Multi-circuit Transmission Lines Research Articles

Eiffel Effect on Towers of UHV AC Transmission Lines

The principle of Eiffel Effect on transmission towers was analyzed, and the necessity of considering Eiffel Effect on transmission towers, especially multi-loop transmission towers, was proposed. A comparative analysis on calculation methods for Eiffel Effect on tower mast structures both at home and abroad was conducted and the applicability of various calculation methods to transmission towers and their advantages/disadvantages are proposed. On this basis, the analysis method for Eiffel Effect on transmission towers is proposed. The Eiffel Effect was calculated by taking four tower types of EHV/UHV AC multi-circuit transmission lines on the same tower as examples, during which the stress state of member bar of each tower type after considering the Eiffel Effect, the influence of the intersection angle between the main members of the tower on the Eiffel Effect, and the minimum bearing capacity requirement of diagonal members etc. were analyzed. The analysis shows that: It is simple, reasonable and convenient to consider the Eiffel Effect on the tower with the rigidity-reduction method for engineering application; both the diagonal member and the diaphragm member of the tower are influenced by Eiffel Effect, where its influence on the latter is higher; it may be unsafe if designing the minimum bearing capacity requirement for the diagonal member with the internal force not less than 5% of the main members to satisfy the Eiffel Effect on the tower for the UHV transmission towers, and especially for the transmission towers with EHV/UHV AC multi-circuit transmission lines on the same tower.

Power Flow Modeling of Multi-Circuit Transmission Lines

To reduce the allocation of land for the construction of electric power facilities, it is possible to leverage multi-circuit overhead transmission lines (MCTLs), in which the conductors of several circuits of different voltage classes are placed on the same tower. The unique features of the arrangement of conductors on MCTL towers cause unequal inductances and capacitances of different phases. In addition, there are significant mutual electromagnetic influences on the line circuits. To account for these factors, it is advisable to model the power flow of electric power systems equipped with MCTLs using the phase frame of reference. On the basis of such models, it is possible to determine the power flows while taking into account lateral and transverse asymmetries and to analyze electromagnetic safety conditions along the routes of multi-circuit transmission lines. We proposed a technique for modeling power flows and electromagnetic fields of multi-circuit power transmission lines, in which conductors of several circuits of different voltage classes are placed on the same tower. The methodology is based on the application of phase coordinates, which are the most natural description of three-phase power systems. The method is versatile enough to be applied to solving the specified problems for MCTLs of different designs. The article presents the results of research aimed at developing a method for modeling MCTL power flows. The results of modeling power flows of an electrical network including a three-circuit power transmission line are presented. The practical use of the models developed by the authors will make it possible to make well-grounded choices regarding the options for the use of multi-circuit power lines.

Optimizing multi-circuit transmission lines for single-phase auto-reclosing

In this paper, novel multi-circuit transmission line (MCTL) designs with low secondary arc current (SAC) values are proposed. The Non-dominated Sorting Genetic Algorithm II (NSGA-II) was used to generate the optimized tower structures. The aim is to select the MCTL configuration that satisfies multiple objectives such as increased capacity, reduced cost, right-of-way (ROW), and tower height, while satisfying several constraints such as SAC limit, ampacity, electric field, etc. The objective function is formulated as a mathematical function of design variables such as sub-conductor position, phase arrangement, etc., and several constraints. Two-port theory is used to calculate the SAC resulting from different faults along the line, which is significantly faster compared with time-domain Electromagnetic Transient (EMT) simulations. Comparisons of MCTLs with and without SAC constraints are presented, clearly showing the importance of taking into account SAC limits during the optimization process. As a result, MCTL structures with SAC reductions of up-to 64% were obtained, indicating that the MCTL are able to successfully handle Single Phase Auto-Reclosing (SPAR).

A Novel and Robust Model of the GUPFC Controller System Based on Adaptive Fuzzy Logic- PI Controller to Enhance the Control System Performance in Following Reference Active and Reactive Power

The optimal electrical power transmission problem in electrical energy transmission lines has led to increased attention to the use of flexible alternating current transmission systems (FACTS) and the design of double- and multi-circuit lines. Hence, recently, multi-converter FACTS devices have been utilized in the literature to control voltage and power of multi-circuit transmission lines. A generalized unified power flow controller (GUPFC) is one of such emerging FACTS devices that can manage voltage and power control crisis in multi-circuit lines. The GUPFC is the most advanced generation of FACTS, which will be able to control active and reactive power in at least two circuits and voltage in one circuit with the best quality possible and satisfy the operator’s all requests. This paper, for the first time, presents the use of an adaptive control system design based on the proportional-integral (PI) controller and fuzzy system to enhance the fast and dynamic responsiveness of the system. PI systems alone cannot control the GUPFC under different operation conditions such as when the default reference values of active and reactive power are changed, or transient faults occur, or a transmission line experience outage. Thus, the use of a fuzzy controller, as a powerful tool, is very efficient in solving the mentioned problems. To analyze the proposed algorithm’s results, a test system and a GUPFC based on a 48-pulse voltage source converter (VSC) are implemented in the MATLAB/Simulink environment. The satisfactory results obtained in the simulation section verify the correct performance of the suggested method.

Non-contact fault location and identification method for same-tower multi-circuit transmission lines

Fault identification and location of the multi-circuit transmission line can ensure the safe and stable operation of the power system. The existing contact method is difficult to install and maintain, and the cost is high. This paper proposes a novel non-contact fault identification and location method, which addressed the aforementioned limitations by using fewer magnetic sensors and making the method suitable for multi-circuit transmission lines. First, a magnetic array with fewer magnetic sensors is constructed based on electromagnetic effects, and a current reconstruction method is determined. Second, failure current characteristics have been determined. Then use the reconstructed current and magnetic field combined with the fault current characteristics to identify and locate the fault. Finally, the double-circuit transmission line was simulated on Ansys Maxwell and Matlab, and an experimental platform was established to verify the effectiveness of the method.

Construction and Modeling of Multi-Circuit Multi-Voltage HVAC Transmission Lines

A transmission network’s main objective is to continuously supply electrical energy to consumers. This article presents an analysis of the use of multi-circuit, multi-voltage overhead lines as a compromise between ensuring the system’s safe operation by increasing the transmission network capacity and managing the constraints related to its expansion. The considerations presented in this work include the construction of such lines, their operation, and modeling aspects. As part of the study, the potential for improving the environmental conditions around the lines is discussed in terms of the necessary area for their construction and the peak electromagnetic field strength in their vicinity. We also present a mechanical analysis of stress and sag coordination in the individual circuits of these lines. Then, we detail the method for determining the electrical parameters of multi-voltage lines’ series impedances and capacitance. Specific attention is given to the possibility of zero-sequence voltage that occurs in the systems despite the symmetric supply and load of circuits—especially in the circuits with the lowest voltages—that result from the line’s geometric asymmetry. We evaluate the impact of the line’s geometric asymmetry on the power system’s correct operation by determining the asymmetry factors. Finally, the accuracy of using a simplified symmetric model for lines with various geometric asymmetries is analyzed by studying the error of the short-circuit currents.

Fault location algorithm for partial coupling double-circuit transmission lines

Multi-circuit transmission lines on the same tower have become the inevitable trend of power grid construction, mostly partial coupling mode. Affected by the partial coupling characteristics, the existing fault location methods have large error. Therefore, this paper develops a study about the fault analysis and fault location method for the partial decoupling double-circuit transmission lines. Based on its structure and characteristics, as well as the lines decoupling theory, the interface equations of demarcation point are built. On the basis of the above study, the new fault location algorithm based on time-domain for partial coupling double-circuit transmission lines are presented. Finally, ATP/EMTP is used to construct the model of partial coupling of double-circuit transmission lines. After the overall simulation and verification, it shows that the presented algorithm is accurate.

Unbalanced currents of EHV multi-circuit lines and coordination of zero-sequence overcurrent relayings

With features of large transmission capability and high utilization efficiency of transmission corridor, multi-circuit transmission lines sharing tower or corridor are widely applied in extremely high voltage (EHV) systems. However, mal-operation of zero-sequence overcurrent relaying for multi-circuit transmission lines could occur, and this paper is focused to solve this problem. Overview of typical multi-circuits transmission lines, including phase arrangement and erection form, are introduced first. Then, simulation model of a typical 500 kV triple-circuit transmission line in real project is established in Power Systems Computer Aided Design (PSCAD), and it is verified by real record data provided by power utility in China. By using this simulation model, factors on current unbalances are discussed in detail, and the simulation results have shown that mal-operation of zero-sequence overcurrent relaying is caused by large unbalanced current in normal operation and under faults. Consequently, a lateral coordination scheme for zero-sequence overcurrent relayings among multi-circuit lines is proposed to avoid the mal-operation caused by unbalanced current to the greatest extent without receiving samples from remote end or adjacent circuits, and the reliability of protective relaying is improved significantly.

Feasibility Analysis and Protection Measures of Live Working on the multi-circuit Transmission Lines on the Same Tower

Live line operation is the most direct and effective means for the maintenance of multi-circuit transmission lines on the same tower. It is also a special operation mode developed to improve the reliability of power supply and the safety of power grid. Therefore, it is necessary to analyze the feasibility of live line operation of multi-circuit transmission lines on the same tower. In this paper, 110 kV, 220 kV and 500 kV multi-circuit transmission lines on the same tower are taken as object, and the safety analysis of live working is carried out for typical working positions. According to the results of operation impact discharge test, the risk rate and safe working distance of live working are obtained; Finally, the minimum effective insulation length of load-bearing tools and operation tools is calculated.

Optimal selection and positioning of conductors in multi-circuit overhead transmission lines using evolutionary computing

This paper presents a new approach for designing transmission lines to transmit more power in a narrower space. Multi-circuits lines are a good alternative to attain this objective. However, the optimum solution is not obtained by just positioning several regular single-circuit transmission lines in a single tower structure. Although double-circuit and multi-circuit transmission lines have been used over the last years, there are not many studies about non-conventional multi-circuit transmission lines. Thus, in this research a mathematical model to represent the problem related to increasing the surge impedance loading level of each circuit, and reducing the costs, the ROW and the height of the towers by optimizing their bundle geometry and conductor type by applying genetic algorithms is proposed. The overall transmission lines presented as examples have an improvement between 52% and 149% in the objective function.

Multi-objective optimization of overhead transmission lines including the phase sequence optimization

Since the human density, technologies, industries and services are in continuous grow, the electrical power consumption increments over the time. To satisfy those power levels the transmission lines should increment their power capacity. However, the increment has to be done taking into account that the line projects should use the lowest possible space to decrease their environmental impact. The present paper proposes the use of optimized multi-circuit transmission lines with several circuits and voltage levels on the same tower. A mixed-integer non-linear programming (MINLP) model with variables in a permutation based space for optimizing the surge impedance loading (SIL), right of way (ROW), costs and height of power transmission lines is presented and solved using evolutionary computation with a multi-objective approach based on the Non-dominated Sorting Genetic Algorithm II (NSGA-II). The optimization is done by choosing the optimal position, type and quantity of conductors as well as the phase sequence in multi-circuit transmission lines. To deal with the different types of decision variables, a custom constraint handling is proposed. As a result of the optimization process, multi-circuit power transmission lines with narrower ROW, lower environmental impact, higher SIL and similar costs to conventional lines are obtained.

Adaptive single-phase/three-phase reclosing scheme for transmission lines in passive network supplied by MMC-HVDC

Modular multilevel converter (MMC) shows prominent advantages on supplying passive networks, which are usually classified by power supply shortage and relatively weak structure. In order to reduce the unnecessary outage time and improve the system stability, an adaptive ac auto-reclosing scheme for passive networks is proposed based on characteristic signal injection. Additional MMC controller is designed to inject the characteristic signals into the healthy line, which in turn induces corresponding signals to the faulty line. Then fault properties are assessed by the travelling wave based fault location method. Finally, an adaptive auto-reclosing scheme is proposed to shorten the reclosing time and avoid the second fault shock to a large extent. The proposed scheme could be applied for both single-circuit and multi-circuit transmission lines. The simulation results obtained from PSCAD/EMTDC verify the effectiveness of the proposed method.

Mechanism and solution of zero-sequence directional protection maloperation caused by broken line faults in multi-circuit transmission lines on the same tower

When one loop line of the multi-circuit transmission lines on the same tower is in states of non-full-phase operation or asymmetric line-breaking faults, the zero-sequence direction of functioning loop lines is likely to maloperation due to zero-sequence voltage compensation. The multi-circuit transmission lines on the same tower with different voltage classes will induce the same zero-sequence voltage distribution trend as the fault line due to the mutual inductance between loop lines, and thus may conduct improper operation as well. This paper analyses the causes of maloperation of zero-sequence directional protection caused by non-full phase operation or line-breaking fault of multi-circuit lines on the same tower, and puts forward a method to prevent maloperation by extracting line status from station domain information. In the case of multi-circuit lines on the same tower with same voltage class, the crossing point of zero-sequence voltage of the line can be calculated and the zero-sequence voltage can be compensated in reverse to prevent maloperation. In the case of multi-circuit lines on the same tower with different voltage class, fault characteristics can be identified according to substation information and the zero-sequence direction protection can be automatically blocked. RTDS is used to simulate and verify the electrical characteristics, malfunction process and the effectiveness of prevention methods of multi-circuit lines on the same tower when a non-full-phase operation or abnormal line breakage occurs.

Evaluation of Corona Loss in 750 kV Four-Circuit Transmission Lines on the Same Tower Considering Complex Meteorological Conditions

As an important index for measuring the operational economy of EHV AC transmission lines, corona loss (CL) is one of important factors worth considering during the operation and design of transmission lines. The 750-kV transmission lines are mainly distributed in high-altitude areas in northwestern China, where sand storm occurs frequently in spring and autumn. At present, a few researches are available on the evaluation of CL in multi-circuit transmission lines on the same tower in sandy and dusty area at high altitudes. Based on a transmission project with four-circuit transmission lines on the same tower in the north of Xi’an, Shaanxi Province, China, the electric field distributions of bundle conductors under two types of arrangement structure, including six and four cross-arms tower, were investigated. Then, by using the CL equivalent theory, the CL under meteorological conditions of fair, rainy, snowy, foggy, and dusty weather were evaluated. Finally, the optimal phase-sequence arrangement under the optimal tower modes was proposed, and the CL and resistance loss under the selected arrangements were compared.

Research on Safety Protection for Live Working on 1000kV AC Transmission Line with AC and DC Multi-circuit Transmission Lines

In recent years, in order to save line corridors and reduce the scope of demolition, some new transmission modes for high voltage AC and DC power transmission line are proposed. According to the characteristics of the parallel transmission line, this paper studies the distribution characteristics of the electric field intensity of multi circuit parallel transmission lines and the single circuit transmission line. Comparing and analysing the simulation results of the electric field strength, the safety measures for live working of 1000kV AC transmission line with multi circuit parallel transmission lines is put forward. That is the electric field protective equipment and measures used in the live line work of the 1000kV UHV AC single circuit line can meet the requirements of the live operation of the 1000kV UHV AC double circuit line.

Research on New Method of Live Working on 220/500kV Mixed-voltage Four-circuit Transmission Lines on the Same Tower

Multi-circuit transmission lines on the same tower are widely used in recent years, and maintenance is an important technical means for ensuring safe and stable operation thereof. This paper aimed at the operation characteristics of multi-circuit transmission lines on the same tower, and presented a “swing method” for getting in the electric field during live working of operating circuit lines, which is applied to actual lines, and the application result show that the method is safe and reliable. The research result of this paper provides strong technical support for maintenance of multi-circuit transmission lines on the same tower.

Research on safety protection for live working on ±800kV DC transmission line with AC and DC multi-circuit transmission lines

In recent years, in order to save line corridors and reduce the scope of demolition, some new transmission modes for high voltage AC and DC power transmission line are proposed. According to the characteristics of the parallel transmission line, this paper studies the distribution characteristics of the electric field intensity of multi circuit parallel transmission lines and the single circuit transmission line. Comparing and analysing the simulation results of the electric field strength, the safety measures for live working of ±800kV DC transmission line with multi circuit parallel transmission lines is put forward. That is the electric field protective equipment and measures used in the live line work of the ±800kV UHDC single circuit line can meet the requirements of the live operation of the ±800kV UHDC multi-circuit transmission line.

Non-Contact Capacitive-Coupling-Based and Magnetic-Field-Sensing-Assisted Technique for Monitoring Voltage of Overhead Power Transmission Lines

Adopting non-contact capacitive coupling for voltage monitoring is promising as it avoids electrical connection with high-voltage transmission lines. However, coupled voltage transformation matrix to correlate voltage of overhead transmission lines and induction bars has not been achieved mathematically due to the lack of equivalent electric circuit model for analyzing the physical phenomenon. Moreover, exact spatial positions of overhead transmission lines are typically unknown and dynamic in practice. In this paper, a technique based on non-contact capacitive-coupling and assisted by magnetic-field sensing for monitoring voltage of overhead transmission lines was designed and implemented. The technique in this paper is demonstrated on a single-circuit transmission line as an example, while it is also applicable for multi-circuit transmission lines. The capacitive coupling between overhead transmission lines and induction bars were modeled as lumped capacitors, and then, the equivalent electric circuit model was established. The coupled voltage transformation matrix to correlate voltage of overhead transmission lines and induced voltage of induction bars mathematically was formed accordingly. This paper was also carried out to analyze the effect of ground wires, sensitivity of induction bars, the ability of high-frequency transient measurement, and the intrinsic capacitance of a measurement instrument. The exact spatial positions of overhead transmission lines were acquired by integrating magnetic-field sensing with the stochastic optimization algorithm. The methodology was verified by simulation on the 10-kV single-circuit three-phase overhead transmission lines taking non-ideality of signal measurement in account, and wavelet de-noising algorithm was supplemented to filter the interferences. A scaled testbed to experiment the technique was built to monitor 220 V overhead transmission lines in the lab, and also the typical waveform of a high-frequency switching surge (up to 1 kHz), which was generated by a programmable ac source. The reconstructed results match well with the actual values. This technique can largely improve transient-fault identification over traditional potential transformers by the virtue of the increased upper measurement limit and bandwidth through capacitive coupling. Moreover, it can be implemented with low-cost copper induction bars and compact magnetoresistive sensors, enabling large-scale application to realize sectional monitoring in the wide area.

Statistical Analysis on Lightning Performance of Transmission Lines in Several Regions of China

Lightning is a substantial cause that leads to serious lightning failures, which has a significant influence on the normal operation of the entire power grid. This paper mainly focused on several regions of China with serious lightning activity, presenting the lightning performance of power grids by statistics obtained from long-term monitoring data, and intended to indicate some general characteristics. The lightning tripout rate, the shielding failure tripout ratio, the occurrence frequency corresponding tripout failures of different phases of single-circuit or double-circuit transmission lines, and the multicircuit simultaneous tripout failures of multicircuit transmission lines were analyzed. These statistical results presented a panorama of the lightning protection effect of transmission lines in China. The statistical data in this paper are informative to guide the future research or engineering practice of lightning protection of transmission lines, and will be helpful to evaluate the analysis methods of lightning performance of transmission lines.

Secondary arc current of ultra‐high voltage transmission line with a mixed voltage of 1000/500 kV on a single tower

Among the ultra-high-voltage (UHV) grids in eastern China, the construction of multi-circuit transmission lines with mixed voltages on a single tower is a novel transmission technology that can significantly reduce line corridor coverage, maximise the use of tower height and significantly improve power transmission capacity per area. However, the electromagnetic interaction between lines is complicated and interferes with the secondary arc current. This study proposes a hybrid tower model that incorporates double-circuit transmission lines with alternating currents at 1000 and 500 kV. Its secondary arc current is investigated according to circuit analysis and EMTDC in consideration of the electromagnetic coupling effect, along with the influences of line length, compensation, phase sequence and transposition on the secondary arc current. Results show that a strong secondary arc current is generated for 1000 kV transmission lines in accordance with the UHV hybrid transmission project from Ximeng to Shanghai. This finding should be emphasised. Furthermore, the influence of quadruple-circuit line length on the secondary arc current depends on line voltage rating. Finally, this study presents several methods that may reduce the secondary arc current, such as transposing lines evenly and installing suitable neutral reactors.