Double-circuit Overhead Transmission Lines Research Articles

Evaluation of the backflashover performance of 150 kV and 400 kV double-circuit overhead transmission lines as affected by lightning attachment models and peak current distributions

The evaluation of the backflashover performance of overhead transmission lines requires the adoption of a lightning attachment model and a peak current distribution. These affect the estimated backflashover rate, BFR, of the lines. The present study aims to quantify the influence of lightning attachment model and peak current distribution on the BFR of double-circuit overhead lines. This is achieved by evaluating typical 150 kV and 400 kV lines. ATP-EMTP simulations are conducted to obtain the critical currents causing backflashover of line insulation. Then, the critical currents are used in lightning incidence computations to obtain BFR. The influencing parameters taken into account in this work are the low current and low frequency tower ground resistance, the location of lightning strike to the shield wire along the span, and the AC voltage phase angle, all affecting the critical backflashover current. Several lightning attachment models and peak current distributions are evaluated. Their influence on BFR is found to be considerable, especially for lower tower ground resistance values. The lightning peak current distributions yield more pronounced effects on BFR. The results of this study stress the need for computing BFR using a more accurate expression than the simplified one based on CIGRE TB 63.

THE INVESTIGATION OF DISTRIBUTION OF THE MAGNETIC FLUX DENSITY OF OPERATING TWO-CIRCUIT POWER LINE 110 KV «CHTPP-CHERNIHIV-330» IN THE RESIDENTIAL AREA AND METHODS OF ITS DECREASING TO A SAFE LEVEL

Purpose. The problem of evaluation and analysis of magnetic flux density of overhead power lines is very relevant now, since the magnetic field of industrial frequency can have a negative effect on human health. The analysis of the magnetic field of the operating double-circuit overhead transmission line was made in this work. This overhead line is in the residential area of Chernihiv, Ukraine. The purpose of this work is to determine safe habitation conditions as a function of the magnetic flux density along the route of two-circuit power line with the voltage 110 kV «ChTPP-Chernihiv-330». Real modes of operation are taken into account. Recommendations are given for reducing the magnetic flux density level in the residential area to a value that will not exceed the standard value. Methodology. Methods of electromagnetic field theory were used to calculate the magnetic field of power lines. The location of the phase wires on different types of supports of the existing power transmission line and the minimum distance between the conductors and the ground were taken into account. The current value of the current in the phases of the transmission line was taken from the Company «Chernihivoblenergo». Also, the calculation of the magnetic flux density was made for the perspective loads of the transmission line. Estimation of the value of the magnetic flux density was made for the zone of one-story and multi-story buildings near power lines. The option of uniform loading of two power transmission lines was considered and the case where the entire load is transferred along one circuit was also considered. Results. In this work, the distribution of magnetic flux density at a height of 1.8 m in the direction perpendicular to the power transmission line for the sections built on supports of the U110-2 and PB110-2 types was obtained. The graphs show that the magnitude of the magnetic flux density at the boundary of the protection zone of the transmission line will be exceed twice the standard value 0.5 μT for the existing and perspective loads. This problem is relevant in the case of transmission lines in single-circuit mode. The graphs of distribution of magnetic flux density on the facade of an apartment building, located at a distance of 20 m from the axis of symmetry of the transmission line, were constructed. As a result, it is shown that at a height of 11 m from the earth's surface, magnetic flux density will be 1.5-2 μT. Practical value. It is determined that safe habitation along the route of two-circuit power line with the voltage 110 kV «ChTPP-Chernihiv-330» can be achieved when facades of an apartment building are removed from the axis of symmetry of the transmission line at a distance of 33 m for high-rise buildings and at a distance of 27 m for one-storey buildings. Recommendations for reducing the magnetic flux density of this power transmission line have been developed.

Distribution of Magnetic Field in 400 kV Double-Circuit Transmission Lines

A high-voltage AC double-circuit 400 kV overhead power transmission line runs from the city of Elk (Poland) to the city of Alytus (Lithuania). This international 400 kV power transmission line is potentially one of the strongest magnetic field-generating sources in the area. This 400 kV voltage double-circuit overhead transmission line and its surroundings were analyzed using the mathematical analytical methods of superposition and reflections. This research paper includes the calculation of the numerical values of the magnetic field and its distribution. The research showed that the values of the magnetic field strength near the international 400 kV power transmission line exceed the threshold values permitted by relevant standards. This overhead power line is connected to the general (50 Hz) power system and generates a highly intense magnetic field. It is suggested that experimental trials should be undertaken in order to determine the maximum values of the magnetic field strength. For the purpose of mitigating these values, it is suggested that the height of the support bars should be increased or that any individual and commercial activities near the object under investigation should be restricted.

Prospect of voltage uprating of a conservatively designed EHV transmission line

Voltage uprating of existing overhead lines provide a useful method to tackle increasing power demands under present circumstances, where there is growing opposition to the construction of new power transmission installations. In the past, voltage uprating techniques have been applied to lines formerly intended to operate up to 275kV, but there is an incentive to examine the prospect of uprating lines of even higher voltages which have been designed conservatively with deterministic procedures. This paper explores the prospect of voltage uprating of an existing 500kV double-circuit overhead transmission line in Pakistan. The study includes statistical evaluation of line insulation under switching overvoltages, lightning and pollution together with assessment of corona effects and low frequency electric and magnetic fields. It has been shown that voltage uprating of the studied line to 735kV is achievable whilst satisfying performance criteria.

Calculation of Power Frequency Electric Field Around Ultra-High Voltage AC Transmission Lines

Under the increasingly stringent situation of environmental protection management, it is necessary to research the distribution law of power frequency electric field around Ultra-High Voltage (UHV) AC transmission lines to provide technical basis for the design of transmission lines and the environmental impact assessment. Firstly the basic principle of equivalent charge method and its mathematical model are introduced in this paper. Then it is researched how to use equivalent charge method to analyze the electric field near the transmission lines. Based on the three-phase double-circuit overhead transmission line model, the influences of several factors on the power frequency electric field have been analyzed. These factors include the conductor-to-ground height, the phase sequence arrangement, the number of split conductors and the split spacing. Finally the frequency electric field of parallel UHV AC transmission lines is discussed. The results can provide reference for engineering design of UHV AC transmission lines.

Assessment of reliability of an overhead transmission line with a split back-up phase

Transmission of electrical energy is the most important component of an electric power system. Optimization, modernization of the electric power transport system, increasing the capacity, as well as variability of connection arrangements, while maintaining the required level of reliability and safety, is regarded today as an urgent task for the energy industry as a whole. The article is devoted to the problem of determining the efficiency of the circuit design solution for a double-circuit three-phase power transmission line with an additional mode of operation — «with a split back-up phase» and determining its main reliability indicators. A circuit design solution for a double-circuit power transmission line with expansion of operating modes is presented in detail. The functional redundancy of the transmission line in accordance with the circuit design solution is based on switching of a conventional double-circuit power transmission line in the emergency mode to the single-circuit split-phase mode, which is the second working circuit. The ways of increasing the natural power of a double-circuit power transmission line are considered. The results of calculation of the capacity of a line with a split back-up phase and a comparison of the main parameters of overhead transmission lines with an additional mode of operation — with a split back-up phase — and power lines in conventional modes of operation, are presented. The results of calculations of reliability indicators are presented, such as the probable relative number of hours of interruption of power supply and the undersupply of electrical energy. A comparison of options have shown that the probable relative under-supply of the electric power of a double-circuit overhead transmission line with an additional operating mode — with a split back-up phase, is lower by approximately 13% than that of a conventional double-circuit power line, which will positively affect the maneuverability and reliability of the entire system.

Magnetic and capacitive couplings influence on power losses in double circuit high voltage overhead transmission line

PurposeThe paper aims to discuss problems of power and energy losses in a double-circuit overhead transmission line. It was observed from energy meters’ readings, that in such a line, active power losses can be measured as “negative”. The “negative” active power losses appear when the active power injected to the circuit is lower than the active power received at the circuit end. The purpose of this paper is to explain this phenomenon.Design/methodology/approachTheoretical considerations based on mathematical model of the transmission line of π-type confirming that effect are presented. Power losses related to series impedance of the line and to shunt admittance are calculated. The theoretical considerations are confirmed by measurements done on the real transmission line.FindingsThe calculations allow to indicate components of the active power losses, i.e. related to electromagnetic coupling among wires of a given circuit, related to electromagnetic coupling between circuits and related to shunt capacitance asymmetry. The authors indicate the influence of the line/wires geometry on the active power losses in a double-circuit overhead transmission line.Originality/valueExplanation of the effect of “negative” active power losses’ measurement in a double-circuit overhead transmission line is provided in this paper.

Особенности расчета наведенного напряжения на отключенной цепи двухцепной воздушной линии электропередачи

Особенности расчета наведенного напряжения на отключенной цепи двухцепной воздушной линии электропередачи

Mitigation of Magnetic Field under Double-Circuit 220kV Overhead Transmission Line

This paper studies the effect of various mitigation loop configurations namely: single horizontal mitigation loop (two conductors), two separate horizontal mitigation loops (four conductors) and single vertical mitigation loop (two conductors), on the magnetic field produced by 220kV double-circuit overhead transmission line. Also, in this paper a further reduction in the magnetic field is achieved by inserting properly-selected capacitors within these mitigation loops. The obtained results indicate that the reduction in the magnetic field by using these mitigation loops largely depends on the arrangements and the locations of these loops with respect to the conductors of 220kV double-circuit overhead transmission line. DOI: http://dx.doi.org/10.11591/telkomnika.v10i8.1521 Full Text: PDF

Evaluation of Continuous Exposure to Magnetic Field From AC Overhead Transmission Lines Via Historical Load Databases: Common Procedures and Innovative Heuristic Formulas

Public concern about electromagnetic fields from power systems calls for a proper evaluation of continuous exposure of the population to power frequency magnetic fields, especially those from overhead transmission lines, felt as impacting human activities and the environment. Sophisticated measuring and computing tools now available for continuous exposure evaluation may be ineffective without a sound knowledge of power system theory and of typical line loads. In this perspective, the paper firstly recalls the fundamentals of power line magnetic field calculation and shows that a proper use of historical load databases is essential for associating residential magnetic fields with load diagrams of the lines. Then, innovative heuristic formulas for ac double-circuit overhead transmission lines with independent circuits are proposed, so that line databases can be used accounting for phase-shift effects between line currents in an easier and faster way. Such formulas provide a good approximation, via one single fixed-load calculation, of the median/mean magnetic field over a reference operational period of the line (e.g., one year) and are successfully applied to an existing line, resorting to a historical load database of the line recorded from 1994 to 2001.

The Role Played by Current Phase Shift on Magnetic Field Established by AC Double-Circuit Overhead Transmission Lines—Part I: Static Analysis

AC double-circuit overhead transmission lines may exhibit large phase-shift angles between current phasor terns of the two circuits. Here, a static analysis (relevant to single time instants or constant load conditions) of the role played by such a phase shift on the magnetic field established by these lines is performed, showing that the phase-shift angle interacts with the phase conductor arrangement, resulting in a wide variety of field profiles at a given line section. The analysis, carried out for two tower topologies and several couples of rms current values, reveals interesting general features of field profiles that depend only on the phase-shift angle. This proves that neglecting, or even misunderstanding, current phase-shift effects for ac double-circuit overhead transmission lines can lead to severe errors in field calculation that may have negative consequences on human exposure estimates, both at the design stage of new lines and at the rearrangement stage of existing lines.

The Role Played by Current Phase Shift on Magnetic Field Established by Double-Circuit Overhead Transmission Lines—Part II: Dynamic Analysis

The Role Played by Current Phase Shift on Magnetic Field Established by Double-Circuit Overhead Transmission Lines—Part II: Dynamic Analysis

Effect of conductor height and terrain on the steady-state induced voltage and transient current through a linesman's body on a de-energized line

In the first part of the paper, vertical conductor height and terrain are shown to have a strong effect on the magnitude of the induced voltage in the de-energized line of a 500 kV double-circuit overhead transmission line. Of the several factors influencing vertical conductor height, the tree effect is investigated in particular. The results of some basic experiments show that tall trees under power lines have the effect of decreasing the vertical conductor height owing to their electrostatic shielding function. It is concluded that tree and terrain effects must be considered when constructing the shunt admittance matrix for calculation of the induced voltage of EHV and UHV power lines which go through mountainous areas. In the second part of the paper, the waveforms of transient touch-currents experienced by linesmen have been analyzed using the modified Fourier transform method. The effects of trees, the terrain and the frequency dependence of line parameters on the transient touch-current have also been investigated. The results show that trees and terrain below the transmission line greatly increase the magnitude of the touch-current, but the use of frequency-dependent line parameters has very little effect on these results.