Normal Steady-state Operation Research Articles

Galvanodynamic Electrochemical Impedance Spectroscopy on a Solid Oxide Cell Stack for In-Operando Diagnostics

In this study, we propose a new experimental setup and methodology that can perform in-situ diagnostic of a solid oxide cell stack without interfering with its normal steady state operation. We establish a floating ground galvanodynamic electrochemical impedance spectroscopy measurement setup connected to a 6-cell short stack. The diagnostic setup is electrically connected in parallel to the electronic load of the stack, so that the respective AC and DC current signals overlap. We demonstrate that this methodology is effective in detecting degradation and assessing the state-of-health of a specific cell or stack without disrupting its operation.

STEADY-STATE ANALYSIS ON COOLANT SYSTEM OPERATING OF THE TRIGA2000 USING FUEL PLATE TYPE

The TRIGA2000 is one of the nuclear research reactors in Indonesia. TRIGA reactor fuel element is rod type, studies of the TRIGA reactor using plate type fuel have been carried out. One primary coolant pump is required to overcome the safety factor on the core which uses plate-type fuel. Besides that, changes in the reactor core configuration have an effect on the ability to transfer heat from the core to the coolant. Therefore, it is necessary to analyze the operating parameters of the cooling system including temperature, pressure and flow rate. This operating data is important, which is required by the operator to estimate the reactor coolant condition. The purpose of this paper is to analyze the cooling system parameters under normal steady-state operation where the primary coolant capacity is 50 kg/s and the reactor power is determined to be 1 MW. Calculation of cooling system at normal condition is carried out using the ChemCAD.6.1.4 computer program. This is also required in providing the reactor's Safety Analysis Report (SAR) document. The results show that the TRIGA reactor which uses plate-type fuel elements can be operated safely. However, in case of coolant temperature to the reactor core exceeding the design data (35 o C), it is necessary to be considered against the operational reliability of the cooling system

Experimental detection of an early developed crack in rotor-bearing systems using an AMB

Purpose– The purpose of this paper is to present a method for early crack detection in rotating shafts. A rotor-bearing system, consisting of an elastic rotor mounted on fluid film bearings, is used to detect the presence of the crack at a depth of around 5 percent of shaft radius. The fluid film bearings, the shaft and the crack introduce coupled bending vibrations both in the horizontal and vertical plane. Experimental time series of the rotor composite response under normal steady-state operation are uncoupled, to develop a signal processing procedure able to reveal the presence of the crack.Design/methodology/approach– The variation of the coupling property that a crack (breathing or not) or a cut (always open) introduces into the system and the localization of the coupling in the time domain is a concept proposed as a means to detect transverse surface cracks in rotating shafts. This consideration is combined with the concept of external excitation for the development of an additional crack-sensitive response during system normal operation. Using an external excitation of an active magnetic bearing of specific duration, frequency and amplitude, the method uses this coupling variation during rotation.Findings– The method is simple, quick and effective for early crack detection, being able to detect cracks as shallow as 5 percent of the shaft radius while the system is under normal operation, and can even be applied real-time. Experimental verification uses a simple elastic rotor with a cut mounted on fluid film bearings, with the cut producing similar coupling phenomena as an opened crack. Experimental results are encouraging.Originality/value– The method used is simple, quick and effective for early crack detection, being able to detect cracks as shallow as 5 percent of the shaft radius while the system is under normal operation, and can even be applied real-time.

Large thermal transport phase lagging improves thermoelectric efficiency

A thermoelectric (TE) generator driven by fast pulse heating is theoretically analyzed using the hyperbolic transient heat conduction equation. Results show that heat leaking in the transient TE generator can be reduced due to the lagging behavior of non-Fourier heat conduction. The total energy conversion efficiency of the transient TE generator is found to exceed that of normal steady-state operation when the dimensionless non-Fourier thermal transport relaxation time, scaled by length squared over thermal diffusivity, is larger than one. These findings may emerge as a new way to improve TE efficiency.

Fault Diagnosis of Generation IV Nuclear HTGR Components Using the Enthalpy-Entropy Graph Approach

Fault diagnosis (FD) is an important component in modern nuclear power plant (NPP) supervision to improve safety, reliability, and availability. In this regard, a significant amount of experience has been gained in FD of generation II and III water-cooled nuclear energy systems through active research. However, new energy conversion methodologies as well as advances in reactor and component technology support the study of different FD methods in modern NPPs. This paper presents the application of the enthalpy-entropy (h-s) graph for FD of generation IV nuclear high temperature gas-cooled reactor (HTGR) components. The h-s graph is adapted for fault signature generation by comparing actual operating plant graphs with reference models. Multiple input feature sets (patterns) are generated for the fault classification algorithm based on the error, area, and direction of the fault residuals. The effectiveness of the FD method is demonstrated by classifying 24 non-critical single faults in the main power system of the Pebble Bed Modular Reactor (PBMR) during normal steady state operation as well as load following of the plant. Reference and fault data are calculated for the thermo-hydraulic network by means of a simulation model in Flownex ® Nuclear. The results show that the proposed FD method produces different uncorrelated fault signatures for all the examined fault conditions.

High-Power Modular Multilevel Converters With SiC JFETs

This paper studies the possibility of building a modular multilevel converter (M2C) using silicon carbide (SiC) switches. The main focus is on a theoretical investigation of the conduction losses of such a converter and a comparison to a corresponding converter with silicon-insulated gate bipolar transistors. Both SiC BJTs and JFETs are considered and compared in order to choose the most suitable technology. One of the submodules of a down-scaled 3 kVA prototype M2C is replaced with a submodule with SiC JFETs without antiparallel diodes. It is shown that the diodeless operation is possible with the JFETs conducting in the negative direction, leaving the possibility to use the body diode during the switching transients. Experimental waveforms for the SiC submodule verify the feasibility during normal steady-state operation. The loss estimation shows that a 300 MW M2C for high-voltage direct current transmission would potentially have an efficiency of approximately 99.8% if equipped with future 3.3 kV 1.2 kA SiC JFETs.

Distributed Circuit Modeling of Multilayer Capacitor Parameters Related to the Metal Film Layer

Linkage between the distributed-circuit capacitor model and multi-layer capacitor structures is demonstrated. Capacitor inductance leading to self-resonance in standard metallized polymer capacitors arises from lead and package inductance and can be represented by lumped inductance external to the capacitor modeling in this paper. Distributed internal capacitor inductance is negligible in metallized polymer capacitors for most applications and therefore is not considered in the analysis. Two different distributed-circuit topologies, both of which arise in practice-one by design and the other by degradation-are considered. One has the two connecting electrodes on opposite ends of the capacitor and the other has both input electrodes on the same end. The electrical performance of the two connection topologies is compared using numerical 10-stage lumped element modeling. Cross comparisons are made using diffusion equation modeling for the single-end connection topology. Strong correspondence between results from numerical lumped element distributed approximations and from diffusion equation analysis for the single-end connection is demonstrated up to 100MHz, this inferring similar accuracy for lumped element modeling of the double-end connected capacitor topology. The results show that the two connection topologies exhibit similar behavior up to at least the typical self resonance frequency of the capacitor, except for the cross-dielectric voltage and cross-width power dissipation profiles which are fundamentally different. Voltage drop across the metallic films is shown to be small in normal steady state operation. The contribution of the metallic film to the equivalent series resistance is shown to be constant with frequency up to a frequency where distributed - filtering becomes significant. Beyond this, both equivalent series resistance and capacitance fall with the square root of frequency for the single-end connected capacitor. Similarly, the dissipation factor initially rises in direct proportion to frequency and power dissipated in the metal film increases with the square of frequency. Progressive disconnection of distant metal film with frequency, due to filtering, is shown to be responsible for the changes in these relationships and the parameters of the capacitor.

Attitude stabilization with actuators subject to switching restrictions: an approach via exact relay control methods

On-off thrusters are frequently used as actuators for attitude control. Typically these thrusters are subject to switching constraints. A limit cycle is the normal steady state operation mode of such attitude control systems. This contribution deals with controller design for precision attitude stabilization using actuators whose switching restrictions are explicitly considered. An exact approach is presented using ideas from established relay control methods. The design procedure is illustrated with an attitude controller design to attain a limit cycle with prescribed characteristics

Preliminary results and lessons learned from upgrading the Tore Supra actively cooled plasma facing components (CIEL project)

The design and fabrication of large areas of actively cooled plasma facing components (PFCs) is a major issue for the next generation of tokamaks. Tore Supra is currently the only large fusion device which has implemented actively cooled PFCs from the beginning of operation in 1988, while maintaining continuous development activities to improve their performances and reliability. High heat flux PFCs based on copper alloy heat sink structures have been developed in order to enable a large increase of power extraction capacity. The result is an actively cooled high heat flux ‘finger’ element (capable of removing up to 10 MW/m 2 in normal steady state operation). It has been used first for the RF antennas edge limiters (200 fingers) and then for the toroidal pump limiter (TPL), which is the main part of the Tore Supra upgrade of in-vessel components (CIEL project). The active part of the TPL structure is made of ≈600 actively cooled elements. Problems appeared during series manufacturing of such a large number of high heat flux elements that finally led to the development of a tile attachment repair process in order to allow the achievement of the manufacturing. The whole limiter was installed inside the Tore Supra inner vessel at the beginning of 2002. Very promising first results have been recently obtained (600 MJ of injected and removed power during 3 min 30 s discharge). Monitoring and technical lessons for future realisations from these more-than-10-year developments, in particular for ITER, are discussed.

An explanation of the observed frequency domain behavior of head-disk interface resonances in the proximity recording regime

Magnetic head-disk interfaces (HDI) which are designed so that the mechanical spacing, between the magnetic recording head and spinning disk media, is so small that frequent intermittent contacts occur during normal steady state operation, can be said to be operating in the "proximity" recording regime. Mechanical spacing ("fly height") modulation, with characteristic frequency well above the estimated air bearing resonance frequencies, but well below slider ringing frequencies, has been observed in the proximity recording regime. In this paper, the effect of slider preload change, and the effect of atmospheric pressure change, on the frequency and amplitude of such fly height modulation, as measured using laser Doppler vibrometry, is reported. A simple analytical model was developed to explain the existence of the modulation and its observed dependence on applied gram load.

Transmission Line, Railroad and Pipeline Common Corridor Study

The sharing of common corridors by electric power transmission lines, pipelines and rail-road facilities is becoming more commonplace. However, such corridor sharing can result in undesired coupling of electromagnetic energy from the power lines to the paralleling facilities. The principal concerns are with respect to both personnel safety and equipment operational compatibility. Induced interfering voltages and currents can result from either magnetic or electrostatic induction from the power line circuits. The induction can occur during either the normal steady-state operation of the power system or during a fault. The situations that give rise to problems, as well as the candidate mitigation measures, depend on the susceptibilities, the excitation parameters and the interaction between the electromagnetically coupled components of the common corridor. This paper presents the results of a recently completed study of a utility common corridor in southern Arizona. A detailed analysis of the voltages and currents induced into the pipeline and rail facilities was performed using a computer program developed during the study. Alternate forms of mitigation were investigated to ensure personnel safety and operational compatibility where likely problems were predicted.

Transmission Line, Railroad and Pipeline Common Corridor Study

The sharing of common corridors by electric power transmission lines, pipelines and rail-road facilities is becoming more commonplace. However, such corridor sharing can result in undesired coupling of electromagnetic energy from the power lines to the paralleling facilities. The principal concerns are with respect to both personnel safety and equipment operational compatibility. Induced interfering voltages and currents can result from either magnetic or electrostatic induction from the power line circuits. The induction can occur during either the normal steady-state operation of the power system or during a fault. The situations that give rise to problems, as well as the candidate mitigation measures, depend on the susceptibilities, the excitation parameters and the interaction between the electromagnetically coupled components of the common corridor. This paper presents the results of a recently completed study of a utility common corridor in southern Arizona. A detailed analysis of the voltages and currents induced into the pipeline and rail facilities was performed using a computer program developed during the study. Alternate forms of mitigation were investigated to ensure personnel safety and operational compatibility where likely problems were predicted.

Transit Operating Strategies: Tentative Guidelines

Transit operating strategies (TOS) are designed to address a set of problems arising from a sudden shock to the normal steady state operation of a transit system. The identification and classification of sets of transit operating strategies, the constraints and environment under which a transit operating strategy is implemented, and the class of problems that each TOS can best address are explored. Heuristic implementation guidelines for each identified transit operating strategy are developed, intending to improve the search process in devising control responses. No attempt is made to optimize the operation of a transit system under non steady-state conditions. Rather, the implementation guidelines serve to search and subsequently implement good control responses.

Effect of prime-mover speed governor characteristics on power-system frequency variations and tie-line power swings

In the normal steady-state operation of a power system, proper load division, frequency, and time are maintained by manual or automatic system control, while the transient swings occasioned by load changes are absorbed by the inertias and speed governors of the individual generating units. With improvements in reliability and performance of systems and their interconnections, it is a natural development that further careful attention and study be given to the basic speed governors and their effects on system operation. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1,5,6</sup> It is desirable to determine the requirements which a good governing mechanism should fulfill, and the effects of specific governor and system characteristics on over-all system performance. Moreover, under certain conditions some governors may accentuate rather than reduce the magnitudes of the frequency swings, and it is desirable to know the conditions for which this may occur.

Effect of Prime-Mover Speed Governor Characteristics on Power-System Frequency Variations and Tie-Line Power Swings

In the normal steady-state operation of a power system, proper load division, frequency, and time are maintained by manual or automatic system control, while the transient swings occasioned by load changes are absorbed by the inertias and speed governors of the individual generating units. With improvements in reliability and performance of systems and their interconnections, it is a natural development that further careful attention and study be given to the basic speed governors and their effects on system operation.1,5,6 It is desirable to determine the requirements which a good governing mechanism should fulfill, and the effects of specific governor and system characteristics on over-all system performance. Moreover, under certain conditions some governors may accentuate rather than reduce the magnitudes of the frequency swings, and it is desirable to know the conditions for which this may occur.