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The effect of splitter plates (SP) on current interruption at medium voltage (MV) level is theoretically investigated in the framework of Mayr's arc model, which is generalized to take into account the electrode fall voltage, V0, of the SP. The model is analytically solved in the current zero (CZ) region where the current (before CZ) and the voltage (after CZ) can be linearized with respect to time. The current turns out to be successfully interrupted if the total electrode fall voltage, NV0, for N − 1 SP plus contact electrodes, is larger than twice the transient recovery voltage, ${\boldsymbol{U}} \approx {\dot{\boldsymbol{U}t}}$ , at the characteristic arc decay time, t = τ, after CZ: ${\boldsymbol{N}}{{\boldsymbol{V}}_0} > 2{\dot{\boldsymbol{U}\tau }}$. For ${\boldsymbol{N}}{{\boldsymbol{V}}_0} < 2{\dot{\boldsymbol{U}\tau }}$ , an additional thermal condition must be satisfied, where also the current rate, ${\dot{\boldsymbol{I}}} = {\boldsymbol{\ dI}}/{\boldsymbol{dt}}$ before CZ, and the arc cooling power, K, are involved. The intuitive results lead to a simple understanding of the electrical effect of SP on current interruption at MV and serve as an initial design rule for the number of SP in different gases. [ABSTRACT FROM AUTHOR]

Ionic wind devices or electrostatic fluid accelerators are becoming of increasing interest as tools for thermal management, in particular for semiconductor devices. In this work, we present a numerical model for predicting the performance of such devices; its main benefit is the ability to accurately predict the amount of charge injected from the corona electrode. Our multiphysics numerical model consists of a highly nonlinear, strongly coupled set of partial differential equations including the Navier-Stokes equations for fluid flow, Poisson's equation for electrostatic potential, charge continuity, and heat transfer equations. To solve this system we employ a staggered solution algorithm that generalizes Gummel's algorithm for charge transport in semiconductors. Predictions of our simulations are verified and validated by comparison with experimental measurements of integral physical quantities, which are shown to closely match. [ABSTRACT FROM AUTHOR]

The influence of the carrier injection properties of electrode contacts on unipolar space-charge limited currents (SCLC) in perfect insulators is theoretically studied. The usual electric transport model consisting of the charge continuity equation and the Poisson equation is supplemented by boundary conditions describing carrier injection. The dependence of the electric behavior on the saturation current density, which is the most important parameter of the boundary condition, is investigated, mainly with FEM simulations. The scenarios in the focus are transient DC current when a constant voltage is switched on, and dielectric (or impedance) spectroscopy (AC). For the latter, higher harmonics up to the 5th order are relevant due to the intrinsic nonlinearity of SCLC. A simplified ordinary differential equation model for transient contact charging is derived, in an analogous way as it is usually done for the early SCLC transient with ideal ohmic contacts. Finally, a specific case with traps that may quench the transit-time peak is briefly discussed to illustrate trapping effects. It turns out that the SCLC dynamics can be separated in three time (or frequency) regimes. Two of them are separated as usual by the time of flight, τtoƒ, of carriers through the sample. A third region at shorter times t<τc≪τtoƒ (or higher frequencies) exists, where τc characterizes the time for space charge formation at the injecting contact. The contact injection properties thus mainly influence the short-time and high-frequency behavior, where the characteristic time decreases with increasing saturation current. This behavior is reflected by the appearance of specific structures in the absorption current and the impedance spectrum. For instance, an additional current maximum associated with the fast diffusive expansion of the locally injected space charge may appear at early times. [ABSTRACT FROM AUTHOR]

Insulator boundaries like electrode contacts, interfaces, and surfaces play decisive roles for the electric field distributions in high-voltage direct-current (HVDC) insulation. Well-known examples are charging effects at injecting and blocking electrode contacts, and at interfaces or surfaces. Reliable modeling of boundaries and interfaces poses a challenge and can be crucial for the quality of the resulting field distributions in HVDC equipment, but is in practice often put in second place of priority in simulation models. This paper emphasizes the macroscopic boundary conditions and related issues for electrical transport and illustrates their relevance with simple examples. Importance is attached to an appropriate compromise between physical generality and practical usability for simulations in the development process of HVDC insulation systems. [ABSTRACT FROM AUTHOR]

Axially blown electric arcs in a model circuit breaker are investigated by electrical measurements and fast imaging with a high-speed camera for visualizing the arc structure. Parameters for a dynamic conductance model (known as the “black-box model” in the arc literature) are extracted from the electrical measurements for currents between a few tens of amperes and a few kiloamperes. The model is used for the prediction of the conductance-dependent cooling power and arc relaxation time, as well as the voltage-current characteristics of the arcs in our system. In order to work out the relevance of the different cooling mechanisms, an alternative and more physically based dynamic model for axially blown arcs is incorporated. It turns out that convective cooling predominates turbulent heat conduction and radiation cooling in the region of validity of the model. The result is consistent with the observed strong dependence of the cooling power on the flow conditions that are controlled by the blow-gas pressure and the geometry. Furthermore, the comparison between air and SF6 arcs indicates a considerable dependence of the conductance-cooling relation on the gas type. [ABSTRACT FROM PUBLISHER]

Electric field grading, or stress control, refers to the technique of reducing local enhancements of the electric field in various devices [1], [2]. As a part of insulation coordination, field grading is crucial for making products competitive, particularly today when voltage levels are increasing, sizes of components are shrinking, installation logistics are an issue, and the demand for integration of different functions in a single device is steadily growing. Design criteria such as cost and safety issues and low electric fields and temperatures are often contradictive and must be balanced. For example, smaller insulation thickness leads to lower material costs and lower temperatures but to higher electric fields, which can lead to electric breakdown, particularly at critical regions such as interfaces or triple points. Appropriate field grading can help attain or improve and optimize a design that outbalances such criteria. [ABSTRACT FROM PUBLISHER]