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Jiang X.,Fuzhou University | Wu W.,Fujian Electricity Science Research Institute | Chen X.,Fuzhou University
Dianli Zidonghua Shebei/Electric Power Automation Equipment

The power transformer life cycle cost model is proposed based on the interval analysis, which covers the investment cost, loss cost, environment cost, operation and maintenance cost, failure cost and discard cost, produced in the life cycle of transformer and undertaken by the yearly-equivalence method. The best economy case is determined by comparing the yearly interval life cycle cost. Different parameters of transformer life cycle costs are reasonably treated as the interval numbers and the uncertainty of each parameter is taken into account in the whole calculation process. The computing software IntervalCal, programmed with C++ language, is used to estimate the interval cost, and only once is necessary to get the transformer life cycle cost containing the uncertain risk. The model is applied in the transformer selection of a 500 kV substation to verify its effectiveness. The interval life cycle costs of three schemes are calculated and the best one is determined by cost comparison. Source

Zheng S.,North China Electrical Power University | Chen J.,Fujian Electricity Science Research Institute | Li C.,North China Electrical Power University | Lin H.,Fujian Electricity Science Research Institute
Gaodianya Jishu/High Voltage Engineering

To verify the feasibility of local partial discharges (PD) inside windings by using ultra-high-frequency (UHF) method, we studied the influence of transformer windings on the propagation of PD-caused UHF electromagnetic waves, and constructed an experimental platform which adopted a real oil-type 220 kV transformer with PD defects embedded in its windings. Moreover, a PD location system was also constructed on the platform. The reduction of UHF signals and the arrival time differences between signals at different sensors were measured, and the PD locations and errors are calculated. It is founded that the UHF electromagnetic waves decrease by 18~22 dB after passing through windings, the errors of time difference caused by the windings are no more than 0.5 ns, and the location errors are no more than 15 cm. Thus, it is concluded that, though the amplitude of UHF signal reduces significantly after passing through windings, the time difference errors are very small, revealing that it is possible to locate PD inside windings by using the UHF method. Source

Xu J.,Fujian Electricity Science Research Institute | Hua J.,Fujian Electricity Science Research Institute | Tang Z.,Fujian Electricity Science Research Institute
Dianli Zidonghua Shebei/Electric Power Automation Equipment

A simple method is proposed for calculating the CT equivalent instantaneous leakage inductance of interturn short circuit, which is based on the test parameters, such as the resistance, leakage inductance and load of secondary winding, and the samplings of secondary current. The analysis of calculated results shows that, the equivalent instantaneous leakage inductance of healthy phase is infinite and it is opposite in phase to that of faulty phase, which is verified by the simulative experimental results. The simulative experimental results also show that the calculated equivalent instantaneous leakage inductance of every phase varies between positive and negative values during normal operation. The two characteristics mentioned above can be taken as the criterions of CT interturn short circuit fault. During normal operation, the amplitude of calculated equivalent instantaneous leakage inductance follows the unbalanced secondary current, which can be used to prevent the protection misoperation caused by the unbalanced current flowing through CT. Source

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