Model Validation for Shipboard Power Cables Using Scattering Parameters

Careful analysis of transients in shipboard power systems is important to achieve long life times of the com ponents in future all-electric ships. In order to accomplish results with high accuracy, it ...     

Experimental investigation and numerical simulation in investment casting

An experimental programme to establish shell thermal conductivity and cooling transients in an investment cast part is presented. This showed that shell thermal conductivity is mildly temperature dependent and has a low value, nominally 0.8 Wm^?1 K^?1. The cooling transients in the cast part were measured with good repeatability and were found to be affected significantly by the addition of forced convection, shell temperature on pour and radiation coupling. Good agreement with an adaptive thermal analysis was achieved using a simple far field radiation model as a basis for establishing heat loss. However, this suggested that the translucent nature of the shell also contributed to heat loss directly from the casting surface.     

A relative-risk framework for evaluating transient pathogen intrusion in distribution systems

Hydraulic transients generate significant negative pressures in water systems that may cause intrusion of contaminated water from the environment into the pipe. This paper expands the consideration of transient intrusion events from their purely hydraulic aspects by developing a risk-based framework for comparing the relative risk-reduction achieved by alternative transient-intrusion mitigation strategies. Alternative strategies may be any combination of changes to system operation or surge controls that would reduce the potential for intrusion of contaminants from the soil-groundwater environment surrounding the pipe. A reference groundwater contamination is assumed, and intrusion volumes and time-varying pathogen concentrations are computed respectively using hydraulic transient and water quality models. Risk-based measures are proposed to provide quantitative assessments of the relative reduction in the risk of receptor infection achieved by alternative mitigation strategies.     

Static VAR compensation of a fixed speed stall control wind turbine during start-up

An installed 900 kW fixed speed stall controlled soft-started wind turbine connected to a weak distribution grid was modeled under start-up conditions. Generator and soft-start control and design parameters were not available, so a modeling process independent of this information was developed. Field measured transients were closely reproduced in simulation using a full-order generator model with generic parameters and a thyristor-based graduated interconnection to the grid. A Static VAR Compensator model was then added to the wind turbine model to explore a method of reducing start-up transients. It was found that for the specific transients modeled, a 300 kVAR SVC supplied sufficient reactive power to limit line voltage variations to within 3% of steady state values. Model details and simulation output are presented in this paper.     

Calibration of electrodiffusion friction probes using a voltage-step transient

Voltage-step transient experiments are used to calibrate electrodiffusion (ED) friction probes. The approach is demonstrated on the probes in high-speed rotating impellers. This calibration has shown that shear rates as high as 106s-1 can be measured reliably using 0.5mm Pt working electrodes in ferro/ferricyanide aqueous solutions. The complete transient calibration experiment provides sufficient information about the dynamics of ED friction probes.     

Analysis of transients in a canal network

A generalised formulation of the mathematical model developed for the analysis of transients in a canal network, under subcritical flow, with any realistic combination of control structures and their multiple operations, has been presented. The model accounts for a large variety of control structures such as weirs, gates, notches etc. discharging under different conditions, namely submerged and unsubmerged. A numerical scheme to compute and approximate steady state flow condition as the initial condition has also been presented. The model can handle complex situations that may arise from multiple gate operations. This has been demonstrated with a problem wherein the boundary conditions change from a gate discharge equation to an energy equation and back to a gate discharge equation. In such a situation the wave strikes a fixed gate and leads to large and rapid fluctuations in both discharge and depth. An erratum to this article is available at .     

Comprehensive Power System Stability Improvement with ROCOF Controlled SMES

Abstract

In order to mitigate most power quality issues in renewable power penetrated systems, load frequency control in automatic generation control based power systems and transient stability concerns in any power system, the deviation in frequency at the point of common coupling is chosen as the driving input for SMES active power control (Δf-control). We report a rate of change of frequency (ROCOF) controlled SMES as a resilient damping device to counter exogenous uncertainties in a wind based multi machine system. Primarily, the ROCOF is contingent on the active power mismatch. SMES reference active power command is issued using a genetic algorithm tuned scheme, participating through ROCOF measurement. The non linear action of SMES is realized by controlling the converter firing angles by a smooth four-zone operation, thus determining the voltage applied across the superconducting inductor. While preserving the dynamics of the DC link and supervising the state of charge (SoC) of the inductor, the effectiveness of the aforementioned control strategy is authenticated by performing non-linear simulations in MATLAB/Simulink. In addition, the dominant modes are also tracked and it is found that the percentage increase in aggregate damping ratio is around 133% using the proposed ROCOF-SMES control.     

李家河水库压力输水管道水锤防护分析与研究

水锤防护是长距离压力输水工程安全的关键问题,采用特征线法对李家河水库压力输水系统进行水力过渡过程计算;分析了在相同历时关闭和开启管道末端阀和中间阀的水锤升压降压幅度变化,提出了操作管道中间阀门是水锤防护措施最优方案,为设计提供依据。     

Interaction of HCO-substances with adsorbed oxygen on platinum electrodes: Open-circuit transient reactions of HCOOH and CO

Transients of open-circuit potential are measured for the interaction of HCOOH (in 0.5 M H₂SO₄) with oxygen preadsorbed on a Pt/Pt electrode. A monolayer of O_ads (ML O_ads) in formic acid solutions is removed much more slowly as compared with CO solutions of equal concentrations. Potentiodynamic pulses show that the reduction of ML O_ads proceeds most slowly in the regions of great O_ads coverages (θ_O ≥ 0.8) for HCOOH solutions and at medium coverages in CO solutions. The difference in the behavior of HCOOH and CO is explained by the fact that chemisorption is dissociative for HCOOH and associative for CO. In the region of medium θ_O, E versus τ dependences for both compounds studied are well described by an equation derived for the mechanism of “conjugated reactions” under the assumption that adsorption of HCO-compounds on sites unoccupied by O_ads is the limiting stage.