High impedance faults(HIFs) often draw too little current to activate conventional overcurrent protection, making the detection of a HIF event a difficult task. A practical and implementable solution to HIF detection and location is presented. In the proposed methodology, wavelet transform used for extracting features of HIFs signals and neural network used for HIF detection are used to develop a novel HIF detector called enhanced FTU(feeder terminal unit). The designed enhanced FTU is a high-performance HIF detector that is the retrofitting of the ready-made FTU with an embedded digital signal processor(DSP) and a high-frequency current sensor. The enhanced FTU monitors the operation of distribution feeder system and sends a fault flag signal to Feeder Dispatch and Control Center(FDCC) when a HIF occurs. Based on the Feeder Automation(FA) mechanism, the HIF detection, isolation, and service restoration(FDIR) can be activated. Consequently, the power reliability can be significantly improved by reducing the outage area and repair time. The validation of the presented technique was evaluated through staged fault testing. Compared with the existing related research, the proposed enhanced FTU is available and feasible.

When applying an active harmonic filter (AHF) to mitigate the harmonic currents of voltage source inverter-fed drives (VSI), the required capacity of the AHF is generally determined by the measured harmonic current of the drives. However, when the AHF is connected to an electrical power distribution system, the total harmonic current distortion of the load actually increases owing to the change in the rectifier commutation behavior. Therefore, a higher AHF output capacity is needed to meet the expected filtering requirement. This paper investigates the impact of the AHF on the changes of the harmonic current distortion of the VSI. For this purpose, correlation analysis models are constructed, and case studies are presented to illustrate the effect with different system short-circuit levels, load conditions, and ac chokes of the VSI. Furthermore, several actual field measurement results are presented for verification. On the basis of the measured and calculated results, a margin factor is recommended for use when determining the capacity of the AHF.

The railway traction loads produce massive harmonics that are injected directly into the traction power system. This causes serious waveform distortion in the supply voltage and even invokes a harmonic parallel resonance, which may lead to significant harmonic current and voltage amplification. Consequently, severe electrical equipment failures and feeder tripping problems occurred frequently in the traction substation. A clear harmonic parallel resonance at a 27.5‐kV feeder can be observed from the field measurement result of the traction substation without filter banks. This paper proposes a high‐performance single‐tuned 3rd passive filter for harmonic mitigation and harmonic resonance suppression in the traction power system. In the ST filter design process, the impact of the quality factor ( Q _f ) design of the filter reactor on the filtering performance is considered. Furthermore, the driving point impedance as seen from the traction load is also studied. The design and the engineering consideration of the harmonic filter are also presented, which comply with the recommendations of the IEEE and IEC standards. Besides, the unbalance‐current protection of a capacitor bank is introduced in this paper. Finally, the proposed filter is implemented in an actual traction substation, from the field measurement results; the proposed harmonic filter delivers very good performance.

A single‐phase electric machine invokes a great reactive power demand in operation, resulting in a large voltage fluctuation in the supply system. Furthermore, the frequent and rapid operating characteristics of an electric welding machine cause a serious voltage flicker problem. The operation of welding equipment also generates significant harmonic current distortion, and distorts the voltage waveform of the supply system. Hence, this study focused on designing and applying a thyristor switched capacitor (TSC) bank for voltage flicker improvement. However, the single‐phase TSC should also satisfy the reactive power demand and compensation speed, considering proper ratings of TSC to bear high harmonic distortion. This study shows the calculation results and discusses the impact of different capacities and different step numbers on TSC design. In addition, thyristor switches and a single‐phase power factor controller were designed and implemented. The experimental results are also presented.

The motivation for this research was to find methods for suppressing harmonics and harmonic resonance in traction power systems. System parameters determined through actual field measurements from a traction substation in China were used to develop mathematical models of a special connection transformer, a traction load, and a traction line. Potential power quality problems arising from traction load operation, including harmonic currents and waveform distortions at the point of common coupling in the power grid, are described. Using frequency scan analysis, the harmonic resonance frequency and high distortion current waveform generated by a system undergoing harmonic resonance were estimated and found to be identical to simulation results. Detuned, single-tuned, and damping passive filters were studied as means of reducing harmonic currents and thus eliminating harmonics. Field measurements and simulation results showed that, although the detuned filter could not provide effective harmonic reduction, the single-tuned filter effectively eliminated harmonics and reduced amplification of the parallel harmonic resonance frequency of a traction network. Although the damping filter was effective in eliminating high-frequency harmonics, the additional power losses it incurred were not economical. These harmonic analyses were simulated using MATLAB/SIMULINK.

This paper presents the improvement of power quality and operational energy efficiency by using an advanced thyristor switched detuning capacitor bank (TSC). The operation of an ac spot welding load invokes serious power quality problems, such voltage fluctuation, poor power factor, and harmonic distortion, resulting in additional power dissipations of the transformer, and also reducing the operational energy efficiency of the load. Hence, this paper proposes a fast reactive power compensating solution to improve the overall power quality of the distribution power system. The selection of compensation capacity and its improvement result are presented and discussed. Furthermore, this study evaluates the specific improving result through various losses and indicators, including power dissipation, harmonic loss factor, maximum permissible load current, and top-oil temperature rise of the transformer. From the calculated curves, the improvement results with different TSC capacity can be observed. Finally, from the implement and the experimental result, the proposed solution can effectively improve the operational energy efficiency as well as the power quality of the power system.