S.C. Bhatt

A time-domain procedure for locating switched capacitors in power distribution systems

This paper develops a method using transient voltage and current measurements at the substation to determine which capacitor in a multicapacitor feeder switched on to cause a measured transient. The procedure is based upon time-domain analysis where a backward Kalman filter estimates the initial voltage of all feeder capacitors, and those estimates indicate which capacitor switched. The result is an automated procedure that can help electric utilities determine if their capacitors are switching properly, and also help pinpoint the source of capacitor switching-related power-quality problems.

Electric power transient disturbance classification using wavelet-based hidden Markov models

We utilize wavelet-based hidden Markov models (HMM) to classify electric power transient disturbances associated with degradation of power quality. Since the wavelet transform extracts power transient disturbance characteristics very well, this wavelet-based HMM classifier illustrates high classification correctness rates. The power transient disturbance is decomposed into multi-resolution wavelet domains, and the wavelet coefficients are modeled by a HMM. Based on this modeling, the maximum likelihood classification is applied to classify actual power quality transient disturbance data recorded on a 7200 V distribution line, and the result is tuned by post-processing. Of 507 power quality events experimentally observed by an electrical utility, 95.5% are correctly classified.

Cross time-frequency distribution function

In this paper, we consider cross time-frequency distributions, with particular emphasis on their ability to preserve phase difference (between two signals) information as a function of time and frequency. In addition, some properties of cross time-frequency distributions are examined and compared with the traditional Cohens class of time-frequency distributions. Finally, the phase preserving properties of appropriately defined cross time-frequency distributions are illustrated with a pair of Gabor logons.

A frequency domain procedure for locating switched capacitors in power distribution systems

This paper addresses the problem of determining, from transient voltage and current measurements at the substation, which capacitor in a multi-capacitor feeder switched on to cause the measured transient. The procedure is based upon frequency-domain analysis, where the Fourier transform of the recorded response is compared to those of simulations for all possible combinations of on-off capacitor states. The result is an automated procedure that can help electric utilities determine if their capacitors are switching properly, and also help pinpoint the source of capacitor switching-related power quality problems.

Optimal Daubechies' wavelet bases for detection of voltage sags in electric power distribution and transmission systems

Wavelet analysis of voltage sag completely depends on the choice of the wavelet basis. For better detection performance via wavelet analysis, the choice of the optimal wavelet basis must be provided within the constraints of the uncertainty principle which restricts arbitrary assignment of time-frequency resolution. In this paper, we describe local properties of the wavelet basis and voltage sag signal in terms of time duration and frequency bandwidth parameters. After comparison of the local properties of the wavelet basis and voltage sag signal, we suggest a set of performance indexes to measure the time-frequency resolution relation between the wavelet basis and the voltage sag signal. This procedure of determining the optimal wavelet basis can be extended to other possible applications of wavelets.