Moisture damp has been identified as one of the most harmful agents of multilayer composited insulation, which can seriously accelerate its degradation, cause unexpected failure, and even lead to catastrophic accidents. This article proposes a nonintrusive method for moisture inspection of multilayer insulation structure based on terahertz (THz) technology with a focus on the cable terminal of the electric multiple units (EMUs). First, a three-layer scattering model is established based on the actual structure of the composite cable terminal, and theoretical analysis is performed to reveal the potential application mechanism. Based on that, an artificial model of a three-layer structure is then built on which the insulation damp test is carried out. Finally, the THz spectrum and THz imaging tests are performed. Results show that the frequency-domain signal can effectively identify the moisture inside the multilayer composited insulation. The imaging results in the frequency domain of the sample can accurately determine the geometric parameters of the damp area. By further analyzing the time-domain spectroscopy, the thickness of insulation affected by moisture can be identified quantitatively. This article verifies the feasibility of THz technology in inspecting the moisture dampness of multilayer composite insulation and its potential application in the damp condition assessment of EMU cable terminals.

Cable terminals of the high-speed electric multiple units (EMUs) are prone to undertake insulation delamination defects due to their special operating conditions. Such a defect is difficult to identify and it may pose a great threat to the safety of the EMUs. To achieve accurate detection of insulation delamination defects, this article proposes a terahertz (THz)-based approach that combines the spectrum of the THz wave and THz imaging techniques. Specifically, a synthetic multilayer composite insulation structure with an air gap is firstly built to simulate the internal delamination defect of the cable terminal. Then THz tests in both time and frequency domains are performed on the synthetic structure. Experimental results show that the delamination defect of the multilayer insulation structure can be quickly detected by observing the absorption spectrum in the THz frequency domain. The location and geometry of the defect can be preliminarily determined by the THz imaging and then further refined through image segmentation. In addition, the thickness of the delamination defect can be quickly calculated by the THz time-domain spectrum (TDS). By combining the THz spectrum and the THz imaging information, the delamination defects are quantitatively detected for the multilayer composite structure or even for the EMU’s cable terminals.

The marine environment in which offshore wind turbines are located is very complex and subjected to a variety of random loads that vary with time and space. As an important component of offshore wind power, the cable also bears the impact of the environment in which most of the turbines are located. Under the long-term action of mechanical stresses such as tension, torsion, and vibration, the cable insulation will crack due to stress fatigue leading to partial discharge, which seriously affects its electrical performance. The study of the mechanism of the change of electrical properties of cable insulation due to mechanical behavior is of great theoretical guidance to improve the reliable operation of cables. This paper first introduces the basic characteristics and operating conditions of torsion-resistant cables and submarine cables. Then the mechanical behavior of the cables is summarized, and the deterioration mechanism and deterioration effect of wind power cable insulation under the influence of multiple factors such as heat, oxygen, and mechanical stress are sorted out. Then, the basic principles of wind power cable operation condition monitoring methods and their characteristics are described. Finally, the relevant methods for the detection of hidden defects inside the insulation are summarized.

This paper proposes a probabilistic health index-based method for estimating the apparent age of power transformer. Compared with the conventional weighted-score-sum based health index, the probabilistic health index is calculated as a data fusion result of kinds of transformer condition monitoring data through a constructed Bayesian belief network. The regression result of such a probabilistic health index is then applied to estimate the apparent age of the transformer through a few steps listed in the paper. The apparent age not only embodies an overall health status a transformer, but also helpful for sorting a transformer fleet based on the estimated apparent age or even make it easy to make comparisons between transformer fleets. The estimated apparent age can be taken as a reference for power utilities to prioritize transformers and pay attention to the unit who owns the maximum apparent age among a fleet, and thus helps to schedule replacement plans. Case studies with different transformers verify the usability and prove the advantages of the proposed method.

Smart grid with great flexibility requirements will not accommodate high proportion of distributed generation with uncertainty in the future. Hence, it becomes indispensable to research scheduling strategy of distributed generation, aiming to reduce serious curtailment of renewable energy. This paper firstly proposes a virtual power supply, which consists of wind power (WP), photovoltaic (PV) power and pumped storage (PS) power. Based on that, a scheduling strategy structure considering stochastic characteristics caused by WP and PV is designed. After that, according to probability distribution of WP and PV, typical virtual power scenarios are obtained via scenario prediction and scenario reduction method. Furthermore, based on flexibility of virtual power and guidance of time-sharing electricity price mechanism, a coordinated scheduling model with optimization objective that maximizes profit is established. Finally, in simulation, validity of proposed model is verified via comparing with different scheduling models. Besides, profits of system under various peak-valley prices are analyzed, which can provide guidance for electricity pricing. The results illustrate that the proposed scheduling strategy can efficiently balance economy and flexibility in optimizing WP and PV consumption and profits of system are increased with 28% at most.

As the performance requirements of insulated gate bipolar transistors (IGBTs) in various fields of power electronic systems are increasing, the IGBT power module package structure, aging mechanism analysis, and selection of health state characteristic parameters are of great significance to ensure the normal operation of power systems. At present, research on the aging failure of welded IGBT modules is relatively comprehensive and can be divided into chip aging failure and package aging failure according to their failure parts. However, there is some research on the relationship between aging failure and the characteristic quantity of power modules, but no definite system has been formed. Therefore, in this paper, the packaging structure of the solder-type IGBT modules and the aging mechanism caused by different aging reasons were summarized. Moreover, the health status monitoring of solder-type IGBT modules from the junction temperature, bonding line, solder layer, and package insulation aging health status monitoring and its quantitative assessment research progress was analyzed in detail. Also, the health state evaluation index system of the solder-type IGBT modules was completed on the basis of voltage, current, thermal, insulation parameters, and other characteristic quantities. Finally, based on the analysis of domestic and international research problems, the development trend and direction of the condition monitoring technology of solder-type IGBT modules is foreseen. The research on condition monitoring for welded IGBT module technology has a certain significance.