Abstract-This paper presents a breaker arrangement concept, the Multi-Line Breaker (MLB), for the protection of multiterminal high voltage dc (MTdc) networks. Based on the design of a hybrid breaker, the MLB is an economically attractive solution for the protection of multiple dc lines in nodal connection using a single main breaker path. By using commutation units, the MLB directs the fault current through the main breaker in a unidirectional way, irrespective of the fault location. Hence, this study presents the design requirements for the MLB, regarding both hardware and control, and evaluates its operation within a grid. For this reason, a four-terminal half-bridge MMC-based MTdc grid in radial configuration was used and pole-to-ground dc fault conditions were investigated. The dc fault response of the grid with one MLB at the central node is compared to the respective response of the grid when one hybrid breaker is employed at each dc line. The simulations show that the MLB is feasible and that the overall MTdc grid fault response for the two protection systems is very similar. As a result, the design advantages of the MLB make it a promising solution for the dc fault isolation in MTdc grids.
Corona behavior of HVDC overhead lines plays a significant role when dimensioning transmission lines. Rain constitutes an important study case since corona effects (e.g. losses, discharge amplitudes) are considerably affected. In this paper, imaging methods are introduced to investigate the impact of rain on corona behavior. Geometrical properties of rain drops on a stranded conductor were extracted. UV-images were used to precisely locate discharges. The methods' capabilities are demonstrated using data from an indoor test line during a simulated rain shower. Optical and electrical data were correlated. These methods aim to support the development of surfaces with favorable corona properties.
a b s t r a c tCorona behavior of HVDC overhead lines plays a significant role when dimensioning transmission lines. Rain constitutes an important study case since corona effects (e.g. losses, discharge amplitudes) are considerably affected. In this paper, imaging methods are introduced to investigate the impact of rain on corona behavior. Geometrical properties of rain drops on a stranded conductor were extracted. UVimages were used to precisely locate discharges. The methods' capabilities are demonstrated using data from an indoor test line during a simulated rain shower. Optical and electrical data were correlated. These methods aim to support the development of surfaces with favorable corona properties.
Mechanical circuit breakers (MCBs) are the limiting component for current injection HVDC circuit breakers. Improving their interruption performance reduces requirements for capacitance and inductance needed in the injection circuit and thus space use and costs. Higher performance can be achieved by creating a period of low current gradient before zero crossing in the MCB, e.g. by using a saturable inductor (SI). In this paper, the impact of duration and steepness during the low currentgradient phase is linked to arc parameters of the investigated model gas circuit breaker. It is shown in a scaled experimental setup that an optimum design of the SI can be derived from arc time constant and interruption limits for constant current gradients. This optimisation results in a considerable increase of interruption performance. The feasibility of implementing an SI in a full-scale HVDC circuit breaker is demonstrated using simulations. Using an improved injection scheme, the stresses for the MCB can be reduced significantly. Consequently, the injection circuit components can be scaled down, making the topology more economical. The reduced interruption requirements might also make it possible to use a single gas interrupter instead of a series connection of vacuum interrupters, reducing the complexity of the mechanical switch.
Current injection circuit breakers consist of a mechanical interrupter (MI) with a current injection and an energy dissipation branch in parallel. The performance of the complete device is largely determined by mechanical operation time and interruption performance of the MI. In the standard configuration, current injection is realised using a pre-charged inductorcapacitor circuit. A higher interruption performance of the MI makes it possible to scale down the resonant injection circuit, and thus have a more economical design. Additionally, the implementation of more complex injection circuits that quickly create zero crossings, while maintaining favourable conditions for interruption, can lead to economic benefits. In this study, the interruption performance of a model gas interrupter as part of a current injection topology is investigated. The results are used to verify a corresponding simulation model and two-dimensional upgrade circuits that influence the injection current to increase the range of interruptible fault currents. On the basis of experimental results, the simulation model is used to investigate the performance of upgrade circuits for the use in high-voltage direct current (HVDC) systems. The results indicate that using improved injection circuits can considerably increase the economic advantage of current injection circuit breakers compared with other topologies.
For the development and optimization of gas circuit breakers and switchgear, a detailed understanding of the arc related processes is of great importance. Ideally, analytical or numerical models with predicitive capability can be found and used during the design process preceding costly and time-consuming experiments.<br /><br />In the present contribution, we report on a novel measurement and evaluation technique to determine the thermal arc time constant ("thermal inertia") that is commonly used in simple black-box models to describe the arc's dynamical properties. The method is introduced and applied to example arcs under varying blow gas conditions in air.<br /><br />
During the last years, more and more renewable power generation units have been connected to the European power grid, creating demands for higher transport capacity as well as longer transport distances. Plans for the construction of HVDC and hybrid HVAC/HVDC corridors in Europe lead to an increased interest in the corona behaviour of direct current overhead lines. Within the scope of this paper, simulations and measurements are conducted to analyse the accuracy of the used simulation tool for rainy conditions, which is constituting an important study case since corona intensity is significantly increased during periods of precipitation. Especially, charge generation at the conductor surface and its influence on total corona current as well as on the ion current distribution at ground level under rainy conditions are investigated. As a result, the idea that a single onset field strength can describe the entire V-I characteristic of an overhead line under rainy conditions is challenged. It is shown that a field dependent correction factor for the onset field strength can improve the accuracy of simulations considerably. Additionally, in order to improve the simulated current distribution at ground level, a method to inversely calculate charge generation profiles is introduced.
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