On the Transient Response and the Frequency Analysis of Transmission Line Towers (original) (raw)
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Evaluating the Transient Impedance of Transmission Line Towers
The low-frequency methods used by most utilities nowadays for measuring the resistance of transmission line ground electrodes are inaccurate or cannot be applied when overhead groundwires are connected to the towers. Moreover, many of them are costly and time consuming. This paper proposes and compares two new methods for evaluating the transient impedance of transmission line towers. Both methods simulate the lightning-like impulse injection into the transmission tower base and measure the resulting potential rise relative to a remote ground.
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Transient behaviour of transmission towers and associated grounding systems exposed to a lightning surge current having a double exponential pulse waveshape is investigated and analyzed. Frequency domain solutions for electromagnetic fields generated by the network of overhead and buried cylindrical conductors subject to the thin -wire approximation are derived based on the field theory approach. Once the scalar potentials and electromagnetic fields in the vicinity of the tower have been computed at selected frequencies, the time domain response is obtained using the inverse Fast Fourier Transform. Simulation models are obtained by the use of HIFREQ and FFTSES modules of the CDEGS (Current Distribution, Electromagnetic Fields, Grounding and Soil Structure Analysis) software package.
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An approach using fitting techniques is proposed for modeling of tall steel towers for analysis of the lightning performance of transmission lines. The frequency-dependent surge impedance of a steel tower is modeled in the time domain using fitting techniques and an equivalent electric circuit composed of lumped elements. The proposed tower model is validated based on results obtained using the well-established Numerical Electromagnetic Code-NEC and inverse transforms. The contribution of the proposed model is the development direct in the time domain, enabling further interactions of the tower modeling with other time-variable power elements in the transmission system. Emphasizing that most of the transient events in power transmission systems are well-established in the time domain as time-variable elements during modeling and simulation processes. This same statement is not true in the frequency domain.
s-DOMAIN ANALYSIS OF LIGHTNING SURGES ON TRANSMISSION TOWERS
Lightning surges are important for power system insulation. In this study, s-domain formulation is used to compute surge response of a tower with a shield wire. Transmission tower is modeled by a single-phase, nonuniform transmission line and expressions for the voltages at tower crossarms are obtained in s-domain. Tower surge response is computed for a tower top stroke and a shield wire mid-span stroke, by considering a double-exponential and a step function lightning current. For frequency to time domain conversion fast inverse Laplace transform (FILT) is used. Voltages, (p.u.) Voltages,
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The backflashover (BF) mechanism caused by direct lightning strikes to towers and overhead wires is one of the main causes of overvoltages on power systems outages. When lightning strikes a tower, the injected current travels its structure, causing an overvoltage. If the voltage between the phase conductor and cross arms exceeds the Critical Flashover Voltage (CFO) of the insulator strings, a BF will take place. The tower surge impedance is an important parameter on the determination of overvoltage and various models have been proposed for its calculation. This paper presents a comparison between measured and calculated surge impedances of a thin cylinder and a reduced-scale transmission tower built for this purpose. Different models have been considered for the calculations. This article also presents a brief literature review and some methods for measuring tower surge impedance.
s-Domain analysis of lightning surge response of a transmission tower with phase conductors
Lightning surges on a transmission tower with a shield wire and phase conductors are analyzed using an sdomain method. The voltages induced on the phase conductors and surges at the position of the tower crossarms are computed to obtain the insulator voltages. Response of the system determined in the s-domain is transformed into the time domain using Fast Inverse Laplace Transform (FILT). It has been shown that lightning surge response of a transmission tower can be determined easily using Coupling Coefficient Matrix (CCM) defined in this paper. The solution procedure is programmed with MATLAB. The results obtained using the proposed method are compared with those obtained using Electromagnetic Transients Program (EMTP).
Nonuniform Transmission Tower Model for Lightning Transient Studies
IEEE Transactions on Power Delivery, 2004
This paper presents a new approach to model a transmission tower for lightning performance studies. It consists of representing each part of the tower by equivalent vertical and/or horizontal transmission lines as required. While horizontal line parameters are obtained from standard line formulas, specific expressions are derived for the parameters of vertical lines. Moreover, mutual coupling between any two parallel vertical transmission lines is taken into account. Transient waveforms obtained using the proposed method are compared with experimental data obtained using a reduced-scale model and field experiments. The agreement between simulated results and experimental measurements is satisfactory.
Modeling of the Direct Lightning Strike on a Towers Cascade Equipped with Its Protections
Progress In Electromagnetics Research M, 2013
In this paper, a direct time domain approach based on the corresponding transmission lines equations and Finite Difference Time Domain (FDTD) method is proposed to analyze a direct lightning strike to a cascade of transmission line towers. The proposed model deals with a real case of towers being connected by ground wires and equipped with grounding systems with different topologies, as well (vertical or horizontal conductor buried in the ground, crow's feet in the ground. . .). In particular, this work realistically represents the tower geometry and accounts for the propagation phenomena along the tower and between the towers. The proposed direct time domain approach deals with rather complex electrical devices (towers, ground wires and grounding systems), but at the same time requires very low computational cost and also provides relatively simple implementation. Some illustrative computational examples related to some engineering applications are given in the paper.
Analysis of lightning surge characteristics for transmission towers
2014 9th International Forum on Strategic Technology (IFOST), 2014
Lightning performance of transmission lines is an important factor for the electric utility companies. Now a day, this matter is getting more priority with the increasing requirement for power quality. In order to understand the lighting surge phenomena clearly, the author used a reduced scale model of tower for the analysis. But in real life, the actual tower is subjected to the lightning. It is then necessary to analyze the characteristics of actual tower when subjected to lighting as in case of reduced scale model tower. So, the authors also simulate an actual tower to obtain the surge characteristics phenomena. In this case, the three-phase conductors and the earth wire have been considered for the analysis. The apparent characteristics of a tower may be influenced by the presence of an earth wire. However, this issue has been paid a little attention in the modeling of a tower for the well-known Numerical Electromagnetic Code (NEC-2) simulations. In this paper, firstly, a reduced scale model is analyzed in different aspect, and then the surge characteristics of an earth-wired tower as well as phase conductors of the tower struck by lightning are studied with the help of NEC-2 in case of direct and indirect stroke.
Computation of Lightning Voltage Surges on Tall and Conventional Transmission Towers
2020
Transmission tower modelling is very important to assess the electromagnetic transient caused by lightning strikes in power systems. In this context, conventional tower models are very well studied in the literature. However, there are few studies on tall transmission towers which have been receiving great attention recently due to their own characteristics. Tall transmission towers are built on river crossings and/or over dense forest canopy to reduce environmental impact in these areas. In this paper, the voltage surge caused by an incident lightning at the top of the conventional and tall towers are determined. For both structures, a lumped electric circuit approximated by Vector Fitting technique is proposed which takes into account the tower-footing grounding system buried in different homogeneous soils. The results show a clear difference in the time domain voltage response for the conventional and tall transmission towers which is more pronounced as the soil resistivity incre...