Relative Air Density Research Articles

Prototipo de aplicativo Android para el dimensionamiento electromecánico de cadenas de aisladores de vidrio bajo norma IEC-60071 Y IEC-60815 (2008)

In this study, a new Android application was developed to help users accurately determine the dimensioning of a string insulator through the analysis of the evaluation of two methods based on IEC-60071 and IEC-60815 (2008) standards. The first method uses equations from IEC-60815-2 (2008), while the second method considers parameters such as relative air density and pressure. To ensure reliability, both methods are evaluated: the first through the creepage factor to determine if the chosen profile is suitable, and the second through lightning and switching critical flashover voltages to avoid insulator flashover. Tests were carried out using data from real projects, and those results were compared with the results obtained from the application. The number of string insulators obtained from the tests was exactly the same as the number obtained from the application, except in two cases. Of the three evaluations, all cases complied satisfactorily with at least two tests.

YÜKSEK GERİLİM LABORATUVARLARI İÇİN IoT TABANLI HAVA İSTASYONU TASARIMI VE UYGULAMASI

This study presents the design and implementation of an internet of things (IoT) based weather station for high voltage laboratories using the Raspberry Pi 4 Model B and two BME680 sensors. The weather station calculates the relative air density and humidity correction coefficients using the temperature, pressure, and relative humidity data obtained from the sensors. The study investigates the effect of the constant and real-time calculation of these coefficients on the measurement of AC, DC and lightning breakdown voltage using spherical electrodes. Measurements were performed within a laboratory setting for a period of 12 hours, and the obtained results were subsequently compared. The findings reveal that the real time calculation of the correction coefficients leads to a reduction in measurement errors. The study also includes the development of a web-based user interface using HTML and CSS, which is hosted on the Raspberry Pi 4 using the Flask web framework. This interface allows users to access the weather station data from any device with a web browser and provides real-time monitoring of the current coefficients, as well as the capability to calculate actual parameters online.

Performance of Regenerative Air Preheater of Pulverized Coal Fired Boilers

Abstract: The air preheater (APH) is the final heat trap in the boiler's flue gas path. Effective pre-combustion coal drying and efficient combustion in the boiler are required for APH to operate efficiently. The effectiveness of heat transfer in APH is significantly influenced by the characteristics of relative humidity and ambient air temperature (AAT). Relative humidity (RH) and air density are also impacted by variations in AAT, which in turn alters the heat capacity of the air. If there is insufficient reserve heat exchange capacity in APH, an increase in AAT will diminish the possibility of waste heat recovery. Additionally, a change in AAT will affect the power consumption of the fans and the leakage through various seals.

Efficiency optimized axial flow compressor stage with a given shape of flow-path

Performance improvement and optimization for Brayton cycle plants include mainly two aspects: one concerns thermodynamic cycle parameters, another concerns component parameters. As one aspect of the power plant optimizations, parameter optimization is an important design practice for performance improvement of axial flow compressor stage (AFCS). Stagnation isentropic efficiency (IEFF) optimization of AFCS is studied preliminarily by using 1-D flow theory. Optimization design model of AFCS with a given shape of flow-path is provided. Five parameters are taken as design variables, including absolute exit and inlet angles of rotor, absolute exit angle of stator, and relative air densities at exit and inlet stations of stator. Energy balance equations for 1-D flow are constraints. Analytical relations about stagnation IEFF and design variables of the AFCS are obtained. Numerical calculations are performed for a constant mean-diameter AFCS. The results illustrate influences of various fixed design parameters on the optimum stagnation IEFF of the AFCS. The results illustrate that optimal stagnation IEFFs with three fixed input parameter combinations of work coefficient and flow coefficient increase 0.78%, 5.15%, and 5.66% than that of reference plan, respectively; optimal stagnation IEFFs increases with increase of work coefficient and decrease of flow coefficient.

The analysis of flutter characteristics based on generalized parameters of eigen modes of vibrations

Flutter numerical analysis of a dynamically scaled model (DSM) of a high aspect ratio wing was performed using experimentally obtained generalized parameters of eigen modes of vibrations. The DSM is made of polymer composite materials and is designed for aeroelastic studies in a high-speed wind tunnel. As a result of the analysis, safe operation conditions (flutter limits) of the DSM were determined. The input data to develop the flutter mathematical model are DSM modal test results, i.e. eigen frequencies, mode shapes, modal damping coefficients, and generalized masses obtained from the experiment. The known methods to determine generalized masses have experimental errors. In this work some of the most practical methods to get generalized masses are used: mechanical loading, quadrature component addition and the complex power method. Errors of the above methods were analyzed, and the most reliable methods were selected for flutter analysis. Comparison was made between the flutter analysis using generalized parameters and a pure theoretical one based on developing the mathematical model from the DSM design specifications. According to the design specifications, the mathematical model utilizes the beam-like schematization of the wing. The analysis was performed for Mach numbers from 0.2 to 0.8 and relative air densities of 0.5, 1, 1.5. Comparison of the two methods showed the difference in critical flutter dynamic pressure no more than 6%, which indicates good prospects of the flutter analysis based on generalized parameters of eigen modes.

The role of low air pressure in the variation of negative corona‐generated space charge in a rod to plane electrode

The corona-generated space charge may vary in different air pressures, and the quantitative law between the corona-generated space charge density and air pressure has never been investigated. This work utilised computational approaches to explore the role of air pressure in the variation of negative corona-generated space charge. A negative fluid model in which the air pressure could be varied was built up to calculate the charged-particle density and electric field under different applied voltages. The continuity equations were solved by flux corrected transport algorithm and the Poisson equation was computed by the successive over relaxation method. The variations of important parameters due to air pressure were analysed. The particles densities of electrons, positive ions and negative ions at standard and low atmosphere pressures were computed, which increased markedly due to the decrease of atmosphere pressure. At fixed applied voltages, the exponential decay law between the maximal values of electron/positive ion densities at the head of the streamer and air pressure could be obtained. The quantitative law between the maximal values of electron/positive ion densities at the head of the streamer and the applied voltage, relative air density was also achieved.

Rugi Daya Dan Energi Akibat Korona Pada Saluran Udara Tegangan Ekstra Tinggi (SUTET) 500 Kv

The use of extra high voltage in electrical power transmission system causing corona. A visual corona phenomenon shown by the appearance of visible light radiation, hissing noise, ozone formation and power losses. The impact of corona affect the environment surrounding the overhead line transmission and power losses in the line. This research discusses power and energy losses due to corona by using quantitative method. Calculations performed by calculating relative air density values, disruptive critical voltages, power losses and corona energy. The research object was taken by extra high voltage overhead line transmission 500kV Tanjung Jati B Power Plant to Ungaran Substation.The result show that corona power losses are 0.41-0.44 kW/mil (0.25-0.27kw/km) per phase, with total 1.25-1.30kW/mil (0.78-0.81k/w/km). corona power losses 107.57-112.08 kW along of line. Average of corona energy losses obtained 2642.67 kWh. The percentage of corona power losses to electrical power supplied is between 0.005% to 0.011%.

Ant-Man and The Wasp: Microscale Respiration and Microfluidic Technology

Insects and other terrestrial arthropods, benefitting from millions of years of evolutionary refinement, manipulate fluids efficiently, including their bodily fluids, air, nectar, and water, at the microscale in their daily lives. Microfluidic technology, though far behind insect fluid handling in terms of performance, is a rapidly developing field, which allows traditional laboratory testing spaces, occupying hundreds of square meters, to be shrunk down to chips occupying less than a square centimetre. These lab-on-a-chip microfluidic devices are positioned to revolutionize fields like exoplanetary composition testing and single cell biology studies, and can provide inexpensive, ubiquitous environmental monitoring and global health testing. Microfluidic technology, in addition, has the potential to bridge the gap between Ant-Man and the Wasp’s human respiratory apparatuses, and the more optimal ones that insects use to breath at the microscale, to help them overcome issues when they shrink in their suits like the “death zone dilemma” and a relative air density similar to that near the peak of Mt. Everest.

Analysis of the three-dimensional hybrid electric fields and the related electrostatic induction effects of 800 kV DC and 500 kV AC parallel transmission lines considering environmental factors

With the great development of ultra high voltage (UHV) transmission technology, there exist some 800kV DC and 500kV AC parallel transmission lines sharing the right of way in China. Due to hybrid electric field induced by 800kV DC and 500kV AC parallel transmission lines, the electromagnetic environment of the parallel lines will become more complex compared to that of either individual line. Furthermore, environmental factors such as relative air humidity, relative air density and wire surface equivalent roughness coefficient will influence hybrid electric field along the long transmission line from west to east China. This paper first establishes the equivalent model of transmission lines, human body and rain drop. Afterwards, the three dimensional electric field and ion flow field below the 800kV DC and 500kV AC parallel transmission lines are calculated by combining the 3-D modified CSM (charge simulation method) and the Deutsch hypothesis respectively. Next, different hybrid electric field distributions are obtained with different environmental factors. Finally, related electrostatic induction effects on human body under the parallel transmission lines are also analyzed. It is concluded that the induced currents on the surface of the human body are within the range of limited values specified by INCIRP with different environmental factors.

An Electro-Geometric Model for Lightning Shielding of Multiple Wind Turbines

Wind turbine blades being struck by lightning is one of the most urgent problems facing wind farms. In order to reduce the probability of lightning accidents on wind farms, this paper presents a new electro-geometric model for multiple turbines. In this new model, based on the physical model of lightning leader development, the striking distance range of the blade tip receptor is calculated, taking into account the influence of the charged particles around the blade. Lightning shielding amongst multiple turbines is provided in combination with the traditional electro-geometric model, and a criterion formula is obtained for mutual shielding for multiple turbines. The influence of environmental factors, such as temperature, atmospheric pressure, air humidity, and altitude, on lightning shielding on large-scale wind farms is also analyzed by studying the lightning shielding distance between wind turbines. The calculation shows that the larger the relative air density and the absolute humidity, and the lower the altitude, and the larger the lightning shielding distance between wind turbines. The method proposed in this paper provides a theoretical basis for the lightning protection on wind farms under different environmental conditions.

Effect of ambient air temperature on the performance of regenerative air preheater of pulverised coal fired boilers

The air preheater (APH) is the last heat trap in flue gas path of boiler. Efficient performance of APH is possible with efficient pre-combustion coal drying and effective combustion in the furnace. The characteristic of ambient air temperature (AAT) has a significant role on the efficiency of heat transfer in APH. The change in AAT in turn changes heat capacity of air that depends on relative humidity (RH) and air density. An increase in AAT will reduce the waste heat recovery opportunity, if sufficient reserve capacity of heat exchange is not available in APH. Besides, change in AAT will have an impact on the power consumption of the fans and leakage through different seals. In this paper, the effect of these factors due to change in AAT is evaluated to assess the performance of regenerative APH with reference to a field study of 135 MWe subcritical steam power plant.

Self-sustained criterion with photoionization for positive dc corona plasmas between coaxial cylinders

The positive dc corona plasmas between coaxial cylinders in air under the application of a self-sustained criterion with photoionization are investigated in this paper. A photon absorption function suitable for cylindrical electrode, which can characterize the total photons within the ionization region, is proposed on the basis of the classic corona onset criteria. Based on the general fluid model with the self-sustained criterion, the role of photoionization in the ionization region is clarified. It is found that the surface electric field keeps constant under a relatively low corona current, while it is slightly weakened with the increase of the corona current. Similar tendencies can be found under different conductor radii and relative air densities. The small change of the surface electric field will become more significant for the electron density distribution as well as the ionization activity under a high corona current, compared with the results under the assumption of a constant surface field. The assumption that the surface electric field remains constant should be corrected with the increase of the corona current when the energetic electrons with a distance from the conductor surface are concerned.

소구경 탄자의 충돌속도 추정방법 제안

This paper proposes a new method to estimate the striking velocity for ballistic limit velocity in MIL-STD-662F. The method from MIL-STD-662F needs relative air density, drag coefficient, form factor, ballistic coefficient for estimating striking velocity. So precedent studies are essential. However, the new method can estimate striking velocity only using measured velocities and distance between the screen and the target. To prove new method, we compared estimation of striking velocity from both the new method and the method from MIL-STD-662F on the basis of datain PRODAS. The new method shows bigger errors in some velocity ranges. But it could still calculate ballistic limit velocity. It also shows smaller errors in most velocity ranges.

선도체 대 평면전극 갭에서 평면전극에 연소화염 존재시 대기의 절연파괴 특성

Breakdown characteristics of air in the vertical arrangement of line conductor and plane electrode in case of combustion flame on the plane electrode are examined by the application of AC. and DC voltages to the gap. In order to investigate the effect of paraffin flame on the breakdown characteristics of air, flashover voltages are measured according to the variation of the gap length and the horizontal distance between the flame and the line conductor. As the result of the experiment, flashover voltages are substantially lowered down to 29.8% in case of the AC voltage, and 16.1% in case of the negative DC voltage, when in the presence of the flame. from 100% when in the absence of flame. <BR> Flashover voltages of air in the range of smaller than 3㎝ at the horizontal distance are increased in the proportion of the gap length and the horizontal distance in case of both AC and negative DC voltages. But before the flashover occurs, the flame is extinguished by such corona wind that is produced from the line conductor when the gap length and the horizontal distance reach to a certain degree. The effect of relative air density and the phenomenon of thermal ionization are analysed as the reduction factors of flashover voltages, due to high temperature of the flame.

Onset conditions for positive direct current corona discharges in air under the action of photoionization

This paper presents a numerical model for the inception of positive dc corona discharges in air near cylindrical anodes, which plays a bridge role between the classic positive corona onset criterion and the photoionization model considering the effective radiation wavelength. The predicted onset voltages agree well with Peek’s experimental data in a wide range of conductor radii and relative air densities. The influence of the collisional quenching of emitting excited states on the surface onset field is significant with low air density or small conductor radius. Within the effective radiation wavelength, numerical expressions for the photon absorption coefficient in air and Townsend’s second coefficient due to photoionization are deduced on the basis of the new model. A different perspective on the classic coefficients is given.

수직배치 구대평판 공기 갭에서 연소화염 존재시의 절연파괴 특성

In this study, breakdown characteristics of a vertical sphere-plane air gap in the presence of combustion flame were examined under the application of a.c. and d.c. high-voltages in order to investigate the effect of flame on the dielectric strength of air. Propane gas is used as the fuel of the flame, and the temperature distribution of air around the flame is measured. The polarity effects for the d.c. voltages and breakdown voltages of air when applied both of a.c. and d.c. voltages were examined in the case of the variation of the gap length and the horizontal distance between the flame and the high-voltage sphere electrode. The influence of relative air density, electrification and shape changes of the flame as factors that affect the breakdown voltages were discussed.

Modeling of Trigger-Wire Corona Effects in Rocket-Triggered Lightning

This paper presents a model for the critical conditions required for a successful launch of rocket-triggered lightning of the classical type under negative cloud. For the first time, the model gives due consideration to the effect of space charge produced by trigger-wire glow-corona on continuous upward leader onset. The model includes the effects of space charge from bush corona resulting in non-uniformity of the ambient field into which the rocket is launched, as well as the effects of rocket speed and ambient relative air density. The paper shows that the effect of trigger-wire glow-corona on continuous upward leader onset is quite substantial, emphasizing the basic difference in this respect between tall static structures and rocket-triggered lightning. The work confirms the importance of two necessary and sufficient criteria for continuous upward leader onset, a global criterion relating to the space potential at the wire-tip height and a local criterion regarding the ambient field aloft. The model has been applied to several previous field experiments characterized by a wide variety of rocket speeds, bush coronas and ambient relative air densities. Comparison between model and experimental results, including the more recent and better instrumented, was found very satisfactory.

Investigation of Lightning Rod Shielding Angle

This paper studies those parameters affecting the shielding angle of the lightning rod (Franklin Rod) above very tall buildings. It was recommended that the shielding angle of the lightning rod is about 45°∼60°. The downward lightning leader is modeled by using discrete line charges to consider the exponential distribution of charges through the downward leader. The voltage condition used by Rizk is used to investigate the inception of the upward lightning leader. Different air conditions (relative air density and air humidity) are considered for more practical simulation. The influences of lightning parameters and lightning rod height on the shielding angle are studied. The results shows that, lightning leader parameters, lightning rod height and ground slope have series effects on the lightning rod shielding angle. Based on the results, a lightning rod shielding angle for shielding design is recommended to decrease the lightning stroke to the lightning rod.

Modeling of Lightning Exposure of Sharp and Blunt Rods

Corona characteristics of lightning rods exposed to ambient fields due to cloud charges prior to negative leader descent are analyzed, taking into account rod slenderness and relative air density. A new formula is introduced to account for the effect such corona on upward connecting leader initiation. This quantifies the tendency of a sharp lightning rod towards self-shielding, which can be detrimental to the protection of a nearby object, particularly if this object is less susceptible to corona formation. The effect of corona due to cloud charge fields on the attractive radius of a solitary rod is also investigated. Based on discharge physics, the characteristics of a non-self shielding air terminal are then defined. Since large electrodes are susceptible to deteriorating corona performance due to protrusions and water drops, preference is given to a corona-free rod with the smallest diameter, under cloud charge fields. For tall rods or rods exposed to high ambient fields, however, the required diameter of a hemispherically capped rod may be impractical. The physical approach described in this paper satisfactorily accounts for the lightning performance of competing sharp and blunt rods in a previous field investigation.

Shielding failure rate calculation by means of downward and upward lightning leader movement models: Effect of environmental conditions

In this paper the effects of environmental conditions on shielding failure rate (SFR) of transmission lines are investigated. The study utilizes a previously published work in which leader progression model for lightning upward and downward leaders are used to calculate the SFR. Taking into account the effects of reduced air density and humidity on the parameters of upward leader model and wind pressure on the movement of lightning leaders and wires, SFR and maximum lightning stroke current causing shielding failure are computed. The electric field in all simulations is calculated by means of charge simulation method. The results of simulation show that the effects of relative air density and height of installation are quite higher than that of the wind pressure and humidity while the humidity has the lowest impact on the SFR of investigated transmission line.