Previous studies have shown that switching operations of gas insulated substations (GIS) can generate transient radiation fields outside the enclosure, namely switching transient electric fields (STEF). The waveform features of STEF can reflect the functioning performance of the switch. To monitor online the working states of disconnecting switches (DS), in this paper, we built an experimental platform to simulate their typical faulty types. Then, under different faulty status, a non-invasive three-dimensional (3D) electric field measurement system was applied to obtain STEF produced by DS. It is difficult for conventional methods to establish an accurate fault-diagnosis model, so we presented a novel method to identify the condition of DS. This innovative approach is based on feature extraction and machine learning and combined signal analysis to classify different defect types of DS. Measured STEF signals were analyzed by the wavelet packet transform(WPT) method in the time-frequency domain, which was transformed to the multi-dimensional feature matrix. The principal component analysis (PCA) algorithm was employed to reduce the dimensionality of the obtained feature matrix, which was also compared to other feature extraction algorithms. In addition, a support vector machine (SVM) with an improved particle swarm optimization (IPSO) algorithm was designed to achieve a PCA-IPSO-SVM model which can be used for signal recognition. The proposed IPSO technique can improve the convergence performance of the PSO through the dynamic adjustment of inertia weight and learning factors. Results show that the proposed fault diagnosis method based on WPT and PCA-IPSO-SVM can effectively identify the insulation faulty signals in STEF.

Commercial graphite anode has advantages such as low potential platform, high electronic conductivity, and abundant reserves. However, its theoretical capacity is only 372 mA h g⁻¹. High-energy lithium-ion batteries have been a research hotspot. The Si anode has an extremely high specific capacity, but its application is hindered by defects such as large volume changes, poor electronic conductivity, and a small lithium-ion diffusion coefficient. Here, the Si/thermally reduced graphite oxide@carbon (Si/RGtO@C) composite was fabricated by electrostatic self-assembly followed by thermal treatment. The RGtO synergistic carbon coating layer can effectively compensate for the low electronic conductivity and buffer the volume expansion effect of the Si nanoparticles during charge/discharge cycles. The Si/RGtO@C anode demonstrated a significantly increased capacity compared to the RGtO. After 300 cycles, Si/RGtO@C kept a discharged capacity of 367.6 mA h g⁻¹ at a high current density of 1.0 A g⁻¹. The Si/RGtO@C anode shows an application potential for commercial high-energy lithium-ion batteries.

A novel nanosecond transient electric field (E-field) measurement system is developed in this paper to measure the E-field pulse caused by the operation of the high-voltage switch (switching E-field pulse) in the substation. An electrically small rod antenna is used as the receiving antenna and is matched by the operational amplifier with high input impedance to achieve broadband frequency response and stable working performance. A broadband analog optical fiber transmission system is further designed based on the high-frequency circuit model of the electronic components. Unlike the traditional frequency domain E-field measurement methods, the developed measurement system can directly output the time domain waveform of the switching E-field pulse. It also has the advantages of adjustable sensitivity, portability, and anti-electromagnetic interference. The calibrated measurement bandwidth ranges from 200 Hz to 680 MHz. Furthermore, the switching E-field pulse in an ultra-high voltage substation is measured and analyzed to verify the effectiveness of the fabricated measurement system.

Humidity sensors with comprehensive performance are of great interest for industrial and environmental applications. Most sensors, however, have to compromise on at least one characteristic such as sensitivity, response speed, and linearity. This paper reports a gravimetric humidity sensor based on a capacitive micromachined ultrasonic transducer (CMUT) with exceptional all-around performance, and presents a side-by-side comparative investigation of two types of gravimetric humidity sensors for a better understanding of their characteristics and sensing mechanisms. For these purposes, a circular CMUT and a quartz crystal microbalance (QCM) with a resonance frequency of 10 MHz were designed and fabricated. Poly(vinyl alcohol) (PVA) was employed as the humidity sensing layer for its hydrophilicity and ease of film formation. The electrical properties of the sensors, including the electrical input impedances and quality factors, were characterized by a vector network analyzer. The relative humidity (RH) sensing performance of the sensors was evaluated and compared from RH levels of 11% to 97%. Both sensors exhibited good repeatability and low hysteresis. The unique microscale resonant structure of the CMUT humidity sensor contributed to a high sensitivity of 2.01 kHz/%RH, short response and recovery times of 8 s and 3 s, respectively, and excellent linearity (R² = 0.973), which were far superior to their QCM counterparts. The underlying mechanism was revealed and discussed.

An electric field (E-field) detector with the features of precise time base, full waveform storage and wireless data transmission has been developed, which can be used in combination with location algorithm for accurate location of the transient electromagnetic radiation source over a large-scale area. The maximum sampling rate is 2 GS/s and the memory depth is up to 128 kByte and can be adjustable. The measurement range can be adjusted from hundreds of V/m to tens of kV/m with different lengths of antennas. With the help of Global Positioning System (GPS), both the clock and the position of the detector can be synchronized. Particularly, the time instant triggered by the signal could be recorded with the time resolution of ten nanoseconds. Therefore, the precise time base alignment among multiple detectors could be achieved, which is crucial for location accuracy. Then, all data including the signal, the position and the time instant could be sent to a remote server by Fourth-generation mobile (4G) communication technology. The calibration results show that the bandwidth of the detector could vary from 10 kHz to 500 MHz, while the time base alignment error between any two detectors is less than 50 ns. An experiment was performed by means of electromagnetic time reversal (EMTR) method to prove the applicability of the detector and its location accuracy. The detector could be used to measure and locate lightning, partial discharge or fault, etc.

Based on multi-gap loop (MGL) antenna and low-noise norm detector, a novel nano-second (ns) level transient magnetic field (H-field) sensor is proposed in this paper. The direct measurement result of the MGL antenna is the differential signal of the H-field, which is capable to be digitized for storage by the norm detector. The original H-field can be restored using the software integral method. The developed ns-level H-field sensor exhibits two major advantages. Firstly, it can measure the H-field in the substation or the coupled H-field inside the hermetically sealed cavities, such as the cockpit of vehicles or aircrafts, which is because the need for transmission line is removed. Secondly, its sensitivity is significantly higher than the measurement system with the hardware passive integrator and the integral error can also be effectively reduced by the low-noise norm detector. In this paper, the realization of the ns-level transient H-field sensor will be detailed. The simulated upper cut-off frequency of the designed MGL antenna is about 1.9 GHz. The sampling rate of the norm detector is 2 GS/s as the maximum. The dynamic range of the detector is about 42 dB and the operation bandwidth ranges from 0.3 kHz to 500 MHz by calibration. The total storage space of 128 kB can record as long as 64 μs at 2 GS/s and is extendable. Test results show that the developed sensor can measure the ns-level H-field accurately.