ELEKTRYKA 2012 Zeszyt 3-4 (223-224) Rok LVIII Olgierd MAŁYSZKO, Michał ZEŃCZAK Katedra Elektroenergetyki i Napędów Elektrycznych, Zachodniopomorski Uniwersytet Technologiczny w Szczecinie w Szczecinie ELECTRIC AND MAGNETIC FIELDS NEAR NEW POWER TRANSMISSION LINES Summary. The article discusses electric and magnetic fields around new power transmission lines. The paper takes into considerations comparison of electric and magnetic fields near PTL with traditional AFL wires, traditional AFL wires with monitoring of temperature and HTLS wires. Keywords: electric field, magnetic field, power transmission lines POLA ELEKTRYCZNE I MAGNETYCZNE WOKÓŁ NOWYCH LINII ELEKTROENERGETYCZNYCH Streszczenie. W artykule omówiono problematykę pola elektrycznego i magnetycznego wokół nowych linii elektroenergetycznych. Tekst uwzględnia zagadnienia: porównanie pola elektromagnetycznego w pobliżu PTL z tradycyjnych przewodów AFL, tradycyjne przewody AFL z monitorowaniem temperatury i HTLS. Słowa kluczowe: pole elektryczne, pole magnetyczne, linie elektroenergetyczne 1. INTRODUCTION The most important parameter of power transmission lines (PTL) is the highest value of power (energy), which can be transmitted by these lines. There are some methods of increase of the highest permissible power: - usage of higher voltage of lines, - usage of conductors with higher current- carrying capacity. The increase of voltage is troublesome, because it is connected not only with change of insulators, but also with change of pylons and distances between phase wires and external objects. On the other hand increase of voltage is connected with increase of electric field
112 O. Małyszko, M. Zeńczak intensity. The higher value of electric field intensity creates problems in natural environment and land development (mainly housing). The increase of current-carrying capacity may be realized by monitoring of temperature of traditional AFL conductors or by application of high temperature low sag conductors (HTLS). The increase of currents in wires causes the increase of magnetic field intensity near PTL. New trends in power transmission relate not only to conductors but also to towers. Nowadays the new towers (EB24, EPW24, Src) are used. Some of them (EB 24, EPW 24) are concrete poles or steel tube poles (Src). They have similar configuration like traditional tower B2 but Src has lower distances between phase-conductors than B2. Transmission of energy is connected with electric (EF) and magnetic fields (MF). There are special safety rules of protection against electromagnetic fields of 50 Hz frequency. The permissible value of EF intensity in natural environment must not exceed 10 kv/m [1], while value of magnetic field intensity in natural environment must not exceed 60 A/m. But in places appropriated for the public building the highest value of EF intensity must not be higher than 1 kv/m, while the MF intensity must not exceed 60 A/m. The paper takes into considerations comparison of electric and magnetic fields near PTL with traditional AFL wires, traditional AFL wires with monitoring of temperature and HTLS wires. 2. COMPARISON OF PROPERTIES OF AFL CONDUCTORS WITH HTLS There are many kinds of HTLS conductors [2]. But the comparison should take into consideration the same mass of conductor, because then the same towers can be used. Therefore conductor AFL-6 240mm2 is compared to HTLS with diameter of 325.7 mm2. Properties of HTLS and common AFL conductors are presented in table 1. The current-carrying capacity is such the current, by which the temperature of conductors does not exceed the design temperature. The design temperature is basis for estimation of permissible sag and distances between conductors and crossed objects. In Poland majority of 110 kv lines have been designed for 40oC. Rest of lines in Poland has been designed for 60oC or 80oC that is for the highest permissible temperature for conductors. Properties of HTLS and AFL conductors Table 1 Sort of conductor AFL-6 240 HTLS Nominal cross-section mm 2 240 AL 325.7 Calculation cross-section mm 2 236.1 AL 325.7
Electric and magnetic fields 113 con. table 1 Outside diameter mm 21.7 22.0 Total mass per km kg/km 971 977 Resistance per 1 km in 20 o C /km 0.124 0.086 Permissible temperature o C 80 180 There are algorithms for estimating current-carrying capacity of wires for different weather conditions [3]. Therefore the most profitable weather is winter night: e.g.: temperature: -10 o C, wind speed: 25 m/s, sun radiation: 0 W/m 2. The worst conditions are in summer day: e.g.: temperature 30 o C, wind speed 0.5 m/s, sun radiation: 900 W/m 2. Results of calculations are presented in table 2. Table 2 Current-carrying capacity in winter night and summer day Type of conductor Current-carrying capacity [A] Winter Summer Traditional AFL 6 240, w = 40 o C (design value) 625 322 Traditional AFL 6 240, w = 80 o C (design value) 735 645 Traditional AFL 6 240, w = 40 o C (monitoring) 2120 0 Traditional AFL 6 240, w = 80 o C (monitoring) 2654 641 HTLS w = 80 o C 3205 773 HTLS w = 100 o C 3432 935 HTLS w = 180 o C 4045 1357 3. ELECTRIC FIELD NEAR NEW POWER TRANSMISSION LINES Electric field intensity depends on configuration of line. Table 3 contains parameters of 110 kv lines hanged up on towers B2 type P and Src type P. Fig 1 presents electric field intensity for both lines in point of maximum sag, where the distance H between conductor and ground is the lowest permissible according to polish regulations [4]: H = 5 + D el, where D el = 0.85 m. Table 3 Configuration of 110 kv lines on tower B2 and Src Wire Section [mm 2 ] Distance from axis of line [m] Height above ground [m] Tower B2 L1 240-2.80 5.85 L2 240 2.80 9.45 L3 240 3.60 5.85 Earth wire 70 0.5 12.45
114 O. Małyszko, M. Zeńczak Tower Src L1 240-2.40 5.85 L2 240 1.80 9.75 L3 240 2.40 5.85 Earth wire 70 0.0 13.95 con. table 3 E [kv/m] 3 2,5 2 B2 Src 1,5 1 0,5 0-15 -10-5 0 5 10 15 x [m] Fig. 1. Electric field intensity near 110 kv lines with tower B2 and Src Rys. 1. Natężenie pola elektrycznego w pobliżu 110 kv linii z wieży B2 i Src Electric field intensity near new line (Src) is lower than electric field intensity near traditional (B2) in all area on the height 2 m above the ground. The area with E > 1 kv/m is shorter too. 4. MAGNETIC FIELD NEAR NEW POWER TRANSMISSION LINES Magnetic field intensity near power transmission lines depends on configuration and currents in wires. Fig. 2 presents magnetic field intensity near power transmission line on tower B2 and Src with traditional conductors AFL6 240 designed for 80oC, thus the current is equal 735 A. Fig. 3 presents magnetic field intensity for the traditional conductor AFL6 240 designed for 80oC (735 A), traditional AFL6 240 designed for 80oC but with monitoring of temperature (2654 A) and HTLS 180oC (4045 A). All wires are hanged on the towers B2.
Electric and magnetic fields 115 H [A/m] 30 25 20 B2 Src 15 10 5 0-15 -10-5 0 5 10 15 x [m] Fig. 2. Magnetic field intensity near power transmission line on tower B2 and Src for current 735 A Rys. 2. Natężenie pola magnetycznego w pobliżu linii elektroenergetycznej na wieży B2 i Src dla bieżącego 735 A Magnetic field intensity near line on towers B2 is higher, because the distances between wires on the tower Src are lower. H [A/m] 160 120 80 AFL AFL M HTLS Perm 40 0-15 -10-5 0 5 10 15 x [m] Fig. 3. Magnetic field intensity for the traditional conductor AFL6 240 (735 A), traditional AFL6 240 with monitoring of temperature (2654 A) and HTLS 180 o C (4045 A); towers B2 Rys. 3. Natężenia pola magnetycznego na tradycyjnych dyrygentach AFL6 240 (735 A), tradycyjne AFL6 240 z monitorowania temperatury (2654 wersja A) i HTLS 180oC (4045 A); wieże B2 Magnetic field intensity near line with traditional AFL 6 240 conductors does not exceed permissible value in natural environment (60 A/m). The problem is with AFL conductor with monitoring of temperature and HTLS conductors. The permissible value (60 A/m) is exceeded when the highest value of current-carrying capacity is used. For the line from fig. 3 the highest current must not exceed 1668 A.
116 O. Małyszko, M. Zeńczak 5. CONCLUSIONS New towers and conductors create no environmental problems with regard to electric field intensity. However if traditional AFL conductors with monitoring of temperature or HTLS conductors are planned the permissible value of magnetic field intensity must not be exceeded. Therefore the criterion for magnetic field intensity [1] should be fulfilled. BIBLIOGRAPHY 1. Rozporządzenie Ministra Środowiska z dnia 30 października 2003 r. w sprawie dopuszczalnych poziomów pól elektromagnetycznych w środowisku oraz sposobów sprawdzania dotrzymania tych poziomów, Dziennik Ustaw RP, 2003, Nr 192, poz. 1883. 2. Sokolik W.A.: Optymalizacja energetycznej efektywności przesyłu i dystrybucji energii elektrycznej za pomocą niskostratnych przewodów o małym zwisie. APE 10, Present-Day Problems of Power Engineering, Jurata, Poland, 8-10 June 2011, 29-40. 3. Małyszko O., Zeńczak M.: Power system with high temperature conductors. Przegląd Elektrotechniczny 2010, nr 4, s. 170-173. 4. Elektroenergetyczne linie napowietrzne prądu przemiennego powyżej 45 kv, Część 3: Zbiór normatywnych warunków krajowych, Polska wersja EN 50341-3-22:2001. Wpłynęło do Redakcji dnia 10 grudnia 2012 r. Recenzent: Prof. dr hab. inż. Marian Pasko Dr inż. Olgierd MAŁYSZKO Dr hab. inż. Michał ZEŃCZAK Zachodniopomorski Uniwersytet Technologiczny w Szczecinie Katedra Elektroenergetyki i Napędów Elektrycznych ul. Sikorskiego 37, 70-313 Szczecin, Tel. (91) 4494634, e-mail: Olgierd.Malyszko@zut.edu.pl Tel. (91) 4494634, e-mail: Michal.Zenczak@zut.edu.pl