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"This paper deals with the electrical insulation of a gap bridged by a solid dielectric between a pair of electrodes in a vacuum, where the dielectric is a model of an insulating spacer holding electrodes in various vacuum devices. Such gap configuration is typical as a model for studying physical mechanisms of an electrical breakdown or a flashover in a vacuum, in which the insulation ability isconsiderably lower than a gap without any insulating spacers. Many researchers have long investigated the mechanisms of flashover, and it is believed that the charging of the insulator surface is the primary drive of such weakness. One of the effective approaches for studying mechanisms is to analyze the characteristic of charge accumulated on the insulator surface both by experiments and bynumerical analyses. This paper reviews previous works conducted by the author’s research group and demonstrates the difficulties we have encountered upon conducting the numerical analyses."

"Skripsi ini dibuat dengan pengkajian dari dua prosedur pengukuran untuk diagnosis sistem isolasi pada generator tegangan tinggi. Pengukuran dapat dibagi menjadi dua bagian, yaitu pengukuran secara online dan offline. pengukuran secara offline terdiri atas resistansi isolator, faktor disipasi, dan peluahan parsial, sedangkan pengukuran secara online hanya terdiri atas peluahan parsial. IEEE and IEC telah membuat standar yang disebut praktik yang direkomendasikan atau spesifikasi teknis untuk mengukur resistansi isolator, faktor disipasi, dan peluahan parsial dengan menggunakan peralatan diagnostik elektris. Pengukuran secara offline akan dibandingkan dengan pengujian sebelumnya untuk melihat sejauh mana degradasi isolator yang terjadi. Pengukuran secara online didasarkan pada perubahan beban dan waktu kerja dari mesin tersebut. Parameter ketika mesin bekerja seperti beban, tekanan gas pendingin akan dianalisis untuk melihat bagaimana parameter tersebut mempengaruhi degradasi dari sistem isolasi. Pengujian secara offline menunjukkan bahwa fasa R memiliki kondisi isolator terburuk, fasa S memiliki penurunan kualitas isolator yang paling signifikan dan, fasa T memiliki kualitas dan stabilitas nilai isolator bila dibandingkan dengan fasa lainnya. Selain itu, pengujian peluahan parsial menunjukkan telah terjadi delaminasi tape layer pada ketiga fasa yang diakibatkan adanya perubahan nilai vibrasi yang signifikan selama pengoperasian mesin. Pengujian secara online menunjukkan bahwa fasa S memiliki perubahan arus dan daya disipasi yang paling besar dibandingkan fasa lainnya seiring bertambahnya waktu pengoperasian dan meningkatnya pembebanan.

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This work is based on the study of two different measurements procedures for the diagnosis of insulation systems of high voltage generators. The measurement can be conducted into two ways, offline or online measurement. The offline measurements consist of Insulation Resistance, Partial Discharge, and Dissipation Factor measurement, meanwhile online measurements consist only partial discharge measurement. The measurements were done in stator windings not only to check the quality but also for the investigation of changes in operating processes.

IEEE and IEC have created standards called recommended practices or technical specifications to address polarization index, dissipation factor, and offline online PD measurement using electrical diagnostic equipment. The offline measurement will be comparated with previous measurement to see how degradation takes place.

The online measurement will be based on on load variable and machine rsquo s working hour. Also, the online parameter such as load, vibration, coolers pressure, and temperature will be analysed to see how it can affect the degradation of the insulation system.

The result of offline measurements show that phase R has the worst condition, phase S has the most significant deterioration, and phase T has the best condition and stability in deterioration.

In addition, partial discharge measurement indicates that the insulation has been undergoing delamination of the tape layer due to significant changes in vibration values during the operation of the machine. The result of online measurements show phase S has the most significant changes in current and power dissipation compared to other phases due to increment of operation time and load."

"The book introduces the reader to the major components of a high voltage system and the different insulating materials applied in particular equipments.During a review of these materials, measurable properties suitable for condition assessment are identified. Analyses are included of some of the insulation fault scenarios that may occur in power equipment.The basic facilities for carrying out tests on the internal and external insulation structures at high and low voltages are described. Tests and measurements according to specifications, on-site requirements and research investigations are considered.Advances in the application of digital techniques for detection and analyses of partial discharges are discussed and methods in use, or under development, for service condition monitoring are described. These include the utilization of new sensors, the solution of online problems associated with noise rejection and the adaptation of artificial intelligence techniques for incipient fault diagnosis.The subject matter of the book is suitable for final year courses in electrical power engineering, short courses in insulation condition assessment and postgraduate programmes. Power system engineers associated with high voltage equipment should find the book of value in relation to fault investigations, maintenance requirements, insulation testing and condition monitoring."

"This book addresses the very latest research and development issues in high voltage technology and is intended as a reference source for researchers and students in the field, specifically covering developments throughout the past decade. This unique blend of expert authors and comprehensive subject coverage means that this book is ideally suited as a reference source for engineers and academics in the field for years to come."