The SEMONT Network Utilization for the Lowfrequency

Transcription

1 The SEMONT Network Utilization for the Lowfrequency EMF Monitoring Nikola Djuric, Jelena Bjelica, Dragan Kljajic, Miodrag Milutinov, Karolina Kasas-Lazetic, Danka Antic Faculty of Technical Sciences, University of Novi Sad, Novi Sad, Serbia {ndjuric, jelenabjelica15, dkljajic, miodragm, kkasas, Abstract The intensive increase of the number of population in modern cities demands a highly reliable power supply, requiring power distribution systems that will accomplish this challenging task. In order to increase the reliability of consumers supply, the additional power distribution substations are commonly installed, which in time become surrounded by the expanded residential areas. In consequence, their presence increases the health concern of residents, having in mind that power substations are known sources of the low-frequency electromagnetic field (EMF). Therefore, the continuous monitoring of EMF is expected, as well as the adequate assessment of corresponding exposure of population in vicinity of such objects. In this paper, the test utilization of a modern, wireless sensors-based monitoring network, the Serbian Electromagnetic Field Monitoring Network SEMONT, was considered for the advanced low-frequency EMF monitoring in the upcoming smart cities environment. The case study and test measurements were performed in vicinity of the power substation NS7 South Telep, located in the city of Novi Sad, the Republic of Serbia, where the acquired results emerge to be far below the Serbian prescribed reference levels. Keywords monitoring of electromagnetic field; non-ionizing radiation exposure; wireless sensors network I. INTRODUCTION The modern day cities entail highly increased power consumption, since a number of activities of the growing population relies on constant power supply. Hence, the power distribution systems face challenges to ensure increased power requirements. From the pure technological aspect, the introduction, installation and lacing of the new power distribution substations prove as a very good approach to increase the robustness and reliability of the power distribution network. In such concept, generally, the high-power substations are built on the peripherals of the city; however, in a number of examples, in time they become surrounded by fast growing residential areas. On becoming the part of the urban area, the power substations trigger the health concerns of the residential population. Those objects frighten the residents who see them as a source of the low-frequency electromagnetic field (EMF), particularly caused by the three-phase power lines that feed the substation. In consequence, the public demands the constant observation of the EMF strength in their vicinity, as well as the assessment of the general population and occupational exposure [1], [2]. Considering the potentially dangerous health effects, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) established the guidelines for limiting the EMF exposure to provide protection against known adverse health effects [3]. A number of countries has adopted ICNIRP recommendations in their national laws, prescribing that the periodic testing or monitoring has to be performed in order to confirm the compliance of the existing, as well as newly installed EMF sources with the prescribed reference levels. Regarding the state-of-the-art understanding of the smart city idea, the test application of the Serbian Electromagnetic Field Monitoring Network SEMONT [4] was considered in this paper, as a modern, wireless sensors network solution for the continuous monitoring of the field strength over an open area, and particularly in vicinity of a power substation. Measurements of the low-frequency magnetic field strength were performed on locality of the NS7 South Telep power substation, in the city of Novi Sad. Besides, the approach for the low-frequency boundary exposure assessment was presented [5], [6], regarding the Serbian prescribed reference levels [7], obtaining the daily fluctuation of potential exposure. This paper is organized so that Section II briefly describes the concept of the SEMONT network and the boundary exposure approach. Section III presents the measurement location, while Section IV displays the results of this initial monitoring campaign. Finally, Section V brings conclusions to the paper. II. THE SEMONT S CONTINUOUS EMF MONITORING This section presents the concept and some of the main features of the SEMONT system, while a number of additional details can be found in previously published papers [4]-[6]. A. The Concept of the SEMONT System The system is basically a wireless network of autonomous and remote EMF monitoring sensor nodes, spatially distributed over the observed area, as depicted in Fig. 1 [4]. User portal GSM network Power lines EFA 3 Instrument GSM base station EMF Sensor EMF Sensor Fig. 1 The concept of the SEMONT monitoring network. Radio and TV broadcasting Source of EMF This paper is supported by the Ministry of Education, Sciences and Technological Development of the Republic of Serbia through the project no. TR /16/$ IEEE

2 The measurement results are intended to be acquired from sensor nodes and transferred over the existing GSM network, storing them into the central database of the SEMONT portal [9]. Later on, the data are processed and disseminated to the public, using graphs, tables and GIS system powered by the Google maps technology. The SEMONT system is designed to be able to observe the high-frequency, as well as low-frequency EMF [4], using adequate field probes for EMF sensors. Besides the utilization of different sensors [1], [11], the SEMONT system is also able to incorporate measurement results obtained from handheld equipment, such as Narda EFA 3 [12], intended for the lowfrequency measurement. In this paper, the testing of particular SEMONT functionality of the EMF monitoring using the Narda EFA 3 equipment is considered. B. The Concept of the Boundary Exposure Assessment The main idea of the SEMONT system is to perform continuous monitoring, for a long-term period, by using the field probes that observe all active EMF sources in vicinity of sensor elements. Such monitoring is named broadband monitoring, resulting with one measurement value per time instance, which represents the cumulative field strength contribution of all EMF sources. This type of EMF monitoring offers the field strength fluctuation over the time, and can be used to feed the so-called EMF register of a particular area. Unfortunately, the broadband field probes are incapable of discriminating frequencies on which in-situ EMF sources operate. Therefore, the broadband monitoring cannot provide the exposure per frequency assessment, as instructed by ICNIRP Guidelines [3]. The Guidelines suggest distinct reference levels for each frequency, which is of course of high importance, since the human tissue reacts differently on each frequency. As a solution, the SEMONT system uses the boundary approach for the global exposure ratio (GER) assessment [5], [6], [13], considering the entire monitoring band of the used field probe. The minimal and maximal reference levels, in this frequency band, are used to calculate the range where real exposure can be positioned, as shown in Fig. 2. User portal GSM network GER Fig. 2 The boundary exposure assessment. Sensor Daily boundaries of GER 24h Source of EMF Upper GER level Lower GER level Regarding the low-frequency magnetic field strength monitoring, the GER boundaries are calculated using the following expressions Bm Bm GER = lower and GERupper, B = B (1) ref max ref min where B m is the measured value, and B ref min and B ref max are minimal and maximal prescribed reference levels for the frequency band of the used field probe. Concerning the operating frequency range for Narda EFA 3 equipment, stretching from 5 Hz to 32 khz, and the Serbian prescribed reference levels [7], [8], the minimal and maximal reference levels used are presented in Table I. TABLE I. THE REFERENCE LEVELS USED FOR GER CALCULATION Referent level Corresponding frequency Value B ref min 32 khz 2.5 μt B ref max 5 Hz 64 μt If another field probe is used, with the different monitoring band, these reference levels have to be recalculated. III. THE TEST MEASUREMENT LOCATION Regrettably, due to uncontrolled and diverse circumstances, in a number of situations, the high-power substations become surrounded by residential areas, as it is the case for the substation NS7 South Telep in the city of Novi Sad. A. Locality of NS7 South Telep Substation The substation is located in the south-west part of the city of Novi Sad, surrounded by the suburb named Telep. This high-power 11/25/35 kv outdoor substation is fed by 11 kv three-phase power lines, which cross Ohridska Street and enter the substation, as presented in Fig. 3. Outdoor substation NS7 - South Telep 11 kv Threephase power lines Fig. 3 Locality of NS7 South Telep substation. Several 25/35 kv underground power cables exit the substation, along Heroja Pinkija Street, proceeding forward to supply consumers of the Telep and other suburbs of Novi Sad. Beside the close proximity of private households, alongside this street there are walking paths where pedestrians pass daily near the substation, additionally effecting the location as a highly sensitive zone, regarding the Serbian legislative. For this paper, the most interesting spot for the magnetic field strength monitoring is located in Ohridska Street near the three-phase power lines, which cross the near household garden and street itself, entering into the substation, as sketched in Fig. 4. In this street, there is no walking trail and pedestrians use the traffic lane to reach households.

3 Private house 6 m Garden Private driveway Grass area 24 m 11 kv threephase power lines Ohridska Street Monitoring point Field scan points 1.55 m Light post Parking lot 2.5 m Commercial driveway Fence Grass area 8 m 2.3 m 2.3 m Commercial building Gate Substation area Fig. 4 The sketch of the monitoring location. TABLE II. THE PRELIMINARY SPATIAL SCAN OF THE MAGNETIC FIELD STRENGTH x [m] B [μt] x [m] B [μt] The nearest private house is located 24 m from the middle conductor of the three-phase lines (measured on the ground). Unluckily, the garden of this house is beneath the power lines. Since the house residents daily perform some gardening work it further increases the concerns of health effects. Moreover, across Ohridska Street, a commercial building is located with the driveway and gates even closer to the middle conductor, as presented in Fig. 4. The height of the middle conductor, above the center of the traffic lane, is 1 m, which can be seen as very low, having in mind that the average height of the person is 1.7 m. The narrow traffic lane, frequently used by pedestrians, as well as the close proximity of parking lots to the conductors of the power lines, distinguish this location as highly attractive for the continuous and long-term field strength monitoring. IV. MEASUREMENT RESULTS The monitoring campaign was carried in two steps: first, a preliminary field scan was performed along the traffic lane, in order to determine the spatial distribution of the field strength, as well as the appropriate spot for the long-term monitoring. The following step was the continuous monitoring, trying to determine the fluctuation of the field strength over the time. A. Preliminary Field Strength Scanning The field scanning was conducted left and right from the vertical projection of the middle conductor, on the height of 1.1 m from the ground. The technician performed the measurements by using the EFA 3 equipment and 1 m steps between consecutive measurement points, as shown in Fig 4. The results of this preliminary field strength scanning are presented in Table II. Beneath the middle conductor, the value of the magnetic field strength of 1.14 µt was measured. Even though those values represent the spatially distributed magnetic field strength, by performing the basic statistical analyses, presented in Table III, it can be noticed that standard deviation is almost negligible, suggesting a very slow change of the field strength near the conductors. TABLE III. STATISTICAL ANALYSIS OF THE SCANNING RESULTS Bmin Bmax STDEV.147 µt 1.15 µt 3.4E-7 In order to verify the results of the field strength scanning, the theoretical modeling of three-phase power lines was performed, regarding the method in [14] and the conductor current intensity of 116 A. The very nice agreement of calculation and measurement results was obtained, as presented in Fig. 5. B [µt] Measurement versus Calculation B measured B calculated (116 A) x [m] Fig. 5 Comparison of scanning results and calculation.

4 By courtesy of the company EPS Distribucija Regionalni centar Elektrovojvodina [18], as the authorized operator for NS7 South Telep substation, the current intensity of the three-phase power lines was provided for the time period from 7:45 AM to 8:1 AM, when the preliminary scanning was performed. The current intensity is presented in Table IV. TABLE IV. THE THREE-PHASE POWER LINES CURRENT INTENSITY Min Max Average A A A In order to easily perform calculation, the intensity of 116 A was chosen for all the following theoretical considerations. B. EFA 3 and Continuous Monitoring The second step of this initial monitoring campaign was the continuous monitoring, performed by EFA 3 measuring equipment, which was set up for continuous monitoring mode [15], and installed on a tripod, as shown in Fig. 6. field strength fluctuation in vicinity of the substation. The results of monitoring are depicted in Fig. 7. B[µT] Magnetic Field Strength Fluctuation B measured B calculated (116 A) 9:6: AM 9:18: AM 9:3: AM 9:42: AM 9:54: AM 1:6: AM 1:18: AM 1:3: AM 1:42: AM 1:54: AM 11:6: AM 11:18: AM 11:3: AM 11:42: AM 11:54: AM 12:6: PM 12:18: PM 12:3: PM 12:42: PM 12:54: PM Fig. 7. Results of continuous monitoring. Time The slow change of the measured magnetic field strength over time can be noticed. Moreover, the results of the statistical analysis, presented in Table V, with the standard deviation of 9.213E-9, additionally confirm that. TABLE V. STATISTICAL ANALYSIS OF THE FIELD FLUCTUATION Bmin Baverage Bmax STDEV.281 μt.33 μt.319 μt 9.213E m -19 m -18 m -2 m Fig. 6. The EFA 3 monitoring in a particular point. Regarding relatively small standard deviation of the spatial field strength change around the power lines, the monitoring point was chosen for the distance of 19 m, on the left side of the middle conductor of the power lines, as presented in Fig. 4. An additional reason for such decision was the intention to cover the commercial driveway, then the parking lots and private driveways in Ohridska Street. The Narda EFA 3 instrument was installed on the height of 1.7 m, performing monitoring in a highly sensitive zone of the human head, since the low-frequency magnetic field dominantly shows the stimulating effects on human tissue [16]. C. Magnetic Field Strength Fluctuation The long-term continuous monitoring was carried out in an unperturbed field conditions, without the presence of people, during the period of four hours, from 9 AM until 1 PM, using 6 minute averaging [13], [17]. It was assumed that the consumption of electric energy was rather significant during this period of the day and that the selected time frame would be quite appropriate to acquire a relevant insight on the magnetic Moreover, the good agreement with the theoretical calculation was obtained, even though the current intensity of 116 A was assumed during the entire period of monitoring. Unfortunately, this cannot be quite true, since the power consumption increases after 8 AM. Therefore, in future studies, the results of theoretical calculations should be improved, though for this initial monitoring they should not be regarded as a constraint. D. Results of the Boundary Exposure Assessment Regarding the averaged values of the field strength measurements, the assessment of the potential exposure of the general population was performed using the boundary approach, described by the equation (1) and the Serbian prescribed reference levels. The results of the GER assessment, in particular the point of monitoring, are presented in Fig. 8. GER :6: AM 9:18: AM 9:3: AM 9:42: AM 9:54: AM 1:6: AM 1:18: AM 1:3: AM 1:42: AM 1:54: AM 11:6: AM 11:18: AM 11:3: AM 11:42: AM 11:54: AM 12:6: PM 12:18: PM 12:3: PM 12:42: PM 12:54: PM Fig. 8. GER exposure assessment. GER Boundaries GER upper Time GER lower The statistical analyses of those curves show that GER upper ranges from.5 to.44, with the deviation of.37, while GER lower ranges from.44 to.5, with even smaller deviation of E-5, as presented in Table VI.

5 TABLE VI. STATISTICAL ANALYSIS OF GER BOUNDARIES GERupper min GERupper avg GERupper max STDEVupper GERlower min GERlower avg GERlower max STDEVlower E-5 The small standard deviation for both GER curves indicates that the potential exposure of the general population was almost constant during the monitoring period. However, the real exposure of population lies between those two boundaries. Having in mind that the maximal allowable level of GER is equal to 1, according to the Serbian legislative [8], and that the maximal value of GER upper is.1276, which is 7.84 times lower than the allowable level, it can be concluded that, considering human health, the exposure of the general population, on the specified location and over the monitoring period, was significantly lower than the allowable level. E. The GER Relative Difference Analysis The boundary exposure assessment approach can be valuable in circumstances where it is difficult or even impossible to estimate radiation frequencies of EMF sources in vicinity of a monitoring location. Using such approach, the GER boundaries can be assessed, as well as the range where real exposure will be situated. Unfortunately, in such cases, the entire frequency range of the used field probe has to be taken into consideration. Analyzing the relative difference between upper and lower GER boundaries, as GERupper GER lower B ref min δ = = 1, (2) GER upper B ref max it can be noticed that, in case of the Narda EFA 3, with 5 Hz to 32 khz monitoring band, the relative difference of % is obtained. Unfortunately, such relative difference is considerable, resulting with a wide range where the real exposure can be positioned. Moreover, it can question the validity and suitability of the boundary exposure assessment. In case that the monitoring band of the field probe can be reduced, the relative difference between GER boundaries can be lowered. Recalculating the new reference levels and using them in the equation (1), the new boundaries can be assessed, as suggested in [19] for the high-frequency monitoring. Analyzing the spectral characteristics of the test location, it can be noticed that the last interesting frequency is 45 Hz, as depicted in Fig. 9. Thus, the monitoring band can be reduced. Fig. 9. Spectral characteristics of the testing location. Regarding the Serbian legislative and prescribed reference levels [8], as well as the reduced monitoring band from 5 Hz to 45 Hz, the new reference levels can be selected, as presented in Table VII. TABLE VII. RECALCULATED REFERENCE LEVELS Reference level Corresponding frequency Value B ref min new 45 Hz μt B ref max new 5 Hz 64 μt Consequently, the new GER boundaries can be assessed, as depicted in Fig 1. GER New GER Boundaries GER upper new 9:6: AM 9:18: AM 9:3: AM 9:42: AM 9:54: AM 1:6: AM 1:18: AM 1:3: AM 1:42: AM 1:54: AM 11:6: AM 11:18: AM 11:3: AM 11:42: AM 11:54: AM 12:6: PM 12:18: PM 12:3: PM 12:42: PM 12:54: PM Fig. 1. Recalculated GER boundaries. Time GER lower new The relative difference in this case is 3.5 %, which is a substantial improvement in the precision of the exposure assessment, as well as the reduction of the range where the real exposure can be found. Additionally, the statistical analyses of new GER boundaries, presented in Table VIII, denote that GER upper ranges from.63 to.72, with the deviation of E-5, while GER lower ranges from.44 to.5, with the deviation of E-5. Those results confirm, once again, that this location has a very slow fluctuation of exposure, and that the exposure is far below the prescribed reference levels. TABLE VIII. STATISTICAL ANALYSIS OF NEW GER BOUNDARIES GERupper min new GERupper avg new GERupper max new STDEVupper ew E-5 GERlower min new GERlower avg new GERlower max new STDEVlower ew E-5 Finally, the narrowing of the monitoring band has resulted with the increased precision of the GER assessment, as well as the considerable reduction of the in situ exposure range. F. Measurement data dissemination The results of monitoring and measurement data are publically available over the portal of the SEMONT system [9], [21]. The process of the measurement data incorporation into the centralized database of the SEMONT system is briefly presented in Fig. 11. In case of the handheld Narda EFA 3 instrument utilization, the data incorporation is performed manually, using the instruments RS-232 connection and specially designed software for data reading from the instrument [12], [2].

6 Data acquisition Uploading the data to the FTP server Data import Online - Automatic Using GSM/GPRS service Presentation of the results Incorporation of the measurement results Method selection Uploading the data directly to the CCS Using the parser Database of the portal Publicly available website Offline - Manual Using RS-232 Downloading the data to a laptop/pc Fig. 11. Methods of data incorporation into the SEMONT database. User The SEMONT portal is user-friendly [9] and designed to be understandable even for the non-technically educated persons, enabling interested users to be informed about present levels of corresponding exposure in monitored areas. V. CONCLUSION This paper has considered the utilization of the SEMONT system for the low-frequency, long-term EMF monitoring, as an innovative and advanced solution for the approaching smart cities environment. The special attention was dedicated to the continuous monitoring of the magnetic field strength, in vicinity of a power substation, testing the SEMONT functionality when utilizing the handheld instrument Narda EFA 3. Additionally, the paper presented the boundary approach for the assessment of the general population exposure, which could be easily extended for the occupational application. Using such approach, the boundaries between which the real exposure is positioned were determined. Regarding the Serbian prescribed reference levels, in particular the in situ test location, the potential exposure showed to be far below the allowed levels, while the fluctuation of the exposure was negligibly low. In a following research, the attention will be on the EMF sensors utilization and monitoring campaigns with the extended duration over a longer time period. REFERENCES [1] A. S. Safigianni, Member, IEEE and C. G. Tsompanidou, Electric- and Magnetic- Field Measurements in an Outdoor Electric Power Substati-on, IEEE Transactions on Power Delivery, vol. 24, no. 1, pp , 29. [2] L. Korpinen, H. Kuisti, R. Pääkkönen, P. Vanhala and J. Elovaara, Occupational Exposure to Electric and Magnetic Fields While Working at Switching and Transforming Stations of 11 kv, Oxford University Press on behalf of the British Occupational Hygiene Society, pp. 1-11, 211. [3] ICNIRP, Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 3 GHz), [4] N. Djuric, D. Kljajic, K. Kasas-Lazetic, M. Milutinov, M. Prsa, V. Bajovic, N. Pekaric-Nadj and V. Milosevic, The Concept of the SEMONT Monitoring System and its Influence on the EM Pollution Protection, IEEE AFRICON 213 Conference, Mauritius, September 9-12, pp [5] N. Djuric and D. Kljajic, Assessment of Daily Exposure in the Broadband Continuous Monitoring System SEMONT, IEEE AFRICON 213 Conference, Mauritius, September 9-12, pp [6] N. Djuric, D. Kljajic, K. Kasas-Lazetic and V. Bajovic, The SEMONT continuous monitoring of daily EMF exposure in an open area environment, Environmental Monitoring and Assessment, Volume 187, Issue 4, 187:191, 215, pp [7] V. Bajovic, N. Djuric, and D. Herceg, Serbian laws and regulations as foundation for electromagnetic field monitoring information network, 1th International Conference on Applied Electromagnetics, PES 211, Nis, Serbia, September 25-29, paper O7_6, pp [8] "Regulation on the limits exposure of non-ionizing radiation", the law of the Republic of Serbia, no. 14/9, 29. [9] N. Djuric and N. Kavecan, portal of the SEMONT information network for the EM field monitoring, The 4th International Conference on Advances in Future AFIN 212, Rome, Italy, August 19 24, pp (best paper). [1] D. Antic, N. Djuric and D. Kljajic, Environmental EMF Monitoring in the SEMONT System Using Quad-band AMB 857/3 Sensor, The 1th IEEE International Conference on Wireless and Mobile Computing, Networking and Communications WiMob 214, October 8-1, Larnaca, Cyprus, pp [11] D. Miskovic, N. Djuric and D. Kljajic, The MonitEM Sensor Employment in the SEMONT System, The 6th PSU-UNS International Conference on Engineering and Technology ICET-213, Novi Sad, Serbia, May 15-17, pp [12] M. Milutinov, N. Djuric, D. Miskovic, D. Knezevic, Utilization of the EFA-3 field meter into the SEMONT information network, 11th International Conference on Applied Electromagnetics PES 213, September 1 4, 213, Niš, Serbia. [13] EN 5492, 28, Basic standard for the in-situ measurement of electro-magnetic field strength related to human exposure in the vicinity of base stations, 28. [14] M. Milutinov, A. Juhas, M. Prša, Electric and magnetic field in vicinity of overhead multi-line power system, 2nd International Conference on Modern Power Systems MPS 28, Cluj-Napoca, Romania, November 28, Acta Electrotehnica, Special Issue, pp , ISSN [15] Narda Safety Test Solutions GmbH, EFA-2/-3 EM Field Analyzer Operating Manual, 2245/98.22, 26 [16] Scientific Committee on Emerging and Newly Identified Health Risks SCENIRH, Final opinion on potential health effects of exposure to electromagnetic fields (EMF), docs/scenihr_o_41.pdf, 215. [17] EN 5413:21, Basic standard on measurement and calculation procedures for human exposure to electric, magnetic and epolectromagnetic fields ( Hz 3 GHz), 21. [18] EPS Distribucija Regionalni centar Elektrovojvodina, accesed July 215. [19] D. Kljajic, N. Djuric, K. Kasas-Lazetic, D. Antic, Adaptive Boundary Approach for EMF Exposure Assessment in Broadband Measurements, Progress In Electromagnetics Re-search Symposium PIERS 215, Prague, Czech Republic, July 6 9, 215, The Electromagnetics Academy, PIERS 215 Draft Proceedings, pp , ISSN: [2] D. Kljajic, N. Djuric, K. Kasas-Lazetic and M. Prsa, Procedure for Incorporation of NBM-55 Measurement Results into the SEMONT Database, IEEE 11th International Symposium on Intelligent Systems and Informatics SISY 213, September 22-26, 213, Subotica, Serbia, pp [21] The SEMONT portal, accessed July 215.