* Corresponding author: Department of Electrical & Electronic Engineering, Rajshahi University of Engineering & Technology, Rajshahi-6204, Bagladesh E-mail addresses: [email protected] (M. S. Hossain)
107
Measurement and Analysis of Power Frequency Magnetic Field by a Three Axes Tesla Meter: Case Studies
M. A. Raquib, M. S. Hossain*, M. M. Rashid, M. F. Reza
Department of Electrical & Electronic Engineering, Rajshahi University of Engineering & Technology, Rajshahi-6204, Bangladesh
ARTICLE INFORMATION ABSTRACT
Received date: 22 Jan 2019 Revised date: 25 May 2019 Accepted date: 08 June 2019
The measurement and exploration of the radiation of electromagnetic (EM) field by three axis Tesla meter for a computer lab of Rajshahi polytechnique Institute (RPI) and Katakhali grid substation are presented in this paper. The measuring tasks are conducted at the exposure echelon of magnetic field at power frequency in some emblematic locations where the students, teachers and ordinary citizens are subjected to the fields. High value of current, in an ordinary setting, radiates sturdy magnetic field that may surpass the safe boundary of possible detrimental health effects if appropriate shielding isn’t ended. By abiding international guideline, radiated magnetic field at the diverse places of substation and computer lab are measured and compared. The exertion place is separated into meshes to achieve space distribution. The results show that the information obtained with the help of three axis Tesla meter is supplementary precise with the calculated data.
Keywords
Electromagnetic Field Radiation
Three-axis Tesla Meter PF Magnetic Field ELF Exposure
1. Introduction
The demand electricity is growing day by day in such a way that it is not possible to realize to live without using electricity even for an instant of time. Whenever electricity flows near the machines that consume electric energy or in the proximity of the supply line, both electric and magnetic fields are produced. The sources made by human usually have superior magnetic field intensities than the fields occurring unsurprisingly. The magnetic flux densities varies between 0.03µT and 30 µT for the dwelling, laboratory and public places are produced approximately from domestic utilities and near transmission lines depending on the electricity flow and the closeness from the stripe, it can be 35 µT [1]. The reason to analyze the excitable cells is, if the induced current goes beyond definite desired value, which might fall a deleterious effect on health which in turns defined as radiation hazard [2-6].
The single-axis magnetometer to measure ultralow field (ULF) relaxometry using numerous sample sizes as well as shapes for the optimal placement of a localized are described in [9-12]. All the radiated values where the data’s are chosen randomly and are not specified. The main exposure assessment of the laymen in various low frequencies
Journal of Engineering and Applied Science
Contents are available at www.jeas-ruet.ac.bd
108 electric fields at outdoor and indoor environment are addressed in [9-12] without occupational settings. The evaluation of the influence of a 3 mT MF, 60 Hz on ours cognitive achivement is shown in the statistical based research presented in [13-15]. The magnetic field exposure is calculated in [13-15] for participants for using wire code which are at the front door and inside the house.
The exceedingly low frequency (ELF) is between 30 to 300 Hz which is the terminal portion of the electromagnetic spectrum [16-17]. Firstly, the electromagnetic fields are often expressed, magnetic flux density (B) with Gauss (CGS) or Tesla unit (SI). In addition, Oersted (CGS) or amperes per meter (SI) are the units of magnetic field intensity (H).
The average value of the exposure level of magnetic field in electrical related services is greater than other employment such as official works [20]. A lot of reports about measurement of ELF-MF in power plants, substations, near high voltage power lines, cities are depicted in [28-29]. A report showing ELF-MF measurement in substations with high voltage at Hamadan City is presented in [32-33]. In addition, various studies have reported difficult effects for individuals exposed to these fields in [32-34].
The requirements for exact measurement of MFs is mentioned the mentioned settings. Therefore, equipment and process have been presented for these fields measurement in [35-37] using single axis Tesla meter. The measurement of magnetic field radiation in a wielding shop for common and working scenery is presented in [7] using single axis Tesla meter. The dilemma of the usage of single axis Tesla meter is to locate the precise magnetic field’s mean square value. To surpass the above-mentioned problem and to get the genuine value, 3-axis Tesla meter is employed to determine the electromagnetic field radiation. At the end of the work, a comparison is made with the calculated data and international commission of nonionizing radiation protection (ICNIRP) rules. The value of the density of current is also found from the determined value to evaluate biological impact for electro-magnetic radiation of field.
2. System Representation and Methodology
The fundamental vector quantities that describe a magnetic flux density, B as well as magnetic field strength, H. These enormities are related by B = µH, where µ denotes the permeability of the environment. Magnetic field is estimated in this work using 3-axis Tesla meter which is able to measure B in mG and µT in a straight procession. The measured and calculated quantities are compared according to the guidelines given by the ICNIRP [6]. The usage of three axis Tesla meter for the measurement of magnetic field at a wielding spot and electrical machine shop suggested in [8].
The proposed cram’s block diagram is shown in figure 1.
Figure 1. Block illustration of the proposed scheme for measurement.
Electrical & Electronic devices: There are huge numbers of electrical & electronic devices used in home and occupational places which draw electric currents & create electromagnetic field radiation. These devices are such as welding machine, transformer, alternator, rice cooker, microwave woven, computer etc.
Measuring process: EMFs are measured by both three axis & single axis Tesla meter. Readings are taken at various point distances from the sources that draw electric currents. Another process was to divide the work places into grid points and data are taken from every grid points.
Corroboration of measured data with the
FCC & ICNIRP guide line
Electrical &
Electronic devices
Measurement of electromagnetic field radiation using three- axis Tesla meter
Comparison between the measured &
calculated value
Comments on the resultant data
109 Comparison: All the data are collected by using three axis and single axis Tesla meter and a comparison is made with the calculated value. These comparisons are shown both for mathematically and graphically and finally these values are compared with the international guide line.
Comments: Collected data are analyzed and EMFs radiations are taken from the devices which draw electric current.
Final results are compared and put comments on the resultant data whether it is our normal range or not.
The radiated magnetic field can be calculated using
r B I
2
(1) The variables are define as, I represents current through the circuit (A), µ denotes permeability of the free space (4π×10-7 H/m), distance is denoted by r from the measuring point to Tesla Meter (cm).The human health causes a dangerous effect the human body is directly affected by the voltages and currents. The induced electricity that travels through the object into earth, if the conductive object is grounded and it is called the body current or short-circuit current Isc which is calculated using the given formula. Micro-Amperes denoted as (µA) is the measuring unit of the body or short-circuit current [7].
E h
ISC 5.4 2 (2) Consider E is in kV/m and h is the symbol to present height in meter. The integral expression of Faraday’s law is given as [7];
B d S
l t d E
C
(3) C is the path of integration all-round the head and cross-section of the head is defined as Ω. In order to the time harmonic field, the induced electric field can be expressed as
E
ind RfB
(4) where the respective induced current densityind
ind
E
J
(5) R is considering as the mean radius of head and the conductivity of head tissue is denoted as σ. This shows that negligible amount of current is flowed at the center of the body and it is high at the periphery of the body.3. Measurement and Analysis
The electromagnetic field exposure at the diverse positions of computer lab of Rajshahi polytechnique Institute (RPI) and Katakhali grid substation, Rajshahi, Bangladesh are measured and a comparison is made with the international guidelines. The space distribution is obtained by alienated the work place into meshes, in comparison the fields are obtained in the grid position. Three axis EMF meter which is also called Gauss meter is used to execute the measurement process.
The calibration of three axis-Tesla meter is done in measurement laboratory at the Electrical & Electronic Engineering department of Rajshahi University of Engineering & Technology, Bangladesh. The calibration results show that the measured and calculated results are near about same. It is observed that the calculated and measured values are 40 µT and 40.14 µT for 30 Amp current carrying devices, respectively.
110 Table 1. Magnetic Field Measurement of Khatakali Grid Substation
50m
1-Axis=2.29 3-Axis=3.18
1-Axis=3.83 3-Axis=4.00
1-Axis=2.03 3-Axis=3.06
1-Axis=3.26 3-Axis=4.13
1-Axis=3.47 3-Axis=4.25
1-Axis=3.59 3-Axis=4.30
1-Axis=3.18 3-Axis=4.22
1-Axis=2.89 3-Axis=4.00
1-Axis=2.67 3-Axis=3.70
1-Axis=2.43 3-Axis=3.50 1-Axis=3.38
3-Axis=3.85
1-Axis=3.78 3-Axis=4.07
1-Axis=2.51 3-Axis=4.06
1-Axis=5.97 3-Axis=2.59
1-Axis=4.13 3-Axis=3.00
1-Axis=4.00 3-Axis=2.90
1-Axis=3.77 3-Axis=3.50
1-Axis=3.02 3-Axis=2.50
1-Axis=2.51 3-Axis=3.80
1-Axis=2.43 3-Axis=3.60 1-Axis=2.66
3-Axis=3.90
1-Axis=3.24 3-Axis=4.00
1-Axis=3.02 3-Axis=2.90
1-Axis=3.96 3-Axis=3.50
1-Axis=4.74 3-Axis=5.00
1-Axis=4.49 3-Axis=4.50
1-Axis=3.90 3-Axis=3.99
1-Axis=3.56 3-Axis=3.20
1-Axis=3.65 3-Axis=3.50
1-Axis=3.74 3-Axis=4.00 1-Axis=2.60
3-Axis=3.50
1-Axis=3.00 3-Axis=3.95
1-Axis=3.21 3-Axis=3.05
1-Axis=4.02 3-Axis=3.83
1-Axis=4.11 3-Axis=4.50
1-Axis=4.71 3-Axis=4.83
1-Axis=4.30 3-Axis=4.32
1-Axis=3.60 3-Axis=3.80
1-Axis=3.74 3-Axis=3.85
1-Axis=3.63 3-Axis=4.02 1-Axis=4.96
3-Axis=5.10
1-Axis=0.79 3-Axis=1.54
1-Axis=1.83 3-Axis=2.93
1-Axis=1.95 3-Axis=3.00
1-Axis=3.41 3-Axis=3.20
1-Axis=3.03 3-Axis=2.92
1-Axis=3.12 3-Axis=2.85
1-Axis=3.01 3-Axis=2.80
1-Axis=2.90 3-Axis=2.75
1-Axis=3.41 3-Axis=3.55 1-Axis=4.90
3-Axis=5.00
1-Axis=0.97 3-Axis=1.54
1-Axis=2.92 3-Axis=2.99
1-Axis=4.00 3-Axis=3.50
1-Axis=4.37 3-Axis=3.80
1-Axis=1.95 3-Axis=2.83
1-Axis=3.24 3-Axis=3.99
1-Axis=3.66 3-Axis=3.49
1-Axis=3.96 3-Axis=3.51
1-Axis=2.51 3-Axis=4.05 1-Axis=3.01
3-Axis=2.96
1-Axis=3.90 3-Axis=2.66
1-Axis=1.87 3-Axis=2.11
1-Axis=3.18 3-Axis=3.79
1-Axis=3.02 3-Axis=2.90
1-Axis=4.52 3-Axis=4.83
1-Axis=2.84 3-Axis=4.00
1-Axis=3.80 3-Axis=3.40
1-Axis=2.92 3-Axis=2.99
1-Axis=3.05 3-Axis=3.99 1-Axis=4.25
3-Axis=4.10
1-Axis=3.75 3-Axis=2.92
1-Axis=3.91 3-Axis=2.60
1-Axis=4.30 3-Axis=4.31
1-Axis=2.84 3-Axis=3.21
1-Axis=2.51 3-Axis=3.79
1-Axis=5.97 3-Axis=2.29
1-Axis=4.00 3-Axis=4.62
1-Axis=3.74 3-Axis=3.78
1-Axis=1.98 3-Axis=3.00 1-Axis=3.56
3-Axis=3.22
1-Axis=4.70 3-Axis=4.11
1-Axis=2.29 3-Axis=3.52
1-Axis=3.89 3-Axis=3.99
1-Axis=3.77 3-Axis=3.52
1-Axis=2.03 3-Axis=3.05
1-Axis=1.98 3-Axis=2.23
1-Axis=2.29 3-Axis=2.01
1-Axis=3.26 3-Axis=3.97
1-Axis=4.74 3-Axis=4.99
Figure 2. Contour Plot of KATAKHALI Grid Substation (magnetic field in
T
)Table 1 shows the experimental data and Figure 2 shows the contour plot for the distribution of electromagnetic field in the Katakhali grid substation. It is observed from the figure that the distribution of thefield is normally high from all over grid area. 132/33kv khatakali grid substation (grid area= 50m. X 45m. Cell area= 5m. X 5m.). Two types of Busbar are used in grid substation. Main busbar and x-fer busbar. Height of Main busbar and x-fer busbar are 17 m and 8 m. All readings are taken 1 m above from the earth. The higest field value is 5.10 µT in one side of the grid substation that are within the limit of the guide line of ICNIRP. The surface plot for the electromagnetic field distribution is shown Figure 3. Grid area consists of 72 cells. Only two cells MFs radiations are below 2 µT. More
45m
111 than 60% area MFs radiations are greater than 4.5 µT. The figure 4 shows the experimental arrangement at Katakhali grid substation.
Figure 3. Surface plot of KATAKHALI Grid Substation (magnetic field in
T
)Figure 4: Experimental setup for Katakhali grid substation
Figure 5 shows the contour plot for the distribution of the electromagnetic field in the Computer Network Lab. The highest distribution of field is observed near the entrance of the door in according to the figure. Table 2 shows the obtained magnetic field from Computer Lab (RPI) where total computer: 29 nos. (Lab size: Length=12m. Breadth=
8m. Cell size: 1.6 m. × 1.5 m. All computers are running). 1.46 µT is the optimum value of field in the laboratory that is in the limit of ICNIRP guide lines. Inside the Lab, radiations are not greater than 1 µT. If MFs radiations are greater than 1 µT, a image will create on the screen of the computer. No image was found in the lab, because all the MFs values are less than 1 µT.
112 Table 2: Magnetic Field Radiation Measurement of Computer Lab
Door- 3-Axis=1.46
1-Axis=0.90 3-Axis=0.82
1-Axis=0.64 3-Axis=0.8
1-Axis=0.57 3-Axis=0.61
1-Axis=0.47 3-Axis=0.47
1-Axis=0.81 3-Axis=0.25 1-Axis=0.69
3-Axis=0.55
1-Axis=0.49 3-Axis=0.36
1-Axis=0.39 3-Axis=0.32
1-Axis=0.31 3-Axis=0.24
1-Axis=0.25 3-Axis=0.23 1-Axis=0.45
3-Axis=0.54
1-Axis=0.37 3-Axis=0.29
1-Axis=0.30 3-Axis=0.16
1-Axis=0.31 3-Axis=0.1
1-Axis=0.30 3-Axis=0.07 1-Axis=0.27
3-Axis=0.13
1-Axis=0.26 3-Axis=0.09
1-Axis=0.25 3-Axis=0.07
1-Axis=0.28 3-Axis=0.072
1-Axis=0.28 3-Axis=0.069 1-Axis=0.22
3-Axis=0.06
1-Axis=0.21 3-Axis=0.04
1-Axis=0.25 3-Axis=0.04
1-Axis=0.27 3-Axis=0.06
1-Axis=0.30 3-Axis=0.75 1-Axis=0.18
3-Axis=0.43
1-Axis=0.18 3-Axis=0.33
1-Axis=0.20 3-Axis=0.66
1-Axis=0.26 3-Axis=0.72
1-Axis=0.24 3-Axis=0.88 1-Axis=0.17
3-Axis=0.51
1-Axis=0.17 3-Axis=0.4
1-Axis=0.22 3-Axis=0.57
1-Axis=0.29 3-Axis=0.72
1-Axis=0.38 3-Axis=0.8 1-Axis=0.20
3-Axis=0.44
1-Axis=0.21 3-Axis=0.54
1-Axis=0.23 3-Axis=0.66
1-Axis=0.26 3-Axis=0.85
1-Axis=0.32 3-Axis=0.93
Figure 5: Contour Plot of Computer Network Lab (RPI) (magnetic field in
T
).Table 3: ICNIRP guidelines of ELF exposure [2]
Public Occupational Basic
Restriction
J(mA/m2) Two Ten
Reference Level
E(kV/m) Five Ten
B (μT) One Hundred Five Hundred
The guide lines of ICNIRP for both the occupation and public settings is given in Table 3. One can seen from the guidelines that these are not only designed to shun immediate high level perils but also don’t consider extended low- level exposures at all. The value of radiated magnetic field of this case study areas are within the ICNIRP guidelines.
113 4. Conclusion
The measured and calculated results of magnetic field that radiates at power frequency have been addressed in this work for computer lab and Katakhali grid substation. To approximate the level of the induced magnetic and electric fields in the body of human, these measurements are necessary and it is required to evaluate the probable unpleasant effects of those fields on health. These types of measurements are helping us to know whether the electrical appliances are maintaining ICNIRP guidelines or not as well as indicating security level for health. It is anticipated that the prelude results shown in this work would assist picturing the current state of affairs of the radiation of magnetic field in the computer lab and Katakhali grid substation. The results show that the case study area is safe and magnetic field radiation within the ICNIRP standard. This investigation is carried out in specific and limited conditions in order to have precise measurements and more methodical investigation that are necessary to express a practical relationship and to approximate the exposure level. Moreover, other variables such as working conditions, position of measurement and frequency band, as well as genuine interaction records in diverse conditions is also considered for the measurement process.
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