 5 th harmonic voltages could be due to the effect of the capacitor bank in minimizing the harmonic injection on the system and/or on the overall reduction of the harmonic system impedance at the corresponding frequency. VIII. ACKNOWLEDGMENT The authors gratefully acknowledge the contributions of University of Wollongong, Integral Energy Power Quality Centre, and Integral Energy staff. IX. REFERENCES [1] IEC TR Electromagnetic Compatibility (EMC) Part 1-: General - Historical rationale for the limitation of power-frequency conducted harmonic current emissions from equipment, in the frequency range up to khz [] Power Semiconductor Applications 199. Philips Semiconductors [] Standby Power Current Status Report -10 Australian Greenhouse Office

6 6 [] Minimum Energy Performance Standards Report Australian Greenhouse Office [5] Integral Energy Power Quality Centre, University of Wollongong Technical Note No Harmonic Distortion in the electricity supply [6] Licentiate Thesis on Harmonic Distortion; Lundquist, Chalmers University of Technology, 001 [7] AS/NZS :00 Compatibility levels for low frequency conducted disturbances and signalling in public low-voltage power system (based on IEC ) X. BIOGRAPHIES Neil Browne (M 1988) is an engineer with Integral Energy s System Development Branch. He received his Bachelor of Engineering Degree from the University of New South Wales in He is involved in protection policy, operational analysis and power quality control and monitoring. Sarath. Perera (M'1995) Received the B.Sc.(Eng) degree in electrical power engineering from the University of Moratuwa, Sri Lanka, a M.Eng.Sc. degree from the University of New South Wales, Australia, and Ph.D. degree from the University of Wollongong, Australia. He has been a lecturer at the University of Moratuwa, Sri Lanka. He is an Associate Professor with the University of Wollongong. He is also the Technical Director of the Integral Energy Power Quality and Reliability Centre at the University of Wollongong. Paulo F. Ribeiro (M'78, S'88,F 0) received a BS in Electrical Engineering from the Federal University of Pernambuco, Brazil, completed the Electric Power Systems Engineering Course with Power Technologies, Inc. (PTI), and received his Ph.D. from the University of Manchester, Manchester, UK. Presently, he is a Professor of Electrical Engineering at Calvin College, Grand Rapids, Michigan, and is currently on sabbatical at the Center for Advanced Power Systems (CAPS) at Florida State University, Tallahassee, Florida. Dr. Ribeiro is active in IEEE, CIGRE and IEC working groups on power systems, power quality and engineering education. Dr. Ribeiro is a PE in the State of Iowa, European Engineer, and Chartered Engineer in the UK.