Determination of current load of ACSR conductor based on average climatic conditions

Transcription

1 POSTER 2018, PRAGUE MAY 10 1 Determination of current load of ACSR conductor based on average climatic conditions Michal ŠPES 1, Jakub URBANSKÝ 1 Michal MÁRTON 2 1 Department of Electrical Power Engineering, Faculty of Electrical Engineering and Informatics, Technical University of Košice, Mäsiarska 74, Košice, Slovak Republic 2 Department of Electronics and Multimedia Telecommunications, Faculty of Electrical Engineering and Informatics, Technical University of Košice, Vysokoškolská 4, Košice, Slovak Republic Michal.Spes@tuke.sk,Jakub.Urbanský@tuke.sk Michal.Marton@tuke.sk Abstract. Maximum permissible current value is one of the most important parameter for design and operation of power system. Since the construction of power lines is financial and time consuming any increase of capacity of existing power lines has to be taken into account. One possibility is to determine the capacity of electrical lines based on climatic conditions. This article compares current load of ACSR conductor 350/59 on the basis of average climate conditions in Slovakia towards to current value given by a calculation accordance standard EN Keywords Power system, overhead lines, climatic condition, Ampacity, Maximum permissible current value 1. Introduction Power system consists of electric power components, which are used for generation, transformation and electricity transmission. For transmission of electricity, we distinguish the transmission and distribution power lines. Transmission lines are represented as ultra-high voltage system, which provides transmission of power from sources to the three local areas of distribution system. Current capacity of all power lines depends on their construction and types of used the conductor. Manufacturer of the conductors specified maximum allowable temperature for the operation of the power line. The maximum allowable temperature is related the current value that can flow through the conductor and leads to the maximum operating temperature [1][2]. For the design of power lines, applies standard EN 50341, which for the calculation of the maximum current value determined the following ambient conditions [3]. The ambient temperature is 35 C, Wind speed is 0.5 m / s at 45 angle of impact, Global temperature solar radiation is 1000W/m 2, Absorption coefficient is 0.5, Emissivity coefficient is 0.5 [3]. 2. Climatic Conditions of Slovakia The Slovak Republic belongs to the northern temperate climatic zone with regular alternation of the seasons with an even distribution of rainfall during the year. The climate is influenced by the prevailing western airflow that brings wet ocean air of moderate zones. It moderates temperature amplitude of day and year and brings atmospheric precipitation. Continental air of moderate zones brings warm, sunny and less humid summers and cold winters with low rainfall [4]. A. Solar radiation Solar radiation consists of direct and diffuse radiation incident on the surface. This is most affected by the duration of sunshine and cloud cover. The annual average values of solar radiation in lowlands are in the range 1200 to 1300 kwh.m -2. In the highest position, it is the kwh.m -2. The middle mountain positions, the average annual solar radiation is kwh.m -2 [4]. Daily course of solar radiation during day is on the following figure (Fig. 1) Fig. 1 The course of solar radiation intensity during the day [5]

2 2 M. ŠPES, J. URBANSKÝ M. MÁRTON DETERMINATION OF CURRENT LOAD OF ACSR CONDUCTOR BASED ON AVERAGE CLIMATIC CONDITIONS B. Air temperature The air temperature is the major climatic factor, as well as the main factors affecting the actual current load of conductor. In a long-term measurement of air temperature in the region of Slovakia warmest zone is Danubian lowland with average air temperature in January -1 to -2 C, in the month of July 18 to 21 C. The annual average of this area is in the range of 9-11 C. The Eastern plains, the average temperature is slightly lower. The basins and valleys of is average annual air temperature 6-8 C. In the upstream basins below 6 C. For the altitude of 1000 meters above sea level average value reaches the interval 4-5 C, at a height of 2000 meters above sea level around -1 C [4]. The average temperature during the months of June to August is shown in Fig. 2 and during the months of December to February is shown in Fig. 3. Wind speed and direction of wind in Slovakia condition are on the following figure. Fig. 4 Wind speed and direction of wind [4] Fig. 2 Average air temperature from June to August [4] Fig. 3 Average temperature from December to February [4] C. Wind conditions Wind conditions of Slovakia are considerable complicated. The main impact has the variability of weather during the year. In the lowland of western Slovakia, the annual average speed is in the range 3-4 m/s. In Eastern Slovakia 2-3 m/s. In the basin, wind speed is influenced by openness or closeness to the flow. In the more open basins, the wind speed is in the range 2-3 m/s. In closed basins, the average wind speed is of 1-2 m/s. In the mountains, depending on the altitude, the average annual speed is in the interval 4-8 m/s [4]. 3. Defining Research problems Current capacity of the power lines means a current value that can be transmitted through the power line without destroying conductors. This state is defined by equation, which depends on determinants that represents the produced and consumed heat [7]. Where: PJ + PM + PS + Pi = PC + Pr + P W (1) P J (W/m) - heat losses in the conductor, P M (W/m) - magnetic heating of magnetic field variations AC, P S (W/m) - solar radiation, P i (W/m) - heating from the corona, P C (W/m) - cooling by heat convection by radiation, P r (W/m) - radiant cooling, P W (W/m) - cooling from water evaporation[7]. From the above expression (1) can be expressed equations for calculating current, while respecting environmental conditions [7]. I P + P P R r k S = (2) In the calculations heating due to the corona neglected. The heating of conductor due to the corona (P C) occurs mainly during the rain and wind, which is cooling conductor highest. It is also possible to neglect cooled by evaporation of water (P w) [7]. ac

3 POSTER 2018, PRAGUE MAY ) Construction of power line In practical terms, for the line of 400 kv voltage level are used trunked conductors where one phase consists of three conductors each and electrically connected at a distance, thereby enhanced radius of the conductor of one phase[6]. As conductors of transmission lines are used aluminum cables with steel soul. Their advantage is greater mechanical strength, which allows its use for large distance. Among their other advantages include greater flexibility, more uniform structure. When wires material mistake can degrade the whole wire, but with ACSR ropes, tearing of one wire not damage the whole conductor[6]. For the design of power lines is currently applicable standard EN where are defined ambient conditions for calculation of maximum allowable current value. This standard recommended maximum operating temperature 70 C of conductor [3]. Parameters of the examined conductor are in the table below. Parameter ACSR 350/59 Rope diameter (mm) Rope cross-section (mm 2 ) Nominal weight (kg.km -1 ) Specific gravity (MN.m -3 ) The maximum permissible stresses (MPa) Elastic modulus (MPa) The coefficient of thermal expansion (1/ C) Rated DC resistance (Ω/km) Tab. 1 Parameters of the examined conductor [6] A.) Impact of solar radiation to the current capacity of conductor Total solar radiation incident on the general plane is the sum of direct radiation, diffuse radiation and reflected radiation. With sufficient precision, it is possible to neglect diffuse and reflected radiation as they affect 2% - 4% [7]. Heat gain due to solar radiation we can obtain from following equation [7]: where P = ε D I (3) S a S ε a (-) is radiation absorption coefficient, D (m) is diameter of the conductor, l s (W/m 2 ) is intensity of solar radiation. For purpose of this article we examine contribution of the solar radiation to the current capacity in Slovakia ambient conditions. Input data of solar intensity radiation are from the Fig. 1. Results of the calculation for ACSR conductor 350/59 with comparing current capacity given by a calculation accordance a standard EN are shown in figure bellow (Fig. 5). As is shown in the Figure 7, current capacity given by a calculation accordance to the ambient conditions intended by a standard is 583,96 A for the one conductor in three beam connections (Red line). Current capacity of ACSR conductor 350/59 for average value of solar radiation intensity during the day in Slovakia are in range from 0 to 820 W/m2 and it does not achieve a significant change of current value. The resulting current capacity of intensity of solar radiation 0 W/m2 is 687,32 A that is 17,70% higher than the capacities given by the standard. On the other side, for intensity of solar radiation 820 W/m2 is current capacity 603,89 A, what is decrease in current capacity for ACSR 350/59 only about 3,41%. Fig. 5 Comparing resulting current capacity based on the average intensity of solar radiation B.) Impact of air flow to the current capacity of conductor Airflow cooling is a physically complex process that depends on the nature of the hydrodynamic and boundary temperature layer, the shape and size of which is affected by the velocity and the flow direction. which are formed near the heat of the exchange surface and the material quantities of the fluid [7]. The magnitude of the thermal loss of the conductor due to airflow is defined by equitation [7]: D ρ w Pk = 0,0119 λ Kuhol ( Θv Θ0) v ( ϕ ) 0,6 ( ) ( ) K = 1,194 cos ϕ + 0,194 cos 2ϕ + uhol + 0,368 cos 2 where ρ (kg/m 3 ) is air density, D (m) is diameter of conductor, (4) (5)

4 4 M. ŠPES, J. URBANSKÝ M. MÁRTON DETERMINATION OF CURRENT LOAD OF ACSR CONDUCTOR BASED ON AVERAGE CLIMATIC CONDITIONS Θ v (K) is conductor temperature, Θ O (K) is ambient temperature, λ (W/(m.K)) is thermal conductivity of the fluid, w (m/s) is velocity of the flowing fluid, v (m 2 /s) is kinematic viscosity, φ ( ) is the angle between the wind direction and the conductor's axis. To determine impact of air velocity to the maximum allowable current capacity of conductor we use wind speed of wind areas of Slovakia (Fig. 4). Map of wind areas has defined for Slovakia territory points with specific air velocity and direction of air flow. To determine current capacity of conductor ACSR 350/59 we create an interval of average values of air velocity from 1,30 to 11,10 m/s. Results from the calculation for ACSR conductor 350/59 with comparing current capacity given by a calculation accordance a standard EN are on the Figure 8. Fig. 6 Comparing resulting current capacity based on the average air velocity A difference between the current ampacity given by calculation standard EN and the current capacity of conductor ACSR 350/59 obtained by a calculation for average values of air velocity were as follows: For air velocity 1,3 m/s is difference between calculation standard and average value 31,28%. Current value in this point is equal 766,65 A. Current value given by a calculation accordance a standard is 583,96 A (Red line). For air velocity 11,10 m/s is growth in current capacity equal to 145,5% of the capacity given by an ambient conditions contained in the standard. C. Impact of natural radiation to the current capacity of conductor The radiation represents a mechanism of heat transfer, which consists of the emission and absorption of the electromagnetic radiation. An object with a non-zero temperature emits electromagnetic radiation according to Planck's law [7]. The total amount of energy emitted from the surface of the object increases with surface temperature. Depending on the temperature of the body surface, the emission spectrum changes. By the increase of the temperature there is a change of the spectrum to shorter wavelengths. Each object in addition to its own radiation captures the photons radiated by nearby objects. The resulting energy balance of the process is given by the difference of radiated and received energy. As the amount of radiated energy increases with temperature, the result radiation is the transfer of energy from warmer units to cooler [7]. The magnitude of the thermal loss of the conductor due to natural radiation is then equal to [7]: where: P = ε S σ ( Θ Θ ) (6) 4 4 r S V 0 ε S (-) is a coefficient of emissivity of radiation, S (mm 2) is cross section of conductor, σ (W/(m 2.K 4 )) is Stefan-Boltzmann constant, Θ v (K) is conductor temperature, Θ O (K) is ambient temperature. To determine impact of natural radiation to the maximum allowable current capacity of conductor we average temperature for summer season (Fig. 2) and winter season (Fig. 3). To determine the current capacity of conductor we choose a two range for examining. First is temperature range for summer season. It is from 8 C to 20 C. Second studying temperature range for winter season is from -10 C to 0 C. Results from the calculation are on the following figures (Fig. 7, Fig. 8). In terms of size of current capacity in the summer season, there is a decrease current value from 826,38 A to 730,22 A. Fig. 7 Comparing resulting current capacity based on the average temperature in summer season

5 POSTER 2018, PRAGUE MAY 10 5 For the winter season, there was a decrease of current capacity from 949,28 A to 883,51A [5] A. Klenovcanova, T. Brestovic: Possibilities of utilization of photovoltaic cells for electricity production in Kosice area (Možnosti využitia fotovoltickych člankov na výrobu elektrickej energie v oblasti Košíc). Acta Mechanica Slovaca 2007, ELFA, s.r.o., 11, 4-D, , ISSN: [6] Š. Fecko, J. Žiaran,L. Varga: Power lines Overhead power lines (Elektrické siete - Vonkajšie silové vedenia), SVŠT Bratislava, [7] IEEE Standard for Calculation the Current-Temperature Relationship of Bare Overhead Conductors, IEEE Std Fig. 8 Comparing resulting current capacity based on the average temperature in winter season 4. Conclusion Power lines are one of the most important part of power system. Temperature of the conductor is function of the current value, ambient conditions, type of used conductor and their properties. Results show that ambient conditions have most influence on the actual value of current capacity. If we can accurately determine the ambient conditions in real time, we can determine the current capacity under these terms and adapt operation of power system or power lines. Increasing current capacity of existing power lines is one of the way how to operate power system in the short term. On the other side, is necessary to build, expand with new power lines which is however time-consuming and costly. Acknowledgement Research described in the paper was supervised by doc. Ing. Ľubomír Beňa Phd. and supported by the Ministry of Education, Science, Research and Sport of the Slovak Republic and the Slovak Academy of Sciences under the contract No. VEGA 1/0132/15. About Authors Michal ŠPES was born in In 2015 graduated (MSc) at the Department of Electrical Power Engineering on the Faculty of Electrical Engineering and Informatics at Technical University in Košice. At present is a Ph.D. student in the Department of Electrical Power Engineering on the Faculty of Electrical Engineering and Informatics at Technical University in Košice. He received a master degree in electric power engineering on subject evaluation of generator exciting outage. His scientific research is mainly focused on research of powerline ampacity system. Jakub URBANSKÝ was born in In 2017 graduated (MSc) at the Department of Electrical Power Engineering on the Faculty of Electrical Engineering and Informatics at Technical University in Košice. Currently is a Ph.D. at the same department. His scientific research is mainly focused on research of renewables sources of energy. Michal MÁRTON was born in In 2016 graduated (MSc) at the Department of Electronics and Multimedia telecommunications. At present is a Ph.D. student in the Department of Electronics and multimedia telecommunications on the Faculty of Electrical Engineering and Informatics at Technical University in Košice. He received a master degree in multimedia telecommunications on measurement with the fibre optic gyroscope system. His scientific research is mainly focused on research of optical communications. References [1] M. Kolcun, V. Griger: Controlling the operation of the power system (Riadenie prevádzky elektrizačnej sústavy), Mercury - Smékal, Košice, 2003, 288 pages, ISBN [2] Böhm V., Popelka A., Vostracký Z.: Ampacity of overhead lines (Ampacita elektrických vedení), CIRED 2010, Tábor [3] EN ED.2 (333300): Elektrická venkovní vedení s napětím nad AC 1 kv - Část 1: Obecné požadavky - Společné specifikace [4] Slovenský hydrometeorologický ústav, Klimatické podmienky na Slovensku <