This document presents experimental research on streamer propagation and breakdown in synthetic ester, natural ester, and mineral oil liquids with pressboard interfaces under lightning impulse voltages. Tests were conducted using a point-plane electrode system with pressboard placed parallel to the electric field. Results show that:
1) Streamers on ester/pressboard interfaces propagate further than on mineral oil/pressboard interfaces at the same voltage levels.
2) Introducing parallel pressboard does not influence streamer stopping length or weaken breakdown voltage up to gap distances of 75mm under both polarities.
3) Presence of parallel pressboard reduces acceleration voltage in mineral oil but has little influence on esters under positive polarity
Fixed span three-point flexural test attachment comprises a base unit with two support contact points and one upper point of contact.
Web: www.TiniusOlsen.com
Contact Us: info@TiniusOlsen.com
It is a motorized, mechanical unit. The speed is adjusted so that the load increase on the specimen is between 4 to 6 kg/sec. A flexure test attachment for keeping the object in position is also supplied. This consists of two rollers 10mm. diameter and spaced 100mm apart, and a third roller of the same diameter equidistant from the first two and for transmitting the applied load to the opposite face of the prism.
The document describes a procedure to determine the flexural strength or modulus of rupture of concrete through third-point loading tests. Steel molds are used to cast concrete prism specimens of either 100x100x500mm or 150x150x700mm size, depending on the maximum aggregate size. The specimens are loaded in a testing machine with rollers spaced at either 200mm or 133mm until failure. The maximum load at failure is then used to calculate the modulus of rupture according to one of two equations depending on the distance between the line of fracture and the near support.
The document summarizes a study that measured and compared the flexural strength of 10 veneering ceramics for zirconia frameworks and 3 veneering ceramics for metal-ceramic restorations. Three types of flexural strength tests were used: three-point flexure, four-point flexure, and biaxial flexure. For the zirconia ceramics, three-point flexure strengths were similar without differences, four-point flexure identified 5 strength groups, and biaxial flexure found 3 groups. One metal-ceramic ceramic had significantly higher strengths than all others. Four-point flexure showed the greatest discrimination between materials. In general,
This document summarizes three common concrete tests: compression, split tension, and flexure strength. The compression test uses cylindrical specimens to determine the compressive strength of concrete, which typically ranges from 21 to 34 MPa. The split tension test measures tensile strength by applying a compressive load along the cylinder's diameter until failure, and the flexure strength test uses a three-point loading apparatus on beam specimens to calculate the modulus of rupture. Both the split tension and flexure strength tests help evaluate properties important for concrete pavements and structures.
This document describes procedures for direct shear testing to determine a material's shear strength. Direct shear testing aims to simulate uniform shear stress across a specimen's cross-section by applying shear forces over small lengths to minimize bending. There are two types of direct shear tests: single shear tests shear across a single surface, while double shear tests shear across two surfaces. The test procedure involves fixing a cylindrical specimen in a shear tool and applying a compressive or tensile load until fracture, then calculating the shear strength from the maximum load and specimen's cross-sectional area.
The document summarizes a summer training report on the characterization of 8 mole% yttria stabilized zirconia obtained from different sources. The objectives were to characterize and compare YSZ powders from ISRO, IRE and TOSOH, and to optimize sintering conditions to achieve high density pellets suitable for use as a solid oxide fuel cell electrolyte. Characterization techniques included tap density measurement, BET surface area analysis, X-ray diffraction for phase analysis, particle size distribution analysis, and density measurement of sintered pellets.
This document discusses magnetorheological abrasive flow finishing (MRAFF), a process that uses a magnetorheological polishing fluid to precisely control finishing forces and achieve a final surface finish. An experimental setup was designed to study the process, consisting of MR polishing fluid cylinders, hydraulic actuators, an electromagnet, and workpiece fixture. Experiments showed no surface roughness change at zero magnetic field but improved surface finish at higher fields, as the MR fluid's viscosity changes with applied field strength. The MRAFF process involves extruding the MR fluid through the workpiece under a magnetic field, where abrasives held by iron chains rub peaks and shear material in a controllable way set by the field strength.
Fixed span three-point flexural test attachment comprises a base unit with two support contact points and one upper point of contact.
Web: www.TiniusOlsen.com
Contact Us: info@TiniusOlsen.com
It is a motorized, mechanical unit. The speed is adjusted so that the load increase on the specimen is between 4 to 6 kg/sec. A flexure test attachment for keeping the object in position is also supplied. This consists of two rollers 10mm. diameter and spaced 100mm apart, and a third roller of the same diameter equidistant from the first two and for transmitting the applied load to the opposite face of the prism.
The document describes a procedure to determine the flexural strength or modulus of rupture of concrete through third-point loading tests. Steel molds are used to cast concrete prism specimens of either 100x100x500mm or 150x150x700mm size, depending on the maximum aggregate size. The specimens are loaded in a testing machine with rollers spaced at either 200mm or 133mm until failure. The maximum load at failure is then used to calculate the modulus of rupture according to one of two equations depending on the distance between the line of fracture and the near support.
The document summarizes a study that measured and compared the flexural strength of 10 veneering ceramics for zirconia frameworks and 3 veneering ceramics for metal-ceramic restorations. Three types of flexural strength tests were used: three-point flexure, four-point flexure, and biaxial flexure. For the zirconia ceramics, three-point flexure strengths were similar without differences, four-point flexure identified 5 strength groups, and biaxial flexure found 3 groups. One metal-ceramic ceramic had significantly higher strengths than all others. Four-point flexure showed the greatest discrimination between materials. In general,
This document summarizes three common concrete tests: compression, split tension, and flexure strength. The compression test uses cylindrical specimens to determine the compressive strength of concrete, which typically ranges from 21 to 34 MPa. The split tension test measures tensile strength by applying a compressive load along the cylinder's diameter until failure, and the flexure strength test uses a three-point loading apparatus on beam specimens to calculate the modulus of rupture. Both the split tension and flexure strength tests help evaluate properties important for concrete pavements and structures.
This document describes procedures for direct shear testing to determine a material's shear strength. Direct shear testing aims to simulate uniform shear stress across a specimen's cross-section by applying shear forces over small lengths to minimize bending. There are two types of direct shear tests: single shear tests shear across a single surface, while double shear tests shear across two surfaces. The test procedure involves fixing a cylindrical specimen in a shear tool and applying a compressive or tensile load until fracture, then calculating the shear strength from the maximum load and specimen's cross-sectional area.
The document summarizes a summer training report on the characterization of 8 mole% yttria stabilized zirconia obtained from different sources. The objectives were to characterize and compare YSZ powders from ISRO, IRE and TOSOH, and to optimize sintering conditions to achieve high density pellets suitable for use as a solid oxide fuel cell electrolyte. Characterization techniques included tap density measurement, BET surface area analysis, X-ray diffraction for phase analysis, particle size distribution analysis, and density measurement of sintered pellets.
This document discusses magnetorheological abrasive flow finishing (MRAFF), a process that uses a magnetorheological polishing fluid to precisely control finishing forces and achieve a final surface finish. An experimental setup was designed to study the process, consisting of MR polishing fluid cylinders, hydraulic actuators, an electromagnet, and workpiece fixture. Experiments showed no surface roughness change at zero magnetic field but improved surface finish at higher fields, as the MR fluid's viscosity changes with applied field strength. The MRAFF process involves extruding the MR fluid through the workpiece under a magnetic field, where abrasives held by iron chains rub peaks and shear material in a controllable way set by the field strength.
This document describes the design and construction of a concentric cylinder viscometer that allows for highly accurate viscosity measurements at extremely low shear stresses. The viscometer uses a single rotating cylinder (rotor) inside a fixed outer cylinder (stator) and can measure viscosities with shear stresses as low as 0.003-0.0008 dynes/cm2. Experimental results show the viscometer was able to detect a phase transition in solutions of poly-(butylisocyanate) in carbon tetrachloride as temperature was varied.
This document summarizes the ultrasonic test method for determining properties of concrete. It discusses using PUNDIT machines to transmit ultrasonic pulses through concrete and measure the transit time. Factors that affect pulse velocity like frequency, path length, and aggregate size are covered. The document outlines how ultrasonic testing can be used to determine uniformity, detect defects, measure changes over time, and estimate modulus of elasticity and Poisson's ratio of concrete. Corrections for the presence of reinforcing steel are also provided.
Impact strength refers to a concrete's ability to resist sudden shock or load. It is important for applications with potential impact loads. There is no direct relationship between impact and compressive strength. Impact strength depends on factors like the aggregate type, size, and roughness, as well as the concrete's flexural strength and storage conditions. Non-destructive tests like the Schmidt hammer and ultrasonic pulse velocity test can provide indications of a concrete's properties, including compressive strength. The Schmidt hammer measures surface hardness while ultrasonic pulse velocity relies on sound waves to determine properties related to density and elasticity.
ESA Module 5 Part-A ME832. by Dr. Mohammed ImranMohammed Imran
The document discusses the brittle coating technique for experimental stress analysis. Some key points:
- Brittle coating involves applying a thin brittle resin or ceramic coating to a specimen. Under stress, cracks in the coating indicate tensile stress regions in the specimen.
- Coating stresses can be determined from specimen stresses using equations that account for properties like modulus and Poisson's ratio.
- Mohr's failure theory is used to predict coating failure, with different crack patterns depending on the principal stresses.
- Examples are given of calculating coating and specimen stresses for different loading conditions.
DYNAMIC RESPONSE RESEARCH OF U SHAPED PIPE WITH VISCOELASTIC DAMPINGVarakala Netha
1) The document analyzes the dynamic response of a U-shaped pipe with a viscoelastic damping layer to reduce vibration.
2) Finite element modeling is used to simulate the pipe with damping layer, accounting for cross-section deformation.
3) Experimental tests validate that the damping layer effectively reduces pipe vibration response by up to 79%, with positioning of the layer more influential than width.
Centrifugation uses centrifugal force to separate mixtures based on density, with denser components moving outward and lighter components staying nearer the center; there are three main types - low-speed for pelleting coarse particles, high-speed for organelles/proteins, and ultracentrifuges which attain very high speeds and are used for lipoprotein separation and analytical measurements due to their cooling systems. Centrifugation has many applications from separating blood components to producing skim milk.
Sedimentation for determining molecular weight of macromoleculesShubhangiSuri1
Process of sedimentation with mechanism of action and mathematical derivations, different methods for separation of macromolecules by sedimentation, viscometry vs sedimentation
The document discusses brittle coating methods for experimental stress analysis. Brittle coatings crack under tensile stresses, allowing stresses in specimens to be determined. Key points:
- A thin brittle coating is applied to the specimen surface. As the specimen is loaded, strains are transmitted to the coating, causing cracks perpendicular to maximum tensile stresses.
- Coating crack patterns indicate stress directions. Multiple crack patterns can form under different stress conditions.
- Refrigeration and load relaxation techniques can induce cracks in low-stress regions.
- Fine coating cracks are detected using oblique light or Statiflux particle methods.
This document provides the standard test method for determining the splitting tensile strength of cylindrical concrete specimens. It describes the procedure which involves applying a diametral compressive force along the length of a concrete cylinder at a controlled rate until failure. The maximum load sustained is used to calculate the splitting tensile strength in psi. Proper specimen preparation, loading rate, and calculations are specified to provide consistent results.
Rate zonal centrifugation and Its applicationsPaul singh
Centrifugation is a technique used to separate particles based on size and shape using centrifugal force. Rate zonal centrifugation separates particles based on mass rather than density. It involves layering a sample solution above a preformed density gradient and centrifuging at low speed for a short time, allowing particles to separate into discrete zones based on their sedimentation rates before reaching the bottom. Rate zonal centrifugation is useful for separating particles like organelles, proteins, antibodies, and nucleic acids that have similar densities but different masses.
This document discusses centrifugation, including its principle, types of centrifuges, and applications. Centrifugation uses centrifugal force to separate mixtures based on density. There are three main types of centrifuges - low-speed, high-speed, and ultracentrifuges - which can achieve different revolutions per minute and relative centrifugal forces. Centrifugation techniques include preparative, which separates particles into pellets and supernatants, and analytical like differential and density gradient centrifugation for measuring properties of particles. Centrifugation is used widely in industry and research labs to separate components of mixtures.
In the material testing laboratory, a Charpy impact test was performed on three different types (hot,cold,and steel alloy)of steels testing each variety at four different temperatures (32°C(RT), 100°C,0°C and -22°C ). From results (shown below), we determined that the a transition is from ductile failures to brittle failures
Rebound hammer test (non destructive testAyaz khan
The rebound hammer test is a non-destructive test used to estimate the compressive strength of hardened concrete. Several factors must be controlled to obtain accurate results, including the concrete's surface condition and moisture level. To correlate rebound number readings to compressive strength, test specimens are measured with both the rebound hammer and compression testing machine. At least 9 readings should be taken on each face of specimens and averaged to estimate strength. The rebound hammer test provides an approximate strength measurement within 25% accuracy.
Ultra sonic pulse velocity tests (Concrete technology)Jayshiv Bhimani
(UPV) testing of concrete is based on the pulse velocity method to provide information on the uniformity of concrete, cavities cracks, and defects or other discontinuities.
This document summarizes a presentation on centrifugation given by Bhavika B. Katariya. It defines centrifugation as a process that uses centrifugal force to separate materials of different densities in a suspension. The key principles of centrifugation are explained, including how centrifuges use very strong centrifugal forces compared to gravity alone to separate particles based on density differences. The main types of centrifugation are described as density gradient, differential, and ultra centrifugation. Applications of centrifugation in various fields like biology, chemistry and forensics are also listed.
Centrifugation is one of
the most important and
widely applied research cellular,
techniques in bio-chemistry and
molecular biology, pharmacy and
in medicine.
Ultracentrifugation is a technique that uses high centrifugal forces generated by rotational speeds of up to 150,000 rpm to separate particles in solution based on differences in size, shape, density, and viscosity. It is an important tool in biochemical research used to isolate molecules like DNA, RNA, lipids, and separate organelles from cells. There are two main types - analytical ultracentrifugation which studies molecular interactions and properties, and preparative ultracentrifugation which isolates and purifies particles using techniques like density gradient centrifugation. Proper rotor selection and maintenance of the centrifuge are important for safe and effective use of this technique.
This lab report details procedures for determining the uniaxial compressive strength of rocks and concrete using Schmidt rebound hammers. Rebound hammers measure the elastic properties of materials by striking a spring-driven pin and measuring its rebound. Readings are used to estimate compressive strength by referencing conversion tables. Tests found that a quartzite rock sample had poor quality based on a rebound number equivalent to 41MPa of compressive strength, while a concrete sample had a good quality layer with a rebound number of 43MPa.
AJK2011-03023 (Conference Paper DR) Modelling Multiphase Jet Flows for High V...David Ryan
This document summarizes CFD simulations of flow inside an industrial static mixer called a Sonolator. Single-phase steady-state simulations were performed for three mass flow rates through a fixed nozzle orifice. Streamline data was used to calculate residence times and turbulent energy dissipation rates, which can provide insight into droplet breakup for emulsification processes. Validation was done against experimental discharge coefficients and predicted droplet sizes may depend on inlet conditions for multiphase mixtures.
Modeling the deposit_thickness_distribution_in_copRick Lee
The document discusses modeling the thickness distribution of copper deposits in electroplating semiconductor wafers. It uses electrochemical computer modeling software to simulate the effects of various cell configurations, seed layer thicknesses, electrolyte properties, flow conditions, and current densities. Simulation results show how factors like seed resistance, edge gap width, rotation speed, and impinging flow affect the current density and mass transport boundary layer across the wafer. Maintaining uniform conditions is important for achieving uniform copper deposition across the entire wafer surface.
This document describes the design and construction of a concentric cylinder viscometer that allows for highly accurate viscosity measurements at extremely low shear stresses. The viscometer uses a single rotating cylinder (rotor) inside a fixed outer cylinder (stator) and can measure viscosities with shear stresses as low as 0.003-0.0008 dynes/cm2. Experimental results show the viscometer was able to detect a phase transition in solutions of poly-(butylisocyanate) in carbon tetrachloride as temperature was varied.
This document summarizes the ultrasonic test method for determining properties of concrete. It discusses using PUNDIT machines to transmit ultrasonic pulses through concrete and measure the transit time. Factors that affect pulse velocity like frequency, path length, and aggregate size are covered. The document outlines how ultrasonic testing can be used to determine uniformity, detect defects, measure changes over time, and estimate modulus of elasticity and Poisson's ratio of concrete. Corrections for the presence of reinforcing steel are also provided.
Impact strength refers to a concrete's ability to resist sudden shock or load. It is important for applications with potential impact loads. There is no direct relationship between impact and compressive strength. Impact strength depends on factors like the aggregate type, size, and roughness, as well as the concrete's flexural strength and storage conditions. Non-destructive tests like the Schmidt hammer and ultrasonic pulse velocity test can provide indications of a concrete's properties, including compressive strength. The Schmidt hammer measures surface hardness while ultrasonic pulse velocity relies on sound waves to determine properties related to density and elasticity.
ESA Module 5 Part-A ME832. by Dr. Mohammed ImranMohammed Imran
The document discusses the brittle coating technique for experimental stress analysis. Some key points:
- Brittle coating involves applying a thin brittle resin or ceramic coating to a specimen. Under stress, cracks in the coating indicate tensile stress regions in the specimen.
- Coating stresses can be determined from specimen stresses using equations that account for properties like modulus and Poisson's ratio.
- Mohr's failure theory is used to predict coating failure, with different crack patterns depending on the principal stresses.
- Examples are given of calculating coating and specimen stresses for different loading conditions.
DYNAMIC RESPONSE RESEARCH OF U SHAPED PIPE WITH VISCOELASTIC DAMPINGVarakala Netha
1) The document analyzes the dynamic response of a U-shaped pipe with a viscoelastic damping layer to reduce vibration.
2) Finite element modeling is used to simulate the pipe with damping layer, accounting for cross-section deformation.
3) Experimental tests validate that the damping layer effectively reduces pipe vibration response by up to 79%, with positioning of the layer more influential than width.
Centrifugation uses centrifugal force to separate mixtures based on density, with denser components moving outward and lighter components staying nearer the center; there are three main types - low-speed for pelleting coarse particles, high-speed for organelles/proteins, and ultracentrifuges which attain very high speeds and are used for lipoprotein separation and analytical measurements due to their cooling systems. Centrifugation has many applications from separating blood components to producing skim milk.
Sedimentation for determining molecular weight of macromoleculesShubhangiSuri1
Process of sedimentation with mechanism of action and mathematical derivations, different methods for separation of macromolecules by sedimentation, viscometry vs sedimentation
The document discusses brittle coating methods for experimental stress analysis. Brittle coatings crack under tensile stresses, allowing stresses in specimens to be determined. Key points:
- A thin brittle coating is applied to the specimen surface. As the specimen is loaded, strains are transmitted to the coating, causing cracks perpendicular to maximum tensile stresses.
- Coating crack patterns indicate stress directions. Multiple crack patterns can form under different stress conditions.
- Refrigeration and load relaxation techniques can induce cracks in low-stress regions.
- Fine coating cracks are detected using oblique light or Statiflux particle methods.
This document provides the standard test method for determining the splitting tensile strength of cylindrical concrete specimens. It describes the procedure which involves applying a diametral compressive force along the length of a concrete cylinder at a controlled rate until failure. The maximum load sustained is used to calculate the splitting tensile strength in psi. Proper specimen preparation, loading rate, and calculations are specified to provide consistent results.
Rate zonal centrifugation and Its applicationsPaul singh
Centrifugation is a technique used to separate particles based on size and shape using centrifugal force. Rate zonal centrifugation separates particles based on mass rather than density. It involves layering a sample solution above a preformed density gradient and centrifuging at low speed for a short time, allowing particles to separate into discrete zones based on their sedimentation rates before reaching the bottom. Rate zonal centrifugation is useful for separating particles like organelles, proteins, antibodies, and nucleic acids that have similar densities but different masses.
This document discusses centrifugation, including its principle, types of centrifuges, and applications. Centrifugation uses centrifugal force to separate mixtures based on density. There are three main types of centrifuges - low-speed, high-speed, and ultracentrifuges - which can achieve different revolutions per minute and relative centrifugal forces. Centrifugation techniques include preparative, which separates particles into pellets and supernatants, and analytical like differential and density gradient centrifugation for measuring properties of particles. Centrifugation is used widely in industry and research labs to separate components of mixtures.
In the material testing laboratory, a Charpy impact test was performed on three different types (hot,cold,and steel alloy)of steels testing each variety at four different temperatures (32°C(RT), 100°C,0°C and -22°C ). From results (shown below), we determined that the a transition is from ductile failures to brittle failures
Rebound hammer test (non destructive testAyaz khan
The rebound hammer test is a non-destructive test used to estimate the compressive strength of hardened concrete. Several factors must be controlled to obtain accurate results, including the concrete's surface condition and moisture level. To correlate rebound number readings to compressive strength, test specimens are measured with both the rebound hammer and compression testing machine. At least 9 readings should be taken on each face of specimens and averaged to estimate strength. The rebound hammer test provides an approximate strength measurement within 25% accuracy.
Ultra sonic pulse velocity tests (Concrete technology)Jayshiv Bhimani
(UPV) testing of concrete is based on the pulse velocity method to provide information on the uniformity of concrete, cavities cracks, and defects or other discontinuities.
This document summarizes a presentation on centrifugation given by Bhavika B. Katariya. It defines centrifugation as a process that uses centrifugal force to separate materials of different densities in a suspension. The key principles of centrifugation are explained, including how centrifuges use very strong centrifugal forces compared to gravity alone to separate particles based on density differences. The main types of centrifugation are described as density gradient, differential, and ultra centrifugation. Applications of centrifugation in various fields like biology, chemistry and forensics are also listed.
Centrifugation is one of
the most important and
widely applied research cellular,
techniques in bio-chemistry and
molecular biology, pharmacy and
in medicine.
Ultracentrifugation is a technique that uses high centrifugal forces generated by rotational speeds of up to 150,000 rpm to separate particles in solution based on differences in size, shape, density, and viscosity. It is an important tool in biochemical research used to isolate molecules like DNA, RNA, lipids, and separate organelles from cells. There are two main types - analytical ultracentrifugation which studies molecular interactions and properties, and preparative ultracentrifugation which isolates and purifies particles using techniques like density gradient centrifugation. Proper rotor selection and maintenance of the centrifuge are important for safe and effective use of this technique.
This lab report details procedures for determining the uniaxial compressive strength of rocks and concrete using Schmidt rebound hammers. Rebound hammers measure the elastic properties of materials by striking a spring-driven pin and measuring its rebound. Readings are used to estimate compressive strength by referencing conversion tables. Tests found that a quartzite rock sample had poor quality based on a rebound number equivalent to 41MPa of compressive strength, while a concrete sample had a good quality layer with a rebound number of 43MPa.
AJK2011-03023 (Conference Paper DR) Modelling Multiphase Jet Flows for High V...David Ryan
This document summarizes CFD simulations of flow inside an industrial static mixer called a Sonolator. Single-phase steady-state simulations were performed for three mass flow rates through a fixed nozzle orifice. Streamline data was used to calculate residence times and turbulent energy dissipation rates, which can provide insight into droplet breakup for emulsification processes. Validation was done against experimental discharge coefficients and predicted droplet sizes may depend on inlet conditions for multiphase mixtures.
Modeling the deposit_thickness_distribution_in_copRick Lee
The document discusses modeling the thickness distribution of copper deposits in electroplating semiconductor wafers. It uses electrochemical computer modeling software to simulate the effects of various cell configurations, seed layer thicknesses, electrolyte properties, flow conditions, and current densities. Simulation results show how factors like seed resistance, edge gap width, rotation speed, and impinging flow affect the current density and mass transport boundary layer across the wafer. Maintaining uniform conditions is important for achieving uniform copper deposition across the entire wafer surface.
- The document discusses numerical simulations of the electrostatic spray painting process using high-speed rotary bell atomizers.
- Experiments were conducted to validate the sensitivity of the simulations to variations in operating conditions like paint flow rate and bell speed, as well as different target geometries.
- The simulations demonstrated good agreement with experimental measurements of film thickness and were able to accurately predict changes based on different operating conditions and target shapes.
Handheld Solution for Measurement of Residual Stresses on Railway Wheels usin...Innerspec Technologies
The braking process used on railroad cars is known to create tensile stresses in the circumferential direction due to the thermal expansion and subsequent cooling of the wheel rim. This tensile stress can significantly accelerate the growth of small cracks on the rolling surface which can cause a spall or catastrophic failure
of the wheel under load. By periodically evaluating the tensile stress, railroad companies can prevent wheel failures and derailments that can be extremely dangerous and costly. Innerspec Technologies has developed the first, portable, battery-operated handheld instrument that can be used to provide rail-side inspections and facilitate operation in any environment. The instrument is coupled with a proprietary, patent-pending, dual-channel sensor that does not need to be rotated during inspection thus simplifying the operation, increasing the reliability and accuracy of results, and reducing complexity and inspection cycle time.
OMAE2014 - 23661 Experimental Assessment of The Behaviour Of A Pipe Vibration...Luan Tochetto
The document describes experiments conducted to assess the behavior of a Pounding Tuned Mass Damper (PTMD) installed on a pipe underwater. A small-scale test apparatus was constructed to model a submarine pipe section. Free and forced oscillation tests were performed on the pipe both with and without a PTMD installed, in air and underwater conditions. The results showed that underwater, the natural frequency decreased due to added water mass, while damping increased due to fluid viscosity. With the PTMD installed, two natural frequencies were observed corresponding to the two-degree-of-freedom system. The PTMD was found to reduce pipe vibration amplitudes both in air and underwater through energy dissipation, though its performance was affected by surrounding fluid
CFD Coursework: An Investigation on a Static MixerAnthony Man
This document summarizes a CFD study conducted on a static mixer. Three key phases were completed:
1) A baseline mesh was created and the effect of modeling the boundary layer was investigated. It was found modeling the boundary layer improved accuracy.
2) A parameter study was done using inlet diameter and angle, finding outlet temperature range increased with diameter and lower second inlet angle.
3) Different turbulence models were tested, with K-ε found to be most suitable for the highly turbulent flow in the static mixer.
Model Analysis of Cymbal Generator Under Different Working ConditionsIJRES Journal
The modal analysis of a cymbal transducer is conducted to determine its natural frequencies and vibration modes under different working conditions. The cymbal transducer consists of a brass metal cap and a PZT-5H piezoelectric ceramic sheet bonded together. Finite element analysis is performed using ANSYS to obtain the first six natural frequencies and mode shapes of the cymbal transducer in free state. The results from ANSYS are validated by comparing with those from simulation, and they match well.
Case Studies from 25 Years of Troubleshooting Vibration Problems.pdfssuser75ec351
This document summarizes several case studies over 25 years that used vibration analysis to troubleshoot problems with rotating and non-rotating equipment:
1) A hydroelectric dam would vibrate at certain turbine loads due to a phenomenon called Rheingan's Influence. Vibration spectra detected the issue but the system was not coupled properly. Modifications allowed operators to avoid problematic loads.
2) Stripes formed on steel strips during induction heating. The furnace frequency matched strip vibrations. Continuously varying the frequency instead of using one fixed frequency eliminated striping.
3) A microscope used in microsurgery vibrated, fatiguing surgeons. Vibration spectra found structural vibrations amplified by mismatched
Flow-induced vibration in heat exchangers has been a major problem for decades. Three main mechanisms that cause vibration are fluid-elastic instability, vortex shedding, and multi-phase buffeting. Fluid-elastic instability is the most important mechanism for shell and tube heat exchangers. Several studies have analyzed vibration experimentally and through computational fluid dynamics simulations. Parameters like damping ratios, tube properties, fluid properties, and flow velocities are important factors in vibration analysis and predicting the onset of instability.
this article covers discussion of variable area flow meter. also it speaks about turbine flow meter, target flow meter, magnetic flow meter, vortex flow meter, ultrasonic flow meter, thermal flow meter.
The Correlation between Surface Tracking and Partial Discharge Characteristic...IJECEIAES
This paper presents the investigation of the surface tracking on pressboard surface immersed in MIDEL eN oil. In this work, the development of surface discharge was analyzed by correlating the visual records of surface tracking on impregnated pressboard and the partial discharge (PD) activities. The PD activities during the surface tracking process were analyzed in terms of Phase Resolved Partial Discharge (PRPD) patterns. Throughout the experiment, surface discharge is found as the development of tree-like patterns in the form of white marks occurring on the oil-pressboard interface. This phenomenon is generally accepted as the drying out process that involves evaporation and decomposition of the oil molecules in the pressboard pores due to the surface discharge activities on the pressboard surface layer. The development of surface discharge on the pressboard surface can continue from minutes to months or even years until failure. Thus, condition monitoring system is important to characterize this type of faulty condition. The experimental results show that there is the decreasing trend of PD magnitude during the development of white mark hallway of a gap distance which is eventually suffered from an unexpected fault.
IRJET- A Research Paper on Design and Experimentation on Continuous Loop Demu...IRJET Journal
This document summarizes a research paper on the design and experimentation of a continuous loop demulsifier. The demulsifier uses electrocoalescence to separate water from crude oil by inducing opposite charges on water droplets using an electrostatic field, causing them to coalesce into larger droplets that settle out of the oil due to gravity. Key components of the developed system include distributor and collector tubes, grid electrodes to generate a uniform electric field, a pump to continuously feed the emulsion, and an acrylic vessel to hold it all. Experimental results showed this to be an effective low-cost method for continuous crude oil demulsification.
In metallurgy, cladding refers to the bonding together of dissimilar metals, normally achieved by extruding two or more metals through a die or pressing sheets together under high pressure. Timely detection of delamination that occurs occasionally during the cladding processes is very important for the industry. This paper presents an EMAT system based on ultrasonic guided wave techniques. The analysis of a three-layer, brass/copper/brass product is also presented including dispersion curves, and interaction of ultrasonic guided wave with delamination defects. The authors observed a cyclic behavior of guided wave propagation with the increase of defect size. An explanation is introduced and proved with finite element analysis. The results presented in this paper will have a very significant impact on understanding of delamination detection in multilayered composite structures including adhesive bonded structures.
1. Laser pulses were used to generate shock waves in solids with peak pressures ranging from 5 to 120 kilobars. Peak pressures of around 35 kilobars were achieved at a fluence of 1000 J/cm2, while applying a transparent overlay increased the peak pressure to 120 kilobars.
2. Measurements found that plasma initiation occurred around 8 nanoseconds into a laser pulse when exposing a graphite coating. The resulting shock wave rose sharply at 37 nanoseconds, with only a small precursor pressure seen earlier.
3. Precursor pressures seen with carbon-resin coatings but not with pure graphite coatings, supporting the idea that precursors are due to surface ablation pressures before plasma formation
Electrospinning, a broadly used technology for electrostatic fiber formation which utilizes electrical forces to produce polymer fiber with diameters ranging from 2 nm to several micrometers using polymer solutions of both natural and synthetic polymers.
The experimental research at the University of California, Irvine Wind Tunnel Facility aims to understand how passive scalars are mixed by turbulent air flows. An electrically heated wire grid generates turbulence in the air, acting as a passive scalar. The decay of turbulence and approach to isotropy was analyzed by measuring velocity fields downstream of the grid. The power decay law was validated, with decay exponents of 1.504 and 1.389 for different turbulence intensities. A region of homogeneous isotropic turbulence was established, becoming isotropic farther downstream for higher flow speeds.
Studies on impact of inlet viscosity ratio, decay rate & length scales in a c...QuEST Global
This document summarizes computational fluid dynamics (CFD) studies on the impact of inlet turbulence parameters on the aerodynamic performance of a cooled turbine stage. The parameters studied include turbulence intensity, length scale, viscosity ratio, and decay rate. The key findings are:
1) Increasing the inlet length scale and turbulence intensity decreases stage efficiency, with higher drops at higher intensities and scales. Efficiency drops more sharply with logarithmic increases in these parameters.
2) Increasing the viscosity ratio and decay rate also decreases efficiency, with impacts becoming more significant at higher ratios and rates. Efficiency drops more sharply with logarithmic increases in viscosity ratio.
3) Higher turbulence parameters result in more uniform total pressure profiles
This document discusses the use of magnetorheological smart dampers to strengthen structures against vibrations. A magnetorheological damper was fabricated using magnetorheological fluid and a magnetic coil. Testing showed that the damper effectively attenuates vibration amplitudes and can generate large damping forces by varying the current input to the magnetic coil. Such smart dampers can be installed in tall buildings, towers, and other structures to strengthen them against wind and seismic loads using semi-active control, improving stability and preventing catastrophic failures. The document concludes that smart dampers are capable of producing very large damping forces by varying the input current to the magnetic coil, providing semi-active control that can stabilize structures subjected to varying loads.
This document summarizes electrorheological (ER) fluids, which are smart materials whose viscosity and yield stress can be controlled by an applied electric field. ER fluids are typically composed of polarizable particles suspended in a non-conductive liquid. When an electric field is applied, the particles form chains that link up into columns, increasing the fluid's viscosity and solid-like properties. The document discusses the microstructure of ER fluids under electric fields, different types of ER fluids, methods for preparing silica-based ER fluids, and potential engineering applications of ER fluids in areas like automotive components, hydraulic valves, fluid seals, and robot joints. ER fluids offer properties like fast response, minimal wear, and electronic control that could
Introduction- e - waste – definition - sources of e-waste– hazardous substances in e-waste - effects of e-waste on environment and human health- need for e-waste management– e-waste handling rules - waste minimization techniques for managing e-waste – recycling of e-waste - disposal treatment methods of e- waste – mechanism of extraction of precious metal from leaching solution-global Scenario of E-waste – E-waste in India- case studies.
Use PyCharm for remote debugging of WSL on a Windo cf5c162d672e4e58b4dde5d797...shadow0702a
This document serves as a comprehensive step-by-step guide on how to effectively use PyCharm for remote debugging of the Windows Subsystem for Linux (WSL) on a local Windows machine. It meticulously outlines several critical steps in the process, starting with the crucial task of enabling permissions, followed by the installation and configuration of WSL.
The guide then proceeds to explain how to set up the SSH service within the WSL environment, an integral part of the process. Alongside this, it also provides detailed instructions on how to modify the inbound rules of the Windows firewall to facilitate the process, ensuring that there are no connectivity issues that could potentially hinder the debugging process.
The document further emphasizes on the importance of checking the connection between the Windows and WSL environments, providing instructions on how to ensure that the connection is optimal and ready for remote debugging.
It also offers an in-depth guide on how to configure the WSL interpreter and files within the PyCharm environment. This is essential for ensuring that the debugging process is set up correctly and that the program can be run effectively within the WSL terminal.
Additionally, the document provides guidance on how to set up breakpoints for debugging, a fundamental aspect of the debugging process which allows the developer to stop the execution of their code at certain points and inspect their program at those stages.
Finally, the document concludes by providing a link to a reference blog. This blog offers additional information and guidance on configuring the remote Python interpreter in PyCharm, providing the reader with a well-rounded understanding of the process.
Harnessing WebAssembly for Real-time Stateless Streaming PipelinesChristina Lin
Traditionally, dealing with real-time data pipelines has involved significant overhead, even for straightforward tasks like data transformation or masking. However, in this talk, we’ll venture into the dynamic realm of WebAssembly (WASM) and discover how it can revolutionize the creation of stateless streaming pipelines within a Kafka (Redpanda) broker. These pipelines are adept at managing low-latency, high-data-volume scenarios.
International Conference on NLP, Artificial Intelligence, Machine Learning an...gerogepatton
International Conference on NLP, Artificial Intelligence, Machine Learning and Applications (NLAIM 2024) offers a premier global platform for exchanging insights and findings in the theory, methodology, and applications of NLP, Artificial Intelligence, Machine Learning, and their applications. The conference seeks substantial contributions across all key domains of NLP, Artificial Intelligence, Machine Learning, and their practical applications, aiming to foster both theoretical advancements and real-world implementations. With a focus on facilitating collaboration between researchers and practitioners from academia and industry, the conference serves as a nexus for sharing the latest developments in the field.
The CBC machine is a common diagnostic tool used by doctors to measure a patient's red blood cell count, white blood cell count and platelet count. The machine uses a small sample of the patient's blood, which is then placed into special tubes and analyzed. The results of the analysis are then displayed on a screen for the doctor to review. The CBC machine is an important tool for diagnosing various conditions, such as anemia, infection and leukemia. It can also help to monitor a patient's response to treatment.
Electric vehicle and photovoltaic advanced roles in enhancing the financial p...IJECEIAES
Climate change's impact on the planet forced the United Nations and governments to promote green energies and electric transportation. The deployments of photovoltaic (PV) and electric vehicle (EV) systems gained stronger momentum due to their numerous advantages over fossil fuel types. The advantages go beyond sustainability to reach financial support and stability. The work in this paper introduces the hybrid system between PV and EV to support industrial and commercial plants. This paper covers the theoretical framework of the proposed hybrid system including the required equation to complete the cost analysis when PV and EV are present. In addition, the proposed design diagram which sets the priorities and requirements of the system is presented. The proposed approach allows setup to advance their power stability, especially during power outages. The presented information supports researchers and plant owners to complete the necessary analysis while promoting the deployment of clean energy. The result of a case study that represents a dairy milk farmer supports the theoretical works and highlights its advanced benefits to existing plants. The short return on investment of the proposed approach supports the paper's novelty approach for the sustainable electrical system. In addition, the proposed system allows for an isolated power setup without the need for a transmission line which enhances the safety of the electrical network
2. IEEE Transactions on Dielectrics and Electrical Insulation Vol. 18, No. 6; December 2011 1909
positive and negative impulse voltages. Current and light signals
as well as high-speed camera captured images were used to
characterize the streamer propagation along pressboard surface in
ester liquids. Breakdown voltages and acceleration voltages were
also determined for various gap distances. For comparison
purposes, tests were also carried out in a mineral oil and used as
the benchmark.
2 EXPERIMENTAL DESCRIPTION
2.1 SAMPLE PREPARATION
Synthetic ester Midel 7131 and natural ester FR3 were
investigated in this paper and mineral oil Gemini X was used
as the benchmark. Detailed descriptions of the liquids’ basic
properties were given in our previous publication [4]. Liquid
samples under tests were directly from the sealed new barrels
without further filtration. The relative humidity of testing
samples was regularly checked during the whole period of
experiments, which ranged approximately from 5% to 20%
RH.
High density pressboards of 1.2 g/cm3
were cut into the
following dimensions for tests at various gap distances: 100
mm long × 40 mm high for 25 mm, 145 mm long × 65 mm
high for 50 mm and 210 mm long × 90 mm high for 75 mm
gap distances. The thickness of pressboard is 3 mm. The
pressboards were firstly dried in an air circulating oven at
105 ℃ for 48 h, and then in vacuum condition below 500 Pa
(5 mbar) at 85 ℃ for 24 h. The pressboards were then
immersed into the insulating liquids under vacuum below
500 Pa (5 mbar) at 85 ℃ for further 48 h to achieve fully-
impregnated conditions. After this procedure, the moisture
content of fully impregnated pressboard samples was below
0.5% by weight.
2.2 TEST SETUP
The test setup is shown in Figure 1. A 10-stage Haefely
impulse generator with maximum voltage 2000 kV and
energy 150 kJ was used to deliver the 1.2/50 µs standard
lightning impulse. Voltage waveform was measured by a
capacitive high voltage divider. A 3.5 kΩ current-limit
resistor was added into the circuit to protect needle electrode
and oil samples when breakdown occurred. Point-plane
electrodes were installed in a cubic-like transparent test cell
with the volume of about 12.5 liters. Tungsten needle was
used as the point electrode, whose tip radius of curvature was
guaranteed to be 50±5 µm after selection using microscope.
The needle was regularly changed after each set of tests i.e.
per liquid type per gap distance. Plane electrode is made of
brass, having a diameter of 200 mm and edge radius of 3 mm.
The gap distance between point-plane electrodes can be
adjusted by a set of thickness gauges with step of 5 mm.
Pressboard was placed in parallel to the point-plane electrode
axis and in tight contact with the point electrode. Current and
light signals were monitored by a non-inductive current
shunt (1Ω) and a photomultiplier tube (PMT) respectively,
and synchronized with the camera imaging operation. All the
experiments were carried out at room temperature and
ambient pressure.
Figure 1. Sketch of test setup.
2.3 STREAMER PHOTOGRAPHING METHODS
A high speed camera SIM-16, which consists of 16 high-
resolution intensified CCD sensors, was used to capture the
streamer images. The exposure time of each CCD sensor can
be adjusted from 5 ns to 10 ms and the interframe time
between CCD sensors can be set from 0 ns to 20 ms. Figure 2
shows the three different ways of streamer photographing
setups used in this study. Shadowgraph setup has the merit to
capture the streamer channel shape with the help of back flash
light. Since pressboard is not transparent, the camera can only
be put in parallel direction to the pressboard surface, as shown
in Figure 2a. Integral light images are collecting the streamer
self-irradiated light information, and camera can be set in both
parallel and perpendicular directions to the pressboard surface
as shown in Figure 2b and 2c respectively, and must be in a
dark room. The setups in Figure 2a and 2b, have the advantage
to see whether or not the streamer propagates along the
surface, and both require careful manipulations to make sure
the camera is properly set in the parallel direction to the
pressboard surface.
Figure 2. Illustration of streamer photographing setups.
3 STREAMER CHARACTERISTIC
3.1 CURRENT, LIGHT AND STREAMER SHAPE
Current and light signals together with streamer shape
feature are usually used to describe the characteristics of
streamer propagation, which vary upon the test conditions, e.g.
applied voltage, polarity or electrode geometry [18, 19].
Generally four modes of streamers are classified in
transformer liquids mainly according to propagation
velocity [20]. In this section, characteristics of streamer
propagation before breakdown along pressboard surface in
ester liquids under both positive and negative impulse voltages
were described.
3. 1910 Q. Liu and Z. D. Wang: Streamer Characteristic and Breakdown in Synthetic and Natural Ester Transformer Liquids
3.1.1 POSITIVE STREAMER
Figure 3 shows an example of positive streamer propagation
at a voltage level just above inception, which was obtained on
FR3/pressboard interface at the gap distance of 50 mm.
Charging process at the wavefront of impulse voltage induces
some noises in both current and light signals, and these noises
are consequently ignored in the following analysis. A train of
discrete intense pulses with increasing amplitude was
observed for both current and light signals, which represents
the typical recording of positive streamers on ester/pressboard
interface at low voltage levels. Light and current pulses
usually correspond to each other in time of occurrence.
Integral light images of the streamer at the same voltage level
obtained in perpendicular and parallel directions are shown in
Figure 3b and 3c respectively. Small tree-like streamer was
observed, of which the intensity is low, since the maximum
amplitude of light signals is less than 0.4 arbitrary units. The
length of streamer in Figure 3c is 10.23 mm, and with
propagating time of 8.60 µs in Figure 3a, an average velocity
of 1.19 km/s (2nd
mode streamer) can be calculated.
Figure 3. Positive streamer propagation on FR3/pressboard interface at low
voltage level, d=50 mm, V= +60 kV; (a) voltage, current and light waveforms;
(b) integral image in perpendicular direction; (c) integral image in parallel
direction, corresponding to the signals in (a).
With the increase of applied voltage, the current and light
pulses become more intense, i.e. larger magnitude, longer
sustaining time and higher repetition rate. Especially for
streamers on Midel 7131/pressboard interface, a continuous dc
component was normally observed for both current and light
signals as shown in Figure 4a, which was obtained at a voltage
level close to breakdown for the 50 mm gap. The continuous
component might be due to the continuous backward travel of
large amount of electrons generated by the intense discharge
activities at the streamer heads. Figure 4b and 4c show the
integral light images of the streamers at the same voltage level
from both perpendicular and parallel directions. It is noted that
there is always a bright luminous phase at the root of streamer,
which should be the initial short-lived 3rd
mode propagation
phenomenon, the same as described in open liquid gaps [1, 4].
The length of streamer in Figure 4c is 29.03 mm with
propagating time of 17.23 µs in Figure 4a, which shows an
average velocity of 1.68 km/s representing the 2nd
mode
positive streamer. It is clearly seen that streamer propagates
along the pressboard surface but with some branches going
into the surrounding liquid.
Figure 4. Positive streamer propagation on Midel 7131/pressboard interface at
high voltage level, d=50 mm, V=+80 kV; (a) voltage, current and light
waveforms; (b) integral image in perpendicular direction; (c) integral image in
parallel direction, corresponding to the signals in (a).
Figure 5 shows the typical shadowgraph images of positive
streamers along pressboard surface in the three liquids. The
channels of positive streamers are so weak (thin) that the
observation is made difficult using our present setup. However
it can still be seen that positive streamer propagates along the
pressboard surface with some other lateral branches injecting
into the surrounding liquid, and similar tree-like structures
with less branches exist for all the liquids.
Figure 5. Shadowgraph images of positive streamers on liquid/pressboard
interface, d=50 mm; (a) Midel 7131, V=+70kV; (b) FR3, V=+80kV; (c)
Gemini X, V=+90kV.
3.1.2 NEGATIVE STREAMER
Figure 6 shows a typical recording of negative streamer
propagation at a voltage level just above inception, which
was obtained on Midel 7131/pressboard interface at the 50
mm gap distance. A train of clearly recognized discrete
pulses with increasing amplitude was observed for both
current and light signals, which is similar to what was
observed in open gaps [1]. Compared with positive polarity,
light and current pulses of negative streamers are less
frequent but with larger amplitude. Integral light images of
the streamer at the same voltage level obtained in
perpendicular and parallel directions are shown in Figure
6b and 6c respectively. Small tree-like streamers were
observed (Figure 6b) and they might even propagate away
from the pressboard surface (Figure 6c). The length of
streamer in Figure 6b is 5.42 mm and the corresponding
propagating time in Figure 6a is 8.72 µs, so the average
velocity is deduced as 0.62 km/s, which is slower than that
of positive streamer, but still belongs to 2nd
mode negative
streamer.
4. IEEE Transactions on Dielectrics and Electrical Insulation Vol. 18, No. 6; December 2011 1911
Figure 6. Negative streamer propagation on Midel 7131/pressboard interface
at low voltage level, d=50 mm, V=-70 kV; (a) voltage, current and light
waveforms; (b) integral image in perpendicular direction, corresponding to the
signals in (a); (c) integral image in parallel direction.
With the increase of applied voltage, the repetition rate of
current and light pulses does not increase but the amplitude
grows greatly as shown in Figure 7a, which was obtained on
FR3/pressboard interface at the 50 mm gap distance. In
addition, a series of large pulses with similar amplitude were
always observed at the beginning of both current and light
signals, followed by the normal train of pulses of increasing
amplitude. This is believed to be the same as the 3rd
+2nd
mode
propagation observed in open gaps [19]. Integral light images
of the streamers also support the above description since a
luminous zone was always observed at the root of streamer, as
shown in Figure 7b and 7c. The length of streamer in
Figure 7b is 21.38 mm and the corresponding propagating
time in Figure 7a is 16.52 µs, thus the average velocity is 1.29
km/s, representing the typical 2nd
mode negative streamer.
Figure 7. Negative streamer propagation on FR3/pressboard interface at high
voltage level, d=50 mm, V=-110 kV; (a) voltage, current and light waveforms;
(b) integral image in perpendicular direction, corresponding to the signals in
(a); (c) integral image in parallel direction.
Figure 8 shows the typical shadowgraph images of negative
streamers along pressboard surface in the three liquids.
Negative streamers have much thicker channels and more side
offshoots than positive streamers. The structures of negative
streamers on ester/pressboard interface are similar to those
observed in open ester gaps [4], only half of which is removed
by the presence of pressboard. It was observed that most of the
negative streamers in ester liquids propagate along the
pressboard surface. As negative streamers in mineral oil
normally have less main branches (only one or two) [4, 18],
with the pressboard being present, the streamer can propagate
either on the pressboard surface or in the adjacent liquid, as
shown in Figure 8c. It is noteworthy that the streamer
propagating in the mineral oil seems always to come back and
touch the pressboard surface at a later stage.
Figure 8. Shadowgraph images of negative streamers on liquid/pressboard
interface, d= 50 mm; (a) Midel 7131, V=-140 kV; (b) FR3, V=-130 kV; (c)
Gemini X, V= -210 kV.
3.2 STOPPING LENGTH
Stopping length means the straight-line distance from the
farthest tip point of a stopped streamer to the point electrode.
Tests were carried out at voltages from inception to the level
close to breakdown with steps of 10 kV or 20 kV. At each
voltage level, the reported results are the average of about 10
measurements.
3.2.1 ON ESTER/PRESSBOARD INTERFACE
Figure 9 shows the stopping length of streamers on Midel
7131/pressboard interface under both positive and negative
polarities at the 50 mm gap (Dashed line shows the results in
open gaps, which are the mixture of the previously published
data [4] and the recent obtained data). Streamer length under
both polarities increases gradually when the applied voltage is
increased. Strong polarity effect exists: at the same voltage
level, positive streamer propagates much further than negative
streamers, leading to the lower breakdown voltage under
positive polarity. It should be stressed that no promotion effect
was observed under both polarities when the pressboard was
introduced. Similar trends were observed on FR3/pressboard
interface as shown in Figure 10. The only difference is that
there is a minor increase of stopping length at high voltage
levels with the presence of pressboard.
Figure 9. Stopping length of streamers on Midel 7131/pressboard interface
under both positive and negative polarities, and compared with those in open
liquid gaps, d=50 mm.
5. 1912 Q. Liu and Z. D. Wang: Streamer Characteristic and Breakdown in Synthetic and Natural Ester Transformer Liquids
Figure 10. Stopping length of streamers on FR3/pressboard interface under
both positive and negative polarities, and compared with those in open liquid
gaps, d=50 mm.
3.2.2 COMPARISON WITH MINERAL OIL
Figure 11 shows the comparisons of stopping lengths of
positive streamers on pressboard surface in ester liquids and
mineral oil at the gap distance of 50 mm. 50% breakdown
voltages, Vb-M, Vb-F and Vb-G, are stated on the figure, which
stand for breakdown voltage on Midel 7131/pressboard
interface, FR3/pressboard interface and Gemini X/pressboard
interface respectively. Below breakdown voltage, the
increasing trend of stopping length with voltage seems in a
linear relationship. In addition, the difference of trend between
ester/pressboard and mineral oil/pressboard is relatively small,
which is the same as what was observed in open gaps [4].
Figure 11. Stopping lengths of positive streamers on pressboard surface in the
three liquids, d= 50 mm.
Figure 12 shows the comparisons of stopping lengths of
negative streamers on pressboard surface in ester liquids and
mineral oil at the gap distance of 50 mm. A significant
difference between ester liquids and mineral oil was observed.
Below 130 kV, negative streamer on Gemini X/pressboard
interface grows slowly with voltage. Afterwards its growth
increases quickly with voltage, showing the similar trend to
streamer on ester/pressboard interface. At the same voltage
level, streamer on ester/pressboard interface propagates much
further than that on mineral oil/pressboard interface. The
overall performance with the presence of pressboard interface
is the same as what was observed in open gaps [4].
Figure 12. Stopping lengths of negative streamers on pressboard surface in
the three liquids, d= 50 mm.
4 BREAKDOWN VOLTAGE
4.1 TESTS AT VARIOUS GAP DISTANCES
Breakdown voltage was measured using step-rising-voltage
procedure, i.e. one shot per step and at least 3 steps applied before
breakdown; the same as stated in [4]. Pressboard sample was
changed after each breakdown. Five tests were carried out at each
gap distance from 25 mm to 75 mm under both positive and
negative polarities, of which the average value was taken as the
50% breakdown voltage. Generally an interval of 10 minutes was
given between two consecutive tests including the time for
changing pressboard samples.
Under positive polarity as shown in Figure 13, breakdown
voltage increases gradually with gap distance. At 25 mm,
breakdown voltages are similar on ester/pressboard interface to
that on mineral oil/pressboard interface. With larger gap distances,
breakdown voltage on mineral oil/pressboard interface becomes
higher than that on ester/pressboard interface. The difference was
further enlarged at gap distances of 100 mm and 200 mm as
reported in [3]. Introduction of pressboard almost does not reduce
the 50% breakdown voltage in both ester liquids and mineral oil.
Figure 13. 50% Breakdown voltages on pressboard surface in the three
liquids at various gap distances under positive polarity.
At breakdown voltage levels under positive polarity, no
obvious mark or damage was observed due to breakdown on
both ester/pressboard and mineral oil/pressboard interfaces for
all the gap distances up to 75 mm.
6. IEEE Transactions on Dielectrics and Electrical Insulation Vol. 18, No. 6; December 2011 1913
Under negative polarity as shown in Figure 14,
breakdown voltage increases with gap distance as well.
The breakdown voltages on mineral oil/pressboard
interface are always higher than those on ester/pressboard
interface for all the gap distances investigated in this
paper. Introduction of pressboard has no influence on the
breakdown voltage in ester liquids, but seems to weaken
the breakdown voltage in mineral oil at large gap
distances, e.g. 20 kV reduction for the 75 mm gap
distance.
However such a reduction in mineral oil was found to
be caused by the accumulative effect of pre-stresses
during the step voltage increase before breakdown, which
is to be discussed in next section. Therefore, the
procedure was improved to that pressboard was changed
after each shot rather than after each breakdown, based on
which the breakdown voltages obtained were exactly the
same as those in open mineral oil gaps. Similar procedure
was also recommended in [3], of which the breakdown
voltages were not weaken by the presence of pressboard
in both ester liquids and mineral oil at the gap distance of
100 mm.
Figure 14. 50% Breakdown voltages on pressboard surface in the three
liquids at various gap distances under negative polarity.* Tests were carried
out by changing pressboard after each shot rather than each breakdown.
At breakdown voltage levels under negative polarity,
permanent black scar was usually observed on
ester/pressboard interface at the gap distance of 75 mm, as
shown in Figure 15a. For Gemini X/pressboard interface, it
was observed at both gap distances of 50 mm and 75 mm, as
shown in Figure 15b and 15c. A long full-path black scar
was normally left by the breakdown arc at the 75 mm gap
distance. In addition tree-like white mark was sometimes
observed on Midel 7131/pressboard interface at the 75 mm
gap distance, as shown in Figure 15d, which is not
permanent damage and disappears in a short period when
exposed to air environment. Therefore white marks are more
likely some enclosed gaseous channels, which are formed by
‘burning’ the oil out of the pressboard surface during the
flashover. It was noted that the main path of flashover arc
tends to produce black scars when the other sub-branches
tend to create white marks.
Figure 15. Surface mark on pressboard at breakdown voltage levels under
negative polarity: (a) Black scar on Midel 7131/pressboard interface, d=75
mm, V=-210 kV, (b) Short black scar on Gemini X/pressboard interface, d=50
mm, V=-230 kV, (c) Long black scar on Gemini X/pressboard interface, d=75
mm, V=-290 kV, (d) White tree on Midel 7131/pressboard interface, d=75
mm, V=-240 kV.
4.2 ACCUMULATED EFFECT IN BREAKDOWN
VOLTAGE TESTS
In lightning tests, multiple shots are inevitably applied on
the testing samples before a breakdown occurs, therefore a
time interval between two consecutive shots is normally
required in standards to avoid the possible accumulative
effect: minimum 30 s in ASTM D 3300 and minimum 60 s in
IEC 60897 are specified. To verify the accumulative effect in
ester liquids and mineral oil with pressboard involved, the
following procedure was defined: a series of 25 shots with
60 s interval at the same voltage level below the breakdown
voltage, were applied on the same position of a pressboard
sample. Streamer images were regularly taken, and the
stopping length of streamer was used as the criterion for
justification of the existence of accumulative effect.
Figure 16 shows the results of multiple-shot test on
ester/pressboard interface under both positive and negative
polarities. Applied voltage was chosen at which the streamer
usually propagates to half of the gap distance and breakdown
would never occur. It was found that streamers were kept
stable during the series of 25 shots on ester/pressboard
interface under both positive and negative polarities. In other
words, no accumulative effect exists on ester/pressboard
interface, or if there is any cause for accumulative effect, 60 s
interval is long enough to eliminate it.
Figure 16. Multiple-shot tests on ester/pressboard interface under both
positive and negative polarities, d=50 mm.
7. 1914 Q. Liu and Z. D. Wang: Streamer Characteristic and Breakdown in Synthetic and Natural Ester Transformer Liquids
Figure 17 depicts the results of multiple-shot tests on
mineral oil/pressboard interface under both positive and
negative polarities. Under positive polarity, the streamer
length decreases slightly with increasing impulse shots, which
is however in a reasonable scattering range. Under negative
polarity, the streamer length increases gradually with each
subsequent shot. At -190 kV, breakdown even occurred after
the 9th
or 12th
shot for two different samples respectively.
Therefore strong accumulative effect on negative streamer
propagation was clearly found on mineral oil/pressboard
interface.
Figure 17. Multiple-shot tests on mineral oil/pressboard interface under both
positive and negative polarities, d=50 mm.
Further tests indicate that the accumulative effect does not
exist in open mineral oil gaps as shown in Figure 18, so it is
confirmed that mineral oil impregnated pressboard is the key
in promoting streamer propagations under the accumulative
stress condition. Such an accumulative effect may lead to the
underestimation of breakdown voltage, as shown in the last
section.
Figure 18. Multiple-shot tests in open mineral oil gap under both positive and
negative polarities, d=50 mm.
It was noted that accumulative effect was only observed on
mineral oil/pressboard interface under negative polarity.
Effects of charge storage and bubble residence on the
pressboard surface are considered to explain the observed
accumulative effect [21]. In terms of the difference between
liquids, charge storage might be dominant: the time constant
of space charge dissipation on mineral oil/pressboard interface
is much longer than that on ester/pressboard interface [22, 23],
so the residual space charges on mineral oil/pressboard
interface could distort the local electric field on the pressboard
surface and thus accelerate the subsequent streamer
propagation. As for the difference between polarities, bubble
residence might be dominant: the gaseous channels of
negative streamers are thicker than positive ones, and this
could mean more micro bubbles are generated after the
collapse of negative streamer and reside on the pressboard
surface, thus promote the subsequent streamer propagation. To
fully understand the underlying mechanisms, further studies
on this phenomenon are needed.
5 ACCELERATION VOLTAGE
When applied voltage is increased further, streamer
propagation can switch from slow modes (1st
and 2nd
) to fast
modes (3rd
and 4th
), of which the transition voltage is called
acceleration voltage [19]. Tests were carried out at gap
distances of 25 mm and 50 mm under both positive and
negative polarities.
5.1 UNDER POSITIVE POLARITY
Figure 19 and 20 show the average propagation velocities of
positive streamers on pressboard surface in the three liquids at
gap distances of 25 mm and 50 mm respectively.
Below acceleration voltage, the streamer velocity increases
slowly with increased voltage level, generally in the range of
1.0 km/s to 3.0 km/s, for both cases of with and without
pressboard interface and for all three liquids. Once the
transition into fast mode is made, the streamer velocity
increases quickly with increased voltage level, finally reaching
25 km/s for the 25 mm gap distance and 50 km/s for the 50
mm gap distance in the present study. The acceleration voltage
on Gemini X/pressboard interface is much higher than that on
ester/pressboard interface. It should be emphasized here that
introduction of pressboard does not influence the streamer
velocity in ester liquids, but significantly promotes the
streamer velocity in mineral oil at overstressed voltages
leading to a large reduction of acceleration voltage: about
60 kV for both 25 mm and 50 mm gap distances. Similar
phenomenon was also observed at the 100 mm gap distance
in [3], of which the acceleration voltage of streamers on
mineral oil/pressboard interface was reduced by about 60 kV
as well.
At overstressed voltages, still no significant damaging mark
was left by flashover on ester/pressboard interface under
positive polarity. As shown in Figure 21a, only minor scar was
observed at the bottom of pressboard. Similar phenomenon of
weak marks on ester/pressboard interface was also reported
in [3] at the gap distance of 200 mm. However, significant
black scar was seen on Gemini X/pressboard interface at an
8. IEEE Transactions on Dielectrics and Electrical Insulation Vol. 18, No. 6; December 2011 1915
extreme overstressed voltage level of 230 kV, which is 120 kV
higher than 50% breakdown voltage, as shown in Figure 21b.
Figure 19. Average propagation velocity of positive streamers on pressboard
surface in the three liquids at gap distance of 25 mm.
Figure 20. Average propagation velocity of positive streamers on pressboard
surface in the three liquids at gap distance of 50 mm.
Figure 21. Surface mark on pressboard at overstressed voltage levels under
positive polarity; (a) minor scar on Midel 7131/pressboard interface, d=50
mm, V=+110 kV, (b) long black scar on Gemini X/pressboard interface, d=50
mm, V=+230 kV.
5.2 UNDER NEGATIVE POLARITY
Figure 22 and 23 depict the average propagation velocities
of negative streamers on pressboard surface in the three
liquids at gap distances of 25 mm and 50 mm respectively.
Similar to those under positive polarity, below acceleration
voltage, the streamer velocity increases slowly with increased
voltage level, in a lower range of about 0.5 km/s to 1.5 km/s.
Over acceleration voltage, streamer velocity starts to increase
gradually with the increase of voltage level, but not as quickly
as under positive polarity. In addition, the difference of
acceleration voltage between ester/pressboard and mineral
oil/pressboard becomes smaller under negative polarity.
At the gap distance of 25 mm, it was found that introduction
of pressboard has no influence on the streamer velocities in
both ester liquids and mineral oil, as shown in Figure 22. With
gap distance increasing to 50 mm, acceleration of velocity by
pressboard was observed at very high voltage levels (higher
than acceleration voltage) in ester liquids, as shown in
Figure 23. Such an effect is more obvious at the large gap
distance of 100 mm, of which the velocity acceleration by
pressboard occurred earlier at lower voltage levels for both
ester liquids and mineral oil, as reported in [3]. Overall, if
taking acceleration voltage as the only criterion, pressboard
has no influence for negative polarity in the investigated range.
Figure 22. Average propagation velocity of negative streamers on pressboard
surface in the three liquids at gap distance of 25 mm.
Figure 23. Average propagation velocity of negative streamers on pressboard
surface in the three liquids at gap distance of 50 mm.
At negative overstressed voltages, long black scar which
connects point and plane electrode was observed on
ester/pressboard interface, as shown in Figure 24a. It is
interesting to see the existence of both black scar and white
mark on the ester/pressboard interface, as shown in
Figure 24b. For Gemini X/pressboard interface, long thick
black scar was usually observed at overstressed voltages as
shown in Figure 24c. With further increased voltage, bulk
protrusion caused by excessive energy could be occasionally
observed, which seems to indicate the under-surface damage
of pressboard, as shown in Figure 24d.
9. 1916 Q. Liu and Z. D. Wang: Streamer Characteristic and Breakdown in Synthetic and Natural Ester Transformer Liquids
Figure 24. Surface mark on pressboard at overstressed voltages under
negative polarity: (a) Long black scar on FR3/pressboard interface, d=50 mm,
V=-250 kV, (b) Black scar with white mark on Midel 7131/pressboard
interface, d=50 mm, V=-255 kV, (c) Long thick black scar on Gemini
X/pressboard interface, d=50 mm, V=-310 kV, (d) Black scar with bulk
protrusion on Gemini X/pressboard interface, d=50 mm, V=-320 kV.
6 CONCLUSIONS
Streamer characteristics and breakdown in synthetic and
natural ester transformer liquids with pressboard interface
were investigated under both positive and negative
lightning impulse voltages. Experiments were carried out in
a divergent point-plane field at three stages of pre-
breakdown, breakdown and overstressed conditions.
At pre-breakdown stage, streamers on ester/pressboard
interface resemble the characteristics of streamers in open
gaps and introduction of pressboard interface has no
influence on the streamer stopping length. Streamers on
ester/pressboard interface generally propagate further than
on mineral oil/pressboard interface at the same voltage
level, especially under negative polarity.
Presence of pressboard does not weaken the 50%
breakdown voltage under both positive and negative
polarities in the investigated gap distances up to 75 mm.
Breakdown voltages on ester/pressboard interface are lower
than those on mineral oil/pressboard interface, and this
difference is magnified at larger gap distances. Surface
damages on the pressboard were only observed after
breakdown under negative polarity, which are more
obvious in mineral oil than in ester liquids. Care should be
taken for breakdown tests on mineral oil/pressboard
interface under negative polarity, since an accumulative
promoting effect from streamer on subsequent streamer
propagation was observed, which however did not occur on
ester/pressboard interface.
At overstressed conditions, introduction of pressboard
interface significantly reduces the positive acceleration
voltage in mineral oil rather than in ester liquids. Surface
mark after positive breakdown can be seen on mineral
oil/pressboard interface but hardly for ester/pressboard
interface. Under negative polarity, presence of pressboard
tends to accelerate the streamer velocity at larger gap
distances and under higher voltages in both ester liquids
and mineral oil. Obvious surface marks including long
thick black scar and white tree were observed on
pressboard after negative breakdown. Overall, acceleration
voltages on ester/pressboard interface are still lower than
those on mineral oil/pressboard interface, which indicates
the lower tolerance to faster streamers on ester/pressboard
interface.
ACKNOWLEDGEMENT
The authors would like to express their gratitude to
ALSTOM Grid, M&I Materials, National Grid, Scottish
Power, TJ|H2b Analytical Services and UK Power Networks
for their financial and technical contributions to the research
consortium on ‘application of alternative oils for large power
transformers’ at The University of Manchester. Sincere
thanks are given to EPSRC Instrument Pool for the loan of
high speed camera. Last but not least, due appreciations are
expressed for the inspiration given by colleagues at CIGRE
WG D1.31 during those extremely useful meetings and
discussions.
REFERENCES
[1] C. T. Duy, O. Lesaint, A. Denat, and N. Bonifaci, "Streamer
propagation and breakdown in natural ester at high voltage", IEEE
Trans. Dielectr. Electr. Insul., Vol. 16, pp. 1582-1594, 2009.
[2] K. J. Rapp, J. Corkran, C. P. McShane, and T. A. Prevost,
"Lightning impulse testing of natural ester fluid gaps and insulation
interfaces", IEEE Trans. Dielectr. Electr. Insul., Vol. 16, pp. 1595-
1603, 2009.
[3] L. Rongsheng, C. Tornkvist, V. Chandramouli, O. Girlanda, and L.
A. A. Pettersson, "Ester fluids as alternative for mineral oil: The
difference in streamer velocity and LI breakdown voltage", IEEE.
Conf. Electr. Insul. Dielectr. Phenomena (CEIDP), Virginia, USA,
pp. 543-548, 2009.
[4] Q. Liu and Z. D. Wang, "Streamer characteristic and breakdown in
synthetic and natural ester transformer liquids under standard
lightning impulse voltage", IEEE Trans. Dielectr. Electr. Insul.,
Vol. 18, pp. 285-294, 2011.
[5] K. J. Rapp, C. P. McShane, J. Vandermaar, D. Vukovic, and S.
Tenbohlen, "Long gap breakdown of natural ester fluid", Intern.
Conf. High Voltage Eng. and Applicat. (ICHVE), New Orleans,
USA, pp. 104-107, 2010.
[6] J. Dai, Z. D. Wang, and P. Jarman, "Creepage discharge on
insulation barriers in aged power transformers", IEEE Trans.
Dielectr. Electr. Insul., Vol. 17, pp. 1327-1335, 2010.
[7] J. C. Devins and S. J. Rzad, "Streamer Propagation in Liquids and
over Liquid-Solid Interfaces", IEEE Trans. Dielectr. Electr. Insul.,
Vol. 17, pp. 512-516, 1982.
[8] O. Lesaint and G. Massala, "Transition to fast streamers in mineral
oil in the presence of insulating solids", IEEE Intern. Symp. Electr.
Insul. (ISEI), Montreal, Canada, pp. 737-740, 1996.
[9] L. Lundgaard, D. Linhjell, G. Berg, and S. Sigmond, "Propagation
of positive and negative streamers in oil with and without
pressboard interfaces", IEEE Trans. Dielectr. Electr. Insul., Vol. 5,
pp. 388-395, 1998.
[10] A. Beroual and L. Kebbabi, "Influence of the voltage waveform
and hydrostatic pressure on morphology and final length of
discharges propagating over solid-liquid interfaces", IEEE Trans.
Dielectr. Electr. Insul., Vol. 16, pp. 1574-1581, 2009.
[11] H. Yamamoto, S. Uozaki, R. Hanaoka, S. Takata, Y. Kanamaru,
and Y. Nakagami, "Creeping discharges in transformer oil under
lightning impulse voltages over 100 kV peak value", IEEE Intern.
Conf. Dielectr. Liquids (ICDL), Poitiers, France, pp. 1-4, 2008.
[12] R. Hanaoka, T. Kohrin, Y. Genba, R. Ishibashi, T. Miyamoto, and
T. Nishi, "Impulse creeping discharge along the surface of
polyethylene wire immersed in transformer oil", Elect. Electron.
Insul. Conf. and Elect. Manufacturing Coil Winding Conf.,
Rosemont, USA, pp. 113-117, 1995.
[13] Y. Nakao, M. Naruse, Y. Suzuki, H. Itoh, Y. Sakai, and H.
Tagashira, "Influence of insulating barrier on the creepage
discharge in transformer oil", IEEE Trans. Dielectr. Electr. Insul,
Vol. 4, pp. 775-779, 1997.
[14] S. Arazoe, D. Saruhashi, Y. Sato, S. Yanabu, G. Ueta, and S.
Okabe, "Electrical characteristics of natural and synthetic
insulating fluids", IEEE Trans. Dielectr. Electr. Insul, Vol. 18, pp.
506-512, 2011.
10. IEEE Transactions on Dielectrics and Electrical Insulation Vol. 18, No. 6; December 2011 1917
[15] L. Rongsheng and A. Jaksts, "Breakdown processes in
transformer insulation under LI voltages", IEEE Intern. Conf.
Dielectr. Liquids (ICDL), Coimbra, Portugal, pp. 75-78, 2005.
[16] A. Beroual and A. Zouaghi, "Barrier effect on the prebreakdown
and breakdown phenomena in long oil gaps", IEEE Intern. Conf.
Dielectr. Liquids (ICDL), Rome, Italy pp. 300-303, 1996.
[17] G. Massala and O. Lesaint, "Positive streamer propagation in
large oil gaps: electrical properties of streamers", IEEE Trans.
Dielectr. Electr. Insul, vol. 5, pp. 371-381, 1998.
[18] G. Massala and O.Lesaint, "A comparison of negative and
positive streamers in mineral oil at large gaps", J. phys. D: Appl.
phys., Vol. 34, p. 1525, 2001.
[19] O. Lesaint and G. Massala, "Positive streamer propagation in
large oil gaps: experimental characterization of propagation
modes", IEEE Trans. on Dielectr. Electr. Insul, Vol. 5, pp. 360-370,
1998.
[20] O. Lesaint, ""Streamers" in liquids: Relation with practical high
voltage insulation and testing of liquids", IEEE Intern. Conf.
Dielectr. Liquids (ICDL), Poitiers, France, pp. 1-6, 2008.
[21] Q. Liu, Z.D.Wang, P. Dyer, and D. Walker, "Accumulative Effect
on Streamer Propagation of Lightning Impulses on Oil/Pressboard
Interface", IEEE Intern. Conf. Dielectr. Liquids (ICDL),
Trondheim, Norway, paper 56, 2011.
[22] T. Chao, G. Chen, M. Fu, and L. Rui-jin, "Space charge behavior
in multi-layer oil-paper insulation under different DC voltages and
temperatures", IEEE Trans. on Dielectr. Electr. Insul., Vol. 17, pp.
775-784, 2010.
[23] K. Nakamura, K. Kato, H. Koide, K. Fujii, and H. Okubo, "Kerr
electro-optic measurement of electric field distribution in rapeseed
ester oil and pressboard composite system", IEEE Intern. Conf.
Dielectr. Liquids (ICDL), Coimbra, Portugal, pp. 405-408, 2005.
Qiang Liu (S’08) received the B.Eng. degree in
electrical engineering from Xi’an Jiaotong
University of China in 2005 and the M.Eng. degree
in high voltage and electrical insulation from Xi’an
Jiaotong University of China in 2008. He is currently
a Ph.D. student at the Electrical Energy and Power
Systems Group of the School of Electrical and
Electronic Engineering at The University of
Manchester, UK. His research interests are on pre-
breakdown and breakdown properties of transformer
liquid and solid insulation under impulse voltage,
streaming electrification of liquids, oxidation of natural esters and in-service
ageing of transformer insulation.
Zhongdong Wang (M’00) received the B.Eng. and
the M.Eng. degrees in high voltage engineering from
Tsinghua University of Beijing in 1991 and 1993,
respectively and the Ph.D. degree in electrical
engineering from UMIST in 1999. Currently she is a
Professor of High Voltage Engineering at the
Electrical Energy and Power Systems Group of the
School of Electrical and Electronic Engineering at
The University of Manchester. Her current research
interests include condition monitoring, transformer
modeling and FRA & transients’ simulation, insulation ageing and alternative
insulation materials for transformers.