Diagnostic Examination of Isolated Bus Ducts
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Vol. 54, No. 3, September, 2020
DIAGNOSTIC EXAMINATION OF ISOLATED BUS DUCTS A. P. Dolin1 Translated from Élektricheskie Stantsii, No. 4, April 2020, pp. 48 – 53.
The paper offers a review of the procedure for diagnostic examination of isolated bus ducts with air insulation. Characteristic examples of isolated-phase and three-phase bus duct defects revealed during visual inspections and thermal imaging are provided. The results of lab-based measurements and acoustic location of partial discharge (PD) in the insulation systems with various defects (cracks, wet and contaminated surfaces) are discussed. Typical amplitude-frequency characteristics of the PD acoustic signals during the development of insulator defects (defect images) were obtained. The results of generator bus duct diagnostics using electromagnetic and acoustic instruments are presented. Keywords: isolated bus ducts; diagnostic examination; particle discharge.
bus duct. Therefore, the strength of magnetic field of the bus duct outside of the shields is almost zero. This provides high electrodynamic resistance of the bus ducts, complete electromagnetic safety of the personnel, and no magnetic field effect on the equipment, including automated equipment and safety controls. The bus ducts manufactured up to about 1980 had “open” shields. Sections of the shields (typically, up to 10 m long) are insulated and grounded in one point (Fig. 1b). Such bus ducts demonstrate reduced losses (and, hence, heat generation) compared to the continuous-shield bus ducts given the same conductor sizes and materials. The main disadvantages of the “open”-isolated bus ducts are as follows: shielding (field strength reduction) of the magnetic field of the buses by only 40 – 60%, and the use of rubber (currently, being replaced with silicone) insulation between the shield sections. Diagnostic examination of the isolated bus ducts during operation includes a visual inspection of the bus ducts, thermal imaging, conducting examinations or tests to assess the condition of the post insulators. When performing a visual inspection of the bus ducts, it is important to first examine the shielding for possible damage, assess the condition of standard insulation, as well as the color of the shields. During inspection of the bus ducts, it was found that the shield seal can sometimes be broken as a result of damaged aluminum shells, compensators, wear of insulation seals of the sections, etc. Such damage can lead to ingress of moisture and dirt into the shielded space, which eventually causes insulator defects. The bus ducts are usually inspected for paint condition, and compliance of the bus duct shield color with the factory
Isolated bus ducts with air insulation are designed to operate within networks with an electric voltage of up to 35 kV and include isolated-phase bus ducts (e.g., generator bus ducts) and isolated bus ducts with a common shield for all three phases. The paper analyzes the procedure for examining isolated bus ducts based on the experience of performing diagnostic ex
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