Reliability Evaluation with Weibull Distribution on AC Withstand Voltage Test of Substation Equipment

R&D Center, Tokyo Electr. Power Co., Yokohama
IEEE Transactions on Dielectrics and Electrical Insulation (Impact Factor: 1.28). 11/2008; 15(5):1242 - 1251. DOI: 10.1109/TDEI.2008.4656231
Source: IEEE Xplore


For the development of a ldquoshort-duration AC withstand voltage testrdquo, an insulation specification of substation equipment, there is a precise method of reliability evaluation using a Weibull distribution function. Regarding this method, there remains a subject of handling coexistence of multiple voltage levels. This paper first defines the two reliability evaluation methods, ldquoindependence methodrdquo; and ldquoaccumulation methodrdquo, applying to Weibull evaluation for coexistence of multiple voltage levels in relation to their physical meanings. Next, the influence of the Weibull parameter values are examined on the cumulative fault probabilities and test voltages calculated using these methods. When the time shape parameter a>1, the accumulation method gives higher values than the independence method; When a=1, the two methods give the same values; When a<1, the former gives lower values than the latter. Then, appropriate reliability evaluation methods are investigated for various insulation media and insulation structures of substation equipment from the viewpoint of inception and development mechanisms of dielectric breakdown and partial discharge. According to the result of engineering evaluation of the presently available data, the independence method may be appropriate for both gas insulated switchgear and oil-immersed transformers.

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    • "The safe operation of high voltage electrical energy transmission grids depends on the reliability of its components, as switchgears, power transformers and gas insulating lines. Their reliability depends primarily on the performance of the insulating structures they contain nanoparticle filled polymers provide advantages over micron filled polymers because they provide resistance to degradation, and improvement in thermo mechanical properties without causing a reduction in dielectric strength [14] [15] [16] [17] [18]. "
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    ABSTRACT: In the deregulated electrical energy market, reliability estimation of electrical components is an increasingly important, but difficult, task. Indeed, utilities face on one hand the degradation of many power system devices and on the other hand the high-reliability of such devices. This paper gives theoretical and practical aids for the proper selection of reliability models for power system components. Firstly, the most adopted reliability models in the literature about electrical components are reviewed and the classical 'direct reliability assessment' is described. Then, phenomenological and physical models for the estimation of ageing and life of electrical insulation (the weakest part of many devices) are illustrated. Finally, numerical and graphical examples show that seemingly similar reliability models can possess very different lifetime percentiles and hazard rates. Thus model selection must be accomplished very carefully, since it involves completely different maintenance actions and costs.
    No preview · Article · Jan 2008 · International Journal of Reliability and Safety
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    ABSTRACT: For the development of test conditions for a short-duration power-frequency withstand voltage test, which is one of the insulation specifications of substation equipment, there is a precise method of evaluating reliability using a Weibull distribution function. For this method, "independence method" and "accumulation method" have been proposed in order to handle the coexistence of multiple voltage levels. In this paper, an insulation test based on the one-minute step-up method as condition for the coexistence of multiple voltage levels is used to calculate and evaluate the test results using these two methods. Consequently, the insulation characteristics obtained from the one-minute step-up test are found to have differences from the true values. If the independence method is adopted, there is a certain deviation regardless of the Weibull time shape parameter "a-value" and, the smaller the Weibull voltage shape parameter "m-value", the larger the deviation. If the accumulation method is adopted, on the other hand, the larger the "a-value" or the smaller the "m-value", the larger the deviation. The 50% breakdown voltage value, the standard deviation "sigma-value", and the "m-value" that can be obtained from the insulation test based on the one-minute step-up method were evaluated for their deviations from the true values. The results suggest that, when a test is conducted on an oil-filled transformer, the design may turn out to be on the dangerous side due to overestimation of the dielectric strength by around 8%.
    No preview · Article · Nov 2008 · IEEE Transactions on Dielectrics and Electrical Insulation
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