Showing papers by "Sivaji Chakravorti published in 2016"

Investigation of charge trapping behavior of LDPE using de-trapping characteristics

Abstract: Formation of space charge in polymeric insulation is a critical issue in the design of high voltage electric systems. Accumulation of space charge accelerates the material aging and may lead to premature breakdown of the insulation. Therefore, it becomes increasingly important to understand the charge injection, trapping and de-trapping processes in dielectric under application of high voltage. In this paper, the charge trapping and de-trapping behavior of low density polyethylene have been investigated. A new experimental set-up has been developed to obtain the de-trapping characteristics of a charged dielectric sample. From the obtained response, the trapping parameters i.e. trap depth, trapped charge etc is evaluated. It was observed, that the trapped charges in LDPE specimen is mainly concentrated to two trap levels, one shallow trap level (0.85 eV) and one deep trap level (1.01 eV).

Investigations on the effect of voltage harmonics on leakage current for condition monitoring in insulators

Abstract: Leakage current pattern and its harmonic content are widely known to be excellent monitoring indices for condition assessment of overhead line insulators. Whenever there is a change in the contamination severity on the insulator surface, a corresponding change in the leakage current is observed. Traditionally, it has been assumed that the changes in leakage current pattern are entirely due to the changes in surface condition of insulators. However, in real-time online monitoring, the system voltage and its harmonic content will also have a certain effect on the leakage current pattern. Changes in the harmonic content of system voltage may also produce changes in the leakage current pattern. This may lead to incorrect interpretation of the obtained results where systems are prone to harmonic distortions. In such cases, there is no way of knowing whether the change in leakage current pattern is entirely due to changes in surface condition of insulators or on account of harmonics in the applied voltage. Keeping this in mind, this work investigates for the first time the effect of presence of harmonics in voltage waveform on the leakage current pattern in overhead insulators. The purpose of this paper is to present the preliminary results on the degree of influence of voltage harmonics on the leakage current pattern, and demonstrate the importance of more detailed research on the topic.