Power system applications of fiber optic sensors

This document is a progress report of work done in 1985 on the Communications and Control for Electric Power Systems Project at the Jet Propulsion Laboratory. These topics are covered: Electric Field Measurement, Fiber Optic Temperature Sensing, and Optical Power transfer. Work was done on the measurement of ac and dc electric fields. A prototype sensor for measuring alternating fields was made using a very simple electroscope approach. An electronic field mill sensor for dc fields was made using a fiber optic readout, so that the entire probe could be operated isolated from ground. There are several instances in which more precise knowledge of the temperature of electrical power apparatus would be useful. This report describes a number of methods whereby the distributed temperature profile can be obtained using a fiber optic sensor. The ability to energize electronics by means of an optical fiber has the advantage that electrical isolation is maintained at low cost. In order to accomplish this, it is necessary to convert the light energy into electrical form by means of photovoltaic cells. JPL has developed an array of PV cells in gallium arsenide specifically for this purpose. This work is described

Power system applications of fiber optics

Power system applications of optical systems, primarily using fiber optics, are reviewed. The first section reviews fibers as components of communication systems. The second section deals with fiber sensors for power systems, reviewing the many ways light sources and fibers can be combined to make measurements. Methods of measuring electric field gradient are discussed. Optical data processing is the subject of the third section, which begins by reviewing some widely different examples and concludes by outlining some potential applications in power systems: fault location in transformers, optical switching for light fired thyristors and fault detection based on the inherent symmetry of most power apparatus. The fourth and final section is concerned with using optical fibers to transmit power to electric equipment in a high voltage situation, potentially replacing expensive high voltage low power transformers. JPL has designed small photodiodes specifically for this purpose, and fabricated and tested several samples. This work is described

Electrostatic Design and Characterization of a 200 keV Photogun and Wien Spin Rotator

High-energy nuclear physics experiments at the Jefferson Lab Continuous Electron Beam Accelerator Facility (CEBAF) require high spin-polarization electron beams produced from strained super-lattice GaAs photocathodes activated to negative electron affinity in a high voltage photogun operating at 130 kV dc. A pair of Wien filter spin rotators in the injector provides precise control of the electron beam polarization at the end station target. An upgrade of the CEBAF injector to better support the upcoming Moller experiment requires increasing the electron beam energy to 200 keV, resulting in better transmission through injector apertures and improved photocathode lifetime. In addition, the energy increase is expected to reduce unwanted helicity correlated intensity and position systematics. These requirements led to the design of a shielding electrode described in this work, which minimizes the electric field at the triple-point junction and linearizes the potential along the insulator, thus reducing the risk of field emission induced insulator arcing. The Wien spin rotator design was modified for increasing the electric field from 1.6 to 2.7 MV/m and the magnetic field from 9.1 to 13 mT. The upgrades required detailed modeling in Solidworks, electrostatic simulations using CST, beam dynamics using GPT, device implementation, and in situ high voltage characterization of the world’s first 200 keV polarized photoelectron gun and compatible Wien filter spin rotator

In Situ Surface Voltage Measurements of Dielectrics Under Electron Beam Irradiation

New instrumentation has been developed for non- contact, in vacuo measurements of the electron beam-induced surface voltage as a function of time and position for non- conductive spacecraft materials in a simulated space environment. The novel compact system uses two movable capacitive sensor electrodes to measure surface charge distributions on samples, using a non-contact method that has little effect on charge dissipation from sample. Design details, calibration and characterization measurements of the system are presented, with \u3c1 V to \u3e30 kV surface voltage range, \u3c0.5 V voltage resolution, and \u3c1.5 mm spatial resolution. Used in conjunction with the capabilities of an existing ultrahigh vacuum electron emission test chamber, the new instrumentation facilitates measurements of charge accumulation, bulk resistivity, effects of charge depletion and accumulation on yield measurements, electron induced electrostatic breakdown potentials, radiation induced conductivity effects, and the radial dispersion of surface voltage. Three types of measurements of surface voltage for polyimide (Kapton HNTM) serve to illustrate the research capabilities of the new system: (i) accumulation using a pulsed electron beam, while periodically measuring the surface voltage; (ii) post charging, as deposited charge dissipated to a grounded substrate; and (iii). the evolution of spatial profile resulting from an incident Gaussian beam. Theoretical models for sample charging and discharge are outlined to predict the time, temperature, and electric field dependence of the sample’s net surface voltage

Lightning protection of floating roof tanks

In tropischen Regionen der Welt können Schwimmdachtanks von Blitzentladungen mit Scheitelwerten von mehr als 200 kA getroffen werden. Ohne geeignete Maßnahmen zur sicheren Ableitung des hochenergetischen Blitzstoßstroms zur Erde kann der Blitzeinschlag zu katastrophalen Tankbränden führen. Ein Schwimmdachtank hat ein Schwimmdach, das den Austritt flüchtiger Dämpfe um mehr als 90% reduziert. Der Spalt zwischen dem Dach und der Tankhülle erzeugt eine elektrische Diskontinuität, an dem bei Blitzeinschlägen eine erhebliche Spannungsdifferenz aufgebaut wird. Etwa 95% aller blitzinduzierten Schwimmdachtankbrände entstehen an diesem Spalt, der mit entzündlichen Dämpfen angereichert ist. Verfügbare Methoden zur Bereitstellung einer direkten elektrischen Verbindung (Potentialausgleich) unter Verwendung von Shunts und Bypass-Kabeln sind unzureichend. Ziel dieser Dissertation ist es, die verschiedenen Auswirkungen des Blitzstroms auf Schwimmdachtanks zu untersuchen und risikoreiche Einschlagstellen zu identifizieren. Abschließend werden Blitzschutzsysteme für Schwimmdachtanks mit konventionellen Ansätzen vorgeschlagen und bewertet. Die Anwendung einer numerischen Simulation zur Ermittlung von Unterschieden in der Wahrscheinlichkeit eines direkten Blitzeinschlages auf die vernetzten Punkte einer modellierten Struktur bietet Vorteile gegenüber der Methode der rollenden Blitzkugel. Das Konzept wurde untersucht sowie Quellen numerischer Fehler und überflüssige Raumpunkte eliminiert, um ein verbessertes dynamisches elektrogeometrisches Modell (IDEGM) mit einer signifikanten Reduzierung der Rechenzeit von über hundert Stunden auf unter dreißig Minuten zu erhalten. Die Wahrscheinlichkeit eines direkten Blitzeinschlages in einen Schwimmdachtank wird durch dessen Höhe und Durchmesser beeinflusst. Für die betrachteten Fälle beträgt die Wahrscheinlichkeit eines direkten Einschlags in den Spaltbereich des Tanks etwa 73% bis 95%, wenn sich das Dach in seiner höchsten Position befindet. Die Simulation der Stahlwand des Tanks beim Blitzeinschlag in MATLAB Simulink zeigte, dass die Spannung am Einschlagpunkt auf dem Tank 55 kV bei einem sehr niedrigen Erdungswiderstand von 0,225 Ω erreichen kann, was ausreicht, um brennbare Dämpfe zu entzünden. Das höchste Risiko eines Tankbrandes besteht, wenn der Blitzstrom auf dem Dach eingespeist wird und dabei die Spannung über dem Luftspalt 211 kV erreicht, selbst bei dem für den Blitzschutz empfohlenen maximalen Erdungswiderstand von 10 Ω. Es werden neun Ausführungen des Blitzschutzsystems vorgeschlagen, bei denen verschiedene Anordnungen von Blitzfangstangen und Blitzfangseilen am Tank verwendet werden. Ihre Fähigkeit, Blitzeinschläge aufzufangen, wurde bewertet. Parallele Fangseile zeigten die beste Wirksamkeit mit einer Einfangeffizienz von 99,93%, wenn sich das Schwimmdach in der höchsten Position befindet.In tropical regions of the world, floating roof tanks can be struck by more than 200 kA lightning peak currents. Without adequate measures to ensure the safe flow of the high energy transient current to the earth, the lightning strike can result in lightning-induced tank fires. A floating roof tank has a floating roof that reduces volatile vapour emissions by more than 90%. The gap separating the tank shell and the roof creates an electrical discontinuity which causes a significant voltage differential when lightning strikes. About 95% of all lightning-induced floating roof tank fires start around this air gap. Available methodologies to provide a direct electrical connection using shunts and bypass cables are inadequate. This dissertation seeks to examine the various impact of the lightning current on the steel sections of the tank and identify high-risk strike points. Ultimately lightning protection systems for floating roof tanks using conventional approaches will be proposed and evaluated. Using a numerical simulation to identify differences in the likelihood of a direct strike to the meshed points on a structure offers a significant advantage instead of the rolling sphere method. The numerical concept is investigated, and sources of numerical errors and superfluous space points were eliminated to create an improved dynamic electro-geometrical model (IDEGM) with a significant reduction in computation time from over one hundred hours to below thirty minutes. The probability of lightning directly striking a floating roof tank is influenced by its height and diameter. For the cases considered, the probability of a direct strike to the air gap region is about 73% to 95% when the roof is at its topmost height. A lightning strike simulation of the tank steel shells in Simulink on MATLAB shows that the voltage at the strike point on the tank can reach 55 kV with a very low grounding resistance of 0.225 Ω, which is sufficient to ignite flammable vapours. The highest risk of a tank fire occurs when the lightning current terminates on the roof with the air gap voltage reaching 211 kV even with the recommended maximum grounding resistance of 10 Ω for lightning protection. Nine lightning protection system models are proposed using various arrangements of air terminals and catenary wires above the tank. Their strike interception capability is evaluated, and parallel catenary wires had the best performance, with an interception efficiency of 99.93% when the roof is at the top

Electrohydrodynamic Driven Airflows for Microelectronics Thermal Management

The increasing demand for effective and compact thermal solutions for the next generation of thin and high-power density consumer electronics is challenging the capability of miniature mechanical systems to meet the required cooling performance. Due to their attractive and unique advantages with no moving parts, design flexibility, small-scale structure, low height profile, silent operation, and effective flow generation, electrohydrodynamic (EHD) air movers are well positioned to become a key emerging cooling technology as alternative to conventional rotary fans. In its general objective, this thesis aims to investigate the benefits and highlight the features of EHD air movers as a thermal management cooling solution in advanced and small-scale microelectronics, supporting all previous efforts in this direction. Due to the strong influence of the geometric parameters of EHD devices on the corona discharge process and the resulting EHD flow, numerical modelling represents a powerful tool to design and optimize EHD devices, especially of complex and small-scale structures, where the capability of experimental investigations is limited or challenging. This study presents an accurate and validated numerical method to solve the coupled equations of electrostatics, charge transport and fluid flow for the two-dimensional (2D) modelling of EHD airflow induced through a wire-to-plane/grid channel configuration, and is the first to develop a three-dimensional model (3D) that couples the EHD flows with conjugate heat transfer modelling. Based on thermal management requirements and from a design perspective, a comprehensive investigation and analysis into the influence of geometric parameters on the efficiency of EHD wire-to-grid blowers is performed and optimal configurations are proposed for a range of heights from 9 to 15 mm. Results reveal that using fine emitter wires is more efficient than thicker ones, and the grounded electrode locations affect significantly the electric field distribution and the blower efficiency. It is also found that using the grid as a further collector increases the blower performance, with higher flow production, lower operating voltage and reduced blower size. Further numerical developments are devoted to optimize the configuration of miniature wire-to-plane EHD blowers for heights up to 10 mm, which is the most preferred geometry for integration in the cooling systems of thin electronic applications. For ranges of fixed operating power and voltage, the efficient optimized electrode gaps are predicted and defined by simple expressions. The influence of channel sidewall on the EHD flow rate and velocity profile are investigated and the results show that the 2D modelling is valid to effectively predict flow rates produced by wide and short EHD blowers compared to that obtained by 3D simulations. A combined EHD air blower that enables a reduction in the level of applied voltage and a control of flow production is developed. Performance comparisons against commercial rotary blowers demonstrate that the optimized miniature EHD blowers are more competitive for cooling miniaturized and extended heated surfaces based on blower size, flow rate with uniform velocity profile, and power consumption. A novel design of an EHD system integrated with compact heat sinks is presented as a thermal management cooling solution for advanced and thin consumer applications. Results of a parametric study demonstrate that the EHD system offers flexible structure design with the ability to reduce the height and increase the width as required, providing a unique feature to be installed in low-profile laptops. Moreover, compared to traditional cooling systems used in the current standard low power laptops, the proposed EHD system offers promising cooling performance with higher thermal design power (TDP), reduced thermal solution volume and lower height profile

A Novel Oil-immersed Medium Frequency Transformer for Offshore HVDC Wind Farms

In this project, a design of an oil type medium frequency transformer for offshore wind farm applications is proposed. The design is intended for applications when series coupling of the output of the DC/DC converters of the wind turbine on their secondary side is done to achieve a cost-effective high voltage solution for collecting energy from offshore wind parks. The focus of the work is on the insulation design of the high voltage side of a medium frequency transformer where the magnetic design constraints should also be satisfied.Above all, a proof of concept is made demonstrating a possible solution for the design of the transformer for such a DC/DC converter unit. The transformer suggested is using oil/paper as insulation medium. Furthermore, characterisation of an eco-friendly biodegradable transformer oil for this type of HVDC transformer application is made. Moreover, an introduction of reliable high frequency characterisation test methods to medium frequency transformer designers is made. In addition, the Non-Linear Maxwell Wagner (NLMW) relations are further developed to form a method for the development of an HVDC MFT transformer. All in all, the DC series concept has been further developed one step closer to pre-commercialization, i.e. from TRL 1 to about 2

High Voltage DC-biased Oil Type Medium Frequency Transformer; A Green Solution for Series DC Wind Park Concept

The electric energy generated by remote offshore wind parks is transported to the consumers using high voltage submarine cables. On the generation site, such transmissions are realized today by collecting the energy produced by several wind turbines in a bulky and expensive transformer placed on a dedicated platform. An alternative solution has been proposed recently, which allows to reduce the installation and maintenance costs by eliminating such a platform. It is suggested to equip each wind turbine in the wind park by an individual DC/DC converter and connect them in series to reach the DC voltage level required for an efficient HVDC energy transportation to the shore. The DC/DC converter is supposed to be a Dual Active Bridge (DAB) converter, which can be made reasonably small to be placed on the wind turbine tower or even in its nacelle. The key element of the converter defining its size and mass is a special transformer, which operates at voltages comprising a high (switching) frequency component superimposed on a high DC offset voltage. DC insulation design of such a transformer and investigation of the effects of a high DC insulation level on the other electromagnetic properties of the transformer is the subject of the present research.In order to verify the concept a prototype of the transformer was built, and its evaluation presented. The unit has been manufactured for the rated power of 50 kW and rated voltages 0.4/5 kV including DC offset of 125 kV and square-shaped oscillations with the frequency of 5 kHz. The magnetic system was made of ferrite material and consisted of 10 shell-type core segments. The magnetic properties have been verified by measuring magnetization and losses at various frequencies in the range 1-10 kHz to cover the operational range of the DAB. The types and dimensions of the windings and their conductors were chosen to minimize the proximity and eddy current effects at higher frequencies. To reduce the size of the transformer and to allow for its efficient cooling, the active part was immersed in oil and cellulose-based materials (paper and pressboard) were used to build the high voltage insulation system. The principles for dimensioning the insulation of the transformer are discussed. The criteria used for selecting insulating distances were based on the consideration of the electric field strength obtained from FEM simulations and using the non-linear Maxwell-Wagner model accounting for local variations of the electric field caused by accumulation of interfacial charges induced by DC stresses. The properties of the materials needed for the calculations were obtained by measuring their dielectric constants and electric conductivities. The methodology used for the measurements conducted for conventional mineral oil and eco-friendly biodegradable transformer oils and, respectively, for oil-impregnated paper/pressboard, is presented. The methodologies used for obtaining parameters of the built transformer prototype needed for its integration in the power electric circuit of the DAB are introduced. A method developed for accurate calculations of the leakage inductance for the shell-type multi core transformers with circular windings is described. Two innovative methods for evaluations of parasitic capacitances based on high frequency equivalent circuits of the transformer are presented. The results of their verifications against performed Frequency Response Analysis measurements and FEM calculations as well as their accuracy are discussed.Thermal performance of the developed transformer prototype is analysed based on the results of computer simulations of heat transfer in its active part under rated load. Identified hot spots and solutions for their elimination are presented.Finally, the expected dimensions, weight, and efficiency of an actual DC/DC converter with the rated parameters corresponding to a 6 MW, 1.8 kV real wind turbine having a 250 kV offset DC voltage are estimated assuming that the developed transformer prototype is scalable. It is shown that the proposed solution allows for installing the full-scale converter having 2.2 Tons in weight and 1.8 m3 in volume on the bottom of the wind turbine’s tower

The ac and dc electric field meters developed for the US Department of Energy

Two space-potential electric field meters developed at the Jet Propulsion Laboratory under the auspices of the U.S. Department of Energy are described. One of the meters was designed to measure dc fields, the other ac fields. Both meters use fiber optics to couple a small measuring probe to a remote readout device, so as to minimize field perturbation due to the presence of the probe. By using coherent detection, it has been possible to produce instruments whose operating range extends from about 10 V/m up to about 2.5 kV/cm, without the need for range switching on the probe. The electrical and mechanical design of both meters are described in detail. Data from laboratory tests are presented, as well as the results of the tests at the National Bureau of Standards and the Electric Power Research Institute's High Voltage Transmission Research Facility

Mechanisms of particle migration in electrostatic precipitators

Electrostatic precipitators are high efficiency gas cleaning devices widely used in industry for removing particulates from process gases. A major factor affecting their performance is particle migration, which is governed by the complex interaction of electrical and hydrodynamic phenomena. A fuller understanding of these fundamental mechanisms is therefore essential to the development of realistic mathematical models. The work described in this thesis concentrates on the fluid-particle interactions in a wire-plate-system. A pilot-scale rig was built using actual components from an industrial precipitator, allowing realistic conditions to be simulated in the laboratory. Hot-wire anemometry and laser-Doppler photon correlation techniques were employed to study the time-averaged velocity field. Several designs of wall strengthener were considered, and in each case the effect on the surrounding flow field was investigated using helium bubble visualisation. The turbulent nature of the fluid was characterised by local dispersion coefficient values and fluctuating velocity components. Alumina test dust in the size range 1-10 pm was used in the precipitator under a variety of operating conditions, and a technique was established for extracting representative dust samples. The samples allowed simultaneous measurement of concentration and size distribution, from which concentration profile development and collection efficiency information was obtained. Two alternative numerical models of the precipitator were developed, both incorporating the results from the fluid flow field experimentation. The first approach was based on the finite difference solution of the convective-diffusion equation, using appropriate boundary conditions. In the second approach, the transport of dust down the precipitator duct was simulated by the step-wise progression of a series of vertical line-sources, whose motion was governed by electrical migration and lateral diffusive spread. The validity of the models was tested by comparison of the predicted concentration profiles with corresponding experimental results