conventional right-of-way is also presented and discussed. This paper also considers six-phase and split phase, double circuit low-reactance configuration, line ...
I
HELWAN UNIVERSITY
IEEE
THE 8 th INTERNATIONAL MIDDLE-EAST POWER SYSTEMS CONFERENCE MEPCON 2001 University of Helwan, Cairo, Egypt, DECEMBER 29-31, 2001
Magnetic Field Mitigation Using Line Compaction M. A. Abd-Allah and
A. S. Alghamdi
Electrical Technology Department College of Technology, Jeddah Kingdom of Saudi Arabia Abstract:- Recent worldwide attention to the harmful effects of magnetic fields emanating from power lines, resulted in a growing motivation to develop methods for magnetic field mitigation aiming at reducing the possibilities of such hazards. Magnetic fields of erected EHV transmission line are compared with compact delta and inverted delta line configurations, carrying the same load. Magnetic field levels from six-phase and threephase double circuit low reactance configuration are also compared with those of three-phase compact line at the same loading and degree of compaction. Keywords:- Magnetic field mitigation, compact line, high phase order, low reactance double circuit line. I. Introduction The question of possible health effects from exposure to extremely low frequency (ELF) magnetic fields associated with high voltage ac transmission systems continues to be posed [14]. In recent years, there has been a great deal of research in this area and vigorous debate about whether there are or are not any health hazards of exposure to magnetic fields at levels associated with the power transmission system. The mitigation of biological effects of magnetic fields aims simply at reducing their values. To reach such a target, many studies have been
performed [5-7]. The magnetic field management techniques included modification of power line designs to obtain power line of low magnetic fields as well as line shielding to benefit from the cancellation effect among magnetic field vectors of different directions. This paper considers a typical 500 kV line of conventional configuration. A comparison between magnetic field levels at mid-span in lateral direction of such line and a compact delta and inverted delta line configurations with the same line loading is carried out. The comparison between the longitudinal magnetic field levels at the center line of tower and the edge of the conventional right-of-way is also presented and discussed. This paper also considers six-phase and split phase, double circuit low-reactance configuration, line carrying the same load and with the same degree of compaction. II. Compact Three-Phase Line Line compaction means that, bringing the conductors closed together with keeping the minimum phase-to-phase spacing constant. Compact high voltage lines allow transmission of equivalent amounts of power to conventionally designed lines of the same voltage, while taking up less space than the conventionally designed lines. A conventional 500 kV line is considered for the purpose of magnetic field levels comparison
with compact lines. The 500 kV line conductors are AAAC conductors with bundle sizes of 4x30.6 mm and 45 cm bundle spacing as shown in Fig.1. The full load current per phase of the line is 2000.0 A. The minimum clearance to ground at the mid-span is 10 m, and the right-ofway is at 25 m from the center line of the tower at both sides of the line. The three-phase compact line has the following characteristics, the line voltage is 500 kV, conductors are arranged in a circular configuration of diameter of 15 m, the distance between phases is 13 m and the current per phase is 2000.0 A. The magnetic field values are calculated at 1.0 m above ground level. The compact lines are arranged in delta and inverted delta configurations as shown in Fig.2.
(2a) Compact delta configuration
13 m
oo oo
15m
oo oo
oo oo
22 m
13 m oo oo oo oo
oo oo
(2b) compact inverted delta configuration
24.35m
22 m
Fig.2 Compact 500 kV line single circuit configurations
Fig.1 Conventional three-phase line
oo oo 15m oo oo
13 m
22 m
oo oo
The lateral distribution of magnetic field values at mid-span of conventional line, con., compact delta configuration, D, and compact inverted delta configuration, ID, lines is shown in Fig.3. The compact delta line has smaller magnetic field values under the line than those for conventional line, while far from the line, the conventional line magnetic field is smaller. The compact inverted delta configuration line has the smallest magnetic field values underneath the line than those of the two other
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Magnetic field (UT)
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C on
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configurations. The inverted delta line reduces the magnetic field value by about 17% at the central line and by about 29% at the conventional right-of-way with respect to the conventional line. Fig.4 shows the longitudinal distribution of the magnetic field values at the central line of the tower. The inverted delta configuration line has the smallest values along the line, while delta configuration line field values are smaller than those for conventional line.
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D
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ID
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Fig.5 Longitudinal distribution of magnetic fields at the edge of right-of-way. III. High Phase Order and Split Phase Lines High phase order was conceived as an extension of the principles of transmission line compaction to further reduce the space required for transmission lines and to allow the compaction of higher voltage bulk power lines. Magnetic field reduction can be brought about by split phase lines of the low reactance doublecircuit line. Compact six-phase line and a split phase, double circuit low-reactance configuration, are considered in this work. A comparison between the inverted delta line which gives the lowest magnetic field values in single circuit lines and the above two configurations will be made. A proper comparison would be made if the three lines have the same degree of compaction, i.e. the same voltage between phases divided by phase-to-phase spacing and carried the same power.
45
C on.
60
Dis tan c e fro m to wer (m )
Fig.3 Lateral distribution of magnetic fields.
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Dis tan c e fro m c en ter lin e (m )
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Magnetic field (UT)
D
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Dis tan c e fro m to wer (m )
Fig.4 Longitudinal distribution of magnetic fields at central line of tower. The longitudinal distribution of the magnetic fields at the edge of the conventional right-ofway for the three configurations is shown in Fig.5. The inverted delta line has the smallest field values, while the delta line fields are larger than those of conventional line.
The six-phase compact line has the following characteristics; the phase voltage is 500/v3 kV, the conductors are arranged in a circular configuration of diameter of 15 m, the distance between phases is 7.5 m and the current per phase is 1000.0 A. The double circuit configuration has the following characteristics; the phase voltage is 500/v3 kV, the conductors are arranged in a circular configuration of diameter of 15v3 m, the distance between phases is 13 m and the current per phase is 1000.0 A.
7.5 m
35
oo
ID
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15m
oo
Magnetic field (UT)
oo
oo
oo 25
6-phas e
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oo
D .C .
15 10 5
22 m
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0 Lateral dis tance from center line (m)
Fig.7 Lateral distribution of magnetic fields for 3-ϕ, 6-ϕ and 3-ϕ double circuit lines. Fig.6a six-phase line oo
oo
13 m 15v3 m
oo oo
oo oo
22 m
Fig.8 shows the longitudinal distribution of the magnetic field values of the inverted delta line, the six-phase line and the low reactance double circuit line, DC, at the central line of the tower. The six-phase line field values are smaller than those of the inverted delta line, while the double circuit line induces the smallest magnetic field values along the line. The longitudinal distribution of the magnetic field values of the inverted delta line, the sixphase line and the low reactance double circuit line, DC, at the edge of the right-of-way is shown in Fig.9. The six-phase line field values are slightly higher than those of the inverted delta line, while the double circuit line induces the smallest magnetic field values along the line.
Fig.6b split phase, double circuit line 35
ID
25 6-phas e
20 15
D .C .
10 5 200
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0 0
The lateral distribution of the magnetic field values of the inverted delta line, the six-phase line and the low reactance double circuit line, DC, at mid-span of the line is shown in Fig.7. The double circuit line is effectively reduced the magnetic field values under the line. Far from the line the inverted delta and six-phase lines have approximately the same field values, while the double circuit lines induces lower field values.
Magnetic field (UT)
30
Longitudenal dis tance from tower (m)
Fig.8 Longitudinal distribution of magnetic fields at central line.
of the inverted delta line and six-phase line of the same degree of compaction.
12
References
Magnetic field (UT)
10
6-phase ID
8 6
D .C .
4 2
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Longitudenal dis tance from tower (m)
Fig.9 Longitudinal distribution of magnetic fields at the edge of the right-of-way.
IV. Conclusions 1. The compact inverted delta configuration line reduced the magnetic field effectively underneath the line. The reduction is about 17% at central line and about 29% at the right-of-way, with respect to the conventional line. 2. The compact delta configuration line reduces the fields under the line, while it has higher magnetic fields far from the line. 3. More reduction in magnetic field values was resulted by using six-phase line of the same degree of compaction, especially underneath the line. 4. The split phase low-reactance type line induces the lowest field values than those
1. N.Hayashi, H.Tarao and K.Isaka, “Influence of Bio-Membrane on Current Characteristics Induced by Ambient ELF Magnetic Field For Spherical Tissue Model”, ISH’99, Session P6, IEE, London, 1999. 2. T.W.Dawson, K.Caputa and M.A.Stuchly, “Influence of Human Model Resolution on Computed Currents Induced in Organs by 60-Hz Magnetic Fields”, Bioelectromagnetics, Vol.18, pp. 478-490, 1997. 3. O.Bottauscio and R.Conti, “Magnetically and Electrically Induced Currents in Human Body Models by ELF Electromagnetic Fields”, ISH’97, Montereal, Quebec, 1997. 4. Robert G.Olsen, “Recent Developments in the ELF Electrical and Magnetic Field Environment Issue”, ISH’97, Montereal, Quebec, 1997. 5. A.S.Farag, et al., “Magnetic Field Measurement and Management in and Around Substations in Saudi Arabia”, CIGRE, Paper 36-201, Paris, 1998. 6. C.J.Durkin and R.P.Forarty, “Five Years of Magnetic Field Management”, IEEE Trans. On Power Delivery, Vol.10, No.1, pp. 219-228, Jan. 1995. 7. P.Pettersson, “Principles in Power System Magnetic Field Reduction”, Power Tech. Conference, pp. 358-363, Stockholm, Sweden, June 1995.
