Search

Two low‐voltage cables, insulated with flame‐retardant ethylene‐propylene‐diene rubber (FR‐EPDM), were removed after being laid in nuclear power plants for many years. We measured the leakage currents flowing through their insulators and found that the resistivity of cable insulation is higher in the two harvested cables than in a similar but new and unused FR‐EPDM one. The reason for this result is discussed in this paper based on a comparison of the leakage currents between new and gamma‐ray irradiated FR‐EPDM sheets. The discussion is continued by referring to our previous papers on mechanical properties and infrared absorption spectra of similar new and gamma‐ray irradiated FR‐EPDM sheets. As a result, it has been clarified that additives such as pigments contained in the cable insulators are likely to act as a source of charge carriers. In addition, the cable insulators became hardened by the long‐term aging in an environment of about 60 °C, which made the ionic conduction difficult and the insulation resistivity higher. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Y‐capacitors are widely used in flyback converters to suppress common‐mode (CM) noise to comply with the strict electromagnetic interference (EMI) standards. However, Y‐capacitors increase the leakage current between the primary and secondary side, which is not allowed in the applications with high safety requirements. In this paper, the displacement current models of two conventional De‐Y methods are quantitatively established to analyze their limitations for the flyback converter. Then, a hybrid EMI‐optimized transformer is proposed to improve the limitations. The proposed structure can completely balance the CM noise between the primary and secondary sides, making the flyback converter comply with the EMI standard under the conditions of no Y‐capacitor. Compared with the traditional methods, the proposed method has a better capability for CM noise suppression, higher universality and the same cost. Finally, the simulation and experimental results verify that the CM noise of the new transformer structure decreases about 10 dB compared with that of the conventional one. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

In order to solve the problem that the metro stray current cannot be directly numerically measured by the existing methods, and the data acquisition distortion caused by the special operating environment of the metro system, a new on‐line monitoring method for stray current was put forward in this paper. First, the stray current distribution function at different positions of metro trains was derived. Then, the equivalent circuit of stray current was built according to the field measured environment, and the numerical calculation formula of stray current was deduced. On the basis of the formula, the metro stray current could be calculated by the real‐time monitoring data, and the calculated data can be filtered and fitted with the stray current distribution function. In order to identify the distorted data, the potential energy function was introduced to judge the deviation degree of data point from the fitting function, so the erroneous data can be effectively eliminated. Thus, the accurate distribution value of stray current along the metro track was obtained. Taking a metro station in a certain city as the prototype, the CDEGS simulation model was built to verify the proposed method. The simulation results showed that even under the condition of sampling data distortion, the method could directly calculate the stray current value in real time, which had strong fault tolerance. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The metro stray current leaked during the subway operation causes the nearby earth surface potential to change, so that the various neutral‐grounded transformers to be at different earth surface potentials, resulting transformer DC bias. In order to analyze the influence of metro stray current on transformer DC bias, the polarization potential monitoring data in metro traction power supply system and neutral point current of nearby transformer were compared, and the positive correlation characteristics between the two were pointed out. By studying the stray current leakage reason in the metro traction power supply system and the circulation path causing transformer DC bias, the mechanism of the transformer DC bias under the subway operating environment was revealed. Based on the discrete model of the stray current distribution, considering the mechanism of stray current on DC bias, the equivalent resistance model of the transformer DC bias caused by metro stray current was built with double‐end power supply environment. Then the calculation formula of transformer neutral point current changing with subway operating conditions was derived, the numerical calculation of DC bias current of transformer caused by metro stray current was realized. The validity of the proposed model was verified by current distribution, electromagnetic field, grounding and soil structure analysis, the simulation results showed that the proposed model can calculate the stray current distribution and the nearby transformer DC bias current with high accuracy, which provided a quantitative analysis method for studying the correlation between metro stray current and transformer DC bias phenomenon. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]