Considering that the working temperature is much higher in high‐voltage direct‐current (HVDC) convert transformers than in conventional AC transformers, the combination of thermally upgraded paper and natural ester might be a better choice to withstand high temperature in long‐term operation. This study compares the chemical structure, DC breakdown voltage, space charge and trap distribution of thermally upgraded paper aged in natural esters and mineral oil. The relationship between DC breakdown and accumulated charges was analyzed. Results show that the thermally upgraded paper aged in natural ester (NEI‐TUP) has a higher volume resistivity and DC breakdown voltage than that aged in mineral oil (MOI‐TUP). The NEI‐TUP group has a larger deep trap density than the MOI‐TUP group due to the chemical structure of natural ester. The larger deep trap density could contribute to the lower charge accumulation quantity and higher DC breakdown voltage. The thermally upgraded paper immersed in natural ester presents better insulation capability under thermal and DC electrical stress than that immersed in conventional mineral oil. This research indicated that the combination of thermally upgraded paper and natural ester might be a potential alternative for the mineral oil immersed paper in the future.

Planar inductive sensors are widely used for non‐contact gap measurement. Usually, a change in size, shape, or material of the target requires a tedious recalibration of the measurement setup. This paper aims to present a new method to measure the gap from irregular and narrow targets using a planar inductive sensor without this tedious calibration process. The magnetic field distribution on this target was numerically studied, and the findings suggested that a simpler calibration would work by modeling the induced current in the target as a virtual planar coil. For this target, we found that the calibration curves corresponding to different materials can be obtained by adding a constant C to the base curve. To validate this approach, three planar coils of different sizes were tested with four metallic turbine blade‐shaped targets. Results showed that the measured gaps matched well with the real gaps, with a maximum error of about 3.703%. The new approach can be applied to various applications including 3D printer build platform calibration, bandsaw blade deviation detection, and blade tip clearance monitoring.

Due to wind and uneven distribution of the field along the insulator, a kind of non‐uniform contamination is deposited on the insulator surface as fan‐shaped and longitudinal pollution. This paper investigates such non‐uniform pollution from theoretical and experimental points of view. For this aim, the residual resistance of the pollution layer is formulated based on the geometry of fan‐shaped and longitudinal non‐uniform pollution. Also, the arc current is formulated using the arc Obenaus's equivalent circuit for a constant arc voltage in terms of arc length propagation. Finally, the AC dynamic theoretical model of pollution flashover is proposed that can estimate flashover parameters for different values of the fan‐shaped density degree (J), extension degree (K) and longitudinal non‐uniform pollution density degree (Z) considering instantaneous variables in arc progression. It results that with increasing Z, the flashover voltage increases, while by increasing the J and K, the flashover voltage decreases. To validate this model, the experimental tests are performed on the sample silicone rubber (SiR) insulator that show acceptable accuracy of theoretical model. Furthermore, based on experimental results, a new correction coefficient is proposed under fan‐shaped and longitudinal pollution that varies in the range of 0.85–1.62.

Digital measurement equipment such as electronic transformers enable real‐time functional control and monitoring systems to be built in power grids to accommodate the large‐scale access of distributed renewable energy to the grid. However, the current offline calibration of electronic transformers is difficult to implement; therefore, an online calibration method for electronic transformers must be developed to ensure their accuracy. The design of a clamp‐on two‐stage current transformer (CTS‐CT) with a passive compensation loop is presented herein. The compensation loop is utilised to reduce both the amplitude and phase errors, thereby achieving high accuracy. The formulas for calculating the resistance and capacitance of the passive compensation loop are presented. The expanded uncertainties (95% confidence level) of the proposed CTS‐CT are estimated to be lower 0.03% for the amplitude error and 1′ for the phase error. Experimental results indicate that the proposed CTS‐CT prototype is not affected by the external magnetic field nor the opening and closing times, thereby enabling good‐quality online calibration for field applications. Moreover, the proposed CTS‐CT adopts neither an active compensatory circuit nor software compensation; therefore, the manufacturing of the CTS‐CT is steady and simple, and the calibration procedures are simplified.

World's ageing population, prevalence of chronic diseases, and shortage of healthcare resources have increased interest in home‐based physical therapy and rehabilitation. However, the standard equipment is often too bulky and unsuited for home use. This paper presents the design, development, and evaluation of a set of wearable orthoses for home‐based physical therapy. Originatively utilising miniature electromagnetic brakes, the system can deliver a low to moderate range of resistive torques suitable for isotonic, isometric, and open‐chain resistance exercises. In human tests with the orthoses, low‐level muscle activation and low‐ to moderate‐level energy expenditure were achieved. This suggests the system's potential for use in a wide range of applications, including postoperative treatments for muscle injury and the early stages of rehabilitation, and tele‐rehabilitation. The orthoses were integrated with a video game console to form a new research platform that can be used to study the effects of force haptics on muscle activation and energy expenditure in exergames. The data obtained aid the future development of exergame prescription standards.