Maximum Operation Time Research Articles

Discriminatory Protection Analysis of Three-Phase Asynchronous Motors During Power Disturbances

The ride through voltage disturbance of an induction motor (IM) reduces the unscheduled shutdown from processes, and the discriminatory protection allows industries to save time, protect machines and to increase the mean time before breakdown. This paper discusses the analyses of the stability performance of an induction motor under disturbance from voltage sags and short interruptions. The work also addresses the challenge associated with the operation of induction motors of power rating from 3 to 100 kW, during voltage dips, brief interruptions, transient overcurrent, and how to select the induction motors protection for a maximum operating time under such circumstances. The study aims to look for the corrected delay time and peak transient of stator current that protection scheme can handle. It is found that the rising stator current during a voltage disturbance (due to voltage sag and short interruption) can reach the per unit value of stator current up to 18 times, and it is recommended that the delay time should be settled between 100 and 200 msec. Therefore, this study is of great significance to the manufacturing industry where IMs are commonly used as it can avoid damage to the motor.

SLOWPOKE-2 alternative core loading configurations analysis for highly improved reactor performance

A thorough analysis was carried out and is presented here exploring the possibilities for improving the performance of the LEU-fueled SLOWPOKE-2 reactor design, mainly with regard to the fuel pins distribution throughout the core. The chosen performance metric to maximize was the thermal neutron flux at the inner irradiation sites, while the essential constraint was to maintain the same Onset of Nucleate Boiling Ratio (ONBR) at nominal power, as safety criterion. MCNP5 and PLTEMP/ANL codes were used for the neutronics and thermal hydraulics simulations respectively, to analyze the reactor behavior under almost 300 different core configurations or fuel loading patterns. The main proposed configuration, comprising 270 fuel pins and minor modifications to the fuel cage, is predicted to allow a performance improvement of about 75% while maintaining the same safety margins. Additional or alternative, more complex modifications of the reactor for further performance increases, involving changes to the fuel, the annular reflector and the control rod, are also suggested and analyzed in some detail. The basis to reduce or recover safety margin to reach higher power and flux levels, with the potential to at least double the current performance when combined with the suggested modifications, is also briefly examined. Possible effects of the higher reactor power on the reactor operation are considered as well, providing potential modifications to extend the maximum continuous operation time and the period between Be shim adjustments. Overall, this work provides a detailed basis for substantial potential performance improvements for SLOWPOKE-2 reactors that are pending conversion to LEU and those that may need refueling in the future. The work also points out potential performance improvements on MNSR reactors.

Grid Interactive Single-Stage Solar Powered Water Pumping System Utilizing Improved Control Technique

This paper proposes a single-stage grid interactive solar powered switched reluctance motor (SRM) driven water pumping system with an efficient control technique. The control of the proposed system provides the proficient maximum power point technique (MPPT) tracking and motor drive control with bidirectional power flow between the photovoltaic (PV) array and single-phase grid. It has harmonics components elimination, improved dynamic performance, and a dc offset rejection capability compared to other control. A PV feed-forward term is also incorporated in developed control to enhance the dynamic performance of the system and to minimize the size of dc link capacitor with improved MPPT performance. The novel scheme of fundamental switching of SRM drive over its maximum operational time (when the grid is present) makes system efficient and reliable. An improved perturb and observe based MPPT algorithm is used in this system to minimize the undesirable losses in a PV array especially under varying insolation levels. The proposed control is tested on a developed prototype and its suitability is authenticated through simulated and test results under various conditions.

Motion Cost Characterisation of an Omnidirectional WMR on Uneven Terrains

Abstract Electrically powered robots are seeing increased adoption for field robotics applications. These applications typically require the platforms be deployed for extended periods, or traverse large distances. Power modelling therefore becomes important, as knowing the energy costs of operation is necessary for the estimation of maximum range and operating time, and the generation of energy-efficient plans. In this paper, we present a physics-based power model for the Swagbot platform--an omnidirectional electric field robot--which can be calibrated from a combination of GPS and proprioceptive data gathered throughout the course of normal operations. This model is then experimentally verified via endurance testing performed on cattle properties featuring uneven terrain. The model was demonstrated to predict the energy consumption for a pasture survey and a weed detection task to within 5% of the measured value.

Protection of MV Closed-Loop Distribution Networks With Bi-Directional Overcurrent Relays and GOOSE Communications

This paper proposes measures to improve the protection of MV distribution networks operating with feeders in a closed-loop arrangement. Bi-directional overcurrent relays (OCRs) are discussed, the selectivity of which is achieved through the timing coordination of their operation. The classic approach is formulated as a minimization of the operating times of all the OCRs. The proposed approach enhances the selectivity by considering the maximum operating time of substation OCRs and the unwanted trips of in-loop OCRs. Moreover, the sensitivity is also increased by introducing an objective function that minimizes the pickup-current settings of all the OCRs together with their operating times. Furthermore, to fulfill the demanding requirements for operating times, variable penalties are introduced. Thus, the optimization procedure is forced towards the region with viable solutions for the optimization problem. Two variants of self-adaptive differential evolution have been used that both show better convergence when compared to the classic differential evolution. Moreover, ten mutation strategies were tested, where “rand/1/bin” showed the best results. A comparison with other methods for timing coordination shows that the proposed optimization results in a comparable value for the OCRs’ operating times. In order to further reduce the operating times, GOOSE communications between the OCRs are adopted. The proposed measures for improved protection operation are fully confirmed through dynamic simulations of the faults in the discussed 20-kV network. Moreover, the proposed protection design is already implemented and permanently operates in a 20-kV network with more than 5000 customers, whereas the field results show selective and reliable protection operation.

Membrane module for pilot scale oxygen production

An oxygen transport membrane module capable of total 596 Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) membranes was constructed and tested under various capacities. The module is designed to operate with up to 20 bar feed pressure and a vacuum on the permeate side. The separation performance was tested with of up to 96 membranes tubes. A maximum oxygen purity of 98.9% was obtained and a maximum oxygen flux of 2.8 ml cm−2 min−1 was measured under a feed pressure of 10 bar. The maximum permeate oxygen flow rate achieved was 22 l min−1. The performance is lower than expected, for which an inhomogeneous module temperature and suboptimal flow distribution can be accounted for, as CFD simulations show. A lot of membrane breakages occurred during operation. Some reasons for that could be identified and the module could be optimized throughout the 2 years of testing. Within that time, three long term tests were performed and a maximum continuous operational time of 1800 h was achieved.

MITRAL VALVE REPLACEMENT ON BEATING HEART;

Introduction: Cardiac reperfusion injury is a well-described complication occurringafter ischemia or following cardioplegic arrest. The primary aim of this study was to evaluateand compare safety of Mitral valve replacement on beating heart without using cross clampwith the conventional Mitral valve replacement. Material and methods: It was a retrospectiveobservational study for study duration from 2012-2014. A total of 50 patients were randomlyselected and were divided in 2 groups, 25 patients in each group. This study was conductedat the Department of Cardiovascular Surgery of Choudhry Pervaiz Elahi Institute of Cardiology,Multan. We divided the patients in two groups. All operations were carried out by team led bya consultant surgeon in our institution. Results: Our patients had the age range from 12 to 65years (Mean ages=32.5 years ± 13.9000) the mostly this study included males 60 %. The studyincluded Group A and Group B (beating heart versus conventional heart surgery) both groupscontained randomized controlled patients with purposeful sampling. Minimum operative time100 minutes or maximum operative time 160 minutes (Mean 195± 95.75) The P value remainednon significant that P <0.001. The CPB time was 22 to 388 minutes (104.8 ± 97.4. Cross Clamptime, ICU stay intubation time, drainage, inotrope remained almost same in both groups. With P<0.001 Outcome variables of the patients. Discussion: The hazards of cardiopulmonary bypassand Cardioplegia are well known. Various studies have demonstrated decreased accumulationof extra cellular fluid, diminished lactate production and greater preservation of high energystores when a strategy of myocardial protection simultaneous antegrade/ retrograde continousnormothermic, normokalemic blood perfusion was used. These findings were the basis forusing beating heart technique for mitral valve replacement, Aortic cross-clamping, Cardioplegia,and reperfusion injury leads to myocardial ischemia and is a critical issue in mitral valve surgerydespite novel approaches to myocardial protection. Myocardial edema induced by the lack ofmyocardial contractions and impaired lymphatic flow due to Cardioplegia in the heart remainingin diastole is another cause of myocardial dysfunction. Conclusions: Outcomes obtained usingthis strategy of myocardial protection seem to compare favorably to those of historical series inwhich conventional myocardial protection with cardioplegic arrest were used.

Stochastic behavior of parallel system with expert repair and maintenance

This paper examines the effect of preventive maintenance and repair done by different repairpersons on the system performance. By means of semi-Markov process and regenerative point technique, the researcher has developed a stochastic model of two unit parallel system. Both units are identical in nature. A usual repairperson visits the system to conduct preventive maintenance at the completion of maximum operation time and repair at the failure stage of the unit. At the elapse of the pre-definite time (called maximum repair time), the usual repairperson inspects the failed unit to examine the feasibility of further repair by the expert repairperson; otherwise that unit will be replaced by a new one with some replacement time. The unit may work as good as new after getting maintenance, repair and replacement as well. The switch devices are considered as perfect. Various measures of system usefulness such as MTSF, availability and profit have been derived to depict the usefulness of expert repair facility.

Operational Time and Melt Fraction Based Optimization of a Phase Change Material Longitudinal Fin Heat Sink

Abstract In the present study, the numerical investigation has been performed for a phase change material (PCM)-based longitudinal fin heat sink. The fins are taken as an integral part of the heat sink and are made up of aluminum. The PCM considered in the study is RT44HC. Heat is transferred to the heat sink through its horizontal base. In order to simulate the melting behavior of the PCM, volume of fluid model has been used. To attain the best configuration with optimum operational time, Taguchi method has been used followed by analysis of melt fraction and maximum base temperature. The optimized heat sink configuration with maximum operational time has been obtained at the critical temperatures of 54.8 °C, 63 °C, and 72.6 °C.

Reliability Modeling and Analysis of a Parallel Unit System with Priority to Repair over Replacement Subject to Maximum Operation and Repair Times

Reliability Modeling and Analysis of a Parallel Unit System with Priority to Repair over Replacement Subject to Maximum Operation and Repair Times

Development and Characterization of an Ecological Hydrogen Stove

In this work we developed and evaluated an ecological stove for food cooking, using hydrogen as the fuel. The operation of the device consists mainly of a renewable energy source, such as a photovoltaic system, which produces the electricity needed to power a bipolar alkaline electrolyzer from 1 kW to 1.9 kW, consisting of 85 stainless steel electrodes, which generates hydrogen for combustion in the cooking system. The prototype evaluation consisted of two main stages. In the first phase the operating parameters of the electrolyzer were obtained, achieving an efficiency of 60 to 77%, gas production from 3 to 6 L / min, with a maximum operating time of 395 minutes. The second phase focused on the cooking system, where the thermal efficiency of the device was determined, as 61.5%.

Profit analysis of a computer system with preventive maintenance and priority subject to maximum operation and repair times

The aim of the present study is to carry out the profit analysis of a computer system by considering the concept of priority to preventive maintenance over different hardware and software repair activities. For this purpose, three stochastic models have been developed under different priority policies. A single repair facility is available to perform all repair activities. The hardware unit undergoes replacement after a pre-specific maximum repair time. The repairman performs the preventive maintenance of the whole system after a pre-fixed maximum operation time. All time-dependent failure rates follow exponential distribution, while the repair rates follow arbitrary distribution. Switch devices, repairs and preventive maintenance are perfect. All random variables are statistically independent. Semi-Markov process and regenerative point technique were used to derive the necessary system effectiveness measure to evaluate the profit function of all the three models. To highlight the importance of the study, graphs for profit difference between models have been depicted for a particular set of values of various parameters with respect to preventive maintenance.

Operation Results and Utility of Dynamic Pricing Response Control-Applied VRF System in Summer Season

Dynamic pricing refers to a system in which a tariff varies, according to a level of charging and applied time depending on time change. The power billing system used in the Korean Electric Power Corporation (KEPCO) is based on time of use (TOU) pricing, which is one of the dynamic pricing systems. This paper aimed to determine the operational results of a variable refrigerant flow system, to which a new control algorithm was applied, in order to respond to dynamic pricing, in summer and the utility of the new control. To do this, real measured data was acquired from a VRF system installed in a building for educational purposes, where dynamic pricing was applied for about 100 days during summer time. At the maximum load operation time period in TOU, the new control minimized operation within the indoor comfort range, an increase in refrigerant evaporation temperature in the indoor unit and the number of revolutions in a compressor in the outdoor unit was limited. As a result, power usage was decreased by 11%, and the operational cost by 14.6%. Furthermore, measurement results using the Predicted Mean Vote (PMV) model, that represented satisfaction of thermal environment, showed that 82.8% to 90.4% of the occupants of the building were satisfied during operation when the new control was applied.

Laparoscopic Cholecystectomy in Patients with Emphysematous and Gangrenous Cholecystitis: An Experience at Khwaja Yunus Ali Medical College & Hospital, Enayetpur, Sirajgonj.

Objective- To look for the feasibility and safety of laparoscopic cholecystectomy in patients with emphysematous and gangrenous cholecystitis.Back ground- Emphysematous and gangrenous cholecystitis are severe form of acute cholecystitis. They are considered as contraindication of laparoscopic cholecystectomy due to peri operative life threatening complications, surgical technical difficulties, frequent conversion to open procedure. This study describe our experience in terms of feasibility and safety with laparoscopic cholecystectomy in patients with emphysematous and gangrenous cholecystitis.Materials and methods- From January 2012 to December 2014,total 37 patients with clinical diagnosis of severe acute cholecystitis under went laparoscopic cholecystectomy within 72 hours of admission. Operative findings and histopathological reports were used to identify patients of emphysematous and gangrenous cholecystitis.Results- 35(94.59%)among 37 patient's laparoscopic cholecystectomy were performed successfully.29 case were emphysematous and 8 cases were gangrenous cholecystitis. Two patient's laparoscopic procedure were converted to open procedure due to various operative difficulties, of which the most common was distorted calot's triangle. Maximum operating time was up to 130 minutes(one case),Post operative major complications occurred in 2 cases(5.40%).maximum patients were discharged by 48 to72 hours. There was no mortality.Conclusion- laparoscopic cholecystectomy is feasible and safe in emphysematous and gangrenous cholecystitis. However the experience of the surgeon and his patience during surgery play key role in over all out come. Based on our experience we recommend an early laparoscopic cholecystectomy for these group of patients, provided expertise & gadgets are available.KYAMC Journal Vol. 5, No.-2, Jan 2015, Page 519-523

ВЛИЯНИЕ ПЫЛЕВОЙ ЭРОЗИИ НА ГАЗОДИНАМИЧЕСКИЕ ХАРАКТЕРИСТИКИ ОСЕВОГО КОМПРЕССОРА ГТД

The results of flow simulation of an axial multi-stage compressor of a gas turbine engine are presented. The relation between the main gas-dynamic characteristics of the compressor and operating time in dusty atmosphere are established. The estimation of the maximum operating time of the engine in terms of loss of the gas-dynamic stability of the compressor is performed.

Mechanisms and Application for Hydraulic Pulsed Cavitating Jet Generator

To improve the rate of penetration (ROP) further, based on analysis of the jet modulating mechanism, a new drilling tool is designed which couples the advantages of both pulsed jet and cavitating jet. When drilling fluid flows through the tool in drilling process, the fluid is modulated to pulsed and cavitating jet by impellers and in self-resonant chamber. Thus, pulsed cavitating jet is formed at the outlet of the bit nozzle. Because of jet pulsation, cavitating erosion and local negative pressure effect, bottom cuttings cleaning efficiency is enhanced and the ROP is improved. The hydraulic pulsed cavitating jet generator has been applied in 8 oil fields and more than 100 wells in China. The results indicated that the maximum density of test drilling fluid was 1.70 g/cm 3 , the maximum test well depth was 6,162 m. The generator could work over 230 h, and the maximum operation time was above 520 h. As the result, the average ROP had been increased by 10.1% to 104.4%. The generator has the characteristics of simple structure and long operation time, and has a well adaptability to the existing drilling equipments, technological parameters, which provides a safe and efficient new drilling technology for deep well.

Extending the maximum operation time of the MNSR reactor

An effective modification to extend the maximum operation time of the Miniature Neutron Source Reactor (MNSR) to enhance the utilization of the reactor has been tested using the MCNP4C code. This modification consisted of inserting manually in each of the reactor inner irradiation tube a chain of three polyethylene-connected containers filled of water. The total height of the chain was 11.5cm. The replacement of the actual cadmium absorber with B10 absorber was needed as well. The rest of the core structure materials and dimensions remained unchanged. A 3-D neutronic model with the new modifications was developed to compare the neutronic parameters of the old and modified cores. The results of the old and modified core excess reactivities (ρex) were: 3.954, 6.241 mk respectively. The maximum reactor operation times were: 428, 1025min and the safety reactivity factors were: 1.654 and 1.595 respectively. Therefore, a 139% increase in the maximum reactor operation time was noticed for the modified core. This increase enhanced the utilization of the MNSR reactor to conduct a long time irradiation of the unknown samples using the NAA technique and increase the amount of radioisotope production in the reactor.

Feasibility of reduced port surgery applying Higuchi's transverse incision.

Objective:Higuchi’s transverse incision is made at a lower position than the Pfannenstiel transverse incision and is superior in terms of cosmetic outcomes. The purpose of this study was to examine the safety and efficacy of novel forms of reduced port surgery for ovarian cysts and uterine fibroids applying Higuchi’s transverse incision.Methods:In 33 patients with ovarian cysts who underwent low-position single-incision laparoscopic surgery (L-SILS)-modified single-port laparoscopy placed in the 2–3-cm Higuchi’s incision above the pubis, patient’s characteristics and perioperative outcomes were compared with those of patients who underwent multiport laparoscopy (n = 53). In addition, 18 patients with uterine fibroids who underwent dual-port laparoscopically assisted myomectomy without using power morcellators and conventional four-port laparoscopically assisted myomectomy were investigated.Results:There were no significant differences between L-SILS and multiport laparoscopy in tumor diameter, bleeding, hospital stay, or postoperative pain. However, the L-SILS group demonstrated significantly shorter operative and pneumoperitoneum times (p < 0.01 and p < 0.01). In comparison with cases of uterine fibroids, no significant differences were found in maximum fibroid diameter, operative time, pneumoperitoneum time, or bleeding. However, the dual-port laparoscopically assisted myomectomy group demonstrated a significantly shorter length of hospital stay than the conventional laparoscopically assisted myomectomy group (p < 0.05).Conclusion:We reported novel forms of reduced port surgery applying Higuchi’s transverse incision. It was suggested that these procedures are relatively simple, but ensure the same safety and efficacy as conventional methods. We intend to increase the number of cases and examine safety, efficacy, and patient satisfaction for these procedures.

Plasma-on-chip device for stable irradiation of cells cultured in media with a low-temperature atmospheric pressure plasma

We have developed a micro electromechanical systems (MEMS) device which enables plasma treatment for cells cultured in media. The device, referred to as the plasma-on-chip, comprises microwells and microplasma sources fabricated together in a single chip. The microwells have through-holes between the microwells and microplasma sources. Each microplasma source is located on the backside of each microwells. The reactive components generated by the microplasma sources pass through the through-holes and reach cells cultured in the microwells. In this study, a plasma-on-chip device was modified for a stable plasma treatment. The use of a dielectric barrier discharge (DBD) technique allowed a stable plasma treatment up to 3 min. The plasma-on-chip with the original electrode configuration typically had the maximum stable operation time of around 1 min. Spectral analysis of the plasma identified reactive species such as O and OH radicals that can affect the activity of cells. Plasma treatment was successfully performed on yeast (Saccharomyces cerevisiae) and green algae (Chlorella) cells. While no apparent change was observed with yeast, the treatment degraded the activity of the Chlorella cells and decreased their fluorescence. The device has the potential to help understand interactions between plasma and cells.

Reliability measure of an integrated H/W and S/W system with redundancy and preventive maintenance

The purpose of the study is to evaluate the reliability measures of an integrated $\mathrm{h} / \mathrm{w}$ and $\mathrm{s} / \mathrm{w}$ system with the concepts of redundancy and preventive maintenance. A stochastic model is developed considering two-identical units of the system- one unit is initially operative and other is in cold standby. In each unit $\mathrm{h} / \mathrm{w}$ and s/w work together and may fail independently from normal mode. There is a single server who visits the system immediately to $\mathrm{h} / \mathrm{w}$ repair and $\mathrm{s} / \mathrm{w}$ up-gradation. The preventive maintenance of the system (unit) is conducted by the server after a maximum operation time. The failure time of $\mathrm{h} / \mathrm{w}$ and $\mathrm{s} / \mathrm{w}$ follows negative exponential distribution while the distributions of preventive maintenance, $\mathrm{h} / \mathrm{w}$ repair and $\mathrm{s} / \mathrm{w}$ up-gradation times are taken as arbitrary. The semi-Markov process and regenerative point technique is adopted to derive expressions for various measures of system effectiveness. The behaviour of some important reliability measures has been observed graphically giving particular values to various costs and parameters.