Investigations of Accelerated Aged Polymeric Insulators Using Partial Discharge Signal Measurement and Analysis

Mekala, K.,Chandrasekar, S.,Ravindran, R. Samson The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.1

Reduction in pollution performance of polymeric insulators, aged due to water absorption stress and thermal stress, is a major threat to the reliable operation of power transmission and distribution system. Formation of partial discharges on the surface of wet polluted insulator plays a major role in determining the life time and pollution performance of outdoor polymeric insulators. However, reports on partial discharge characteristics of water absorption stress aged and thermal aged polymeric insulators are scanty. This paper discusses the pollution performance characteristics of accelerated aged polymeric insulators using the advanced ultra wide band PD signal measurement and analysis. Laboratory experiments on accelerated aged polymeric insulators were carried out as per IEC 60507 under AC voltage, at different humidity and contamination levels using NaCl as a contaminant. PRPD pattern and Time-Frequency map analysis of PD signals were carried out. From the results, it can be speculated that PD analysis is a well suited technique to understand the pollution performance of aged polymeric insulators.

Synthesis and Biological Evaluation of Some Novel [4-(1H-Benzoimidazol-2-yl)-thiazol-2-yl]-benzylidene-amines and N-[4-(1H-Benzoimidazol-2-yl)-thiazol-2-yl]-N'-benzylidene-hydrazines

Mekala, Raghu Vardhan Reddy,Danda, Ravinder Reddy,Gadegoni, Hemalatha Korean Chemical Society 2013 대한화학회지 Vol.57 No.1

A new family of thiazole heterocycles, namely [4-(1H-benzoimidazol-2-yl)-thiazol-2-yl]-benzylidene-amines has been synthesized by the condensation of 4-(1H-Benzoimidazol-2-yl)-thiazol-2-ylamine with various aromatic aldehydes and N-[4-(1H-benzoimidazol-2-yl)-thiazol-2-yl]-N'-benzylidene-hydrazines through the cyclization of 1-(1H-benzoimidazol-2-yl)-2-bromo-ethanone with arylthiosemicarbazones. The target compounds are achieved by using 1-(1H-Benzoimidazol-2-yl)-ethanone as starting material. The chemical structures of all newly synthesized compounds were confirmed by their IR, $^1H$ NMR and Mass spectral data. Further the compounds were used to evaluate their antimicrobial activity and found that the appreciable antimicrobial activity by some of the title compounds.

Preparation of Activated Carbon Fibers from Cost Effective Commercial Textile Grade Acrylic Fibers

Mekala Bikshapathi,Nishith Verma,Rohitashaw Kumar Singh,Harish Chandra Joshi,Anurag Srivastava 한국탄소학회 2011 Carbon Letters Vol.12 No.1

Activated carbon fibers (ACFs) were prepared from cost effective commercial textiles through stabilization, carbonization, and subsequently activation by carbon dioxide. ACFs were characterized for surface area and pore size distribution by physical adsorption of nitrogen at 77 K. ACFs were also examined for various surface characteristics by scanning electron microscopy, Fourier transform infrared spectroscopy, and CHNO elemental analyzer. The prepared ACFs exhibited good surface textural properties with well developed micro porous structure. With improvement in physical strength, the commercial textile grade acrylic precursor based ACFs developed in this study may have great utility as cost effective adsorbents in environmental remediation applications.

Investigations of Accelerated Aged Polymeric Insulators Using Partial Discharge Signal Measurement and Analysis

K. Mekala,S. Chandrasekar,R. Samson Ravindran 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.1

Reduction in pollution performance of polymeric insulators, aged due to water absorption stress and thermal stress, is a major threat to the reliable operation of power transmission and distribution system. Formation of partial discharges on the surface of wet polluted insulator plays a major role in determining the life time and pollution performance of outdoor polymeric insulators. However, reports on partial discharge characteristics of water absorption stress aged and thermal aged polymeric insulators are scanty. This paper discusses the pollution performance characteristics of accelerated aged polymeric insulators using the advanced ultra wide band PD signal measurement and analysis. Laboratory experiments on accelerated aged polymeric insulators were carried out as per IEC 60507 under AC voltage, at different humidity and contamination levels using NaCl as a contaminant. PRPD pattern and Time-Frequency map analysis of PD signals were carried out. From the results, it can be speculated that PD analysis is a well suited technique to understand the pollution performance of aged polymeric insulators.

Osteoblast Differentiation of Umbilical Cord Blood-Derived Mesenchymal Stem Cells and Enhanced Cell Adhesion by Fibronectin

( Naveen Kumar Mekala ),( Rama Raju Baadhe ),( Sreenivasa Rao Parcha ),( Prameela Devi Y ) 한국조직공학·재생의학회 2012 조직공학과 재생의학 Vol.9 No.5

Mononuclear cells isolated from human umbilical cord blood were differentiated in to spindle shaped fibrous mesenchymal stem cells (MSCs) in DMEM with 10% fetal bovine serum. These progenitor cells were further examined for their ability to differentiate into osteoblasts by culturing them in osteogenic differentiation media (Stem Pro(R)). Calcium mineralization assay, alizarin red S, von kossa staining confirmed that MSCs from cord blood were capable of mineralization when they were cultured in osteogenic medium. The adhesion studies shown that MSCs have greater affinity towards fibronectin (FN) coated dishes, compared to albumin (Alb) coated dishes due to CD29and CD44 surface receptors.

Molecular Level Characterization of L-Ascorbic Acid Induced Osteoblasts from Umbilical Cord Blood Source

Naveen Kumar Mekala,Rama Raju Baadhe,Sreenivasa Rao Parcha 한국조직공학과 재생의학회 2013 조직공학과 재생의학 Vol.10 No.4

Mesenchymal stem cells (MSCs) isolated from umbilical card blood were capable of differentiated in to multiple mesenchymal cell lineages. The objective of the current study was to establish a reproducible system for the in vitro osteogenic differentiation of human MSCs, and to characterize the effect of changes in the microenvironment upon differentiation. In our previous studies, MSCs cultured in varying concentrations of L-ascorbic acid (50µM to 500µM) had shown the various levels of osteoblast differentiation, as determined by morphology, alkaline phosphatase activity, modulations in osteocalcin mRNA expression, and mineralized extracellular matrix (ECM) deposition holding inorganic hydroxyapatite (HA) and Tricalcium phosphate (TCP). In present study, we noticed a study increase in APase activity up to 250µM L-ascorbic acid and by end of 16 days, cells gained cuboidal morphology, which is characteristic feature of osteoblasts. The intense sharp difractograms (peaks) between 30o-35o demonstrate the deposition of HA and TCP, which are major inorganic components of bone. The reproducible results of our studies provided a useful model for evaluating the factors responsible for the stepwise progression of cells from undifferentiated precursors to secretary osteoblasts, and eventually terminally differentiated osteocytes.

Investigations on properties of ceno PCM produced via sonication process for thermal comfort building

R. Greesan,C. Mekala,M. Ravichandran 한양대학교 세라믹연구소 2021 Journal of Ceramic Processing Research Vol.22 No.6

The sustainable development can be achieved by means of optimal usage of energy in each and every industry. According toour building sector, eco-friendly construction is achieved by utilizing the resources in right way with minimal wastage andmaximum usage. The Phase Change Material is such a solution to build an energy efficient building with minimal consumptionof energy resources because of its thermal characteristics. The paper revealed the usage of encapsulated PCM in buildingconstruction to achieve thermal stability structure without affecting its strength and durability. Sonication method isimplemented to make a encapsulated PCM called Ceno-PCM. For the composite sample, cenosphere of 100 μm is mixedthoroughly with liquid paraffin under ultrasonic heat waves and the sample specimen shows the better results after it gettingdried in oven up to 80ºC. The experimental investigations are examined through FESEM EDX, TGA etc, to observe theperformance of the sample and it also gives the appreciable results. Mechanical properties are examined through the respectivetesting with the mortar specimen of different percentage level of Composite PCM and the results are summarized to concludethe optimal level of PCM.

Tracking/Erosion Resistance Analysis of Nano-Al(OH)₃ Filled Silicone Rubber Insulating Materials for High Voltage DC Applications

Kannan, P.,Sivakumar, M.,Mekala, K.,Chandrasekar, S. The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.1

HVDC technology has become popular as an economic mode of bulk power transmission over very long distances. Polymeric insulators in HVDC power transmission lines are affected by surface tracking and erosion problems due to contamination deposit, which pose a greater challenge in maintaining the reliability of the HVDC system. In addition, polymeric insulators are also naturally affected by aging due to various environmental stresses, which in turn accelerates the surface tracking and erosion problems. Research works towards the improvement of tracking and erosion resistance of polymeric insulators by adding nano-sized fillers in the base material are being carried out worldwide. However, surface tracking and erosion performance of nano-filled aged polymeric insulators for HVDC applications are not well reported. Hence, in the present work, tracking and erosion resistance of the nano $Al(OH)_3$ filled silicone rubber insulation material has been evaluated under DC voltages at different filler concentrations and aged conditions, as per IEC 60587 test procedures. Leakage current and contact angle measurements were carried out to understand the surface hydrophobicity. Moving average technique was used to analyze the trend followed by leakage current. Water aged specimen shows less tracking resistance when compared with thermal aged specimen. It is observed that nano-filler concentration of 5% is even sufficient to get better tracking/erosion resistance under DC voltages.

Tracking/Erosion Resistance Analysis of Nano-Al(OH)₃ Filled Silicone Rubber Insulating Materials for High Voltage DC Applications

P. Kannan,M. Sivakumar,K. Mekala,S. Chandrasekar 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.1

HVDC technology has become popular as an economic mode of bulk power transmission over very long distances. Polymeric insulators in HVDC power transmission lines are affected by surface tracking and erosion problems due to contamination deposit, which pose a greater challenge in maintaining the reliability of the HVDC system. In addition, polymeric insulators are also naturally affected by aging due to various environmental stresses, which in turn accelerates the surface tracking and erosion problems. Research works towards the improvement of tracking and erosion resistance of polymeric insulators by adding nano-sized fillers in the base material are being carried out worldwide. However, surface tracking and erosion performance of nano-filled aged polymeric insulators for HVDC applications are not well reported. Hence, in the present work, tracking and erosion resistance of the nano Al(OH)₃ filled silicone rubber insulation material has been evaluated under DC voltages at different filler concentrations and aged conditions, as per IEC 60587 test procedures. Leakage current and contact angle measurements were carried out to understand the surface hydrophobicity. Moving average technique was used to analyze the trend followed by leakage current. Water aged specimen shows less tracking resistance when compared with thermal aged specimen. It is observed that nanofiller concentration of 5% is even sufficient to get better tracking/erosion resistance under DC voltages.

Conductivity enhancement in K+-ion conducting solid polymer electrolyte [PEG : KNO3] and its application as an electrochemical cell

Polu Anji Reddy,Kareem Aseel Abdulameer,Kim Kwangmin,Kim Dongkyu,Venkanna Mekala,Rasheed Hussein Kh.,Kumar Kanapuram Uday 한국화학공학회 2023 Korean Journal of Chemical Engineering Vol.40 No.12

The solution-cast method was used to prepare new solid polymer electrolytes (SPEs) that conduct potassium ions and are based on polyethylene glycol (PEG) complexed with potassium nitrate (KNO3). This polymer electrolyte system was characterized using different experimental techniques, such as X-ray diffraction (XRD), differential scanning calorimetry (DSC), composition vs. conductivity, temperature vs. conductivity, frequency-dependent conductivity, and dielectric measurements. The degree of crystallinity decreased with increasing salt concentration, according to the X-ray diffraction and DSC patterns of PEG with KNO3 salt. For PEG: KNO3 (80 : 20) composition, an optimum conductivity of 8.24× KT−6 S/cm was recorded at 30 °C. Compared with pure PEG, the optimum conducting composition (OCC) conductivity increased by two orders of magnitude. The temperature range of 303 to 333 K was used for the temperature-dependent conductivity experiments. The findings demonstrate that the conductivity obeys the Arrhenius rule and increases as the temperature rises. A dc plateau and a dispersive zone were observed in the conductance spectrum, which also follows Jonscher’s power law. It was investigated how temperature and frequency affect the dielectric permittivity. An electrochemical cell with the configuration K/(80PEG : 20KNO3)/(I2+C+electrolyte) was constructed using an 80 : 20 electrolyte system, and its discharge properties were investigated. The cell’s open circuit voltage was measured at 2.48 V.