Abstract
Power transformer bushings withstand great electrical and mechanical stress during high voltage and high current working conditions. Sealing failure poses a great threat to the long-term and reliable operation of the bushing and power transformer; however, the criterion to evaluate the sealing status of a bushing caused by mechanical problems is still lacking. In this paper, a transformer bushing model is established to gain theoretical insight into the relationship between temperature and pressure of a compact multilayer bushing. To evaluate the bushing mechanical status, different sealing conditions are tested based on the temperature and pressure monitoring within the physical 110 kV bushing. The results show that mechanical sealing failure can be diagnosed when the fluctuation of the oil pressure value exceeds the theoretical curve in steady state by 3 kPa. With different reliability coefficients, gas leakage and oil leakage are available to be further determined. The primary and auxiliary criteria based on oil pressure and its gradient are proposed to evaluate comprehensively the actual sealing condition of the bushing, and a wireless oil pressure module is developed at the bottom valve, which is quite beneficial to field online application. It is promising to extend the online mechanical monitoring and diagnosis to oil-immersed power equipment.
Highlights
Transformer bushings are one of the most important components in power transformers, which are used to conduct high current and insulate the high voltage
According to CIGRE transformer failure statistics, 14.4% of transformer failures are caused by bushings [6]
4b0askicP56Ta00alhldyeurceroiiTnnsg↑saitsshtiegennhti.efiaTctahinnegtcdpoirnfofcecaTreve↓sinst.yceTahbneedtswicmoeeniPTTlnrvaooefferstsoghixutialeirysteytih78n00oecfourtrehvteiecsparliseashnsidugrhmedecauhsrauinnrggeedtshvewalciutoheolatietnmagbpaoenurd-t ature are opposite when the temperature is rising. The reasons for this process are: (1) the p botto40m oil temperature data fluctuate; there is a 6w0 ide range of changes during 5–15 h, which directly leads to no correspondence with the theoretical calculation results; (2) the mea3s0ured temperature is considered as the averag5e0 temperature and it is adopted in the theoretical calculation
Summary
Transformer bushings are one of the most important components in power transformers, which are used to conduct high current and insulate the high voltage. During the installation process, deviations in the position of the conductor bring in uneven force around the rubber ring, and the rubber is subjected to varying degrees of aging and leads to sealing defects These failures are difficult to observe at the very beginning, but it is necessary to be detected in time to prevent damping of the bushing and the transformer. The physical condition of the bushing could be evaluated by the concentration and combination of different gases These methods, based on the parameters such as capacitance, tanδ, gas concentration, etc., are effective to insulation defects in bushings, but unavailable for mechanical failure.
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