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Summary A tremendous increase in the industrial and commercial applications of low voltage variable frequency drives (VFD) has been observed in the last decade. VFD are mainly used for energy saving and reliable speed control of industrial motors in an electrical system. However, power quality issues are becoming more apparent due to the installation of VFD. In this paper, a nonintrusive technique has been employed to determine the optimum operation of VFD system for improving the performance of heating, ventilation, and air conditioning centrifugal chiller system. The effect of load and speed ratios of VFD systems on total harmonic distortion (THD), power factor, distortion loss ratio, temperature, and efficiency has been investigated. The measurement of these parameters has been carried out by performing a series of experiments under variable operating conditions. The binomial relations have been developed between the various performance parameters and the operating conditions. Based on experimental results, optimum operating conditions have been proposed and implemented for the VFD system. Moreover, the results have been compared with the existing operating conditions and indicate a considerable improvement in THD, power factor, distortion loss ratio, efficiency, and the annual cost of energy consumed.

In modern power systems, condition based monitoring and diagnosis is essential to ensure the effective and reliable operation of different high voltage equipment (HVE). Compared to other monitoring techniques, partial discharges (PD) measurement is considered as a key method for assessing the insulation health condition. The benefits of PD condition monitoring of HVE can be extended by proper detection, identification, and interpretation of PD signal. Among both online and offline PD monitoring techniques, online PD monitoring is a very promising technique that assists in robust monitoring system which reduces the power failure incidents in power system components. Therefore, to understand recent developments and trends in theory and in practice, it is necessary to establish a holistic analysis of current online PD monitoring techniques for HVE in power systems. This paper presents an intensive literature review of current online PD monitoring techniques used for different high voltage electric components in power system. Finally, a smart PD monitoring techniques based on wireless sensor board is proposed. The proposed smart PD monitoring framework may be used to correctly estimate the insulation degradation in HVE and enhance the overall performance of power systems. INDEX TERMSDetection methods, feature extraction, high voltage equipment (HVE), online partial discharges (PD) measurement, PD monitoring, PD classification.

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.

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