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Polymeric composite insulators are subjected to varying work conditions like rain and heat, which create an impact on degradation during their long service period. Electrical tracking under the Alternating Current (AC) field plays a predominant role in surface degradation, which can be different for fresh and aged insulations. The tracking studies on the fresh and aged polymeric insulation therefore become significant. Motivated by this, an indigenous low-cost electrical tracking setup was developed, and the tracking studies were carried out as per International Electro technical Commission standard (IEC) 60587 on fresh, thermal-aged and water-aged silicone rubber samples. Contact angles of samples were measured to analyse the effect of ageing on hydrophobicity. Further, to analyse the influence of ageing on insulation integrity, tracking tests were conducted and parameters like leakage current pattern and magnitudes, tracking length and loss of weight in the material due to tracking were examined. The physicochemical impacts of ageing on the surface degradation of the samples were also analysed using X-ray diffraction analysis and Fourier Transform Infrared Spectroscopy analysis. The investigations added insight into the degradation mechanism of polymeric insulators in terms of their electrical performance and physicochemical changes in the material. Comparison of these changes showed that ageing could influence surface degradation of samples.

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The preliminary signs of diabetic retinopathy include micro aneurysms, haemorrhages and exudates. Early diagnosis and timely treatment can prevent vision loss in patients with long term diabetes. In this paper we used two algorithm based on filtering operations, morphological transformation and region growing method to extract features for detection of micro aneurysms, haemorrhage and non linear diffusion segmentation followed by colour histogram based clustering techniques is used to differentiate hard and soft exudates. Experimental evaluation of the algorithm has been done with images collected from Deepam Eye Hospital, Chennai, Tamilnadu, India and a database consisting of 77 abnormal and 20 normal images was created. In addition performance of the proposed algorithm is also verified on the publically available DIARETDBO database. Based on the features obtained, each image is classified as normal or abnormal with Support Vector Machine, BayesianNetwork. Classification rate of 95% is obtained with SVM and 90% with Bayesian classifier.

The theory of reference frames and switching functions are effective in analyzing the performance of the induction motor fed from VSI (Voltage Source Inverter). In this work, mathematical model of Adjustable Speed Drive (ASD) is developed by taking synchronous reference frame equations for induction motor, switching function concept for VSI and non-switching concept for diode bridge rectifier. Simulation model of induction machine is implemented using dq0 axis transformations of the stator and rotor variables in the arbitrary reference frame. The corresponding equations are given in the beginning and then the developed model is implemented using MATLAB/Simulink. In this work, the proposed model is implemented using basic function blocks. The performance of induction motor is analysed for different frequencies. The developed model is tested for the steady state behavior of machine drive. The proposed mathematical model is validated by the simulation results. Keyword: Converters INTRODUCTIONIn many industrial applications Adjustable speed drives (ASD) are most commonly seen workhorses. In order to supply the motor with variable AC voltage or AC current with variable frequency Variable Frequency Drives (VFD) are employed. ASDs are used in pumping applications, in sugar cane industries, conveyor applications etc. The common VFD consists of a three phase diode bridge rectifier, dc link and a pulse width modulated inverter. It is necessary to develop a model for VFD for power system dynamic studies. In literature, for the three phase diode bridge rectifier dq impedance model is employed [1]. State-space averaging method is used for modeling a three phase four wire diode bridge rectifier [2]. Dynamic average value modeling methods are utilized for conventional three phase diode bridge rectifier and are validated [3]. This can capture the steady-state and transient characteristics of the diode bridge rectifier. An approximate switching function of the diode bridge rectifier is used in order to obtain the estimating function for the fundamental current harmonics [4].This method is proven to be effective in finding out the input current harmonic content. A switching function model for voltage source inverter is derived and also it is validated using MATLAB/Simulink [5].Modulation function theory is effectively utilized for deriving the Pulse Width Modulated (PWM) inverter which makes use of the Iterative Harmonic and Interharmonics Analysis (IHIA) [6]. Space vector pulse width modulation method is employed for inverter and the method is validated using MATLAB/Simulink [7]. A three phase boost dc-ac converter is used to supply the induction motor [8]. AC output voltage that is greater than the input dc voltage is obtained without the need of additional boost converter.

Single Inductor (SI) converters with the advantage of using one inductor for any number of inputs/outputs find wide applications in portable electronic gadgets and electrical vehicles. SI converters can be used in Single Input Multiple Output (SIMO) and Multiple Input Multiple Output (MIMO) configurations but they need controllers to achieve good transient and steady state responses, to improve the stability against load and line disturbances and to reduce cross regulation. Cross regulation is the change in an output voltage due to change in the load current at another output and it is an added constraint in SI converters. In this paper, Single Input Dual Output (SIDO) and Dual Input Dual Output (DIDO) converters with applications capable of handling high load current working in Continuous Conduction Mode (CCM) of operation are taken under study. Conventional multivariable PID and optimal Linear Quadratic Regulator (LQR) controllers are developed and their performances are compared for the above configurations to meet the desired objectives. Generalized mathematical models for SIMO and MIMO are developed and a Genetic Algorithm (GA) is used to find the parameters of a multivariable PID controller and the weighting matrices of optimal LQR where the objective function includes cross regulation as a constraint. The simulated responses reveal that LQR controller performs well for both the systems over multivariable PID controller and they are validated by hardware prototype model with the help of DT9834® Data Acquisition Module (DAQ). The methodologies used here generate a fresh dimension for the case of such converters in practical applications.

Micro-sized aluminum trihydrate (ATH) filled silicone rubber is useful as insulation in the electric power system. The addition of nanofillers can improve further, its overall performance. However, the degradation of such silicone insulator due to ageing has not yet been thoroughly analysed. Motivated by this, an investigation was done to observe the effect of ageing on the tracking, and the material characteristics of SiO2 nanofillers added micro-sized ATH-filled Silicone rubber. For this, the samples were prepared using different weight percentage of SiO2 nanofillers and were thermally-aged and water-aged in the laboratory environment. A well-regulated tracking-test setup was assembled, and the leakage current characteristics of the fresh, thermal-aged and water-aged samples were observed, as per international electro technical commission standard (IEC) 60,587. After tracking, the surface morphology of these samples was studied using scanning electron microscopy (SEM). Further, energy dispersive X-ray analysis (EDAX) was carried out to observe the elements present at the surface and, Fourier transform infra-red (FTIR) spectroscopy was conducted to study the changes in the chemical structure. Investigations through the leakage current, SEM, EDAX and FTIR revealed that the addition of nanofillers improved the tracking characteristics of the aged hybrid composite insulation samples, thereby minimising any early failures.

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