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: The base polymer properties have been developed experimentally by adding small amounts of different fillers but they are expensive to the polymer material. Thus, it has been investigated that the incorporation of cost-less nanoparticles like clay and fumed silica nanoparticles into low density polyethylene LDPE and high density polyethylene HDPE which controlled the breakdown strength and voltage endurance significantly of new nanocomposite materials which compared with unfilled industrial materials. This paper simplified the breakdown test model which has been used as a basis for experimental treatment for several new nano-composite specimens of industrial polymer materials. So that, it has been experiment the dielectric strength of new nano-composite industrial materials for ac applications which have been improved significantly with respect to the basis, unfilled materials. Finally, according to the experiment test model, it has been presented measurements of electric field strength of new nanocomposite materials that exceeds unfilled industrial materials.
  • [Show abstract] [Hide abstract]
    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%.
    IEEE Transactions on Dielectrics and Electrical Insulation 11/2008; 15(5-15):1261 - 1270. DOI:10.1109/TDEI.2008.4656233 · 1.28 Impact Factor
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    ABSTRACT: Reliability evaluation method with Weibull distribution function is used for development of test conditions for short-duration power frequency withstand voltage test. Although the evaluations by ldquoindependent methodrdquo and ldquocumulative methodrdquo are proposed, the handling of multiple voltage application still remains as one of the subjects. Therefore, insulation test with one-minute step-up method is studied as an insulation test with coexistence of multiple voltage level. As a result, the insulation characteristics by one-minute step-up method deviated from their true values. In this paper, it was calculated and evaluated by two methods with parameters of test condition. For the one-minute step-up method, the deviations from the true values were found to be influenced by test conditions: the larger the test voltage step width, or the lower the test starting voltage, or the greater the number of voltage steps, the smaller the deviations from the true values. Furthermore, the approaches to designing appropriate conditions for the test were summarized in order to design test conditions for oil-filled transformer and gas insulated switchgear. As a result, the reasonable test conditions were evaluated as follows: for oil-filled transformers, the test starting voltage was 70% of the one-minute breakdown voltage value and the voltage step was 7% and, for gas insulated switchgear, the test starting voltage was 80% and the voltage step was 5%. This result is approximately the same as the test conditions used for the actual measurement data in the past. These examinations will help to establish appropriate test conditions in the one-minute step-up method and to evaluate insulation characteristics obtained from the test.
    IEEE Transactions on Dielectrics and Electrical Insulation 11/2008; 15(5-15):1271 - 1280. DOI:10.1109/TDEI.2008.4656234 · 1.28 Impact Factor
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