Informatics Publishing Limited

Ramesh P. Nair ¹, B. V. Sumangala ², Chandrashekhar D. Keri ³

Affiliations
1 Senior Research Fellow, Cables and Diagnostics Division, Central Power Research Institute, Bengaluru - 560080, IN
2 Professor Dr. Ambedkar Institute of Technology, Department of EEE, Bengaluru - 560056, IN
3 Scientific officer, Cables and Diagnostics Division, Central Power Research Institute, Bengaluru - 560080, IN

Abstract

Partial Discharge (PD) in rotating machine insulation system is deleterious. Even though the main insulation of rotating machine is Mica, which is highly PD resistant, the discharges taking place in slot region and end windings are highly deteriorating to insulation system. In this paper, PD measurements are taken in Mica-Epoxy-Glass insulation sample using cylindrical-plane electrode system. The sample contains a defined void on the surface. Distinguished Phase Resolved Partial Discharge (PRPD) patterns are obtained for different location of void. The different PRPD patterns obtained corresponds to internal void in the bulk of insulation, void between high voltage electrode and insulation surface, void between ground electrode and insulation surface; and surface discharge. The PRPD patterns obtained from void between high voltage electrode and insulation surface, in the actual scenario, indicates PD originating near the conductor surface inside the insulation system of rotating machines. The PRPD patterns obtained from void between ground electrode and insulation surface indicates PD originating on the surface of insulation such as slot discharge, end winding discharge in rotating machine insulation system. The variation of PD parameters like Charge magnitude (q) with respect to applied voltage is shown for different location of void. Further statistical parameters like skewness and kurtosis are calculated for charge distribution (n-q) and phase distribution (n-Φ) for different PRPD patterns. It is inferred that statistical analysis of PD parameters is a good tool to classify of partial discharge sources.

Keywords

Stator Insulation, slot discharge, surface discharge, skewness and kurtosis.

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Ramesh P. Nair ¹, Sumangala B. V. ²

Affiliations
1 Senior Research Fellow, Diagnostic Cables & Capacitors Division, Central Power Research Institute, Bangalore - 560080, IN
2 Professor and Head of EEE Department, Dr. Ambedkar Institute of Technology, Bangalore - 560056, IN

Abstract

The reliability of any high voltage equipment depends to a large extent on the insulation quality. And in high voltage rotating machines, the stator insulation is an important part with respect to the manufacturing cost as well as maintenance and lifetime aspects. During operation, insulation is subjected to one or combination of electrical, thermal, mechanical and environmental stresses. The insulation ages over time due to these stresses and eventually fails. These unexpected failures can be avoided by conducting diagnostic tests. From the diagnosis results the extent of insulation degradation can be quantified and necessary actions could be planned to avoid in-service failure of vital machines and thereby enhancing the reliability. Every diagnostic test gives a certain information about the insulation condition. In this paper, the significance of diagnostic tests are discussed and how these tests can be used to evaluate the insulation condition is presented.

Keywords

Insulation Resistance, Polarization Index, Tan Delta, Tan Delta Tip-up, Partial Discharge

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