Most traditional voltage transformers in transmission and distribution networks are installed inside the substations. Nearly no accessible voltage information in the real-time scale is available for ...field engineers to carry out the field measurement for the purposes of the power quality inspection and the equipment maintenance. In order to offer an on-site and easy-to-use solution for the field measurement, the authors propose a novel electric-field (EF) sensor array based technique for measuring the overhead-line voltage. Based on the EFs measured by the EF sensor array and the partially known overhead-line geometry information from utilities, the proposed voltage algorithm can accurately calculate each-phase voltage without an on-site calibration before conducting the field measurement. The simulation results demonstrate that the authors’ proposed technique with only three EF sensors can accurately calculate the overhead-line voltages and successfully reconstruct the real-time three-phase waveforms. The experiment results verify the feasibility of the proposed voltage sensor for the overhead-line voltage measurement.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Multi-circuit, multi-voltage overhead lines (MMOLs) are becoming a favorable solution in the perspective of ensuring the efficient transmission of electrical energy and limitations relating to the ...expansion of the transmission network. The main part of this manuscript contains a method that minimizes the effects of risks on the operation of the power system due to asymmetrical MMOLs, with particular emphasis on the circuit with the lowest-rated voltage. The selected set of criteria includes elements such as the determination of the neutral point displacement voltage in the network with the lowest-rated voltage (zero voltage, U0), selected voltage quality factors, and short-circuit analyses to examine the impact of differences between the use of accurate and simplified mathematical models on the calculation of short-circuit currents. Methods to minimize the effects of MMOL geometric asymmetry have been proposed using simple technical steps, such as selecting the appropriate pole silhouette (indication of the methodology for identifying such supporting structures), changing the way of supplying individual circuits, or using partial transposition in the circuit with the lowest-rated voltage. The proposed methods are verified by analyzing a case study of the development of the transmission network in Poland.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Unbalanced tension is one of the most important loads for the design of transmission towers under ice accretion in cold regions. A V-shaped sliding groove, which is a new type of connection for ...suspension strings, is developed as one of the most effective ways to release unbalanced tension. Eight typical experiments on the V-shaped sliding groove for releasing exceeding unbalanced tensions in transmission lines were designed and performed. The variation mechanism of unbalanced tensions was investigated, and the calculation theory of the critical sliding angle was verified. The experimental results showed that all specimens under all load cases could effectively simulate to release the unbalanced tension when the unbalanced tension increased to the critical value and the suspension string began to slide. Besides, the variation of conductor tensions for 100 m span could be simulated by adopting the curved orbit developed in this study, and the transmission-line parameters could be changed easily and the experiment became flexible. On the basis of the comparison of theoretical values with the test results of the conductor tension, the design method and practical use of the curved orbit were reasonable and feasible.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This study proposes a three-dimensional (3D) quasi-static modelling of the electric field produced by high voltage (HV) overhead power lines using charge simulation method combined with intelligent ...optimisation algorithms, such as particle swarm optimisation, genetic algorithm and grey Wolf optimiser (GWO), to find the optimal values of parameters for an accurate calculation. Results show that the GWO works better than other algorithms. Several parameters affecting the electric field have been studied; it is observed that taking into account the effect of the exact catenary curve of the power line conductors is much more interesting particularly at the mid-span level where the electric field becomes very significant. According to these values, the limits set by the International Commission on Non-Ionising Radiation Protection guidelines for electric field strength are met for occupational and public exposure. The simulation results are compared with those obtained by the 3D Integration method, a fairly good agreement is found. To confirm the performance and effectiveness of the proposed method, the results obtained are also verified with measurement values available in the literature, a good similarity is achieved.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The modular multilevel converter (MMC) is a promising candidate for voltage-sourced-converter-based high-voltage direct current (VSC-HVDC) transmission. The dc short-circuit fault management is a ...crucial issue especially for overhead line transmission, where the nonpermanent dc short-circuit faults occasionally occur. In this paper, a comprehensive dc short-circuit fault ride through (FRT) strategy is proposed for a hybrid MMC which combines half-bridge submodules and full-bridge submodules. By the proposed method, the hybrid MMC-based VSC-HVDC system is able to ride through a pole-to-pole short-circuit fault supporting the ac grid as a static synchronous compensator. Moreover, the transmission system can still transmit one-half of the rated active power in case of a pole-to-ground short-circuit fault without increasing power semiconductor stresses or requiring higher insulation levels of the electric equipment. The proposed method ensures successful regulation of arm currents and submodule capacitor voltages during the FRT process. Validity of the proposed strategy is verified by both computer simulation and experiment results.
An approach is demonstrated to visualise overhead line failure rates and estimated wind power output during extreme wind events on transmission networks. Reanalysis data is combined with network data ...and line failure models to illustrate spatially resolved line failure probability with data corrected for asset altitude and exposure. Wind output is estimated using a corrected power curve to account for high speed shutdown with wind speed corrected for altitude. Case studies demonstrate these methods' application on representations of real networks of different scales. The proposed methods allow users to determine at‐risk regions of overhead line networks and to estimate the impact on wind power output. Such techniques could equally be applied to forecasted weather conditions to aid in resilience planning. The methods are shown to be particularly sensitive to the weather data used, especially when modelling risk on overhead lines, but are still shown to be useful as an indicative representation of system risk. The techniques also provide a more robust method of representing weather‐related failure rates on lines considerate of the altitude, voltage level, and their varying exposure to weather conditions than current techniques typically provide, which can be used to usefully represent failure probability of lines during storms.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This paper presents a new modelling approach based on idempotent decomposition of the nodal admittance matrix for representation of cables and overhead lines (OHL). By subjecting the idempotent ...matrices rather than the nodal admittance matrix to rational fitting, the poor observability of the smallest eigenvalues in the lower frequency range is overcome. Unlike the well-known method of characteristics (MoC), this alternative representation yields a so general fully-coupled admittance matrix suitable to tackle scenarios encompassing short and long lengths. Besides retaining the frequency dependence of parameters, the proposed phase-domain model showed to be accurate and suitable to circumvent the requirement of small time-steps.
•New approach for line/cable modelling exploiting the idempotent decomposition of the nodal admittance matrix.•Linear transformation to overcome some issues encountered in the direct fitting of the nodal admittance matrix.•Time-domain results validated with the Numerical Laplace Transform algorithm.•Alternative to circumvent the presence of short and long line/cable lengths.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Phase-to-phase air gap is a type of external insulation in power transmission and transformation projects. The dielectric strength of phase-to-phase air gaps affects the safety and reliability of ...power systems. Currently, in the external insulation design of power transmission and transformation projects, discharge tests are mainly used to obtain the dielectric strength of air gaps. Due to the lack of reasonable prediction model of dielectric strength, the design of the tests is not reasonable enough, which are time consuming and costly. In order to solve the problem, an engineering model of dielectric strength in phase-to-phase air gaps was proposed in this study. The engineering model could predict the dielectric strength in phase-to-phase air gaps by finite-element method simulation and numerical calculation. In this study, the engineering model was applied in ultra high voltage (UHV) substations and UHV compact transmission lines to predict the dielectric strength of tubular busbar phase-to-phase air gaps and conductor phase-to-phase air gaps. The predicted results were in good agreement with discharge test results, and the errors were <6%, which proved the engineering model has certain applicability in power transmission and transformation projects.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Utilities are continuously investigating methods to economically reinforce their overhead line (OHL) networks by reconductoring with larger conductors or with novel high-temperature low-sag (HTLS) ...conductor technologies. To further optimise the OHL design, conductor creep ageing is calculated and mitigated at installation, which economically improves an OHLs’ performance. An already established methodology is used to investigate common and HTLS conductors ageing effect on sag and tension in order to highlight the benefits and risks that could result from existing creep mitigation methods particularly on HTLS conductors. The study aims to identify the impact of important design factors such as ice loading and emergency operation events and their frequency of occurrence on creep mitigation as well as to highlight the creep variation of the same materials used particularly on different HTLS conductors. The analysis presented here indicates that pre-tensioning could be more beneficial on soft aluminium HTLS conductors while over-tensioning can result in extensive durations of conductor over-stressing on steel supported and Gap-type conductors. Furthermore, the conductor technology majorly affects the creep of steel core which cannot be considered always as zero. The accuracy of the methodology is also re-validated using recent experimental data from Gap conductor.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
This paper presents an enhanced independent pole control scheme for hybrid modular multilevel converter based on a full-bridge submodule and half-bridge submodule. A detailed analysis of the power ...distribution between upper and lower arms under asymmetrical dc pole voltages is presented. It is found that the fundamental ac currents in the upper and lower arms are asymmetrical. To enable operation under asymmetrical dc pole voltages, an enhanced independent pole control scheme is proposed. The controller is composed of two dc control loops, two ac control loops, and circulating current suppression control based on current injection. Six modulation indices are presented to independently control the upper and lower arms. With this controller, the dc voltage operating region is significantly extended. To ride through a pole-to-ground dc fault without bringing dc bias at the neutral point of the interface transformer, a pole-to-ground dc fault ride through strategy is proposed. The feasibility and effectiveness of the proposed control scheme are verified by simulation results using PSCAD/EMTDC.
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