A. Krishnan

K. S. Rangasamy College of Technology, Periyār, Tamil Nadu, India

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Publications (77)

  • M. Srinivasan · A. Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: The Hot Spot Temperature (HST) value depends on the ambient temperature, the rise in the top oil temperature (TOT) over the ambient temperature, and the rise in the winding HST over the top oil temperature. In this paper a new semi-physical model comprising of the environmental variables for the estimation of HST in transformer is proposed and also MATLAB/Simulink-based valid model of hot spot temperature under variable environmental condition is proposed. The winding hot-spot temperature can be calculated as a function of the top-oil temperature that can be estimated using the transformer loading data, top oil temperature lagged regressor value, ambient temperature, wind velocity and solar heat radiation effect. The estimated HST is compared with measured data of a power transformer in operation. The proposed model has been validated using real data gathered from a 100 MVA power transformer.
    Article · Jan 2013 · WSEAS Transactions on Power Systems
  • Source
    M.Srinivasan · A.Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: The Hot Spot Temperature (HST) value depends on the ambient temperature, the rise in the top oil temperature (TOT) over the ambient temperature, and the rise in the winding HST over the top oil temperature. In this paper a new semi-physical model comprising of the environmental variables for the estimation of HST and loss of insulation life in transformer is proposed. The winding hot-spot temperature can be calculated as a function of the top-oil temperature that can be estimated using the transformer loading data, top oil temperature lagged regressor value, ambient temperature, wind velocity and solar heat radiation effect. The estimated HST is compared with measured data of a power transformer in operation. The proposed model has been validated using real data gathered from a 100 MVA power transformer
    Full-text available · Article · Oct 2012
  • Source
    M Srinivasan · A Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: The hot spot temperature (HST) plays a most important role in the insulation life of the transformer. Ambient temperature and environmental variable factors involved in the top oil temperature (TOT) computations in all transformer thermal models affects insu-lation lifetime either directly or indirectly. The importance of the ambient temperature in transformer's insulation life, a new semi-physically-based model for the estimation of TOT in transformers has been proposed in this paper. The winding hot-spot tem-perature can be calculated as function of the TOT that can be estimated by using the ambient temperature, wind velocity and solar heat radiation effect and transformer loading measured data. The estimated TOT is compared with measured data of a dis-tribution transformer in operation. The proposed model has been validated using real data gathered from a 100 MVA power transformer. For a semi-physically-based model to be acceptable, it must have the qualities of: adequacy, accuracy and consistency. We assess model adequacy using the scale: prediction R 2 , and plot of residuals against fitted values. To assess model consistency, we use: variance inflation factor (VIF) (which mea-sure multicollinearity), condition number. To assess model accuracy we use mean square error, maximum and minimum error values of semi-physically-based model parameters to the existing model parameters.
    Full-text available · Article · Oct 2012 · International Journal of Reliability Quality and Safety Engineering
  • M.Srinivasan · A.krishnan
    [Show abstract] [Hide abstract] ABSTRACT: The Hot Spot Temperature (HST) value depends on the ambient temperature, the rise in the Top Oil Temperature (TOT) over the ambient temperature, and the rise in the winding HST over the top oil temperature. In this paper a new semi-physical model comprising of the environmental variables for the estimation of HST in transformer is proposed and also MATLAB/Simulink-based valid model of hot spot temperature under variable environmental condition is proposed. The winding hot-spot temperature can be calculated as a function of the top-oil temperature that can be estimated using the transformer loading data, top oil temperature lagged regressor value, ambient temperature, wind velocity and solar heat radiation effect. The estimated HST is compared with measured data of a power transformer in operation
    Article · Jun 2012
  • Thangaprakash Sengodan · Ammasai Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: This paper presents a modification in pulse width modulation (PWM) scheme with unequal shoot-through distribution for the Z-source inverter (ZSI) which can minimize ripples in the current through the Z-source inductors as well as the voltage across the Z-source capacitors. For the same system parameters, the proposed control technique provides better voltage boost across the Z-source capacitor, DC-link, and also the AC output voltage than the traditional PWM. The ripples in the Z-network elements are found to be reduced by 75% in the proposed modulation scheme with optimum harmonic profile in the AC output. Since the Z-network requirement will be based on the ripple profile of the elements, the Z-network requirements can be greatly reduced. The effectiveness of the proposed modulation scheme has been simulated in Matlab/Simulink software and the results are validated by the experiment in the laboratory. © 2012 Institute of Automation, Chinese Academy of Sciences and Springer-Verlag Berlin Heidelberg.
    Article · Apr 2012 · International Journal of Automation and Computing
  • P. Babu · A. Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: In this paper a modified version of the Akthar's method for online secondary path modeling in active noise control systems is proposed. The proposed method defines two variable step sizes for control filter and modeling filter. The control filter step size μm is adapted by using the variable threshold value Tj and the modeling filter step size μm is adapted by using a new modified variable step size (MVSS) in least mean square (LMS) algorithm. The step size of the modeling filter is varied in accordance with the ratio of power of the disturbance signals. In many ANC applications, online secondary path modeling method using white noise as training signal is required to ensure convergence of the system. The proposed method stops injection of white noise, when desired signal d(n) is equal to secondary signal ù(n) using wavelet denoising. The method uses two types of wavelet thresholds. One is modified soft threshold and other is soft threshoding. It is shown in the proposed ANC system with modified soft threshoding, in addition to soft threshoding, the residual error signal and the secondary path modeling error can be reduced at a fast convergence rate than Akthar's method. The computer simulation results indicate the effectiveness of the proposed approach.
    Article · May 2011
  • Ponnusamy Kumar · A. Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: This paper presents a performance study of the distributed coordination function (DCF) of 802.11 networks considering erroneous channel and capture effects under non-saturated traffic conditions employing a basic access method. The aggregate throughput of a practical wireless local area network (WLAN) strongly depends on the channel conditions. In a real radio environment, the received signal power at the access point from a station is subjected to deterministic path loss, shadowing, and fast multipath fading. The binary exponential backoff (BEB) mechanism of IEEE 802.11 DCF severely suffers from more channel idle time under high bit error rate (BER). To alleviate the low performance of IEEE 802.11 DCF, a new mechanism is introduced, which greatly outperforms the existing methods under a high BER. A multidimensional Markov chain model is used to characterize the behavior of DCF in order to account both non-ideal channel conditions and capture effects. KeywordsIEEE 802.11–distributed coordination function (DCF)–binary exponential backoff (BEB)–erroneous channel–capture–fading–bit error rate (BER)–non-saturation throughput
    Article · May 2011 · International Journal of Automation and Computing
  • M. Arun · A Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: Problem statement: In this study we discus about Signature Detection Technique (SDT) used in Network Intrusion Detection System (NIDS). Design of SDT using Content Addressable Memory (CAM) is discussed. Approach: Two novel architectures, XOR and ones count based Pre computation CAM architectures are proposed and implemented in third party back end tool with 0.18 mm technology, power consumptions are compared. Results: Proposed architecture consumes 90% less power added with 5.2% increment in speed. Conclusion: Power reduction was achieved by reducing the number of bit comparisons of pre computation technique.
    Article · Apr 2011 · Journal of Computer Science
  • E. Jayabalan · A. Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: Image Registration is the basic step used for the target tracking in aerial videos. Image Registration is a process, which finds the location where optimal matching is obtained by matching a template image called the reference image over the searching region of an input image using a suitable similarity measures. The method although computationally intensive, is simple, straightforward and robust and requires no apriori information about the two images. A number of image registration algorithms are studied on images with varying size of search space and reference image. All these algorithms are based on similarity measure between the reference image and search space. The key issues in image registration are the time required for registration and the accuracy of registration viz., measure of how close is the match between sub image in the search space and the reference image.
    Article · Mar 2011
  • E. Jayabalan · A. Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: In real time situations, non rigid object tracking is a challenging and important problem. Due to the non rigid nature of objects in most of the tracking applications, deformable models are appealing in tracking tasks because of their capability and flexibility. The proposed approach uses an observation model based on optical flow information used to know the displacement of the objects present in the scene. After finding the moving regions in the initial frame, we are applying active contour model (ACM) to track the moving objects in the further frames dynamically. These models have been used as a natural means of incorporating flow information into the tracking. The formulation of the Active Contour Model by incorporating an additional force driven optical flow field improves the tracking speed. This algorithm efficiently works to track for low contrast videos like Aerial videos.
    Article · Mar 2011
  • P. Babu · A. Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: In this paper a modified version of the Akthar's method for online secondary path modeling in active noise control systems is proposed. The proposed method defines two variable step sizes for control filter and modeling filter respectively. The control filter step size μw is adapted by using the variable threshold value Tj and the modeling filter step sizeμm is adapted by using a new modified variable step size (MVSS) in least mean square (LMS) algorithm. The step size of the modeling filter is varied in accordance with the ratio of power of the disturbance signals. In many ANC applications, online secondary path modeling method using a white noise as a training signal is required to ensure convergence of the system. The proposed method also uses white noise as a training signal, which is optimized based on the error signal. The method stops injection of the white noise, when desired signal d(n) is equal to secondary path signal u'(n). In addition that, the error e(n) is denoised using wavelet transform on the hope of improving signal to noise ratio. The computer simulation shows that the residual error and the secondary path modeling error of the proposed method can be reduced at a fast convergence rate than the Akthar's method.
    Article · Feb 2011
  • E. Jayabalan · A. Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: A technique is proposed to drastically reduce the update cost. Specifically, we propose to model the current position of a moving object as the distance from its starting position, along a given route. The distance continuously increases as a function of time, without being updated. In the context of position attributes that change continuously with time, the main issues that are addressed are position-update policies and imprecision. To accomplish tracking with certain accuracy, each wireless device monitors its real position (its TRAVEL DATABASE position) and compares this with a local copy of the position that the central database assumes. When needed in order to maintain the required accuracy in the database, the wireless device issues an update to the server. KeywordsTracking–Video–Database–Wireless–Travel-Database–Update–Moving Object
    Chapter · Jan 2011
  • M. Arun · A Krishnan
    Article · Jan 2011
  • E. Jayabalan · A. Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: Object tracking in video sequences is a very important topic and has various applications in video compression, surveillance, robot technology, etc. In many applications, the focus is on tracking moving object. Object tracking is the problem of generating an inference about the motion of an object from the sequence of frames in a video. In this paper, we propose a method for tracking moving objects in video sequences. KeywordsObject–Tracking–Video–frames–Compression
    Chapter · Jan 2011
  • Source
    M Srinivasan · S Paramasivam · A Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: This paper describes a fully automated method of measuring the cold and hot resistance of a transformer. The measuring scheme was developed by using a code composer studio (CCS) environment, TMS320F2812 digital signal processor and external interface hardware. The CCS allows a high degree of software modularity and provides the features that are required for sensor zero adjustment, data acquisition through ADC and analysis, and automated presentation of results. Furthermore, the experimental setup described in this paper could be used to obtain the cold and hot resistance of other electromechanical devices. The real-time implementation of cold and hot resistance measured setup and the results from a test on transformer are presented in the paper.
    Full-text available · Article · Jan 2011
  • [Show abstract] [Hide abstract] ABSTRACT: Modified switching patterns for Z-source inverters (ZSIs) from the traditional inverter schemes have reached the point where further improvements in firing the switches and inserting the shoot-through (simultaneous conduction of same phase leg switches) periods bring crucial benefits. A large variety of control methods, different in concept and performance, have been developed and described. This paper analyses the implementation logics, and comparative merits and demerits of recently-developed carrier-based and space-vector-based modulation techniques of ZSIs. Carrier-based pulse-width modulation (PWM) schemes, such as maximum boost control with third harmonic injection and constant boost control with third harmonic injection, and space vector modulation-based PWM schemes for three-phase ZSIs are investigated. The suitability of these techniques for various applications is also outlined. The objective of this paper is to provide a comprehensive assessment of the above PWM schemes, thereby giving a framework and guidance for the selection of the best technique for each area of application. The analysis is performed with respect to switching stress, boosting capability, voltage gain, total harmonic distortion, ripples in impedance network elements and the range of controllability. All the above control methods are simulated by Matlab/Simulink software and verified by experiments.
    Article · Jan 2011
  • S.Thangaprakash · A.Krishnan
    Article · Jan 2011
  • E. Jayabalan · A. Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: Today surveillance cameras are used in many places like hospitals, museums, ATM centres etc for security purpose. Since videos captured by such cameras are time consuming, most of them are never watched. Inorder to conserve time, an abstract of the video is generated using the Rack-through Method. In the abstract video, most of the activity of the long video is condensed by simultaneously showing several actions, even when they originally occurred at different times. The abstract video also gives an index into the original video by pointing to the original time of each activity. KeywordsImage Processing–Background Subtraction–Object Detection–Rack-through Method
    Chapter · Jan 2011
  • M. Arun · A. Krishnan
    Article · Jan 2011
  • M. Arun · A Krishnan
    [Show abstract] [Hide abstract] ABSTRACT: To meet the future internet traffic challenges, enhancement of hardware architectures related to network security has vital role where software security algorithms are incompatible with high speed in terms of Giga bits per second (Gbps). In this paper, we discuss signature detection technique (SDT) used in network intrusion detection system (NIDS). Design of most commonly used hardware based techniques for signature detection such as finite automata, discrete comparators, Knuth-Morris-Pratt (KMP) algorithm, content addressable memory (CAM) and Bloom filter are discussed. Two novel architectures, XOR based pre computation CAM (XPCAM) and multi stage look up technique (MSLT) Bloom filter architectures are proposed and implemented in third party field programmable gate array (FPGA), and area and power consumptions are compared. 10Gbps network traffic generator (TNTG) is used to test the functionality and ensure the reliability of the proposed architectures. Our approach involves a unique combination of algorithmic and architectural techniques that outperform some of the current techniques in terms of performance, speed and powerefficiency.
    Article · Jan 2011 · International Journal of Automation and Computing