Известия Томского политехнического университета: Инжиниринг георесурсов (Aug 2016)
Equipment for non-contact search of hidden defects in thin dielectric films by corona discharge
Abstract
Relevance of a subject is caused by the need of diagnostics and prevention of isolation condition of electrical machines in mining and oil branches, where reliability and safety of operation of electric equipment are important. Diagnostics of latent defects allows predicting a residual resource of electric isolation operation, planning preventive tests and timely repairs of electrotechnical equipment of high and low tension. The aim of the research is to develop the installation, which allows no-contact detecting of various defects: through holes, air pockets, conducting inclusions, reduction of thickness of the thin dielectric coverings, applied on metal base which can be electric conductors with current, printed circuit boards. Research methods. For obtaining volt-ampere characteristics of the studied corona discharge the constant voltage of different polarity was applied to the studied object, current was recorded in a certain interval in the range of 1…100 mkA by means of the M4204 and high voltage was measured within the studied interval in the range of 1…15 kV by means of the electrostatic C196 kilovoltmeter. The visual picture of the corona discharge was recorded by means of «Micron 800» type digital microscope. Results. The paper demonstrates the possibility to determine the through and latent defects of about 10 microns and more measuring the corona discharge current in the needle electrode-plane electrode system and a visual picture of the corona discharge. The paper introduces the experimental results of application of the corona discharge with adjustable parameters of current and tension for determining latent defects in dielectric coverings, applied on the current carrying metal bases, and in thin dielectric films, applied as isolation in modern electrical machines of high and low power. The feature of the installation is application of nonlinear element to restrict short circuit current to the values, which do not cause the damage of a dielectric covering and the corona discharge of adjustable current and tension parameters as the diagnosing tool. The installation contains an adjustable source of constant tension (0 … 30 kV), the nonlinear adjustable current limiter for preventing short circuit in case of breakdown, the corona current recorder, photo and video registration of optical phenomena of a corona effect.
