Stoffels M, Simon S, Nikolic P G, Stoller P, Carstensen J
Appl Opt. 2017 Mar 1;56(7):2007-2019. doi: 10.1364/AO.56.002007.
High-voltage gas circuit breakers, which play an important role in the operation and protection of the power grid, function by drawing an arc between two contacts and then extinguishing it by cooling it using a transonic gas flow. Improving the design of circuit breakers requires an understanding of the physical processes in the interruption of the arc, particularly during the zero crossing of the alternating current (the point in time when the arc can be interrupted). Most diagnostic techniques currently available focus on measurement of current, voltage, and gas pressure at defined locations. However, these integral properties do not give sufficient insight into the arc physics. To understand the current interruption process, spatially resolved information about the density, temperature, and conductivity of the arc and surrounding gas flow is needed. Owing to the three-dimensional, unstable nature of the arc in a circuit breaker, especially near current zero, a spatially resolved, tomographic diagnostic technique is required that is capable of freezing the rapid, transient behavior and that is insensitive to the vibrations and electromagnetic interference inherent in the interruption of short-circuit current arcs. Here a new measurement system, based on background-oriented schlieren (BOS) imaging, is presented and assessed. BOS imaging using four beams consisting of white light sources, a background pattern, imaging optics, and a camera permits measurement of the line-of-sight integrated refractive index. Tomographic reconstruction is used to determine the three-dimensional, spatially resolved index of refraction distribution that in turn is used to calculate the density. The quantitative accuracy of a single beam of the BOS setup is verified by using a calibration lens with a known focal length. The ability of the tomographic reconstruction to detect asymmetric features of the arc and surrounding gas flow is assessed semiquantitatively using a nozzle that generates two gas jets, as described in [Exp. Fluids43, 241 (2007)EXFLDU0723-486410.1007/s00348-007-0331-1]. Experiments using a simple model of a circuit breaker, which provides optical access to an ∼1 kA arc that burns between two contacts and is blown through a nozzle system by synthetic air from a high pressure reservoir, are also described. The density in the decaying arc and surrounding gas flow is reconstructed, and the limitations of the technique, which are related to the temporal and spatial resolution, are addressed.
高压气体断路器在电网的运行和保护中起着重要作用，其工作原理是在两个触头之间产生电弧，然后通过跨音速气流冷却电弧将其熄灭。改进断路器的设计需要了解电弧中断过程中的物理过程，特别是在交流电过零期间（即电弧可以被中断的时刻）。目前大多数可用的诊断技术都集中在测量特定位置的电流、电压和气体压力。然而，这些整体特性并不能充分洞察电弧物理过程。为了理解电流中断过程，需要有关电弧和周围气流的密度、温度和电导率的空间分辨信息。由于断路器中电弧的三维、不稳定性质，特别是在电流零点附近，需要一种空间分辨的断层诊断技术，该技术能够冻结快速、瞬态行为，并且对短路电流电弧中断时固有的振动和电磁干扰不敏感。本文介绍并评估了一种基于背景纹影（BOS）成像的新型测量系统。使用由白光源、背景图案、成像光学器件和相机组成的四束光进行BOS成像，可以测量视线积分折射率。断层重建用于确定三维、空间分辨的折射率分布，进而用于计算密度。通过使用具有已知焦距的校准透镜，验证了BOS装置单束光的定量精度。如[《实验流体》43, 241 (2007)EXFLDU0723-486410.1007/s00348-007-0331-1]所述，使用产生两股气体射流的喷嘴，半定量评估了断层重建检测电弧和周围气流不对称特征的能力。还描述了使用断路器简单模型进行的实验，该模型提供了对在两个触头之间燃烧并由高压储气罐中的合成空气通过喷嘴系统吹过的约1 kA电弧的光学观察。重建了衰减电弧和周围气流中的密度，并讨论了与时间和空间分辨率相关的技术局限性。
