High Voltage Switchgear Thermal Distribution Analysis

Cílem této práce je analýza teplotního pole vysokonapěťového rozvaděče. Tato analýza je založena na kombinaci experimentálního měření a CFD simulace proudění vzduchu v prostoru rozvaděče. Na základě výsledků pro referenční geometrii jsou předloženy návrhy na úpravu topologie rozvaděče, které mají za cíl snížení teploty kritických komponent rozvaděče během jeho provozu. Druhá část práce je spojena s problematikou oteplení plošných spojů, jakožto hlavních zdrojů tepla v prostoru rozvaděče. Pro popis závislosti oteplení plošného spoje na jeho charakteru byla použita statistická metoda design experimentu. Výsledky z experimentálního měření jsou podpořeny konečně prvkovým modelem kontaktu spoje.This thesis deals with analysis of thermal field inside high voltage switchgear cabin. It de-scribes applied methodology based on combination of CFD simulation of air flow inside switch-gear cabin and series of experimental measurements. Based on results for reference geometry it provides proposals of switchgear layout modification to decrease temperature rise on switch-gear critical components during its operation. In the second part of this thesis problem of bus-bar joints is discussed. Busbar joints are one of the key thermal sources inside switchgear cab-in. Statistical method of design of experiment is applied for experimental investigation of bus-bar joint temperature rise. Results from design of experiment are supported by finite element simulation of contact in busbar joint.

Time domain analysis of switching transient fields in high voltage substations

Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho

Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

Computer Simulation and Visualisation of Complex Systems: Arcs and Hot Gas Flow in Auto-expansion Circuit Breakers

Auto-expansion circuit breakers (also known as the self-blast circuit breakers) are an advanced generation of high voltage switchgear. This type of circuit breaker uses the arc's energy to generate a high pressure SOurce in the expansion volume (also known as the heating chamber) to create the required thermal and aerodynamic conditions for interrupting the circuit at a current zero. Ablation of the arc confining nozzle at high current is the main mechanism for pressurisation of the expansion volume. The operation of such a breaker is extremely complex and its performance depends on the whole arcing history as well as a number of geometrical factors characterising the geometry of the interrupter. It is a complex system with inter-related mechanical parts (moving pistons, valves, ablating nozzles, and moving contact) and physical processes (radiation, thermodynamics, aerodynamics, turbulence and ablation of solid materials). The relationship between all the constituent parts and physical processes gives rise to the collective behaviour of the whole system. Computer simulation of the arcing process in such a breaker has been carried out in the present work. Because of the very high power level encountered in such a breaker the arc interacts intensely with its surroundings. The objective of the work is to establish a computer model to simulate the whole arcing process, validate the model and then perform an extensive analysis of system behaviour to extract useful information for the optimisation design of such devices. The history of circuit breaker development, fundamental aspects related to the operation of high voltage circuit breakers, and history of computer modelling of switching arcs are first reviewed in chapter I, which provides an overall background picture for the present work. The mathematical description of the important physical processes is then given in chapter 2 which includes the governing equations for arc flow, the modelling of radiation and turbulence, the calculation of nozzle ablation, and the computation of electrical and magnetic fields for Lorentz force and Ohmic heating. The temperature and pressure encountered in computer simulation of the autoexpansion circuit breaker arc covers a wide range, from 300K to possibly 40, OOOK and from atmospheric pressure to 100 bar. The material and transport properties of the mixture of the working gas and ablated nozzle vapour are highly non-linear functions of plasma parameters. Thus a robust computational fluid dynamics (CFO) solver is essential. In the present work, a commercial CFO package, PHOENICS, is used for the simulation. The practically important issues, such as the implementation of the arc model with input of material properties into the solver, the specification of initial and boundary conditions, the approximate of the circuit breaker geometry, and choice of time step and control of convergence, are discussed in chapter 3. In the operation of an ABB auto-expansion circuit breaker, there are a number of mechanical parts that move with time during an operation process. The operation of over pressure valves, with one of them attached to the moving piston, has to be correctly modelled. This is detailed in chapter 4 where validation of the numerical meth~ ' ods is provided by comparing the prediction with analytical results from isentropic compression and also with measurement from ABB. Results show that the proposed numerical scheme can satisfactorily model the valve operation and the piston movement. Typical results of the gas flow in such a circuit breaker without the presence of an arc (no-load operation) are presented and discussed. In chapter 5 the operation of the ABB breaker under specified arcing current is then simulated for almost a whole arcing period. Results indicate that Lorentz force has a profound effect on the flow field as well as the arc shape. Detailed energy and mass balance calculation is performed for the arcing space and also for the expansion volume, which clearly shows the importance of radiation transfer, convection at different nozzle exits and the change of energy and mass storage at different instants in the arcing process. It is also shown that the pressurisation of the expansion volume is due to the influx of thermal energy, not the mass influx. The predicted arc voltage overally agrees with the test results within 15% for all three cases simulated with different breaker geometry. The predicted pressure at current zero is within 10% of the test results. On the whole the prediction is considered satisfactory in consideration of the approximations that have been introduced in the geometry and radiation model. It has been found that for the auto-expansion circuit breaker the pressure in the arcing space can fluctuate rapidly in the period shortly before the thermal recovery period. Pressure fluctuation with several bars around the current zero period results in a scatter of thermal interruption and dielectric recovery performances. Large pressure variation is therefore not desirable. Optimisation of design parameters is necessary in order to avoid pressure variation and to ensure maximum pressure and lowest temperature possible in the arcing voll!-me. A systematic study of the mechanisms responsible for the pressure fluctuation is therefore carried out in chapter 6. It has been found that the evolution of pressure and temperature fields in the arcing space around current zero depend on the supply rate of gas from the expansion volume and the exhaustion rate at the nozzle exits. Thus, an optimum design is directly linked with the design of the expansion volume and the link channel between the arcing space and the expansion volume. A systematic study of the influence of various design parameters is also carried out to identify the most influencing parameter, which is the dimension of the channel link. Based on the knowledge and understanding derived from this study a new design has been simulated which produces very promising result in smoothing the pressure fluctuation in the arcing space. Pressure and temperature fields at current zero depend on the whole arcing history as well as the contact movement which determines the gas exhaust passage. Arcing processes with different arcing time (altogether three cases with different arcing times) are finally performed to assess the efficiency of the new design. In all cases it has been shown that with the addition of a buffer volume the pressure smoothly changes in the period approaching the final current zero. In summary, the three objectives stated in chapter 1 have all been achieved by the work presented in chapters 2 to 6. Nevertheless, there are still several aspects of the model that need to be improved. This is discussed in the final chapter

Environmental Compatible Circuit Breaker Technologies

Recent research and development in the field of high-current circuit breaker technology are devoted to meeting two challenges: the environmental compatibility and new demands on electrical grids caused by the increasing use of renewable energies. Electric arcs in gases or a vacuum are the key component in the technology at present and will play a key role also in future concepts, e.g., for hybrid and fast switching required for high-voltage direct-current (HVDC) transmission systems. In addition, the replacement of the environmentally harmful SF6 in gas breakers and gas-insulated switchgear is an actual issue. This Special Issue comprises eight peer-reviewed papers, which address recent studies of switching arcs and electrical insulation at high and medium voltage. Three papers consider issues of the replacement of the environmentally harmful SF6 by CO2 in high-voltage gas circuit breakers. One paper deals with fast switching in air with relevance for hybrid fault current limiters and hybrid HVDC interrupters. The other four papers illustrate actual research on vacuum current breakers as an additional option for environmentally compatible switchgear; fundamental studies of the vacuum arc ignition, as well as concepts for the use of vacuum arcs for DC interruption

Salt-gradient Solar Ponds: Summary of US Department of Energy Sponsored Research

The solar pond research program conducted by the United States Department of Energy was discontinued after 1983. This document summarizes the results of the program, reviews the state of the art, and identifies the remaining outstanding issues. Solar ponds is a generic term but, in the context of this report, the term solar pond refers specifically to saltgradient solar pond. Several small research solar ponds have been built and successfully tested. Procedures for filling the pond, maintaining the gradient, adjusting the zone boundaries, and extracting heat were developed. Theories and models were developed and verified. The major remaining unknowns or issues involve the physical behavior of large ponds; i.e., wind mixing of the surface, lateral range or reach of horizontally injected fluids, ground thermal losses, and gradient zone boundary erosion caused by pumping fluid for heat extraction. These issues cannot be scaled and must be studied in a large outdoor solar pond