Informatics Publishing Limited

K. Mallikarjunappa ¹, Chandrashekar D. Keri ¹, V. Vaidyanathan ¹, T. R. Afzal Ahmed ¹, Dillip Kumar Puhan ¹

Affiliations
1 Diagnostics cable & capocitres division, Central Power Research Institute, Bangalore - 560 080, IN

Abstract

In this era of reformation, liberalization and unbundling of electricity markets, asset management in power sector has assumed greater prominence. Power transformers are key components in any transmission & distribution network and loss of a transformer can have an enormous impact on reliability and availability of power supply and on cost. As society is more and more dependent on electricity for development, the utilities are under pressure to meet the ever-growing demands for reliable power supply. Economic factors are the main consideration and in order to minimize capital expenditure on new equipment, it is a common policy among utilities to maximize the use of existing networks by operating at their design capability. This can be achieved by according importance to the maintenance practice. A survey of the literature indicates that there are more failures of transformer due to poor maintenance, improper operation, severe weather conditions and manufacturing and design defects than due to insulation ageing. The utilities shall have a systematic O & M practice that include diagnostic tests for condition assessment and health checkup of the equipment. The objective of the condition monitoring tests is to detect the first symptoms of incipient faults, ageing development or other problems and monitor their evolution to enable the operator to take appropriate action to avoid major failure. The paper reviews the results of various diagnostic tests including dielectric response methods for condition assessment of power transformers.

Keywords

Transformer, Diagnostic, Frequency, Moisture, Polarisation Spectrum, Dielectric spectroscopy, Partial discharge

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K. Mallikarjunappa ¹, Chandrashekar D. Keri ¹, V. Vaidhyanathan ¹, Thirumurthy ¹, T. R. Afzal Ahmed ¹

Affiliations
1 Diagnostic, Cables and Capacitors Division, Central Power Research Institute, Banga, IN

Abstract

Majority of the generating sets operating in our country are turbo generators contributing nearly 70 % of the total electrical power generated. Many of these generators are about 30–40 years old and have already come to the end of their notional design life. The important components that have direct bearing on the operational reliability and life of the machine are: (1) Stator winding, (2) Stator core, and (3) Rotor winding. The stator winding is the most important and expensive part of the generator, where full power is generated. The life of the stator is affected by one or more combinations of various stresses, like electrical, thermal, mechanical and environmental, at any point of time during operation of the machine. Since the mechanical stresses are relatively higher in turbo generators, many of the stator winding failures are mechanically induced electrical failures. Some of the degradation processes include loosening of wedges and coils, slot and end-winding discharges, erosion of stress grading and corona shielding coatings, de-lamination of insulation, de-bonding of copper from insulation, etc.

Keywords

Degradation processes, Insulation resistance and polarisation index, DC Leakage current measurement, Dielectric loss angle, Partial discharge, Surge comparison, Wedge tightness detection, Electromagnetic core imperfection detection

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