This paper deals with metal oxide varistors (MOVs) in direct current (dc) circuit breakers (DCCBs). Two significant features of the MOVs are studied. First, the manufacturing parameters of MOVs are reviewed, and impacts of various main and dopant materials on the electrical parameters of MOVs are explored. Breakdown voltage and leakage current are primarily considered under different ceramic semiconductor materials. Second, MOVs’ practical issues in DCCBs are discussed. Results show that MOVs bring reliability issues in DCCBs and significantly reduce the voltage utilization rate of the main switch. Experiments of 375 V/100 A are conducted to reveal thermal runaway failure in MOVs and highlight the corresponding reliability issue.

Power line inspections are essential to maintain safety and reliability of power grids. Transmission lines in many locations are difficult to access, making aerial inspections the only practical means for assessing line conditions. Although various commercial drones target this application, not enough is known about the methods implemented to overcome challenges of flying near transmission lines. This paper discusses the developments of an unmanned aircraft system (UAS) for transmission line inspections. It considers several practical challenges in the real implementation of such a system, such as EMI. Furthermore, a practical FEA model for simulating the magnetic field of a single phase and three phase line is developed in Ansys Maxwell. A drone testbed prototype is designed using commercial-off-the-shelf (COTS) components based on a PX4 controller and the Ardupilot platform, to serve as a testbed for both assessing the challenges and testing solutions.

This paper demonstrates the development of a wireless power transfer (WPT) workbench for undergraduate education. This WPT workbench combines both photovoltaic (PV) and inductive power transfer (IPT), which aims to involve photovoltaics, IPT technology, resonant circuits as well as plenty of hands-on engineering work in undergraduates’ education. A LED-matrix-based light source is designed to build a laboratory PV system and a self-excited inverter is designed to construct a parallel-series IPT system. The implemented PV system presents the basic working characteristics of a solar panel and a 3.8% conversion efficiency is achieved. The IPT system demonstrates the WPT technology via electromagnetic induction and transfer efficiency of 81.7% is achieved at a transfer distance of 2.5cm. With a complete WPT workbench, an output power of 5.546W is achieved with an overall system efficiency of 2.26%.

This paper designed a 2.1 kW 3 MHz capacitive power transfer (CPT) system with a sleeve-type coupler for rotary applications. A new M1-SS CPT topology is proposed with a compact receiver circuit. On the receiver side, only a small series compensation inductor is used while a mutual inductive coupling link is used on the transmitter side to improve the power transfer capability and achieve load-independent constant-voltage (CV) output. To verify the proposed design, a 3 MHz CPT prototype is implemented. With a wide load range, the maximum output power achieves 2.122 kW. Meantime, the experimental results also validate the load-independent CV output and the zero-phase-angle (ZPA) property. When the output power is within 1.54 kW, the measured dc-ac efficiency achieves above 92%, and the maximum efficiency of 93.19% is achieved at 755W output.

This paper presents an ultrafast solid-state dc circuit breaker (SSCB) with 1) fault current bypass tripping and 2) transient commutation current injection (TCCI) assisted soft turn-off tripping schemes. It aims to provide two different adjustable tripping schemes to address technical issues in light and heavy fault conditions, respectively. There are four major contributions. First, an improved fault bypass tripping branch is proposed to handle light faults where a low-cost thyristor is paired with metal oxide varistor (MOV) to reduce its voltage stress. Second, an auxiliary TCCI branch is proposed to handle heavy faults, which removes the gate distortion and eliminates power shock of a full-control main switch by achieving soft turnoff at high fault current. Third, the proposed TCCI branch achieves natural self-charging operation, which does not need any external charger. Fourth, the proposed SSCB achieves operating duty of reclosing and reopening following IEEE Std C37.14. The proposed SSCB is validated by experiments of 1) 375 V/44 A with fault bypass scheme and 2) 375 V/ 180 A with TCCI soft tripping scheme. Experimental results also verify an ultrafast response speed of 5.2 µs and 28 µs, respectively.

In this article, we propose a bilaterally transmitted domino-type multiload inductive power transfer (IPT) system for constant-voltage (CV) outputs, low voltage attenuation, and high efficiency. There are three major contributions. First, the series–series/parallel (S–SP) topology is developed to design the multiload IPT system, which can realize the load-independent CV outputs without using compensation inductors, enabling a compact IPT system. Second, a bilateral IPT structure is proposed with two parallel power transfer routes to mitigate the practical output voltage attenuation issue, resulting in a better CV property. Third, system efficiency is improved by the proposed bilateral IPT structure. With the bilateral S–SP compensated multiload IPT design, the output voltage attenuation analysis and system efficiency are investigated considering parasitic resistances. A 70 W six-load bilateral IPT prototype is implemented and compared with the unilateral counterpart. Withk= 0.26 andQ= 300, the proposed bilateral IPT system validates an improved CV output with a small attenuation rate of 10.22%, which is much lower than the unilateral one. The maximum efficiency achieves 90.39%, showing 5.17% higher than the unilateral IPT system in the identical load condition.

This article proposes a long-distance capacitive power transfer (CPT) system in the freshwater environment. The theoretical model of the capacitive coupler is derived in the freshwater scenario, considering the impact of the insulation. The finite element analysis by high-frequency structure simulator (HFSS) is used to simulate the coupler structure. Compared with the system in air, the coupling capacitance in a freshwater system is less sensitive to the distance variation. The transfer distance is therefore significantly extended in the freshwater environment. Then, a prototype is implemented to validate the analysis, in which the plate length is 200 mm. In the freshwater testing, experiments show that the system achieves 219.6 W output power across a distance of 500 mm with the efficiency of 60.17%. When the misalignment is 100 mm, the variation of output power is within 3.3%, and the efficiency is still maintained at 54.9%. When the transfer distance is 350 mm, the system efficiency is 69.0%. Therefore, the experimental results validate that the proposed long-distance CPT system is achieved in the freshwater environment.