In Nordic Countries, distribution networks are traditionally unearthed and increasingly compensated. For such networks, switching their neutral point to the earth is practically applied through a resistor for better selectivity functions of earth faults. In this paper, the neutral switching and consequently an arrival time of the aerial mode traveling wave reflected from the fault point are utilized to accurately determine the earth fault distance. A concept to create traveling waves is implemented by earthing the neutral via a controlled-thyristor that provides a short period of high fault current and produces traveling waves to estimate the fault distance. Much higher transient signals are generated by earthing through an opposite charged capacitor. A capacitor-resistor divider is utilized to measure the reflected surge over a heterogeneous distribution feeder. An adaptive setting is proposed for stamping the arrival surge. The results provide evidence of the efficacy of the proposed fault distance estimation. Index Terms-Unearthed and compensated MV networks, earth faults, fault distance estimation, traveling waves. 0885-8977 (c)

In this paper, an accurate model for computing dielectric constant of dielectric nanocomposites is presented. The effect of interaction zone between the nanofiller and the resin material is calculated and taken into consideration in the developed model for polymer and ceramic resins. Also, the effect of filler volume fraction, filler dielectric constant and particle shape is studied through the proposed model. Finally, the validity of the proposed model for evaluating the dielectric constant of a uniform composite system of discrete particles dispersed within a matrix is achieved by comparison with experimental results. The proposed model shows simplicity and gives accurate results as compared to the other theoretical models.

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Surge arresters are usually used to protect distribution feeders against randomly distributed lightning overvoltages. However, there is a probability of surge arrester failure due to an increase in its absorbed energy over the withstand capability. This paper experimentally and theoretically evaluates the application of a compound overvoltage protection scheme to avoid this failure. The compound overvoltage protection consists of an installed spark gap in parallel with an existing surge arrester to limit the risk of surge arrester failure. The experimental evaluation is performed by applying standard lightning impulse voltage waveform, 1.2/50 µs according to IEC Standard 60060-1. The evaluation is carried out without and with sparkgap adjusted at different lengths. The energy stress of the surge arrester with and without sparkgap is theoretically carried out using the ATP/EMTP software considering an overhead distribution feeder. The statistical evaluation for the failure risk assessment is performed using the MATLAB software. The results indicate that the installation of the spark gap in parallel with the surge arrester relieves the thermal stress on the surge arrester, and thus eliminates any risk of surge arrester failure using the proposed coordination.